text: /* ----------
   * pgstat.c
   *
   *	All the statistics collector stuff hacked up in one big, ugly file.
   *
   *	TODO:	- Separate collector, postmaster and backend stuff
   *			  into different files.
   *
   *			- Add some automatic call for pgstat vacuuming.
   *
   *			- Add a pgstat config column to pg_database, so this
   *			  entire thing can be enabled/disabled on a per db basis.
   *
   *	Copyright (c) 2001-2021, PostgreSQL Global Development Group
   *
   *	src/backend/postmaster/pgstat.c
   * ----------
   */
  #include "postgres.h"
  
  #include <unistd.h>
  #include <fcntl.h>
  #include <sys/param.h>
  #include <sys/time.h>
  #include <sys/socket.h>
  #include <netdb.h>
  #include <netinet/in.h>
  #include <arpa/inet.h>
  #include <signal.h>
  #include <time.h>
  #ifdef HAVE_SYS_SELECT_H
  #include <sys/select.h>
  #endif
  
  #include "access/heapam.h"
  #include "access/htup_details.h"
  #include "access/tableam.h"
  #include "access/transam.h"
  #include "access/twophase_rmgr.h"
  #include "access/xact.h"
  #include "catalog/pg_database.h"
  #include "catalog/pg_proc.h"
  #include "common/ip.h"
  #include "executor/instrument.h"
  #include "libpq/libpq.h"
  #include "libpq/pqsignal.h"
  #include "mb/pg_wchar.h"
  #include "miscadmin.h"
  #include "pg_trace.h"
  #include "pgstat.h"
  #include "postmaster/autovacuum.h"
  #include "postmaster/fork_process.h"
  #include "postmaster/interrupt.h"
  #include "postmaster/postmaster.h"
  #include "replication/slot.h"
  #include "replication/walsender.h"
  #include "storage/backendid.h"
  #include "storage/dsm.h"
  #include "storage/fd.h"
  #include "storage/ipc.h"
  #include "storage/latch.h"
  #include "storage/lmgr.h"
  #include "storage/pg_shmem.h"
  #include "storage/procsignal.h"
  #include "storage/sinvaladt.h"
  #include "utils/ascii.h"
  #include "utils/guc.h"
  #include "utils/memutils.h"
  #include "utils/ps_status.h"
  #include "utils/rel.h"
  #include "utils/snapmgr.h"
  #include "utils/timestamp.h"
  
  /* ----------
   * Timer definitions.
   * ----------
   */
  #define PGSTAT_STAT_INTERVAL	500 /* Minimum time between stats file
  									 * updates; in milliseconds. */
  
  #define PGSTAT_RETRY_DELAY		10	/* How long to wait between checks for a
  									 * new file; in milliseconds. */
  
  #define PGSTAT_MAX_WAIT_TIME	10000	/* Maximum time to wait for a stats
  										 * file update; in milliseconds. */
  
  #define PGSTAT_INQ_INTERVAL		640 /* How often to ping the collector for a
  									 * new file; in milliseconds. */
  
  #define PGSTAT_RESTART_INTERVAL 60	/* How often to attempt to restart a
  									 * failed statistics collector; in
  									 * seconds. */
  
  #define PGSTAT_POLL_LOOP_COUNT	(PGSTAT_MAX_WAIT_TIME / PGSTAT_RETRY_DELAY)
  #define PGSTAT_INQ_LOOP_COUNT	(PGSTAT_INQ_INTERVAL / PGSTAT_RETRY_DELAY)
  
  /* Minimum receive buffer size for the collector's socket. */
  #define PGSTAT_MIN_RCVBUF		(100 * 1024)
  
  
  /* ----------
   * The initial size hints for the hash tables used in the collector.
   * ----------
   */
  #define PGSTAT_DB_HASH_SIZE		16
  #define PGSTAT_TAB_HASH_SIZE	512
  #define PGSTAT_FUNCTION_HASH_SIZE	512
  
  
  /* ----------
   * Total number of backends including auxiliary
   *
   * We reserve a slot for each possible BackendId, plus one for each
   * possible auxiliary process type.  (This scheme assumes there is not
   * more than one of any auxiliary process type at a time.) MaxBackends
   * includes autovacuum workers and background workers as well.
   * ----------
   */
  #define NumBackendStatSlots (MaxBackends + NUM_AUXPROCTYPES)
  
  
  /* ----------
   * GUC parameters
   * ----------
   */
  bool		pgstat_track_activities = false;
  bool		pgstat_track_counts = false;
  int			pgstat_track_functions = TRACK_FUNC_OFF;
  int			pgstat_track_activity_query_size = 1024;
  
  /* ----------
   * Built from GUC parameter
   * ----------
   */
  char	   *pgstat_stat_directory = NULL;
  char	   *pgstat_stat_filename = NULL;
  char	   *pgstat_stat_tmpname = NULL;
  
  /*
   * BgWriter and WAL global statistics counters.
   * Stored directly in a stats message structure so they can be sent
   * without needing to copy things around.  We assume these init to zeroes.
   */
  PgStat_MsgBgWriter BgWriterStats;
  PgStat_MsgWal WalStats;
  
  /*
   * WAL usage counters saved from pgWALUsage at the previous call to
   * pgstat_report_wal(). This is used to calculate how much WAL usage
   * happens between pgstat_report_wal() calls, by substracting
   * the previous counters from the current ones.
   */
  static WalUsage prevWalUsage;
  
  /*
   * List of SLRU names that we keep stats for.  There is no central registry of
   * SLRUs, so we use this fixed list instead.  The "other" entry is used for
   * all SLRUs without an explicit entry (e.g. SLRUs in extensions).
   */
  static const char *const slru_names[] = {
  	"CommitTs",
  	"MultiXactMember",
  	"MultiXactOffset",
  	"Notify",
  	"Serial",
  	"Subtrans",
  	"Xact",
  	"other"						/* has to be last */
  };
  
  #define SLRU_NUM_ELEMENTS	lengthof(slru_names)
  
  /*
   * SLRU statistics counts waiting to be sent to the collector.  These are
   * stored directly in stats message format so they can be sent without needing
   * to copy things around.  We assume this variable inits to zeroes.  Entries
   * are one-to-one with slru_names[].
   */
  static PgStat_MsgSLRU SLRUStats[SLRU_NUM_ELEMENTS];
  
  /* ----------
   * Local data
   * ----------
   */
  NON_EXEC_STATIC pgsocket pgStatSock = PGINVALID_SOCKET;
  
  static struct sockaddr_storage pgStatAddr;
  
  static time_t last_pgstat_start_time;
  
  static bool pgStatRunningInCollector = false;
  
  /*
   * Structures in which backends store per-table info that's waiting to be
   * sent to the collector.
   *
   * NOTE: once allocated, TabStatusArray structures are never moved or deleted
   * for the life of the backend.  Also, we zero out the t_id fields of the
   * contained PgStat_TableStatus structs whenever they are not actively in use.
   * This allows relcache pgstat_info pointers to be treated as long-lived data,
   * avoiding repeated searches in pgstat_initstats() when a relation is
   * repeatedly opened during a transaction.
   */
  #define TABSTAT_QUANTUM		100 /* we alloc this many at a time */
  
  typedef struct TabStatusArray
  {
  	struct TabStatusArray *tsa_next;	/* link to next array, if any */
  	int			tsa_used;		/* # entries currently used */
  	PgStat_TableStatus tsa_entries[TABSTAT_QUANTUM];	/* per-table data */
  } TabStatusArray;
  
  static TabStatusArray *pgStatTabList = NULL;
  
  /*
   * pgStatTabHash entry: map from relation OID to PgStat_TableStatus pointer
   */
  typedef struct TabStatHashEntry
  {
  	Oid			t_id;
  	PgStat_TableStatus *tsa_entry;
  } TabStatHashEntry;
  
  /*
   * Hash table for O(1) t_id -> tsa_entry lookup
   */
  static HTAB *pgStatTabHash = NULL;
  
  /*
   * Backends store per-function info that's waiting to be sent to the collector
   * in this hash table (indexed by function OID).
   */
  static HTAB *pgStatFunctions = NULL;
  
  /*
   * Indicates if backend has some function stats that it hasn't yet
   * sent to the collector.
   */
  static bool have_function_stats = false;
  
  /*
   * Tuple insertion/deletion counts for an open transaction can't be propagated
   * into PgStat_TableStatus counters until we know if it is going to commit
   * or abort.  Hence, we keep these counts in per-subxact structs that live
   * in TopTransactionContext.  This data structure is designed on the assumption
   * that subxacts won't usually modify very many tables.
   */
  typedef struct PgStat_SubXactStatus
  {
  	int			nest_level;		/* subtransaction nest level */
  	struct PgStat_SubXactStatus *prev;	/* higher-level subxact if any */
  	PgStat_TableXactStatus *first;	/* head of list for this subxact */
  } PgStat_SubXactStatus;
  
  static PgStat_SubXactStatus *pgStatXactStack = NULL;
  
  static int	pgStatXactCommit = 0;
  static int	pgStatXactRollback = 0;
  PgStat_Counter pgStatBlockReadTime = 0;
  PgStat_Counter pgStatBlockWriteTime = 0;
  static PgStat_Counter pgStatActiveTime = 0;
  static PgStat_Counter pgStatTransactionIdleTime = 0;
  SessionEndType pgStatSessionEndCause = DISCONNECT_NORMAL;
  
  /* Record that's written to 2PC state file when pgstat state is persisted */
  typedef struct TwoPhasePgStatRecord
  {
  	PgStat_Counter tuples_inserted; /* tuples inserted in xact */
  	PgStat_Counter tuples_updated;	/* tuples updated in xact */
  	PgStat_Counter tuples_deleted;	/* tuples deleted in xact */
  	PgStat_Counter inserted_pre_trunc;	/* tuples inserted prior to truncate */
  	PgStat_Counter updated_pre_trunc;	/* tuples updated prior to truncate */
  	PgStat_Counter deleted_pre_trunc;	/* tuples deleted prior to truncate */
  	Oid			t_id;			/* table's OID */
  	bool		t_shared;		/* is it a shared catalog? */
  	bool		t_truncated;	/* was the relation truncated? */
  } TwoPhasePgStatRecord;
  
  /*
   * Info about current "snapshot" of stats file
   */
  static MemoryContext pgStatLocalContext = NULL;
  static HTAB *pgStatDBHash = NULL;
  
  /* Status for backends including auxiliary */
  static LocalPgBackendStatus *localBackendStatusTable = NULL;
  
  /* Total number of backends including auxiliary */
  static int	localNumBackends = 0;
  
  /*
   * Cluster wide statistics, kept in the stats collector.
   * Contains statistics that are not collected per database
   * or per table.
   */
  static PgStat_ArchiverStats archiverStats;
  static PgStat_GlobalStats globalStats;
  static PgStat_WalStats walStats;
  static PgStat_SLRUStats slruStats[SLRU_NUM_ELEMENTS];
  static PgStat_ReplSlotStats *replSlotStats;
  static int	nReplSlotStats;
  
  /*
   * List of OIDs of databases we need to write out.  If an entry is InvalidOid,
   * it means to write only the shared-catalog stats ("DB 0"); otherwise, we
   * will write both that DB's data and the shared stats.
   */
  static List *pending_write_requests = NIL;
  
  /*
   * Total time charged to functions so far in the current backend.
   * We use this to help separate "self" and "other" time charges.
   * (We assume this initializes to zero.)
   */
  static instr_time total_func_time;
  
  
  /* ----------
   * Local function forward declarations
   * ----------
   */
  #ifdef EXEC_BACKEND
  static pid_t pgstat_forkexec(void);
  #endif
  
  NON_EXEC_STATIC void PgstatCollectorMain(int argc, char *argv[]) pg_attribute_noreturn();
  static void pgstat_beshutdown_hook(int code, Datum arg);
  
  static PgStat_StatDBEntry *pgstat_get_db_entry(Oid databaseid, bool create);
  static PgStat_StatTabEntry *pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry,
  												 Oid tableoid, bool create);
  static void pgstat_write_statsfiles(bool permanent, bool allDbs);
  static void pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent);
  static HTAB *pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep);
  static void pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash, bool permanent);
  static void backend_read_statsfile(void);
  static void pgstat_read_current_status(void);
  
  static bool pgstat_write_statsfile_needed(void);
  static bool pgstat_db_requested(Oid databaseid);
  
  static int	pgstat_replslot_index(const char *name, bool create_it);
  static void pgstat_reset_replslot(int i, TimestampTz ts);
  
  static void pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg);
  static void pgstat_send_funcstats(void);
  static void pgstat_send_slru(void);
  static HTAB *pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid);
  static void pgstat_send_connstats(bool disconnect, TimestampTz last_report);
  
  static PgStat_TableStatus *get_tabstat_entry(Oid rel_id, bool isshared);
  
  static void pgstat_setup_memcxt(void);
  
  static const char *pgstat_get_wait_activity(WaitEventActivity w);
  static const char *pgstat_get_wait_client(WaitEventClient w);
  static const char *pgstat_get_wait_ipc(WaitEventIPC w);
  static const char *pgstat_get_wait_timeout(WaitEventTimeout w);
  static const char *pgstat_get_wait_io(WaitEventIO w);
  
  static void pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype);
  static void pgstat_send(void *msg, int len);
  
  static void pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len);
  static void pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len);
  static void pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len);
  static void pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len);
  static void pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len);
  static void pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len);
  static void pgstat_recv_resetsinglecounter(PgStat_MsgResetsinglecounter *msg, int len);
  static void pgstat_recv_resetslrucounter(PgStat_MsgResetslrucounter *msg, int len);
  static void pgstat_recv_resetreplslotcounter(PgStat_MsgResetreplslotcounter *msg, int len);
  static void pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len);
  static void pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len);
  static void pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len);
  static void pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len);
  static void pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len);
  static void pgstat_recv_wal(PgStat_MsgWal *msg, int len);
  static void pgstat_recv_slru(PgStat_MsgSLRU *msg, int len);
  static void pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len);
  static void pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len);
  static void pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len);
  static void pgstat_recv_deadlock(PgStat_MsgDeadlock *msg, int len);
  static void pgstat_recv_checksum_failure(PgStat_MsgChecksumFailure *msg, int len);
  static void pgstat_recv_connstat(PgStat_MsgConn *msg, int len);
  static void pgstat_recv_replslot(PgStat_MsgReplSlot *msg, int len);
  static void pgstat_recv_tempfile(PgStat_MsgTempFile *msg, int len);
  
  /* ------------------------------------------------------------
   * Public functions called from postmaster follow
   * ------------------------------------------------------------
   */
  
  /* ----------
   * pgstat_init() -
   *
   *	Called from postmaster at startup. Create the resources required
   *	by the statistics collector process.  If unable to do so, do not
   *	fail --- better to let the postmaster start with stats collection
   *	disabled.
   * ----------
   */
  void
  pgstat_init(void)
  {
  	ACCEPT_TYPE_ARG3 alen;
  	struct addrinfo *addrs = NULL,
  			   *addr,
  				hints;
  	int			ret;
  	fd_set		rset;
  	struct timeval tv;
  	char		test_byte;
  	int			sel_res;
  	int			tries = 0;
  
  #define TESTBYTEVAL ((char) 199)
  
  	/*
  	 * This static assertion verifies that we didn't mess up the calculations
  	 * involved in selecting maximum payload sizes for our UDP messages.
  	 * Because the only consequence of overrunning PGSTAT_MAX_MSG_SIZE would
  	 * be silent performance loss from fragmentation, it seems worth having a
  	 * compile-time cross-check that we didn't.
  	 */
  	StaticAssertStmt(sizeof(PgStat_Msg) <= PGSTAT_MAX_MSG_SIZE,
  					 "maximum stats message size exceeds PGSTAT_MAX_MSG_SIZE");
  
  	/*
  	 * Create the UDP socket for sending and receiving statistic messages
  	 */
  	hints.ai_flags = AI_PASSIVE;
  	hints.ai_family = AF_UNSPEC;
  	hints.ai_socktype = SOCK_DGRAM;
  	hints.ai_protocol = 0;
  	hints.ai_addrlen = 0;
  	hints.ai_addr = NULL;
  	hints.ai_canonname = NULL;
  	hints.ai_next = NULL;
  	ret = pg_getaddrinfo_all("localhost", NULL, &hints, &addrs);
  	if (ret || !addrs)
  	{
  		ereport(LOG,
  				(errmsg("could not resolve \"localhost\": %s",
  						gai_strerror(ret))));
  		goto startup_failed;
  	}
  
  	/*
  	 * On some platforms, pg_getaddrinfo_all() may return multiple addresses
  	 * only one of which will actually work (eg, both IPv6 and IPv4 addresses
  	 * when kernel will reject IPv6).  Worse, the failure may occur at the
  	 * bind() or perhaps even connect() stage.  So we must loop through the
  	 * results till we find a working combination. We will generate LOG
  	 * messages, but no error, for bogus combinations.
  	 */
  	for (addr = addrs; addr; addr = addr->ai_next)
  	{
  #ifdef HAVE_UNIX_SOCKETS
  		/* Ignore AF_UNIX sockets, if any are returned. */
  		if (addr->ai_family == AF_UNIX)
  			continue;
  #endif
  
  		if (++tries > 1)
  			ereport(LOG,
  					(errmsg("trying another address for the statistics collector")));
  
  		/*
  		 * Create the socket.
  		 */
  		if ((pgStatSock = socket(addr->ai_family, SOCK_DGRAM, 0)) == PGINVALID_SOCKET)
  		{
  			ereport(LOG,
  					(errcode_for_socket_access(),
  					 errmsg("could not create socket for statistics collector: %m")));
  			continue;
  		}
  
  		/*
  		 * Bind it to a kernel assigned port on localhost and get the assigned
  		 * port via getsockname().
  		 */
  		if (bind(pgStatSock, addr->ai_addr, addr->ai_addrlen) < 0)
  		{
  			ereport(LOG,
  					(errcode_for_socket_access(),
  					 errmsg("could not bind socket for statistics collector: %m")));
  			closesocket(pgStatSock);
  			pgStatSock = PGINVALID_SOCKET;
  			continue;
  		}
  
  		alen = sizeof(pgStatAddr);
  		if (getsockname(pgStatSock, (struct sockaddr *) &pgStatAddr, &alen) < 0)
  		{
  			ereport(LOG,
  					(errcode_for_socket_access(),
  					 errmsg("could not get address of socket for statistics collector: %m")));
  			closesocket(pgStatSock);
  			pgStatSock = PGINVALID_SOCKET;
  			continue;
  		}
  
  		/*
  		 * Connect the socket to its own address.  This saves a few cycles by
  		 * not having to respecify the target address on every send. This also
  		 * provides a kernel-level check that only packets from this same
  		 * address will be received.
  		 */
  		if (connect(pgStatSock, (struct sockaddr *) &pgStatAddr, alen) < 0)
  		{
  			ereport(LOG,
  					(errcode_for_socket_access(),
  					 errmsg("could not connect socket for statistics collector: %m")));
  			closesocket(pgStatSock);
  			pgStatSock = PGINVALID_SOCKET;
  			continue;
  		}
  
  		/*
  		 * Try to send and receive a one-byte test message on the socket. This
  		 * is to catch situations where the socket can be created but will not
  		 * actually pass data (for instance, because kernel packet filtering
  		 * rules prevent it).
  		 */
  		test_byte = TESTBYTEVAL;
  
  retry1:
  		if (send(pgStatSock, &test_byte, 1, 0) != 1)
  		{
  			if (errno == EINTR)
  				goto retry1;	/* if interrupted, just retry */
  			ereport(LOG,
  					(errcode_for_socket_access(),
  					 errmsg("could not send test message on socket for statistics collector: %m")));
  			closesocket(pgStatSock);
  			pgStatSock = PGINVALID_SOCKET;
  			continue;
  		}
  
  		/*
  		 * There could possibly be a little delay before the message can be
  		 * received.  We arbitrarily allow up to half a second before deciding
  		 * it's broken.
  		 */
  		for (;;)				/* need a loop to handle EINTR */
  		{
  			FD_ZERO(&rset);
  			FD_SET(pgStatSock, &rset);
  
  			tv.tv_sec = 0;
  			tv.tv_usec = 500000;
  			sel_res = select(pgStatSock + 1, &rset, NULL, NULL, &tv);
  			if (sel_res >= 0 || errno != EINTR)
  				break;
  		}
  		if (sel_res < 0)
  		{
  			ereport(LOG,
  					(errcode_for_socket_access(),
  					 errmsg("select() failed in statistics collector: %m")));
  			closesocket(pgStatSock);
  			pgStatSock = PGINVALID_SOCKET;
  			continue;
  		}
  		if (sel_res == 0 || !FD_ISSET(pgStatSock, &rset))
  		{
  			/*
  			 * This is the case we actually think is likely, so take pains to
  			 * give a specific message for it.
  			 *
  			 * errno will not be set meaningfully here, so don't use it.
  			 */
  			ereport(LOG,
  					(errcode(ERRCODE_CONNECTION_FAILURE),
  					 errmsg("test message did not get through on socket for statistics collector")));
  			closesocket(pgStatSock);
  			pgStatSock = PGINVALID_SOCKET;
  			continue;
  		}
  
  		test_byte++;			/* just make sure variable is changed */
  
  retry2:
  		if (recv(pgStatSock, &test_byte, 1, 0) != 1)
  		{
  			if (errno == EINTR)
  				goto retry2;	/* if interrupted, just retry */
  			ereport(LOG,
  					(errcode_for_socket_access(),
  					 errmsg("could not receive test message on socket for statistics collector: %m")));
  			closesocket(pgStatSock);
  			pgStatSock = PGINVALID_SOCKET;
  			continue;
  		}
  
  		if (test_byte != TESTBYTEVAL)	/* strictly paranoia ... */
  		{
  			ereport(LOG,
  					(errcode(ERRCODE_INTERNAL_ERROR),
  					 errmsg("incorrect test message transmission on socket for statistics collector")));
  			closesocket(pgStatSock);
  			pgStatSock = PGINVALID_SOCKET;
  			continue;
  		}
  
  		/* If we get here, we have a working socket */
  		break;
  	}
  
  	/* Did we find a working address? */
  	if (!addr || pgStatSock == PGINVALID_SOCKET)
  		goto startup_failed;
  
  	/*
  	 * Set the socket to non-blocking IO.  This ensures that if the collector
  	 * falls behind, statistics messages will be discarded; backends won't
  	 * block waiting to send messages to the collector.
  	 */
  	if (!pg_set_noblock(pgStatSock))
  	{
  		ereport(LOG,
  				(errcode_for_socket_access(),
  				 errmsg("could not set statistics collector socket to nonblocking mode: %m")));
  		goto startup_failed;
  	}
  
  	/*
  	 * Try to ensure that the socket's receive buffer is at least
  	 * PGSTAT_MIN_RCVBUF bytes, so that it won't easily overflow and lose
  	 * data.  Use of UDP protocol means that we are willing to lose data under
  	 * heavy load, but we don't want it to happen just because of ridiculously
  	 * small default buffer sizes (such as 8KB on older Windows versions).
  	 */
  	{
  		int			old_rcvbuf;
  		int			new_rcvbuf;
  		ACCEPT_TYPE_ARG3 rcvbufsize = sizeof(old_rcvbuf);
  
  		if (getsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
  					   (char *) &old_rcvbuf, &rcvbufsize) < 0)
  		{
  			ereport(LOG,
  					(errmsg("getsockopt(%s) failed: %m", "SO_RCVBUF")));
  			/* if we can't get existing size, always try to set it */
  			old_rcvbuf = 0;
  		}
  
  		new_rcvbuf = PGSTAT_MIN_RCVBUF;
  		if (old_rcvbuf < new_rcvbuf)
  		{
  			if (setsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
  						   (char *) &new_rcvbuf, sizeof(new_rcvbuf)) < 0)
  				ereport(LOG,
  						(errmsg("setsockopt(%s) failed: %m", "SO_RCVBUF")));
  		}
  	}
  
  	pg_freeaddrinfo_all(hints.ai_family, addrs);
  
  	/* Now that we have a long-lived socket, tell fd.c about it. */
  	ReserveExternalFD();
  
  	return;
  
  startup_failed:
  	ereport(LOG,
  			(errmsg("disabling statistics collector for lack of working socket")));
  
  	if (addrs)
  		pg_freeaddrinfo_all(hints.ai_family, addrs);
  
  	if (pgStatSock != PGINVALID_SOCKET)
  		closesocket(pgStatSock);
  	pgStatSock = PGINVALID_SOCKET;
  
  	/*
  	 * Adjust GUC variables to suppress useless activity, and for debugging
  	 * purposes (seeing track_counts off is a clue that we failed here). We
  	 * use PGC_S_OVERRIDE because there is no point in trying to turn it back
  	 * on from postgresql.conf without a restart.
  	 */
  	SetConfigOption("track_counts", "off", PGC_INTERNAL, PGC_S_OVERRIDE);
  }
  
  /*
   * subroutine for pgstat_reset_all
   */
  static void
  pgstat_reset_remove_files(const char *directory)
  {
  	DIR		   *dir;
  	struct dirent *entry;
  	char		fname[MAXPGPATH * 2];
  
  	dir = AllocateDir(directory);
  	while ((entry = ReadDir(dir, directory)) != NULL)
  	{
  		int			nchars;
  		Oid			tmp_oid;
  
  		/*
  		 * Skip directory entries that don't match the file names we write.
  		 * See get_dbstat_filename for the database-specific pattern.
  		 */
  		if (strncmp(entry->d_name, "global.", 7) == 0)
  			nchars = 7;
  		else
  		{
  			nchars = 0;
  			(void) sscanf(entry->d_name, "db_%u.%n",
  						  &tmp_oid, &nchars);
  			if (nchars <= 0)
  				continue;
  			/* %u allows leading whitespace, so reject that */
  			if (strchr("0123456789", entry->d_name[3]) == NULL)
  				continue;
  		}
  
  		if (strcmp(entry->d_name + nchars, "tmp") != 0 &&
  			strcmp(entry->d_name + nchars, "stat") != 0)
  			continue;
  
  		snprintf(fname, sizeof(fname), "%s/%s", directory,
  				 entry->d_name);
  		unlink(fname);
  	}
  	FreeDir(dir);
  }
  
  /*
   * pgstat_reset_all() -
   *
   * Remove the stats files.  This is currently used only if WAL
   * recovery is needed after a crash.
   */
  void
  pgstat_reset_all(void)
  {
  	pgstat_reset_remove_files(pgstat_stat_directory);
  	pgstat_reset_remove_files(PGSTAT_STAT_PERMANENT_DIRECTORY);
  }
  
  #ifdef EXEC_BACKEND
  
  /*
   * pgstat_forkexec() -
   *
   * Format up the arglist for, then fork and exec, statistics collector process
   */
  static pid_t
  pgstat_forkexec(void)
  {
  	char	   *av[10];
  	int			ac = 0;
  
  	av[ac++] = "postgres";
  	av[ac++] = "--forkcol";
  	av[ac++] = NULL;			/* filled in by postmaster_forkexec */
  
  	av[ac] = NULL;
  	Assert(ac < lengthof(av));
  
  	return postmaster_forkexec(ac, av);
  }
  #endif							/* EXEC_BACKEND */
  
  
  /*
   * pgstat_start() -
   *
   *	Called from postmaster at startup or after an existing collector
   *	died.  Attempt to fire up a fresh statistics collector.
   *
   *	Returns PID of child process, or 0 if fail.
   *
   *	Note: if fail, we will be called again from the postmaster main loop.
   */
  int
  pgstat_start(void)
  {
  	time_t		curtime;
  	pid_t		pgStatPid;
  
  	/*
  	 * Check that the socket is there, else pgstat_init failed and we can do
  	 * nothing useful.
  	 */
  	if (pgStatSock == PGINVALID_SOCKET)
  		return 0;
  
  	/*
  	 * Do nothing if too soon since last collector start.  This is a safety
  	 * valve to protect against continuous respawn attempts if the collector
  	 * is dying immediately at launch.  Note that since we will be re-called
  	 * from the postmaster main loop, we will get another chance later.
  	 */
  	curtime = time(NULL);
  	if ((unsigned int) (curtime - last_pgstat_start_time) <
  		(unsigned int) PGSTAT_RESTART_INTERVAL)
  		return 0;
  	last_pgstat_start_time = curtime;
  
  	/*
  	 * Okay, fork off the collector.
  	 */
  #ifdef EXEC_BACKEND
  	switch ((pgStatPid = pgstat_forkexec()))
  #else
  	switch ((pgStatPid = fork_process()))
  #endif
  	{
  		case -1:
  			ereport(LOG,
  					(errmsg("could not fork statistics collector: %m")));
  			return 0;
  
  #ifndef EXEC_BACKEND
  		case 0:
  			/* in postmaster child ... */
  			InitPostmasterChild();
  
  			/* Close the postmaster's sockets */
  			ClosePostmasterPorts(false);
  
  			/* Drop our connection to postmaster's shared memory, as well */
  			dsm_detach_all();
  			PGSharedMemoryDetach();
  
  			PgstatCollectorMain(0, NULL);
  			break;
  #endif
  
  		default:
  			return (int) pgStatPid;
  	}
  
  	/* shouldn't get here */
  	return 0;
  }
  
  void
  allow_immediate_pgstat_restart(void)
  {
  	last_pgstat_start_time = 0;
  }
  
  /* ------------------------------------------------------------
   * Public functions used by backends follow
   *------------------------------------------------------------
   */
  
  
  /* ----------
   * pgstat_report_stat() -
   *
   *	Must be called by processes that performs DML: tcop/postgres.c, logical
   *	receiver processes, SPI worker, etc. to send the so far collected
   *	per-table and function usage statistics to the collector.  Note that this
   *	is called only when not within a transaction, so it is fair to use
   *	transaction stop time as an approximation of current time.
   *
   *	"disconnect" is "true" only for the last call before the backend
   *	exits.  This makes sure that no data is lost and that interrupted
   *	sessions are reported correctly.
   * ----------
   */
  void
  pgstat_report_stat(bool disconnect)
  {
  	/* we assume this inits to all zeroes: */
  	static const PgStat_TableCounts all_zeroes;
  	static TimestampTz last_report = 0;
  
  	TimestampTz now;
  	PgStat_MsgTabstat regular_msg;
  	PgStat_MsgTabstat shared_msg;
  	TabStatusArray *tsa;
  	int			i;
  
  	/* Don't expend a clock check if nothing to do */
  	if ((pgStatTabList == NULL || pgStatTabList->tsa_used == 0) &&
  		pgStatXactCommit == 0 && pgStatXactRollback == 0 &&
  		!have_function_stats && !disconnect)
  		return;
  
  	/*
  	 * Don't send a message unless it's been at least PGSTAT_STAT_INTERVAL
  	 * msec since we last sent one, or the backend is about to exit.
  	 */
  	now = GetCurrentTransactionStopTimestamp();
  	if (!disconnect &&
  		!TimestampDifferenceExceeds(last_report, now, PGSTAT_STAT_INTERVAL))
  		return;
  
  	/* for backends, send connection statistics */
  	if (MyBackendType == B_BACKEND)
  		pgstat_send_connstats(disconnect, last_report);
  
  	last_report = now;
  
  	/*
  	 * Destroy pgStatTabHash before we start invalidating PgStat_TableEntry
  	 * entries it points to.  (Should we fail partway through the loop below,
  	 * it's okay to have removed the hashtable already --- the only
  	 * consequence is we'd get multiple entries for the same table in the
  	 * pgStatTabList, and that's safe.)
  	 */
  	if (pgStatTabHash)
  		hash_destroy(pgStatTabHash);
  	pgStatTabHash = NULL;
  
  	/*
  	 * Scan through the TabStatusArray struct(s) to find tables that actually
  	 * have counts, and build messages to send.  We have to separate shared
  	 * relations from regular ones because the databaseid field in the message
  	 * header has to depend on that.
  	 */
  	regular_msg.m_databaseid = MyDatabaseId;
  	shared_msg.m_databaseid = InvalidOid;
  	regular_msg.m_nentries = 0;
  	shared_msg.m_nentries = 0;
  
  	for (tsa = pgStatTabList; tsa != NULL; tsa = tsa->tsa_next)
  	{
  		for (i = 0; i < tsa->tsa_used; i++)
  		{
  			PgStat_TableStatus *entry = &tsa->tsa_entries[i];
  			PgStat_MsgTabstat *this_msg;
  			PgStat_TableEntry *this_ent;
  
  			/* Shouldn't have any pending transaction-dependent counts */
  			Assert(entry->trans == NULL);
  
  			/*
  			 * Ignore entries that didn't accumulate any actual counts, such
  			 * as indexes that were opened by the planner but not used.
  			 */
  			if (memcmp(&entry->t_counts, &all_zeroes,
  					   sizeof(PgStat_TableCounts)) == 0)
  				continue;
  
  			/*
  			 * OK, insert data into the appropriate message, and send if full.
  			 */
  			this_msg = entry->t_shared ? &shared_msg : &regular_msg;
  			this_ent = &this_msg->m_entry[this_msg->m_nentries];
  			this_ent->t_id = entry->t_id;
  			memcpy(&this_ent->t_counts, &entry->t_counts,
  				   sizeof(PgStat_TableCounts));
  			if (++this_msg->m_nentries >= PGSTAT_NUM_TABENTRIES)
  			{
  				pgstat_send_tabstat(this_msg);
  				this_msg->m_nentries = 0;
  			}
  		}
  		/* zero out PgStat_TableStatus structs after use */
  		MemSet(tsa->tsa_entries, 0,
  			   tsa->tsa_used * sizeof(PgStat_TableStatus));
  		tsa->tsa_used = 0;
  	}
  
  	/*
  	 * Send partial messages.  Make sure that any pending xact commit/abort
  	 * gets counted, even if there are no table stats to send.
  	 */
  	if (regular_msg.m_nentries > 0 ||
  		pgStatXactCommit > 0 || pgStatXactRollback > 0)
  		pgstat_send_tabstat(&regular_msg);
  	if (shared_msg.m_nentries > 0)
  		pgstat_send_tabstat(&shared_msg);
  
  	/* Now, send function statistics */
  	pgstat_send_funcstats();
  
  	/* Send WAL statistics */
  	pgstat_report_wal();
  
  	/* Finally send SLRU statistics */
  	pgstat_send_slru();
  }
  
  /*
   * Subroutine for pgstat_report_stat: finish and send a tabstat message
   */
  static void
  pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg)
  {
  	int			n;
  	int			len;
  
  	/* It's unlikely we'd get here with no socket, but maybe not impossible */
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	/*
  	 * Report and reset accumulated xact commit/rollback and I/O timings
  	 * whenever we send a normal tabstat message
  	 */
  	if (OidIsValid(tsmsg->m_databaseid))
  	{
  		tsmsg->m_xact_commit = pgStatXactCommit;
  		tsmsg->m_xact_rollback = pgStatXactRollback;
  		tsmsg->m_block_read_time = pgStatBlockReadTime;
  		tsmsg->m_block_write_time = pgStatBlockWriteTime;
  		pgStatXactCommit = 0;
  		pgStatXactRollback = 0;
  		pgStatBlockReadTime = 0;
  		pgStatBlockWriteTime = 0;
  	}
  	else
  	{
  		tsmsg->m_xact_commit = 0;
  		tsmsg->m_xact_rollback = 0;
  		tsmsg->m_block_read_time = 0;
  		tsmsg->m_block_write_time = 0;
  	}
  
  	n = tsmsg->m_nentries;
  	len = offsetof(PgStat_MsgTabstat, m_entry[0]) +
  		n * sizeof(PgStat_TableEntry);
  
  	pgstat_setheader(&tsmsg->m_hdr, PGSTAT_MTYPE_TABSTAT);
  	pgstat_send(tsmsg, len);
  }
  
  /*
   * Subroutine for pgstat_report_stat: populate and send a function stat message
   */
  static void
  pgstat_send_funcstats(void)
  {
  	/* we assume this inits to all zeroes: */
  	static const PgStat_FunctionCounts all_zeroes;
  
  	PgStat_MsgFuncstat msg;
  	PgStat_BackendFunctionEntry *entry;
  	HASH_SEQ_STATUS fstat;
  
  	if (pgStatFunctions == NULL)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_FUNCSTAT);
  	msg.m_databaseid = MyDatabaseId;
  	msg.m_nentries = 0;
  
  	hash_seq_init(&fstat, pgStatFunctions);
  	while ((entry = (PgStat_BackendFunctionEntry *) hash_seq_search(&fstat)) != NULL)
  	{
  		PgStat_FunctionEntry *m_ent;
  
  		/* Skip it if no counts accumulated since last time */
  		if (memcmp(&entry->f_counts, &all_zeroes,
  				   sizeof(PgStat_FunctionCounts)) == 0)
  			continue;
  
  		/* need to convert format of time accumulators */
  		m_ent = &msg.m_entry[msg.m_nentries];
  		m_ent->f_id = entry->f_id;
  		m_ent->f_numcalls = entry->f_counts.f_numcalls;
  		m_ent->f_total_time = INSTR_TIME_GET_MICROSEC(entry->f_counts.f_total_time);
  		m_ent->f_self_time = INSTR_TIME_GET_MICROSEC(entry->f_counts.f_self_time);
  
  		if (++msg.m_nentries >= PGSTAT_NUM_FUNCENTRIES)
  		{
  			pgstat_send(&msg, offsetof(PgStat_MsgFuncstat, m_entry[0]) +
  						msg.m_nentries * sizeof(PgStat_FunctionEntry));
  			msg.m_nentries = 0;
  		}
  
  		/* reset the entry's counts */
  		MemSet(&entry->f_counts, 0, sizeof(PgStat_FunctionCounts));
  	}
  
  	if (msg.m_nentries > 0)
  		pgstat_send(&msg, offsetof(PgStat_MsgFuncstat, m_entry[0]) +
  					msg.m_nentries * sizeof(PgStat_FunctionEntry));
  
  	have_function_stats = false;
  }
  
  
  /* ----------
   * pgstat_vacuum_stat() -
   *
   *	Will tell the collector about objects he can get rid of.
   * ----------
   */
  void
  pgstat_vacuum_stat(void)
  {
  	HTAB	   *htab;
  	PgStat_MsgTabpurge msg;
  	PgStat_MsgFuncpurge f_msg;
  	HASH_SEQ_STATUS hstat;
  	PgStat_StatDBEntry *dbentry;
  	PgStat_StatTabEntry *tabentry;
  	PgStat_StatFuncEntry *funcentry;
  	int			len;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	/*
  	 * If not done for this transaction, read the statistics collector stats
  	 * file into some hash tables.
  	 */
  	backend_read_statsfile();
  
  	/*
  	 * Read pg_database and make a list of OIDs of all existing databases
  	 */
  	htab = pgstat_collect_oids(DatabaseRelationId, Anum_pg_database_oid);
  
  	/*
  	 * Search the database hash table for dead databases and tell the
  	 * collector to drop them.
  	 */
  	hash_seq_init(&hstat, pgStatDBHash);
  	while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
  	{
  		Oid			dbid = dbentry->databaseid;
  
  		CHECK_FOR_INTERRUPTS();
  
  		/* the DB entry for shared tables (with InvalidOid) is never dropped */
  		if (OidIsValid(dbid) &&
  			hash_search(htab, (void *) &dbid, HASH_FIND, NULL) == NULL)
  			pgstat_drop_database(dbid);
  	}
  
  	/* Clean up */
  	hash_destroy(htab);
  
  	/*
  	 * Lookup our own database entry; if not found, nothing more to do.
  	 */
  	dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
  												 (void *) &MyDatabaseId,
  												 HASH_FIND, NULL);
  	if (dbentry == NULL || dbentry->tables == NULL)
  		return;
  
  	/*
  	 * Similarly to above, make a list of all known relations in this DB.
  	 */
  	htab = pgstat_collect_oids(RelationRelationId, Anum_pg_class_oid);
  
  	/*
  	 * Initialize our messages table counter to zero
  	 */
  	msg.m_nentries = 0;
  
  	/*
  	 * Check for all tables listed in stats hashtable if they still exist.
  	 */
  	hash_seq_init(&hstat, dbentry->tables);
  	while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&hstat)) != NULL)
  	{
  		Oid			tabid = tabentry->tableid;
  
  		CHECK_FOR_INTERRUPTS();
  
  		if (hash_search(htab, (void *) &tabid, HASH_FIND, NULL) != NULL)
  			continue;
  
  		/*
  		 * Not there, so add this table's Oid to the message
  		 */
  		msg.m_tableid[msg.m_nentries++] = tabid;
  
  		/*
  		 * If the message is full, send it out and reinitialize to empty
  		 */
  		if (msg.m_nentries >= PGSTAT_NUM_TABPURGE)
  		{
  			len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
  				+ msg.m_nentries * sizeof(Oid);
  
  			pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
  			msg.m_databaseid = MyDatabaseId;
  			pgstat_send(&msg, len);
  
  			msg.m_nentries = 0;
  		}
  	}
  
  	/*
  	 * Send the rest
  	 */
  	if (msg.m_nentries > 0)
  	{
  		len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
  			+ msg.m_nentries * sizeof(Oid);
  
  		pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
  		msg.m_databaseid = MyDatabaseId;
  		pgstat_send(&msg, len);
  	}
  
  	/* Clean up */
  	hash_destroy(htab);
  
  	/*
  	 * Now repeat the above steps for functions.  However, we needn't bother
  	 * in the common case where no function stats are being collected.
  	 */
  	if (dbentry->functions != NULL &&
  		hash_get_num_entries(dbentry->functions) > 0)
  	{
  		htab = pgstat_collect_oids(ProcedureRelationId, Anum_pg_proc_oid);
  
  		pgstat_setheader(&f_msg.m_hdr, PGSTAT_MTYPE_FUNCPURGE);
  		f_msg.m_databaseid = MyDatabaseId;
  		f_msg.m_nentries = 0;
  
  		hash_seq_init(&hstat, dbentry->functions);
  		while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&hstat)) != NULL)
  		{
  			Oid			funcid = funcentry->functionid;
  
  			CHECK_FOR_INTERRUPTS();
  
  			if (hash_search(htab, (void *) &funcid, HASH_FIND, NULL) != NULL)
  				continue;
  
  			/*
  			 * Not there, so add this function's Oid to the message
  			 */
  			f_msg.m_functionid[f_msg.m_nentries++] = funcid;
  
  			/*
  			 * If the message is full, send it out and reinitialize to empty
  			 */
  			if (f_msg.m_nentries >= PGSTAT_NUM_FUNCPURGE)
  			{
  				len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
  					+ f_msg.m_nentries * sizeof(Oid);
  
  				pgstat_send(&f_msg, len);
  
  				f_msg.m_nentries = 0;
  			}
  		}
  
  		/*
  		 * Send the rest
  		 */
  		if (f_msg.m_nentries > 0)
  		{
  			len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
  				+ f_msg.m_nentries * sizeof(Oid);
  
  			pgstat_send(&f_msg, len);
  		}
  
  		hash_destroy(htab);
  	}
  }
  
  
  /* ----------
   * pgstat_collect_oids() -
   *
   *	Collect the OIDs of all objects listed in the specified system catalog
   *	into a temporary hash table.  Caller should hash_destroy the result
   *	when done with it.  (However, we make the table in CurrentMemoryContext
   *	so that it will be freed properly in event of an error.)
   * ----------
   */
  static HTAB *
  pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid)
  {
  	HTAB	   *htab;
  	HASHCTL		hash_ctl;
  	Relation	rel;
  	TableScanDesc scan;
  	HeapTuple	tup;
  	Snapshot	snapshot;
  
  	hash_ctl.keysize = sizeof(Oid);
  	hash_ctl.entrysize = sizeof(Oid);
  	hash_ctl.hcxt = CurrentMemoryContext;
  	htab = hash_create("Temporary table of OIDs",
  					   PGSTAT_TAB_HASH_SIZE,
  					   &hash_ctl,
  					   HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
  
  	rel = table_open(catalogid, AccessShareLock);
  	snapshot = RegisterSnapshot(GetLatestSnapshot());
  	scan = table_beginscan(rel, snapshot, 0, NULL);
  	while ((tup = heap_getnext(scan, ForwardScanDirection)) != NULL)
  	{
  		Oid			thisoid;
  		bool		isnull;
  
  		thisoid = heap_getattr(tup, anum_oid, RelationGetDescr(rel), &isnull);
  		Assert(!isnull);
  
  		CHECK_FOR_INTERRUPTS();
  
  		(void) hash_search(htab, (void *) &thisoid, HASH_ENTER, NULL);
  	}
  	table_endscan(scan);
  	UnregisterSnapshot(snapshot);
  	table_close(rel, AccessShareLock);
  
  	return htab;
  }
  
  
  /* ----------
   * pgstat_drop_database() -
   *
   *	Tell the collector that we just dropped a database.
   *	(If the message gets lost, we will still clean the dead DB eventually
   *	via future invocations of pgstat_vacuum_stat().)
   * ----------
   */
  void
  pgstat_drop_database(Oid databaseid)
  {
  	PgStat_MsgDropdb msg;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DROPDB);
  	msg.m_databaseid = databaseid;
  	pgstat_send(&msg, sizeof(msg));
  }
  
  
  /* ----------
   * pgstat_drop_relation() -
   *
   *	Tell the collector that we just dropped a relation.
   *	(If the message gets lost, we will still clean the dead entry eventually
   *	via future invocations of pgstat_vacuum_stat().)
   *
   *	Currently not used for lack of any good place to call it; we rely
   *	entirely on pgstat_vacuum_stat() to clean out stats for dead rels.
   * ----------
   */
  #ifdef NOT_USED
  void
  pgstat_drop_relation(Oid relid)
  {
  	PgStat_MsgTabpurge msg;
  	int			len;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	msg.m_tableid[0] = relid;
  	msg.m_nentries = 1;
  
  	len = offsetof(PgStat_MsgTabpurge, m_tableid[0]) + sizeof(Oid);
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
  	msg.m_databaseid = MyDatabaseId;
  	pgstat_send(&msg, len);
  }
  #endif							/* NOT_USED */
  
  
  /* ----------
   * pgstat_send_connstats() -
   *
   *	Tell the collector about session statistics.
   *	The parameter "disconnect" will be true when the backend exits.
   *	"last_report" is the last time we were called (0 if never).
   * ----------
   */
  static void
  pgstat_send_connstats(bool disconnect, TimestampTz last_report)
  {
  	PgStat_MsgConn msg;
  	long		secs;
  	int			usecs;
  
  	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_CONNECTION);
  	msg.m_databaseid = MyDatabaseId;
  
  	/* session time since the last report */
  	TimestampDifference(((last_report == 0) ? MyStartTimestamp : last_report),
  						GetCurrentTimestamp(),
  						&secs, &usecs);
  	msg.m_session_time = secs * 1000000 + usecs;
  
  	msg.m_disconnect = disconnect ? pgStatSessionEndCause : DISCONNECT_NOT_YET;
  
  	msg.m_active_time = pgStatActiveTime;
  	pgStatActiveTime = 0;
  
  	msg.m_idle_in_xact_time = pgStatTransactionIdleTime;
  	pgStatTransactionIdleTime = 0;
  
  	/* report a new session only the first time */
  	msg.m_count = (last_report == 0) ? 1 : 0;
  
  	pgstat_send(&msg, sizeof(PgStat_MsgConn));
  }
  
  
  /* ----------
   * pgstat_reset_counters() -
   *
   *	Tell the statistics collector to reset counters for our database.
   *
   *	Permission checking for this function is managed through the normal
   *	GRANT system.
   * ----------
   */
  void
  pgstat_reset_counters(void)
  {
  	PgStat_MsgResetcounter msg;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETCOUNTER);
  	msg.m_databaseid = MyDatabaseId;
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* ----------
   * pgstat_reset_shared_counters() -
   *
   *	Tell the statistics collector to reset cluster-wide shared counters.
   *
   *	Permission checking for this function is managed through the normal
   *	GRANT system.
   * ----------
   */
  void
  pgstat_reset_shared_counters(const char *target)
  {
  	PgStat_MsgResetsharedcounter msg;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	if (strcmp(target, "archiver") == 0)
  		msg.m_resettarget = RESET_ARCHIVER;
  	else if (strcmp(target, "bgwriter") == 0)
  		msg.m_resettarget = RESET_BGWRITER;
  	else if (strcmp(target, "wal") == 0)
  		msg.m_resettarget = RESET_WAL;
  	else
  		ereport(ERROR,
  				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
  				 errmsg("unrecognized reset target: \"%s\"", target),
  				 errhint("Target must be \"archiver\", \"bgwriter\" or \"wal\".")));
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSHAREDCOUNTER);
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* ----------
   * pgstat_reset_single_counter() -
   *
   *	Tell the statistics collector to reset a single counter.
   *
   *	Permission checking for this function is managed through the normal
   *	GRANT system.
   * ----------
   */
  void
  pgstat_reset_single_counter(Oid objoid, PgStat_Single_Reset_Type type)
  {
  	PgStat_MsgResetsinglecounter msg;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSINGLECOUNTER);
  	msg.m_databaseid = MyDatabaseId;
  	msg.m_resettype = type;
  	msg.m_objectid = objoid;
  
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* ----------
   * pgstat_reset_slru_counter() -
   *
   *	Tell the statistics collector to reset a single SLRU counter, or all
   *	SLRU counters (when name is null).
   *
   *	Permission checking for this function is managed through the normal
   *	GRANT system.
   * ----------
   */
  void
  pgstat_reset_slru_counter(const char *name)
  {
  	PgStat_MsgResetslrucounter msg;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSLRUCOUNTER);
  	msg.m_index = (name) ? pgstat_slru_index(name) : -1;
  
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* ----------
   * pgstat_reset_replslot_counter() -
   *
   *	Tell the statistics collector to reset a single replication slot
   *	counter, or all replication slots counters (when name is null).
   *
   *	Permission checking for this function is managed through the normal
   *	GRANT system.
   * ----------
   */
  void
  pgstat_reset_replslot_counter(const char *name)
  {
  	PgStat_MsgResetreplslotcounter msg;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	if (name)
  	{
  		ReplicationSlot *slot;
  
  		/*
  		 * Check if the slot exits with the given name. It is possible that by
  		 * the time this message is executed the slot is dropped but at least
  		 * this check will ensure that the given name is for a valid slot.
  		 */
  		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
  		slot = SearchNamedReplicationSlot(name);
  		LWLockRelease(ReplicationSlotControlLock);
  
  		if (!slot)
  			ereport(ERROR,
  					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
  					 errmsg("replication slot \"%s\" does not exist",
  							name)));
  
  		/*
  		 * Nothing to do for physical slots as we collect stats only for
  		 * logical slots.
  		 */
  		if (SlotIsPhysical(slot))
  			return;
  
  		strlcpy(msg.m_slotname, name, NAMEDATALEN);
  		msg.clearall = false;
  	}
  	else
  		msg.clearall = true;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETREPLSLOTCOUNTER);
  
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* ----------
   * pgstat_report_autovac() -
   *
   *	Called from autovacuum.c to report startup of an autovacuum process.
   *	We are called before InitPostgres is done, so can't rely on MyDatabaseId;
   *	the db OID must be passed in, instead.
   * ----------
   */
  void
  pgstat_report_autovac(Oid dboid)
  {
  	PgStat_MsgAutovacStart msg;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_AUTOVAC_START);
  	msg.m_databaseid = dboid;
  	msg.m_start_time = GetCurrentTimestamp();
  
  	pgstat_send(&msg, sizeof(msg));
  }
  
  
  /* ---------
   * pgstat_report_vacuum() -
   *
   *	Tell the collector about the table we just vacuumed.
   * ---------
   */
  void
  pgstat_report_vacuum(Oid tableoid, bool shared,
  					 PgStat_Counter livetuples, PgStat_Counter deadtuples)
  {
  	PgStat_MsgVacuum msg;
  
  	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_VACUUM);
  	msg.m_databaseid = shared ? InvalidOid : MyDatabaseId;
  	msg.m_tableoid = tableoid;
  	msg.m_autovacuum = IsAutoVacuumWorkerProcess();
  	msg.m_vacuumtime = GetCurrentTimestamp();
  	msg.m_live_tuples = livetuples;
  	msg.m_dead_tuples = deadtuples;
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* --------
   * pgstat_report_analyze() -
   *
   *	Tell the collector about the table we just analyzed.
   *
   * Caller must provide new live- and dead-tuples estimates, as well as a
   * flag indicating whether to reset the changes_since_analyze counter.
   * --------
   */
  void
  pgstat_report_analyze(Relation rel,
  					  PgStat_Counter livetuples, PgStat_Counter deadtuples,
  					  bool resetcounter)
  {
  	PgStat_MsgAnalyze msg;
  
  	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
  		return;
  
  	/*
  	 * Unlike VACUUM, ANALYZE might be running inside a transaction that has
  	 * already inserted and/or deleted rows in the target table. ANALYZE will
  	 * have counted such rows as live or dead respectively. Because we will
  	 * report our counts of such rows at transaction end, we should subtract
  	 * off these counts from what we send to the collector now, else they'll
  	 * be double-counted after commit.  (This approach also ensures that the
  	 * collector ends up with the right numbers if we abort instead of
  	 * committing.)
  	 */
  	if (rel->pgstat_info != NULL)
  	{
  		PgStat_TableXactStatus *trans;
  
  		for (trans = rel->pgstat_info->trans; trans; trans = trans->upper)
  		{
  			livetuples -= trans->tuples_inserted - trans->tuples_deleted;
  			deadtuples -= trans->tuples_updated + trans->tuples_deleted;
  		}
  		/* count stuff inserted by already-aborted subxacts, too */
  		deadtuples -= rel->pgstat_info->t_counts.t_delta_dead_tuples;
  		/* Since ANALYZE's counts are estimates, we could have underflowed */
  		livetuples = Max(livetuples, 0);
  		deadtuples = Max(deadtuples, 0);
  	}
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_ANALYZE);
  	msg.m_databaseid = rel->rd_rel->relisshared ? InvalidOid : MyDatabaseId;
  	msg.m_tableoid = RelationGetRelid(rel);
  	msg.m_autovacuum = IsAutoVacuumWorkerProcess();
  	msg.m_resetcounter = resetcounter;
  	msg.m_analyzetime = GetCurrentTimestamp();
  	msg.m_live_tuples = livetuples;
  	msg.m_dead_tuples = deadtuples;
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* --------
   * pgstat_report_recovery_conflict() -
   *
   *	Tell the collector about a Hot Standby recovery conflict.
   * --------
   */
  void
  pgstat_report_recovery_conflict(int reason)
  {
  	PgStat_MsgRecoveryConflict msg;
  
  	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RECOVERYCONFLICT);
  	msg.m_databaseid = MyDatabaseId;
  	msg.m_reason = reason;
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* --------
   * pgstat_report_deadlock() -
   *
   *	Tell the collector about a deadlock detected.
   * --------
   */
  void
  pgstat_report_deadlock(void)
  {
  	PgStat_MsgDeadlock msg;
  
  	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DEADLOCK);
  	msg.m_databaseid = MyDatabaseId;
  	pgstat_send(&msg, sizeof(msg));
  }
  
  
  
  /* --------
   * pgstat_report_checksum_failures_in_db() -
   *
   *	Tell the collector about one or more checksum failures.
   * --------
   */
  void
  pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount)
  {
  	PgStat_MsgChecksumFailure msg;
  
  	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_CHECKSUMFAILURE);
  	msg.m_databaseid = dboid;
  	msg.m_failurecount = failurecount;
  	msg.m_failure_time = GetCurrentTimestamp();
  
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* --------
   * pgstat_report_checksum_failure() -
   *
   *	Tell the collector about a checksum failure.
   * --------
   */
  void
  pgstat_report_checksum_failure(void)
  {
  	pgstat_report_checksum_failures_in_db(MyDatabaseId, 1);
  }
  
  /* --------
   * pgstat_report_tempfile() -
   *
   *	Tell the collector about a temporary file.
   * --------
   */
  void
  pgstat_report_tempfile(size_t filesize)
  {
  	PgStat_MsgTempFile msg;
  
  	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TEMPFILE);
  	msg.m_databaseid = MyDatabaseId;
  	msg.m_filesize = filesize;
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* ----------
   * pgstat_report_replslot() -
   *
   *	Tell the collector about replication slot statistics.
   * ----------
   */
  void
  pgstat_report_replslot(const char *slotname, int spilltxns, int spillcount,
  					   int spillbytes, int streamtxns, int streamcount, int streambytes)
  {
  	PgStat_MsgReplSlot msg;
  
  	/*
  	 * Prepare and send the message
  	 */
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_REPLSLOT);
  	strlcpy(msg.m_slotname, slotname, NAMEDATALEN);
  	msg.m_drop = false;
  	msg.m_spill_txns = spilltxns;
  	msg.m_spill_count = spillcount;
  	msg.m_spill_bytes = spillbytes;
  	msg.m_stream_txns = streamtxns;
  	msg.m_stream_count = streamcount;
  	msg.m_stream_bytes = streambytes;
  	pgstat_send(&msg, sizeof(PgStat_MsgReplSlot));
  }
  
  /* ----------
   * pgstat_report_replslot_drop() -
   *
   *	Tell the collector about dropping the replication slot.
   * ----------
   */
  void
  pgstat_report_replslot_drop(const char *slotname)
  {
  	PgStat_MsgReplSlot msg;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_REPLSLOT);
  	strlcpy(msg.m_slotname, slotname, NAMEDATALEN);
  	msg.m_drop = true;
  	pgstat_send(&msg, sizeof(PgStat_MsgReplSlot));
  }
  
  /* ----------
   * pgstat_ping() -
   *
   *	Send some junk data to the collector to increase traffic.
   * ----------
   */
  void
  pgstat_ping(void)
  {
  	PgStat_MsgDummy msg;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DUMMY);
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* ----------
   * pgstat_send_inquiry() -
   *
   *	Notify collector that we need fresh data.
   * ----------
   */
  static void
  pgstat_send_inquiry(TimestampTz clock_time, TimestampTz cutoff_time, Oid databaseid)
  {
  	PgStat_MsgInquiry msg;
  
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_INQUIRY);
  	msg.clock_time = clock_time;
  	msg.cutoff_time = cutoff_time;
  	msg.databaseid = databaseid;
  	pgstat_send(&msg, sizeof(msg));
  }
  
  
  /*
   * Initialize function call usage data.
   * Called by the executor before invoking a function.
   */
  void
  pgstat_init_function_usage(FunctionCallInfo fcinfo,
  						   PgStat_FunctionCallUsage *fcu)
  {
  	PgStat_BackendFunctionEntry *htabent;
  	bool		found;
  
  	if (pgstat_track_functions <= fcinfo->flinfo->fn_stats)
  	{
  		/* stats not wanted */
  		fcu->fs = NULL;
  		return;
  	}
  
  	if (!pgStatFunctions)
  	{
  		/* First time through - initialize function stat table */
  		HASHCTL		hash_ctl;
  
  		hash_ctl.keysize = sizeof(Oid);
  		hash_ctl.entrysize = sizeof(PgStat_BackendFunctionEntry);
  		pgStatFunctions = hash_create("Function stat entries",
  									  PGSTAT_FUNCTION_HASH_SIZE,
  									  &hash_ctl,
  									  HASH_ELEM | HASH_BLOBS);
  	}
  
  	/* Get the stats entry for this function, create if necessary */
  	htabent = hash_search(pgStatFunctions, &fcinfo->flinfo->fn_oid,
  						  HASH_ENTER, &found);
  	if (!found)
  		MemSet(&htabent->f_counts, 0, sizeof(PgStat_FunctionCounts));
  
  	fcu->fs = &htabent->f_counts;
  
  	/* save stats for this function, later used to compensate for recursion */
  	fcu->save_f_total_time = htabent->f_counts.f_total_time;
  
  	/* save current backend-wide total time */
  	fcu->save_total = total_func_time;
  
  	/* get clock time as of function start */
  	INSTR_TIME_SET_CURRENT(fcu->f_start);
  }
  
  /*
   * find_funcstat_entry - find any existing PgStat_BackendFunctionEntry entry
   *		for specified function
   *
   * If no entry, return NULL, don't create a new one
   */
  PgStat_BackendFunctionEntry *
  find_funcstat_entry(Oid func_id)
  {
  	if (pgStatFunctions == NULL)
  		return NULL;
  
  	return (PgStat_BackendFunctionEntry *) hash_search(pgStatFunctions,
  													   (void *) &func_id,
  													   HASH_FIND, NULL);
  }
  
  /*
   * Calculate function call usage and update stat counters.
   * Called by the executor after invoking a function.
   *
   * In the case of a set-returning function that runs in value-per-call mode,
   * we will see multiple pgstat_init_function_usage/pgstat_end_function_usage
   * calls for what the user considers a single call of the function.  The
   * finalize flag should be TRUE on the last call.
   */
  void
  pgstat_end_function_usage(PgStat_FunctionCallUsage *fcu, bool finalize)
  {
  	PgStat_FunctionCounts *fs = fcu->fs;
  	instr_time	f_total;
  	instr_time	f_others;
  	instr_time	f_self;
  
  	/* stats not wanted? */
  	if (fs == NULL)
  		return;
  
  	/* total elapsed time in this function call */
  	INSTR_TIME_SET_CURRENT(f_total);
  	INSTR_TIME_SUBTRACT(f_total, fcu->f_start);
  
  	/* self usage: elapsed minus anything already charged to other calls */
  	f_others = total_func_time;
  	INSTR_TIME_SUBTRACT(f_others, fcu->save_total);
  	f_self = f_total;
  	INSTR_TIME_SUBTRACT(f_self, f_others);
  
  	/* update backend-wide total time */
  	INSTR_TIME_ADD(total_func_time, f_self);
  
  	/*
  	 * Compute the new f_total_time as the total elapsed time added to the
  	 * pre-call value of f_total_time.  This is necessary to avoid
  	 * double-counting any time taken by recursive calls of myself.  (We do
  	 * not need any similar kluge for self time, since that already excludes
  	 * any recursive calls.)
  	 */
  	INSTR_TIME_ADD(f_total, fcu->save_f_total_time);
  
  	/* update counters in function stats table */
  	if (finalize)
  		fs->f_numcalls++;
  	fs->f_total_time = f_total;
  	INSTR_TIME_ADD(fs->f_self_time, f_self);
  
  	/* indicate that we have something to send */
  	have_function_stats = true;
  }
  
  
  /* ----------
   * pgstat_initstats() -
   *
   *	Initialize a relcache entry to count access statistics.
   *	Called whenever a relation is opened.
   *
   *	We assume that a relcache entry's pgstat_info field is zeroed by
   *	relcache.c when the relcache entry is made; thereafter it is long-lived
   *	data.  We can avoid repeated searches of the TabStatus arrays when the
   *	same relation is touched repeatedly within a transaction.
   * ----------
   */
  void
  pgstat_initstats(Relation rel)
  {
  	Oid			rel_id = rel->rd_id;
  	char		relkind = rel->rd_rel->relkind;
  
  	/* We only count stats for things that have storage */
  	if (!RELKIND_HAS_STORAGE(relkind))
  	{
  		rel->pgstat_info = NULL;
  		return;
  	}
  
  	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
  	{
  		/* We're not counting at all */
  		rel->pgstat_info = NULL;
  		return;
  	}
  
  	/*
  	 * If we already set up this relation in the current transaction, nothing
  	 * to do.
  	 */
  	if (rel->pgstat_info != NULL &&
  		rel->pgstat_info->t_id == rel_id)
  		return;
  
  	/* Else find or make the PgStat_TableStatus entry, and update link */
  	rel->pgstat_info = get_tabstat_entry(rel_id, rel->rd_rel->relisshared);
  }
  
  /*
   * get_tabstat_entry - find or create a PgStat_TableStatus entry for rel
   */
  static PgStat_TableStatus *
  get_tabstat_entry(Oid rel_id, bool isshared)
  {
  	TabStatHashEntry *hash_entry;
  	PgStat_TableStatus *entry;
  	TabStatusArray *tsa;
  	bool		found;
  
  	/*
  	 * Create hash table if we don't have it already.
  	 */
  	if (pgStatTabHash == NULL)
  	{
  		HASHCTL		ctl;
  
  		ctl.keysize = sizeof(Oid);
  		ctl.entrysize = sizeof(TabStatHashEntry);
  
  		pgStatTabHash = hash_create("pgstat TabStatusArray lookup hash table",
  									TABSTAT_QUANTUM,
  									&ctl,
  									HASH_ELEM | HASH_BLOBS);
  	}
  
  	/*
  	 * Find an entry or create a new one.
  	 */
  	hash_entry = hash_search(pgStatTabHash, &rel_id, HASH_ENTER, &found);
  	if (!found)
  	{
  		/* initialize new entry with null pointer */
  		hash_entry->tsa_entry = NULL;
  	}
  
  	/*
  	 * If entry is already valid, we're done.
  	 */
  	if (hash_entry->tsa_entry)
  		return hash_entry->tsa_entry;
  
  	/*
  	 * Locate the first pgStatTabList entry with free space, making a new list
  	 * entry if needed.  Note that we could get an OOM failure here, but if so
  	 * we have left the hashtable and the list in a consistent state.
  	 */
  	if (pgStatTabList == NULL)
  	{
  		/* Set up first pgStatTabList entry */
  		pgStatTabList = (TabStatusArray *)
  			MemoryContextAllocZero(TopMemoryContext,
  								   sizeof(TabStatusArray));
  	}
  
  	tsa = pgStatTabList;
  	while (tsa->tsa_used >= TABSTAT_QUANTUM)
  	{
  		if (tsa->tsa_next == NULL)
  			tsa->tsa_next = (TabStatusArray *)
  				MemoryContextAllocZero(TopMemoryContext,
  									   sizeof(TabStatusArray));
  		tsa = tsa->tsa_next;
  	}
  
  	/*
  	 * Allocate a PgStat_TableStatus entry within this list entry.  We assume
  	 * the entry was already zeroed, either at creation or after last use.
  	 */
  	entry = &tsa->tsa_entries[tsa->tsa_used++];
  	entry->t_id = rel_id;
  	entry->t_shared = isshared;
  
  	/*
  	 * Now we can fill the entry in pgStatTabHash.
  	 */
  	hash_entry->tsa_entry = entry;
  
  	return entry;
  }
  
  /*
   * find_tabstat_entry - find any existing PgStat_TableStatus entry for rel
   *
   * If no entry, return NULL, don't create a new one
   *
   * Note: if we got an error in the most recent execution of pgstat_report_stat,
   * it's possible that an entry exists but there's no hashtable entry for it.
   * That's okay, we'll treat this case as "doesn't exist".
   */
  PgStat_TableStatus *
  find_tabstat_entry(Oid rel_id)
  {
  	TabStatHashEntry *hash_entry;
  
  	/* If hashtable doesn't exist, there are no entries at all */
  	if (!pgStatTabHash)
  		return NULL;
  
  	hash_entry = hash_search(pgStatTabHash, &rel_id, HASH_FIND, NULL);
  	if (!hash_entry)
  		return NULL;
  
  	/* Note that this step could also return NULL, but that's correct */
  	return hash_entry->tsa_entry;
  }
  
  /*
   * get_tabstat_stack_level - add a new (sub)transaction stack entry if needed
   */
  static PgStat_SubXactStatus *
  get_tabstat_stack_level(int nest_level)
  {
  	PgStat_SubXactStatus *xact_state;
  
  	xact_state = pgStatXactStack;
  	if (xact_state == NULL || xact_state->nest_level != nest_level)
  	{
  		xact_state = (PgStat_SubXactStatus *)
  			MemoryContextAlloc(TopTransactionContext,
  							   sizeof(PgStat_SubXactStatus));
  		xact_state->nest_level = nest_level;
  		xact_state->prev = pgStatXactStack;
  		xact_state->first = NULL;
  		pgStatXactStack = xact_state;
  	}
  	return xact_state;
  }
  
  /*
   * add_tabstat_xact_level - add a new (sub)transaction state record
   */
  static void
  add_tabstat_xact_level(PgStat_TableStatus *pgstat_info, int nest_level)
  {
  	PgStat_SubXactStatus *xact_state;
  	PgStat_TableXactStatus *trans;
  
  	/*
  	 * If this is the first rel to be modified at the current nest level, we
  	 * first have to push a transaction stack entry.
  	 */
  	xact_state = get_tabstat_stack_level(nest_level);
  
  	/* Now make a per-table stack entry */
  	trans = (PgStat_TableXactStatus *)
  		MemoryContextAllocZero(TopTransactionContext,
  							   sizeof(PgStat_TableXactStatus));
  	trans->nest_level = nest_level;
  	trans->upper = pgstat_info->trans;
  	trans->parent = pgstat_info;
  	trans->next = xact_state->first;
  	xact_state->first = trans;
  	pgstat_info->trans = trans;
  }
  
  /*
   * pgstat_count_heap_insert - count a tuple insertion of n tuples
   */
  void
  pgstat_count_heap_insert(Relation rel, PgStat_Counter n)
  {
  	PgStat_TableStatus *pgstat_info = rel->pgstat_info;
  
  	if (pgstat_info != NULL)
  	{
  		/* We have to log the effect at the proper transactional level */
  		int			nest_level = GetCurrentTransactionNestLevel();
  
  		if (pgstat_info->trans == NULL ||
  			pgstat_info->trans->nest_level != nest_level)
  			add_tabstat_xact_level(pgstat_info, nest_level);
  
  		pgstat_info->trans->tuples_inserted += n;
  	}
  }
  
  /*
   * pgstat_count_heap_update - count a tuple update
   */
  void
  pgstat_count_heap_update(Relation rel, bool hot)
  {
  	PgStat_TableStatus *pgstat_info = rel->pgstat_info;
  
  	if (pgstat_info != NULL)
  	{
  		/* We have to log the effect at the proper transactional level */
  		int			nest_level = GetCurrentTransactionNestLevel();
  
  		if (pgstat_info->trans == NULL ||
  			pgstat_info->trans->nest_level != nest_level)
  			add_tabstat_xact_level(pgstat_info, nest_level);
  
  		pgstat_info->trans->tuples_updated++;
  
  		/* t_tuples_hot_updated is nontransactional, so just advance it */
  		if (hot)
  			pgstat_info->t_counts.t_tuples_hot_updated++;
  	}
  }
  
  /*
   * pgstat_count_heap_delete - count a tuple deletion
   */
  void
  pgstat_count_heap_delete(Relation rel)
  {
  	PgStat_TableStatus *pgstat_info = rel->pgstat_info;
  
  	if (pgstat_info != NULL)
  	{
  		/* We have to log the effect at the proper transactional level */
  		int			nest_level = GetCurrentTransactionNestLevel();
  
  		if (pgstat_info->trans == NULL ||
  			pgstat_info->trans->nest_level != nest_level)
  			add_tabstat_xact_level(pgstat_info, nest_level);
  
  		pgstat_info->trans->tuples_deleted++;
  	}
  }
  
  /*
   * pgstat_truncate_save_counters
   *
   * Whenever a table is truncated, we save its i/u/d counters so that they can
   * be cleared, and if the (sub)xact that executed the truncate later aborts,
   * the counters can be restored to the saved (pre-truncate) values.  Note we do
   * this on the first truncate in any particular subxact level only.
   */
  static void
  pgstat_truncate_save_counters(PgStat_TableXactStatus *trans)
  {
  	if (!trans->truncated)
  	{
  		trans->inserted_pre_trunc = trans->tuples_inserted;
  		trans->updated_pre_trunc = trans->tuples_updated;
  		trans->deleted_pre_trunc = trans->tuples_deleted;
  		trans->truncated = true;
  	}
  }
  
  /*
   * pgstat_truncate_restore_counters - restore counters when a truncate aborts
   */
  static void
  pgstat_truncate_restore_counters(PgStat_TableXactStatus *trans)
  {
  	if (trans->truncated)
  	{
  		trans->tuples_inserted = trans->inserted_pre_trunc;
  		trans->tuples_updated = trans->updated_pre_trunc;
  		trans->tuples_deleted = trans->deleted_pre_trunc;
  	}
  }
  
  /*
   * pgstat_count_truncate - update tuple counters due to truncate
   */
  void
  pgstat_count_truncate(Relation rel)
  {
  	PgStat_TableStatus *pgstat_info = rel->pgstat_info;
  
  	if (pgstat_info != NULL)
  	{
  		/* We have to log the effect at the proper transactional level */
  		int			nest_level = GetCurrentTransactionNestLevel();
  
  		if (pgstat_info->trans == NULL ||
  			pgstat_info->trans->nest_level != nest_level)
  			add_tabstat_xact_level(pgstat_info, nest_level);
  
  		pgstat_truncate_save_counters(pgstat_info->trans);
  		pgstat_info->trans->tuples_inserted = 0;
  		pgstat_info->trans->tuples_updated = 0;
  		pgstat_info->trans->tuples_deleted = 0;
  	}
  }
  
  /*
   * pgstat_update_heap_dead_tuples - update dead-tuples count
   *
   * The semantics of this are that we are reporting the nontransactional
   * recovery of "delta" dead tuples; so t_delta_dead_tuples decreases
   * rather than increasing, and the change goes straight into the per-table
   * counter, not into transactional state.
   */
  void
  pgstat_update_heap_dead_tuples(Relation rel, int delta)
  {
  	PgStat_TableStatus *pgstat_info = rel->pgstat_info;
  
  	if (pgstat_info != NULL)
  		pgstat_info->t_counts.t_delta_dead_tuples -= delta;
  }
  
  
  /* ----------
   * AtEOXact_PgStat
   *
   *	Called from access/transam/xact.c at top-level transaction commit/abort.
   * ----------
   */
  void
  AtEOXact_PgStat(bool isCommit, bool parallel)
  {
  	PgStat_SubXactStatus *xact_state;
  
  	/* Don't count parallel worker transaction stats */
  	if (!parallel)
  	{
  		/*
  		 * Count transaction commit or abort.  (We use counters, not just
  		 * bools, in case the reporting message isn't sent right away.)
  		 */
  		if (isCommit)
  			pgStatXactCommit++;
  		else
  			pgStatXactRollback++;
  	}
  
  	/*
  	 * Transfer transactional insert/update counts into the base tabstat
  	 * entries.  We don't bother to free any of the transactional state, since
  	 * it's all in TopTransactionContext and will go away anyway.
  	 */
  	xact_state = pgStatXactStack;
  	if (xact_state != NULL)
  	{
  		PgStat_TableXactStatus *trans;
  
  		Assert(xact_state->nest_level == 1);
  		Assert(xact_state->prev == NULL);
  		for (trans = xact_state->first; trans != NULL; trans = trans->next)
  		{
  			PgStat_TableStatus *tabstat;
  
  			Assert(trans->nest_level == 1);
  			Assert(trans->upper == NULL);
  			tabstat = trans->parent;
  			Assert(tabstat->trans == trans);
  			/* restore pre-truncate stats (if any) in case of aborted xact */
  			if (!isCommit)
  				pgstat_truncate_restore_counters(trans);
  			/* count attempted actions regardless of commit/abort */
  			tabstat->t_counts.t_tuples_inserted += trans->tuples_inserted;
  			tabstat->t_counts.t_tuples_updated += trans->tuples_updated;
  			tabstat->t_counts.t_tuples_deleted += trans->tuples_deleted;
  			if (isCommit)
  			{
  				tabstat->t_counts.t_truncated = trans->truncated;
  				if (trans->truncated)
  				{
  					/* forget live/dead stats seen by backend thus far */
  					tabstat->t_counts.t_delta_live_tuples = 0;
  					tabstat->t_counts.t_delta_dead_tuples = 0;
  				}
  				/* insert adds a live tuple, delete removes one */
  				tabstat->t_counts.t_delta_live_tuples +=
  					trans->tuples_inserted - trans->tuples_deleted;
  				/* update and delete each create a dead tuple */
  				tabstat->t_counts.t_delta_dead_tuples +=
  					trans->tuples_updated + trans->tuples_deleted;
  				/* insert, update, delete each count as one change event */
  				tabstat->t_counts.t_changed_tuples +=
  					trans->tuples_inserted + trans->tuples_updated +
  					trans->tuples_deleted;
  			}
  			else
  			{
  				/* inserted tuples are dead, deleted tuples are unaffected */
  				tabstat->t_counts.t_delta_dead_tuples +=
  					trans->tuples_inserted + trans->tuples_updated;
  				/* an aborted xact generates no changed_tuple events */
  			}
  			tabstat->trans = NULL;
  		}
  	}
  	pgStatXactStack = NULL;
  
  	/* Make sure any stats snapshot is thrown away */
  	pgstat_clear_snapshot();
  }
  
  /* ----------
   * AtEOSubXact_PgStat
   *
   *	Called from access/transam/xact.c at subtransaction commit/abort.
   * ----------
   */
  void
  AtEOSubXact_PgStat(bool isCommit, int nestDepth)
  {
  	PgStat_SubXactStatus *xact_state;
  
  	/*
  	 * Transfer transactional insert/update counts into the next higher
  	 * subtransaction state.
  	 */
  	xact_state = pgStatXactStack;
  	if (xact_state != NULL &&
  		xact_state->nest_level >= nestDepth)
  	{
  		PgStat_TableXactStatus *trans;
  		PgStat_TableXactStatus *next_trans;
  
  		/* delink xact_state from stack immediately to simplify reuse case */
  		pgStatXactStack = xact_state->prev;
  
  		for (trans = xact_state->first; trans != NULL; trans = next_trans)
  		{
  			PgStat_TableStatus *tabstat;
  
  			next_trans = trans->next;
  			Assert(trans->nest_level == nestDepth);
  			tabstat = trans->parent;
  			Assert(tabstat->trans == trans);
  			if (isCommit)
  			{
  				if (trans->upper && trans->upper->nest_level == nestDepth - 1)
  				{
  					if (trans->truncated)
  					{
  						/* propagate the truncate status one level up */
  						pgstat_truncate_save_counters(trans->upper);
  						/* replace upper xact stats with ours */
  						trans->upper->tuples_inserted = trans->tuples_inserted;
  						trans->upper->tuples_updated = trans->tuples_updated;
  						trans->upper->tuples_deleted = trans->tuples_deleted;
  					}
  					else
  					{
  						trans->upper->tuples_inserted += trans->tuples_inserted;
  						trans->upper->tuples_updated += trans->tuples_updated;
  						trans->upper->tuples_deleted += trans->tuples_deleted;
  					}
  					tabstat->trans = trans->upper;
  					pfree(trans);
  				}
  				else
  				{
  					/*
  					 * When there isn't an immediate parent state, we can just
  					 * reuse the record instead of going through a
  					 * palloc/pfree pushup (this works since it's all in
  					 * TopTransactionContext anyway).  We have to re-link it
  					 * into the parent level, though, and that might mean
  					 * pushing a new entry into the pgStatXactStack.
  					 */
  					PgStat_SubXactStatus *upper_xact_state;
  
  					upper_xact_state = get_tabstat_stack_level(nestDepth - 1);
  					trans->next = upper_xact_state->first;
  					upper_xact_state->first = trans;
  					trans->nest_level = nestDepth - 1;
  				}
  			}
  			else
  			{
  				/*
  				 * On abort, update top-level tabstat counts, then forget the
  				 * subtransaction
  				 */
  
  				/* first restore values obliterated by truncate */
  				pgstat_truncate_restore_counters(trans);
  				/* count attempted actions regardless of commit/abort */
  				tabstat->t_counts.t_tuples_inserted += trans->tuples_inserted;
  				tabstat->t_counts.t_tuples_updated += trans->tuples_updated;
  				tabstat->t_counts.t_tuples_deleted += trans->tuples_deleted;
  				/* inserted tuples are dead, deleted tuples are unaffected */
  				tabstat->t_counts.t_delta_dead_tuples +=
  					trans->tuples_inserted + trans->tuples_updated;
  				tabstat->trans = trans->upper;
  				pfree(trans);
  			}
  		}
  		pfree(xact_state);
  	}
  }
  
  
  /*
   * AtPrepare_PgStat
   *		Save the transactional stats state at 2PC transaction prepare.
   *
   * In this phase we just generate 2PC records for all the pending
   * transaction-dependent stats work.
   */
  void
  AtPrepare_PgStat(void)
  {
  	PgStat_SubXactStatus *xact_state;
  
  	xact_state = pgStatXactStack;
  	if (xact_state != NULL)
  	{
  		PgStat_TableXactStatus *trans;
  
  		Assert(xact_state->nest_level == 1);
  		Assert(xact_state->prev == NULL);
  		for (trans = xact_state->first; trans != NULL; trans = trans->next)
  		{
  			PgStat_TableStatus *tabstat;
  			TwoPhasePgStatRecord record;
  
  			Assert(trans->nest_level == 1);
  			Assert(trans->upper == NULL);
  			tabstat = trans->parent;
  			Assert(tabstat->trans == trans);
  
  			record.tuples_inserted = trans->tuples_inserted;
  			record.tuples_updated = trans->tuples_updated;
  			record.tuples_deleted = trans->tuples_deleted;
  			record.inserted_pre_trunc = trans->inserted_pre_trunc;
  			record.updated_pre_trunc = trans->updated_pre_trunc;
  			record.deleted_pre_trunc = trans->deleted_pre_trunc;
  			record.t_id = tabstat->t_id;
  			record.t_shared = tabstat->t_shared;
  			record.t_truncated = trans->truncated;
  
  			RegisterTwoPhaseRecord(TWOPHASE_RM_PGSTAT_ID, 0,
  								   &record, sizeof(TwoPhasePgStatRecord));
  		}
  	}
  }
  
  /*
   * PostPrepare_PgStat
   *		Clean up after successful PREPARE.
   *
   * All we need do here is unlink the transaction stats state from the
   * nontransactional state.  The nontransactional action counts will be
   * reported to the stats collector immediately, while the effects on live
   * and dead tuple counts are preserved in the 2PC state file.
   *
   * Note: AtEOXact_PgStat is not called during PREPARE.
   */
  void
  PostPrepare_PgStat(void)
  {
  	PgStat_SubXactStatus *xact_state;
  
  	/*
  	 * We don't bother to free any of the transactional state, since it's all
  	 * in TopTransactionContext and will go away anyway.
  	 */
  	xact_state = pgStatXactStack;
  	if (xact_state != NULL)
  	{
  		PgStat_TableXactStatus *trans;
  
  		for (trans = xact_state->first; trans != NULL; trans = trans->next)
  		{
  			PgStat_TableStatus *tabstat;
  
  			tabstat = trans->parent;
  			tabstat->trans = NULL;
  		}
  	}
  	pgStatXactStack = NULL;
  
  	/* Make sure any stats snapshot is thrown away */
  	pgstat_clear_snapshot();
  }
  
  /*
   * 2PC processing routine for COMMIT PREPARED case.
   *
   * Load the saved counts into our local pgstats state.
   */
  void
  pgstat_twophase_postcommit(TransactionId xid, uint16 info,
  						   void *recdata, uint32 len)
  {
  	TwoPhasePgStatRecord *rec = (TwoPhasePgStatRecord *) recdata;
  	PgStat_TableStatus *pgstat_info;
  
  	/* Find or create a tabstat entry for the rel */
  	pgstat_info = get_tabstat_entry(rec->t_id, rec->t_shared);
  
  	/* Same math as in AtEOXact_PgStat, commit case */
  	pgstat_info->t_counts.t_tuples_inserted += rec->tuples_inserted;
  	pgstat_info->t_counts.t_tuples_updated += rec->tuples_updated;
  	pgstat_info->t_counts.t_tuples_deleted += rec->tuples_deleted;
  	pgstat_info->t_counts.t_truncated = rec->t_truncated;
  	if (rec->t_truncated)
  	{
  		/* forget live/dead stats seen by backend thus far */
  		pgstat_info->t_counts.t_delta_live_tuples = 0;
  		pgstat_info->t_counts.t_delta_dead_tuples = 0;
  	}
  	pgstat_info->t_counts.t_delta_live_tuples +=
  		rec->tuples_inserted - rec->tuples_deleted;
  	pgstat_info->t_counts.t_delta_dead_tuples +=
  		rec->tuples_updated + rec->tuples_deleted;
  	pgstat_info->t_counts.t_changed_tuples +=
  		rec->tuples_inserted + rec->tuples_updated +
  		rec->tuples_deleted;
  }
  
  /*
   * 2PC processing routine for ROLLBACK PREPARED case.
   *
   * Load the saved counts into our local pgstats state, but treat them
   * as aborted.
   */
  void
  pgstat_twophase_postabort(TransactionId xid, uint16 info,
  						  void *recdata, uint32 len)
  {
  	TwoPhasePgStatRecord *rec = (TwoPhasePgStatRecord *) recdata;
  	PgStat_TableStatus *pgstat_info;
  
  	/* Find or create a tabstat entry for the rel */
  	pgstat_info = get_tabstat_entry(rec->t_id, rec->t_shared);
  
  	/* Same math as in AtEOXact_PgStat, abort case */
  	if (rec->t_truncated)
  	{
  		rec->tuples_inserted = rec->inserted_pre_trunc;
  		rec->tuples_updated = rec->updated_pre_trunc;
  		rec->tuples_deleted = rec->deleted_pre_trunc;
  	}
  	pgstat_info->t_counts.t_tuples_inserted += rec->tuples_inserted;
  	pgstat_info->t_counts.t_tuples_updated += rec->tuples_updated;
  	pgstat_info->t_counts.t_tuples_deleted += rec->tuples_deleted;
  	pgstat_info->t_counts.t_delta_dead_tuples +=
  		rec->tuples_inserted + rec->tuples_updated;
  }
  
  
  /* ----------
   * pgstat_fetch_stat_dbentry() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	the collected statistics for one database or NULL. NULL doesn't mean
   *	that the database doesn't exist, it is just not yet known by the
   *	collector, so the caller is better off to report ZERO instead.
   * ----------
   */
  PgStat_StatDBEntry *
  pgstat_fetch_stat_dbentry(Oid dbid)
  {
  	/*
  	 * If not done for this transaction, read the statistics collector stats
  	 * file into some hash tables.
  	 */
  	backend_read_statsfile();
  
  	/*
  	 * Lookup the requested database; return NULL if not found
  	 */
  	return (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
  											  (void *) &dbid,
  											  HASH_FIND, NULL);
  }
  
  
  /* ----------
   * pgstat_fetch_stat_tabentry() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	the collected statistics for one table or NULL. NULL doesn't mean
   *	that the table doesn't exist, it is just not yet known by the
   *	collector, so the caller is better off to report ZERO instead.
   * ----------
   */
  PgStat_StatTabEntry *
  pgstat_fetch_stat_tabentry(Oid relid)
  {
  	Oid			dbid;
  	PgStat_StatDBEntry *dbentry;
  	PgStat_StatTabEntry *tabentry;
  
  	/*
  	 * If not done for this transaction, read the statistics collector stats
  	 * file into some hash tables.
  	 */
  	backend_read_statsfile();
  
  	/*
  	 * Lookup our database, then look in its table hash table.
  	 */
  	dbid = MyDatabaseId;
  	dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
  												 (void *) &dbid,
  												 HASH_FIND, NULL);
  	if (dbentry != NULL && dbentry->tables != NULL)
  	{
  		tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
  													   (void *) &relid,
  													   HASH_FIND, NULL);
  		if (tabentry)
  			return tabentry;
  	}
  
  	/*
  	 * If we didn't find it, maybe it's a shared table.
  	 */
  	dbid = InvalidOid;
  	dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
  												 (void *) &dbid,
  												 HASH_FIND, NULL);
  	if (dbentry != NULL && dbentry->tables != NULL)
  	{
  		tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
  													   (void *) &relid,
  													   HASH_FIND, NULL);
  		if (tabentry)
  			return tabentry;
  	}
  
  	return NULL;
  }
  
  
  /* ----------
   * pgstat_fetch_stat_funcentry() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	the collected statistics for one function or NULL.
   * ----------
   */
  PgStat_StatFuncEntry *
  pgstat_fetch_stat_funcentry(Oid func_id)
  {
  	PgStat_StatDBEntry *dbentry;
  	PgStat_StatFuncEntry *funcentry = NULL;
  
  	/* load the stats file if needed */
  	backend_read_statsfile();
  
  	/* Lookup our database, then find the requested function.  */
  	dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
  	if (dbentry != NULL && dbentry->functions != NULL)
  	{
  		funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
  														 (void *) &func_id,
  														 HASH_FIND, NULL);
  	}
  
  	return funcentry;
  }
  
  
  /* ----------
   * pgstat_fetch_stat_beentry() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	our local copy of the current-activity entry for one backend.
   *
   *	NB: caller is responsible for a check if the user is permitted to see
   *	this info (especially the querystring).
   * ----------
   */
  PgBackendStatus *
  pgstat_fetch_stat_beentry(int beid)
  {
  	pgstat_read_current_status();
  
  	if (beid < 1 || beid > localNumBackends)
  		return NULL;
  
  	return &localBackendStatusTable[beid - 1].backendStatus;
  }
  
  
  /* ----------
   * pgstat_fetch_stat_local_beentry() -
   *
   *	Like pgstat_fetch_stat_beentry() but with locally computed additions (like
   *	xid and xmin values of the backend)
   *
   *	NB: caller is responsible for a check if the user is permitted to see
   *	this info (especially the querystring).
   * ----------
   */
  LocalPgBackendStatus *
  pgstat_fetch_stat_local_beentry(int beid)
  {
  	pgstat_read_current_status();
  
  	if (beid < 1 || beid > localNumBackends)
  		return NULL;
  
  	return &localBackendStatusTable[beid - 1];
  }
  
  
  /* ----------
   * pgstat_fetch_stat_numbackends() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	the maximum current backend id.
   * ----------
   */
  int
  pgstat_fetch_stat_numbackends(void)
  {
  	pgstat_read_current_status();
  
  	return localNumBackends;
  }
  
  /*
   * ---------
   * pgstat_fetch_stat_archiver() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	a pointer to the archiver statistics struct.
   * ---------
   */
  PgStat_ArchiverStats *
  pgstat_fetch_stat_archiver(void)
  {
  	backend_read_statsfile();
  
  	return &archiverStats;
  }
  
  
  /*
   * ---------
   * pgstat_fetch_global() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	a pointer to the global statistics struct.
   * ---------
   */
  PgStat_GlobalStats *
  pgstat_fetch_global(void)
  {
  	backend_read_statsfile();
  
  	return &globalStats;
  }
  
  /*
   * ---------
   * pgstat_fetch_stat_wal() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	a pointer to the WAL statistics struct.
   * ---------
   */
  PgStat_WalStats *
  pgstat_fetch_stat_wal(void)
  {
  	backend_read_statsfile();
  
  	return &walStats;
  }
  
  /*
   * ---------
   * pgstat_fetch_slru() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	a pointer to the slru statistics struct.
   * ---------
   */
  PgStat_SLRUStats *
  pgstat_fetch_slru(void)
  {
  	backend_read_statsfile();
  
  	return slruStats;
  }
  
  /*
   * ---------
   * pgstat_fetch_replslot() -
   *
   *	Support function for the SQL-callable pgstat* functions. Returns
   *	a pointer to the replication slot statistics struct and sets the
   *	number of entries in nslots_p.
   * ---------
   */
  PgStat_ReplSlotStats *
  pgstat_fetch_replslot(int *nslots_p)
  {
  	backend_read_statsfile();
  
  	*nslots_p = nReplSlotStats;
  	return replSlotStats;
  }
  
  /* ------------------------------------------------------------
   * Functions for management of the shared-memory PgBackendStatus array
   * ------------------------------------------------------------
   */
  
  static PgBackendStatus *BackendStatusArray = NULL;
  static PgBackendStatus *MyBEEntry = NULL;
  static char *BackendAppnameBuffer = NULL;
  static char *BackendClientHostnameBuffer = NULL;
  static char *BackendActivityBuffer = NULL;
  static Size BackendActivityBufferSize = 0;
  #ifdef USE_SSL
  static PgBackendSSLStatus *BackendSslStatusBuffer = NULL;
  #endif
  #ifdef ENABLE_GSS
  static PgBackendGSSStatus *BackendGssStatusBuffer = NULL;
  #endif
  
  
  /*
   * Report shared-memory space needed by CreateSharedBackendStatus.
   */
  Size
  BackendStatusShmemSize(void)
  {
  	Size		size;
  
  	/* BackendStatusArray: */
  	size = mul_size(sizeof(PgBackendStatus), NumBackendStatSlots);
  	/* BackendAppnameBuffer: */
  	size = add_size(size,
  					mul_size(NAMEDATALEN, NumBackendStatSlots));
  	/* BackendClientHostnameBuffer: */
  	size = add_size(size,
  					mul_size(NAMEDATALEN, NumBackendStatSlots));
  	/* BackendActivityBuffer: */
  	size = add_size(size,
  					mul_size(pgstat_track_activity_query_size, NumBackendStatSlots));
  #ifdef USE_SSL
  	/* BackendSslStatusBuffer: */
  	size = add_size(size,
  					mul_size(sizeof(PgBackendSSLStatus), NumBackendStatSlots));
  #endif
  #ifdef ENABLE_GSS
  	/* BackendGssStatusBuffer: */
  	size = add_size(size,
  					mul_size(sizeof(PgBackendGSSStatus), NumBackendStatSlots));
  #endif
  	return size;
  }
  
  /*
   * Initialize the shared status array and several string buffers
   * during postmaster startup.
   */
  void
  CreateSharedBackendStatus(void)
  {
  	Size		size;
  	bool		found;
  	int			i;
  	char	   *buffer;
  
  	/* Create or attach to the shared array */
  	size = mul_size(sizeof(PgBackendStatus), NumBackendStatSlots);
  	BackendStatusArray = (PgBackendStatus *)
  		ShmemInitStruct("Backend Status Array", size, &found);
  
  	if (!found)
  	{
  		/*
  		 * We're the first - initialize.
  		 */
  		MemSet(BackendStatusArray, 0, size);
  	}
  
  	/* Create or attach to the shared appname buffer */
  	size = mul_size(NAMEDATALEN, NumBackendStatSlots);
  	BackendAppnameBuffer = (char *)
  		ShmemInitStruct("Backend Application Name Buffer", size, &found);
  
  	if (!found)
  	{
  		MemSet(BackendAppnameBuffer, 0, size);
  
  		/* Initialize st_appname pointers. */
  		buffer = BackendAppnameBuffer;
  		for (i = 0; i < NumBackendStatSlots; i++)
  		{
  			BackendStatusArray[i].st_appname = buffer;
  			buffer += NAMEDATALEN;
  		}
  	}
  
  	/* Create or attach to the shared client hostname buffer */
  	size = mul_size(NAMEDATALEN, NumBackendStatSlots);
  	BackendClientHostnameBuffer = (char *)
  		ShmemInitStruct("Backend Client Host Name Buffer", size, &found);
  
  	if (!found)
  	{
  		MemSet(BackendClientHostnameBuffer, 0, size);
  
  		/* Initialize st_clienthostname pointers. */
  		buffer = BackendClientHostnameBuffer;
  		for (i = 0; i < NumBackendStatSlots; i++)
  		{
  			BackendStatusArray[i].st_clienthostname = buffer;
  			buffer += NAMEDATALEN;
  		}
  	}
  
  	/* Create or attach to the shared activity buffer */
  	BackendActivityBufferSize = mul_size(pgstat_track_activity_query_size,
  										 NumBackendStatSlots);
  	BackendActivityBuffer = (char *)
  		ShmemInitStruct("Backend Activity Buffer",
  						BackendActivityBufferSize,
  						&found);
  
  	if (!found)
  	{
  		MemSet(BackendActivityBuffer, 0, BackendActivityBufferSize);
  
  		/* Initialize st_activity pointers. */
  		buffer = BackendActivityBuffer;
  		for (i = 0; i < NumBackendStatSlots; i++)
  		{
  			BackendStatusArray[i].st_activity_raw = buffer;
  			buffer += pgstat_track_activity_query_size;
  		}
  	}
  
  #ifdef USE_SSL
  	/* Create or attach to the shared SSL status buffer */
  	size = mul_size(sizeof(PgBackendSSLStatus), NumBackendStatSlots);
  	BackendSslStatusBuffer = (PgBackendSSLStatus *)
  		ShmemInitStruct("Backend SSL Status Buffer", size, &found);
  
  	if (!found)
  	{
  		PgBackendSSLStatus *ptr;
  
  		MemSet(BackendSslStatusBuffer, 0, size);
  
  		/* Initialize st_sslstatus pointers. */
  		ptr = BackendSslStatusBuffer;
  		for (i = 0; i < NumBackendStatSlots; i++)
  		{
  			BackendStatusArray[i].st_sslstatus = ptr;
  			ptr++;
  		}
  	}
  #endif
  
  #ifdef ENABLE_GSS
  	/* Create or attach to the shared GSSAPI status buffer */
  	size = mul_size(sizeof(PgBackendGSSStatus), NumBackendStatSlots);
  	BackendGssStatusBuffer = (PgBackendGSSStatus *)
  		ShmemInitStruct("Backend GSS Status Buffer", size, &found);
  
  	if (!found)
  	{
  		PgBackendGSSStatus *ptr;
  
  		MemSet(BackendGssStatusBuffer, 0, size);
  
  		/* Initialize st_gssstatus pointers. */
  		ptr = BackendGssStatusBuffer;
  		for (i = 0; i < NumBackendStatSlots; i++)
  		{
  			BackendStatusArray[i].st_gssstatus = ptr;
  			ptr++;
  		}
  	}
  #endif
  }
  
  
  /* ----------
   * pgstat_initialize() -
   *
   *	Initialize pgstats state, and set up our on-proc-exit hook.
   *	Called from InitPostgres and AuxiliaryProcessMain. For auxiliary process,
   *	MyBackendId is invalid. Otherwise, MyBackendId must be set,
   *	but we must not have started any transaction yet (since the
   *	exit hook must run after the last transaction exit).
   *	NOTE: MyDatabaseId isn't set yet; so the shutdown hook has to be careful.
   * ----------
   */
  void
  pgstat_initialize(void)
  {
  	/* Initialize MyBEEntry */
  	if (MyBackendId != InvalidBackendId)
  	{
  		Assert(MyBackendId >= 1 && MyBackendId <= MaxBackends);
  		MyBEEntry = &BackendStatusArray[MyBackendId - 1];
  	}
  	else
  	{
  		/* Must be an auxiliary process */
  		Assert(MyAuxProcType != NotAnAuxProcess);
  
  		/*
  		 * Assign the MyBEEntry for an auxiliary process.  Since it doesn't
  		 * have a BackendId, the slot is statically allocated based on the
  		 * auxiliary process type (MyAuxProcType).  Backends use slots indexed
  		 * in the range from 1 to MaxBackends (inclusive), so we use
  		 * MaxBackends + AuxBackendType + 1 as the index of the slot for an
  		 * auxiliary process.
  		 */
  		MyBEEntry = &BackendStatusArray[MaxBackends + MyAuxProcType];
  	}
  
  	/*
  	 * Initialize prevWalUsage with pgWalUsage so that pgstat_report_wal() can
  	 * calculate how much pgWalUsage counters are increased by substracting
  	 * prevWalUsage from pgWalUsage.
  	 */
  	prevWalUsage = pgWalUsage;
  
  	/* Set up a process-exit hook to clean up */
  	on_shmem_exit(pgstat_beshutdown_hook, 0);
  }
  
  /* ----------
   * pgstat_bestart() -
   *
   *	Initialize this backend's entry in the PgBackendStatus array.
   *	Called from InitPostgres.
   *
   *	Apart from auxiliary processes, MyBackendId, MyDatabaseId,
   *	session userid, and application_name must be set for a
   *	backend (hence, this cannot be combined with pgstat_initialize).
   *	Note also that we must be inside a transaction if this isn't an aux
   *	process, as we may need to do encoding conversion on some strings.
   * ----------
   */
  void
  pgstat_bestart(void)
  {
  	volatile PgBackendStatus *vbeentry = MyBEEntry;
  	PgBackendStatus lbeentry;
  #ifdef USE_SSL
  	PgBackendSSLStatus lsslstatus;
  #endif
  #ifdef ENABLE_GSS
  	PgBackendGSSStatus lgssstatus;
  #endif
  
  	/* pgstats state must be initialized from pgstat_initialize() */
  	Assert(vbeentry != NULL);
  
  	/*
  	 * To minimize the time spent modifying the PgBackendStatus entry, and
  	 * avoid risk of errors inside the critical section, we first copy the
  	 * shared-memory struct to a local variable, then modify the data in the
  	 * local variable, then copy the local variable back to shared memory.
  	 * Only the last step has to be inside the critical section.
  	 *
  	 * Most of the data we copy from shared memory is just going to be
  	 * overwritten, but the struct's not so large that it's worth the
  	 * maintenance hassle to copy only the needful fields.
  	 */
  	memcpy(&lbeentry,
  		   unvolatize(PgBackendStatus *, vbeentry),
  		   sizeof(PgBackendStatus));
  
  	/* These structs can just start from zeroes each time, though */
  #ifdef USE_SSL
  	memset(&lsslstatus, 0, sizeof(lsslstatus));
  #endif
  #ifdef ENABLE_GSS
  	memset(&lgssstatus, 0, sizeof(lgssstatus));
  #endif
  
  	/*
  	 * Now fill in all the fields of lbeentry, except for strings that are
  	 * out-of-line data.  Those have to be handled separately, below.
  	 */
  	lbeentry.st_procpid = MyProcPid;
  	lbeentry.st_backendType = MyBackendType;
  	lbeentry.st_proc_start_timestamp = MyStartTimestamp;
  	lbeentry.st_activity_start_timestamp = 0;
  	lbeentry.st_state_start_timestamp = 0;
  	lbeentry.st_xact_start_timestamp = 0;
  	lbeentry.st_databaseid = MyDatabaseId;
  
  	/* We have userid for client-backends, wal-sender and bgworker processes */
  	if (lbeentry.st_backendType == B_BACKEND
  		|| lbeentry.st_backendType == B_WAL_SENDER
  		|| lbeentry.st_backendType == B_BG_WORKER)
  		lbeentry.st_userid = GetSessionUserId();
  	else
  		lbeentry.st_userid = InvalidOid;
  
  	/*
  	 * We may not have a MyProcPort (eg, if this is the autovacuum process).
  	 * If so, use all-zeroes client address, which is dealt with specially in
  	 * pg_stat_get_backend_client_addr and pg_stat_get_backend_client_port.
  	 */
  	if (MyProcPort)
  		memcpy(&lbeentry.st_clientaddr, &MyProcPort->raddr,
  			   sizeof(lbeentry.st_clientaddr));
  	else
  		MemSet(&lbeentry.st_clientaddr, 0, sizeof(lbeentry.st_clientaddr));
  
  #ifdef USE_SSL
  	if (MyProcPort && MyProcPort->ssl_in_use)
  	{
  		lbeentry.st_ssl = true;
  		lsslstatus.ssl_bits = be_tls_get_cipher_bits(MyProcPort);
  		strlcpy(lsslstatus.ssl_version, be_tls_get_version(MyProcPort), NAMEDATALEN);
  		strlcpy(lsslstatus.ssl_cipher, be_tls_get_cipher(MyProcPort), NAMEDATALEN);
  		be_tls_get_peer_subject_name(MyProcPort, lsslstatus.ssl_client_dn, NAMEDATALEN);
  		be_tls_get_peer_serial(MyProcPort, lsslstatus.ssl_client_serial, NAMEDATALEN);
  		be_tls_get_peer_issuer_name(MyProcPort, lsslstatus.ssl_issuer_dn, NAMEDATALEN);
  	}
  	else
  	{
  		lbeentry.st_ssl = false;
  	}
  #else
  	lbeentry.st_ssl = false;
  #endif
  
  #ifdef ENABLE_GSS
  	if (MyProcPort && MyProcPort->gss != NULL)
  	{
  		const char *princ = be_gssapi_get_princ(MyProcPort);
  
  		lbeentry.st_gss = true;
  		lgssstatus.gss_auth = be_gssapi_get_auth(MyProcPort);
  		lgssstatus.gss_enc = be_gssapi_get_enc(MyProcPort);
  		if (princ)
  			strlcpy(lgssstatus.gss_princ, princ, NAMEDATALEN);
  	}
  	else
  	{
  		lbeentry.st_gss = false;
  	}
  #else
  	lbeentry.st_gss = false;
  #endif
  
  	lbeentry.st_state = STATE_UNDEFINED;
  	lbeentry.st_progress_command = PROGRESS_COMMAND_INVALID;
  	lbeentry.st_progress_command_target = InvalidOid;
  
  	/*
  	 * we don't zero st_progress_param here to save cycles; nobody should
  	 * examine it until st_progress_command has been set to something other
  	 * than PROGRESS_COMMAND_INVALID
  	 */
  
  	/*
  	 * We're ready to enter the critical section that fills the shared-memory
  	 * status entry.  We follow the protocol of bumping st_changecount before
  	 * and after; and make sure it's even afterwards.  We use a volatile
  	 * pointer here to ensure the compiler doesn't try to get cute.
  	 */
  	PGSTAT_BEGIN_WRITE_ACTIVITY(vbeentry);
  
  	/* make sure we'll memcpy the same st_changecount back */
  	lbeentry.st_changecount = vbeentry->st_changecount;
  
  	memcpy(unvolatize(PgBackendStatus *, vbeentry),
  		   &lbeentry,
  		   sizeof(PgBackendStatus));
  
  	/*
  	 * We can write the out-of-line strings and structs using the pointers
  	 * that are in lbeentry; this saves some de-volatilizing messiness.
  	 */
  	lbeentry.st_appname[0] = '\0';
  	if (MyProcPort && MyProcPort->remote_hostname)
  		strlcpy(lbeentry.st_clienthostname, MyProcPort->remote_hostname,
  				NAMEDATALEN);
  	else
  		lbeentry.st_clienthostname[0] = '\0';
  	lbeentry.st_activity_raw[0] = '\0';
  	/* Also make sure the last byte in each string area is always 0 */
  	lbeentry.st_appname[NAMEDATALEN - 1] = '\0';
  	lbeentry.st_clienthostname[NAMEDATALEN - 1] = '\0';
  	lbeentry.st_activity_raw[pgstat_track_activity_query_size - 1] = '\0';
  
  #ifdef USE_SSL
  	memcpy(lbeentry.st_sslstatus, &lsslstatus, sizeof(PgBackendSSLStatus));
  #endif
  #ifdef ENABLE_GSS
  	memcpy(lbeentry.st_gssstatus, &lgssstatus, sizeof(PgBackendGSSStatus));
  #endif
  
  	PGSTAT_END_WRITE_ACTIVITY(vbeentry);
  
  	/* Update app name to current GUC setting */
  	if (application_name)
  		pgstat_report_appname(application_name);
  }
  
  /*
   * Shut down a single backend's statistics reporting at process exit.
   *
   * Flush any remaining statistics counts out to the collector.
   * Without this, operations triggered during backend exit (such as
   * temp table deletions) won't be counted.
   *
   * Lastly, clear out our entry in the PgBackendStatus array.
   */
  static void
  pgstat_beshutdown_hook(int code, Datum arg)
  {
  	volatile PgBackendStatus *beentry = MyBEEntry;
  
  	/*
  	 * If we got as far as discovering our own database ID, we can report what
  	 * we did to the collector.  Otherwise, we'd be sending an invalid
  	 * database ID, so forget it.  (This means that accesses to pg_database
  	 * during failed backend starts might never get counted.)
  	 */
  	if (OidIsValid(MyDatabaseId))
  		pgstat_report_stat(true);
  
  	/*
  	 * Clear my status entry, following the protocol of bumping st_changecount
  	 * before and after.  We use a volatile pointer here to ensure the
  	 * compiler doesn't try to get cute.
  	 */
  	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
  
  	beentry->st_procpid = 0;	/* mark invalid */
  
  	PGSTAT_END_WRITE_ACTIVITY(beentry);
  }
  
  
  /* ----------
   * pgstat_report_activity() -
   *
   *	Called from tcop/postgres.c to report what the backend is actually doing
   *	(but note cmd_str can be NULL for certain cases).
   *
   * All updates of the status entry follow the protocol of bumping
   * st_changecount before and after.  We use a volatile pointer here to
   * ensure the compiler doesn't try to get cute.
   * ----------
   */
  void
  pgstat_report_activity(BackendState state, const char *cmd_str)
  {
  	volatile PgBackendStatus *beentry = MyBEEntry;
  	TimestampTz start_timestamp;
  	TimestampTz current_timestamp;
  	int			len = 0;
  
  	TRACE_POSTGRESQL_STATEMENT_STATUS(cmd_str);
  
  	if (!beentry)
  		return;
  
  	if (!pgstat_track_activities)
  	{
  		if (beentry->st_state != STATE_DISABLED)
  		{
  			volatile PGPROC *proc = MyProc;
  
  			/*
  			 * track_activities is disabled, but we last reported a
  			 * non-disabled state.  As our final update, change the state and
  			 * clear fields we will not be updating anymore.
  			 */
  			PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
  			beentry->st_state = STATE_DISABLED;
  			beentry->st_state_start_timestamp = 0;
  			beentry->st_activity_raw[0] = '\0';
  			beentry->st_activity_start_timestamp = 0;
  			/* st_xact_start_timestamp and wait_event_info are also disabled */
  			beentry->st_xact_start_timestamp = 0;
  			proc->wait_event_info = 0;
  			PGSTAT_END_WRITE_ACTIVITY(beentry);
  		}
  		return;
  	}
  
  	/*
  	 * To minimize the time spent modifying the entry, and avoid risk of
  	 * errors inside the critical section, fetch all the needed data first.
  	 */
  	start_timestamp = GetCurrentStatementStartTimestamp();
  	if (cmd_str != NULL)
  	{
  		/*
  		 * Compute length of to-be-stored string unaware of multi-byte
  		 * characters. For speed reasons that'll get corrected on read, rather
  		 * than computed every write.
  		 */
  		len = Min(strlen(cmd_str), pgstat_track_activity_query_size - 1);
  	}
  	current_timestamp = GetCurrentTimestamp();
  
  	/*
  	 * If the state has changed from "active" or "idle in transaction",
  	 * calculate the duration.
  	 */
  	if ((beentry->st_state == STATE_RUNNING ||
  		 beentry->st_state == STATE_FASTPATH ||
  		 beentry->st_state == STATE_IDLEINTRANSACTION ||
  		 beentry->st_state == STATE_IDLEINTRANSACTION_ABORTED) &&
  		state != beentry->st_state)
  	{
  		long		secs;
  		int			usecs;
  
  		TimestampDifference(beentry->st_state_start_timestamp,
  							current_timestamp,
  							&secs, &usecs);
  
  		if (beentry->st_state == STATE_RUNNING ||
  			beentry->st_state == STATE_FASTPATH)
  			pgStatActiveTime += secs * 1000000 + usecs;
  		else
  			pgStatTransactionIdleTime += secs * 1000000 + usecs;
  	}
  
  	/*
  	 * Now update the status entry
  	 */
  	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
  
  	beentry->st_state = state;
  	beentry->st_state_start_timestamp = current_timestamp;
  
  	if (cmd_str != NULL)
  	{
  		memcpy((char *) beentry->st_activity_raw, cmd_str, len);
  		beentry->st_activity_raw[len] = '\0';
  		beentry->st_activity_start_timestamp = start_timestamp;
  	}
  
  	PGSTAT_END_WRITE_ACTIVITY(beentry);
  }
  
  /*-----------
   * pgstat_progress_start_command() -
   *
   * Set st_progress_command (and st_progress_command_target) in own backend
   * entry.  Also, zero-initialize st_progress_param array.
   *-----------
   */
  void
  pgstat_progress_start_command(ProgressCommandType cmdtype, Oid relid)
  {
  	volatile PgBackendStatus *beentry = MyBEEntry;
  
  	if (!beentry || !pgstat_track_activities)
  		return;
  
  	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
  	beentry->st_progress_command = cmdtype;
  	beentry->st_progress_command_target = relid;
  	MemSet(&beentry->st_progress_param, 0, sizeof(beentry->st_progress_param));
  	PGSTAT_END_WRITE_ACTIVITY(beentry);
  }
  
  /*-----------
   * pgstat_progress_update_param() -
   *
   * Update index'th member in st_progress_param[] of own backend entry.
   *-----------
   */
  void
  pgstat_progress_update_param(int index, int64 val)
  {
  	volatile PgBackendStatus *beentry = MyBEEntry;
  
  	Assert(index >= 0 && index < PGSTAT_NUM_PROGRESS_PARAM);
  
  	if (!beentry || !pgstat_track_activities)
  		return;
  
  	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
  	beentry->st_progress_param[index] = val;
  	PGSTAT_END_WRITE_ACTIVITY(beentry);
  }
  
  /*-----------
   * pgstat_progress_update_multi_param() -
   *
   * Update multiple members in st_progress_param[] of own backend entry.
   * This is atomic; readers won't see intermediate states.
   *-----------
   */
  void
  pgstat_progress_update_multi_param(int nparam, const int *index,
  								   const int64 *val)
  {
  	volatile PgBackendStatus *beentry = MyBEEntry;
  	int			i;
  
  	if (!beentry || !pgstat_track_activities || nparam == 0)
  		return;
  
  	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
  
  	for (i = 0; i < nparam; ++i)
  	{
  		Assert(index[i] >= 0 && index[i] < PGSTAT_NUM_PROGRESS_PARAM);
  
  		beentry->st_progress_param[index[i]] = val[i];
  	}
  
  	PGSTAT_END_WRITE_ACTIVITY(beentry);
  }
  
  /*-----------
   * pgstat_progress_end_command() -
   *
   * Reset st_progress_command (and st_progress_command_target) in own backend
   * entry.  This signals the end of the command.
   *-----------
   */
  void
  pgstat_progress_end_command(void)
  {
  	volatile PgBackendStatus *beentry = MyBEEntry;
  
  	if (!beentry || !pgstat_track_activities)
  		return;
  
  	if (beentry->st_progress_command == PROGRESS_COMMAND_INVALID)
  		return;
  
  	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
  	beentry->st_progress_command = PROGRESS_COMMAND_INVALID;
  	beentry->st_progress_command_target = InvalidOid;
  	PGSTAT_END_WRITE_ACTIVITY(beentry);
  }
  
  /* ----------
   * pgstat_report_appname() -
   *
   *	Called to update our application name.
   * ----------
   */
  void
  pgstat_report_appname(const char *appname)
  {
  	volatile PgBackendStatus *beentry = MyBEEntry;
  	int			len;
  
  	if (!beentry)
  		return;
  
  	/* This should be unnecessary if GUC did its job, but be safe */
  	len = pg_mbcliplen(appname, strlen(appname), NAMEDATALEN - 1);
  
  	/*
  	 * Update my status entry, following the protocol of bumping
  	 * st_changecount before and after.  We use a volatile pointer here to
  	 * ensure the compiler doesn't try to get cute.
  	 */
  	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
  
  	memcpy((char *) beentry->st_appname, appname, len);
  	beentry->st_appname[len] = '\0';
  
  	PGSTAT_END_WRITE_ACTIVITY(beentry);
  }
  
  /*
   * Report current transaction start timestamp as the specified value.
   * Zero means there is no active transaction.
   */
  void
  pgstat_report_xact_timestamp(TimestampTz tstamp)
  {
  	volatile PgBackendStatus *beentry = MyBEEntry;
  
  	if (!pgstat_track_activities || !beentry)
  		return;
  
  	/*
  	 * Update my status entry, following the protocol of bumping
  	 * st_changecount before and after.  We use a volatile pointer here to
  	 * ensure the compiler doesn't try to get cute.
  	 */
  	PGSTAT_BEGIN_WRITE_ACTIVITY(beentry);
  
  	beentry->st_xact_start_timestamp = tstamp;
  
  	PGSTAT_END_WRITE_ACTIVITY(beentry);
  }
  
  /* ----------
   * pgstat_read_current_status() -
   *
   *	Copy the current contents of the PgBackendStatus array to local memory,
   *	if not already done in this transaction.
   * ----------
   */
  static void
  pgstat_read_current_status(void)
  {
  	volatile PgBackendStatus *beentry;
  	LocalPgBackendStatus *localtable;
  	LocalPgBackendStatus *localentry;
  	char	   *localappname,
  			   *localclienthostname,
  			   *localactivity;
  #ifdef USE_SSL
  	PgBackendSSLStatus *localsslstatus;
  #endif
  #ifdef ENABLE_GSS
  	PgBackendGSSStatus *localgssstatus;
  #endif
  	int			i;
  
  	Assert(!pgStatRunningInCollector);
  	if (localBackendStatusTable)
  		return;					/* already done */
  
  	pgstat_setup_memcxt();
  
  	/*
  	 * Allocate storage for local copy of state data.  We can presume that
  	 * none of these requests overflow size_t, because we already calculated
  	 * the same values using mul_size during shmem setup.  However, with
  	 * probably-silly values of pgstat_track_activity_query_size and
  	 * max_connections, the localactivity buffer could exceed 1GB, so use
  	 * "huge" allocation for that one.
  	 */
  	localtable = (LocalPgBackendStatus *)
  		MemoryContextAlloc(pgStatLocalContext,
  						   sizeof(LocalPgBackendStatus) * NumBackendStatSlots);
  	localappname = (char *)
  		MemoryContextAlloc(pgStatLocalContext,
  						   NAMEDATALEN * NumBackendStatSlots);
  	localclienthostname = (char *)
  		MemoryContextAlloc(pgStatLocalContext,
  						   NAMEDATALEN * NumBackendStatSlots);
  	localactivity = (char *)
  		MemoryContextAllocHuge(pgStatLocalContext,
  							   pgstat_track_activity_query_size * NumBackendStatSlots);
  #ifdef USE_SSL
  	localsslstatus = (PgBackendSSLStatus *)
  		MemoryContextAlloc(pgStatLocalContext,
  						   sizeof(PgBackendSSLStatus) * NumBackendStatSlots);
  #endif
  #ifdef ENABLE_GSS
  	localgssstatus = (PgBackendGSSStatus *)
  		MemoryContextAlloc(pgStatLocalContext,
  						   sizeof(PgBackendGSSStatus) * NumBackendStatSlots);
  #endif
  
  	localNumBackends = 0;
  
  	beentry = BackendStatusArray;
  	localentry = localtable;
  	for (i = 1; i <= NumBackendStatSlots; i++)
  	{
  		/*
  		 * Follow the protocol of retrying if st_changecount changes while we
  		 * copy the entry, or if it's odd.  (The check for odd is needed to
  		 * cover the case where we are able to completely copy the entry while
  		 * the source backend is between increment steps.)	We use a volatile
  		 * pointer here to ensure the compiler doesn't try to get cute.
  		 */
  		for (;;)
  		{
  			int			before_changecount;
  			int			after_changecount;
  
  			pgstat_begin_read_activity(beentry, before_changecount);
  
  			localentry->backendStatus.st_procpid = beentry->st_procpid;
  			/* Skip all the data-copying work if entry is not in use */
  			if (localentry->backendStatus.st_procpid > 0)
  			{
  				memcpy(&localentry->backendStatus, unvolatize(PgBackendStatus *, beentry), sizeof(PgBackendStatus));
  
  				/*
  				 * For each PgBackendStatus field that is a pointer, copy the
  				 * pointed-to data, then adjust the local copy of the pointer
  				 * field to point at the local copy of the data.
  				 *
  				 * strcpy is safe even if the string is modified concurrently,
  				 * because there's always a \0 at the end of the buffer.
  				 */
  				strcpy(localappname, (char *) beentry->st_appname);
  				localentry->backendStatus.st_appname = localappname;
  				strcpy(localclienthostname, (char *) beentry->st_clienthostname);
  				localentry->backendStatus.st_clienthostname = localclienthostname;
  				strcpy(localactivity, (char *) beentry->st_activity_raw);
  				localentry->backendStatus.st_activity_raw = localactivity;
  #ifdef USE_SSL
  				if (beentry->st_ssl)
  				{
  					memcpy(localsslstatus, beentry->st_sslstatus, sizeof(PgBackendSSLStatus));
  					localentry->backendStatus.st_sslstatus = localsslstatus;
  				}
  #endif
  #ifdef ENABLE_GSS
  				if (beentry->st_gss)
  				{
  					memcpy(localgssstatus, beentry->st_gssstatus, sizeof(PgBackendGSSStatus));
  					localentry->backendStatus.st_gssstatus = localgssstatus;
  				}
  #endif
  			}
  
  			pgstat_end_read_activity(beentry, after_changecount);
  
  			if (pgstat_read_activity_complete(before_changecount,
  											  after_changecount))
  				break;
  
  			/* Make sure we can break out of loop if stuck... */
  			CHECK_FOR_INTERRUPTS();
  		}
  
  		beentry++;
  		/* Only valid entries get included into the local array */
  		if (localentry->backendStatus.st_procpid > 0)
  		{
  			BackendIdGetTransactionIds(i,
  									   &localentry->backend_xid,
  									   &localentry->backend_xmin);
  
  			localentry++;
  			localappname += NAMEDATALEN;
  			localclienthostname += NAMEDATALEN;
  			localactivity += pgstat_track_activity_query_size;
  #ifdef USE_SSL
  			localsslstatus++;
  #endif
  #ifdef ENABLE_GSS
  			localgssstatus++;
  #endif
  			localNumBackends++;
  		}
  	}
  
  	/* Set the pointer only after completion of a valid table */
  	localBackendStatusTable = localtable;
  }
  
  /* ----------
   * pgstat_get_wait_event_type() -
   *
   *	Return a string representing the current wait event type, backend is
   *	waiting on.
   */
  const char *
  pgstat_get_wait_event_type(uint32 wait_event_info)
  {
  	uint32		classId;
  	const char *event_type;
  
  	/* report process as not waiting. */
  	if (wait_event_info == 0)
  		return NULL;
  
  	classId = wait_event_info & 0xFF000000;
  
  	switch (classId)
  	{
  		case PG_WAIT_LWLOCK:
  			event_type = "LWLock";
  			break;
  		case PG_WAIT_LOCK:
  			event_type = "Lock";
  			break;
  		case PG_WAIT_BUFFER_PIN:
  			event_type = "BufferPin";
  			break;
  		case PG_WAIT_ACTIVITY:
  			event_type = "Activity";
  			break;
  		case PG_WAIT_CLIENT:
  			event_type = "Client";
  			break;
  		case PG_WAIT_EXTENSION:
  			event_type = "Extension";
  			break;
  		case PG_WAIT_IPC:
  			event_type = "IPC";
  			break;
  		case PG_WAIT_TIMEOUT:
  			event_type = "Timeout";
  			break;
  		case PG_WAIT_IO:
  			event_type = "IO";
  			break;
  		default:
  			event_type = "???";
  			break;
  	}
  
  	return event_type;
  }
  
  /* ----------
   * pgstat_get_wait_event() -
   *
   *	Return a string representing the current wait event, backend is
   *	waiting on.
   */
  const char *
  pgstat_get_wait_event(uint32 wait_event_info)
  {
  	uint32		classId;
  	uint16		eventId;
  	const char *event_name;
  
  	/* report process as not waiting. */
  	if (wait_event_info == 0)
  		return NULL;
  
  	classId = wait_event_info & 0xFF000000;
  	eventId = wait_event_info & 0x0000FFFF;
  
  	switch (classId)
  	{
  		case PG_WAIT_LWLOCK:
  			event_name = GetLWLockIdentifier(classId, eventId);
  			break;
  		case PG_WAIT_LOCK:
  			event_name = GetLockNameFromTagType(eventId);
  			break;
  		case PG_WAIT_BUFFER_PIN:
  			event_name = "BufferPin";
  			break;
  		case PG_WAIT_ACTIVITY:
  			{
  				WaitEventActivity w = (WaitEventActivity) wait_event_info;
  
  				event_name = pgstat_get_wait_activity(w);
  				break;
  			}
  		case PG_WAIT_CLIENT:
  			{
  				WaitEventClient w = (WaitEventClient) wait_event_info;
  
  				event_name = pgstat_get_wait_client(w);
  				break;
  			}
  		case PG_WAIT_EXTENSION:
  			event_name = "Extension";
  			break;
  		case PG_WAIT_IPC:
  			{
  				WaitEventIPC w = (WaitEventIPC) wait_event_info;
  
  				event_name = pgstat_get_wait_ipc(w);
  				break;
  			}
  		case PG_WAIT_TIMEOUT:
  			{
  				WaitEventTimeout w = (WaitEventTimeout) wait_event_info;
  
  				event_name = pgstat_get_wait_timeout(w);
  				break;
  			}
  		case PG_WAIT_IO:
  			{
  				WaitEventIO w = (WaitEventIO) wait_event_info;
  
  				event_name = pgstat_get_wait_io(w);
  				break;
  			}
  		default:
  			event_name = "unknown wait event";
  			break;
  	}
  
  	return event_name;
  }
  
  /* ----------
   * pgstat_get_wait_activity() -
   *
   * Convert WaitEventActivity to string.
   * ----------
   */
  static const char *
  pgstat_get_wait_activity(WaitEventActivity w)
  {
  	const char *event_name = "unknown wait event";
  
  	switch (w)
  	{
  		case WAIT_EVENT_ARCHIVER_MAIN:
  			event_name = "ArchiverMain";
  			break;
  		case WAIT_EVENT_AUTOVACUUM_MAIN:
  			event_name = "AutoVacuumMain";
  			break;
  		case WAIT_EVENT_BGWRITER_HIBERNATE:
  			event_name = "BgWriterHibernate";
  			break;
  		case WAIT_EVENT_BGWRITER_MAIN:
  			event_name = "BgWriterMain";
  			break;
  		case WAIT_EVENT_CHECKPOINTER_MAIN:
  			event_name = "CheckpointerMain";
  			break;
  		case WAIT_EVENT_LOGICAL_APPLY_MAIN:
  			event_name = "LogicalApplyMain";
  			break;
  		case WAIT_EVENT_LOGICAL_LAUNCHER_MAIN:
  			event_name = "LogicalLauncherMain";
  			break;
  		case WAIT_EVENT_PGSTAT_MAIN:
  			event_name = "PgStatMain";
  			break;
  		case WAIT_EVENT_RECOVERY_WAL_STREAM:
  			event_name = "RecoveryWalStream";
  			break;
  		case WAIT_EVENT_SYSLOGGER_MAIN:
  			event_name = "SysLoggerMain";
  			break;
  		case WAIT_EVENT_WAL_RECEIVER_MAIN:
  			event_name = "WalReceiverMain";
  			break;
  		case WAIT_EVENT_WAL_SENDER_MAIN:
  			event_name = "WalSenderMain";
  			break;
  		case WAIT_EVENT_WAL_WRITER_MAIN:
  			event_name = "WalWriterMain";
  			break;
  			/* no default case, so that compiler will warn */
  	}
  
  	return event_name;
  }
  
  /* ----------
   * pgstat_get_wait_client() -
   *
   * Convert WaitEventClient to string.
   * ----------
   */
  static const char *
  pgstat_get_wait_client(WaitEventClient w)
  {
  	const char *event_name = "unknown wait event";
  
  	switch (w)
  	{
  		case WAIT_EVENT_CLIENT_READ:
  			event_name = "ClientRead";
  			break;
  		case WAIT_EVENT_CLIENT_WRITE:
  			event_name = "ClientWrite";
  			break;
  		case WAIT_EVENT_GSS_OPEN_SERVER:
  			event_name = "GSSOpenServer";
  			break;
  		case WAIT_EVENT_LIBPQWALRECEIVER_CONNECT:
  			event_name = "LibPQWalReceiverConnect";
  			break;
  		case WAIT_EVENT_LIBPQWALRECEIVER_RECEIVE:
  			event_name = "LibPQWalReceiverReceive";
  			break;
  		case WAIT_EVENT_SSL_OPEN_SERVER:
  			event_name = "SSLOpenServer";
  			break;
  		case WAIT_EVENT_WAL_SENDER_WAIT_WAL:
  			event_name = "WalSenderWaitForWAL";
  			break;
  		case WAIT_EVENT_WAL_SENDER_WRITE_DATA:
  			event_name = "WalSenderWriteData";
  			break;
  			/* no default case, so that compiler will warn */
  	}
  
  	return event_name;
  }
  
  /* ----------
   * pgstat_get_wait_ipc() -
   *
   * Convert WaitEventIPC to string.
   * ----------
   */
  static const char *
  pgstat_get_wait_ipc(WaitEventIPC w)
  {
  	const char *event_name = "unknown wait event";
  
  	switch (w)
  	{
  		case WAIT_EVENT_BACKUP_WAIT_WAL_ARCHIVE:
  			event_name = "BackupWaitWalArchive";
  			break;
  		case WAIT_EVENT_BGWORKER_SHUTDOWN:
  			event_name = "BgWorkerShutdown";
  			break;
  		case WAIT_EVENT_BGWORKER_STARTUP:
  			event_name = "BgWorkerStartup";
  			break;
  		case WAIT_EVENT_BTREE_PAGE:
  			event_name = "BtreePage";
  			break;
  		case WAIT_EVENT_BUFFER_IO:
  			event_name = "BufferIO";
  			break;
  		case WAIT_EVENT_CHECKPOINT_DONE:
  			event_name = "CheckpointDone";
  			break;
  		case WAIT_EVENT_CHECKPOINT_START:
  			event_name = "CheckpointStart";
  			break;
  		case WAIT_EVENT_EXECUTE_GATHER:
  			event_name = "ExecuteGather";
  			break;
  		case WAIT_EVENT_HASH_BATCH_ALLOCATE:
  			event_name = "HashBatchAllocate";
  			break;
  		case WAIT_EVENT_HASH_BATCH_ELECT:
  			event_name = "HashBatchElect";
  			break;
  		case WAIT_EVENT_HASH_BATCH_LOAD:
  			event_name = "HashBatchLoad";
  			break;
  		case WAIT_EVENT_HASH_BUILD_ALLOCATE:
  			event_name = "HashBuildAllocate";
  			break;
  		case WAIT_EVENT_HASH_BUILD_ELECT:
  			event_name = "HashBuildElect";
  			break;
  		case WAIT_EVENT_HASH_BUILD_HASH_INNER:
  			event_name = "HashBuildHashInner";
  			break;
  		case WAIT_EVENT_HASH_BUILD_HASH_OUTER:
  			event_name = "HashBuildHashOuter";
  			break;
  		case WAIT_EVENT_HASH_GROW_BATCHES_ALLOCATE:
  			event_name = "HashGrowBatchesAllocate";
  			break;
  		case WAIT_EVENT_HASH_GROW_BATCHES_DECIDE:
  			event_name = "HashGrowBatchesDecide";
  			break;
  		case WAIT_EVENT_HASH_GROW_BATCHES_ELECT:
  			event_name = "HashGrowBatchesElect";
  			break;
  		case WAIT_EVENT_HASH_GROW_BATCHES_FINISH:
  			event_name = "HashGrowBatchesFinish";
  			break;
  		case WAIT_EVENT_HASH_GROW_BATCHES_REPARTITION:
  			event_name = "HashGrowBatchesRepartition";
  			break;
  		case WAIT_EVENT_HASH_GROW_BUCKETS_ALLOCATE:
  			event_name = "HashGrowBucketsAllocate";
  			break;
  		case WAIT_EVENT_HASH_GROW_BUCKETS_ELECT:
  			event_name = "HashGrowBucketsElect";
  			break;
  		case WAIT_EVENT_HASH_GROW_BUCKETS_REINSERT:
  			event_name = "HashGrowBucketsReinsert";
  			break;
  		case WAIT_EVENT_LOGICAL_SYNC_DATA:
  			event_name = "LogicalSyncData";
  			break;
  		case WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE:
  			event_name = "LogicalSyncStateChange";
  			break;
  		case WAIT_EVENT_MQ_INTERNAL:
  			event_name = "MessageQueueInternal";
  			break;
  		case WAIT_EVENT_MQ_PUT_MESSAGE:
  			event_name = "MessageQueuePutMessage";
  			break;
  		case WAIT_EVENT_MQ_RECEIVE:
  			event_name = "MessageQueueReceive";
  			break;
  		case WAIT_EVENT_MQ_SEND:
  			event_name = "MessageQueueSend";
  			break;
  		case WAIT_EVENT_PARALLEL_BITMAP_SCAN:
  			event_name = "ParallelBitmapScan";
  			break;
  		case WAIT_EVENT_PARALLEL_CREATE_INDEX_SCAN:
  			event_name = "ParallelCreateIndexScan";
  			break;
  		case WAIT_EVENT_PARALLEL_FINISH:
  			event_name = "ParallelFinish";
  			break;
  		case WAIT_EVENT_PROCARRAY_GROUP_UPDATE:
  			event_name = "ProcArrayGroupUpdate";
  			break;
  		case WAIT_EVENT_PROC_SIGNAL_BARRIER:
  			event_name = "ProcSignalBarrier";
  			break;
  		case WAIT_EVENT_PROMOTE:
  			event_name = "Promote";
  			break;
  		case WAIT_EVENT_RECOVERY_CONFLICT_SNAPSHOT:
  			event_name = "RecoveryConflictSnapshot";
  			break;
  		case WAIT_EVENT_RECOVERY_CONFLICT_TABLESPACE:
  			event_name = "RecoveryConflictTablespace";
  			break;
  		case WAIT_EVENT_RECOVERY_PAUSE:
  			event_name = "RecoveryPause";
  			break;
  		case WAIT_EVENT_REPLICATION_ORIGIN_DROP:
  			event_name = "ReplicationOriginDrop";
  			break;
  		case WAIT_EVENT_REPLICATION_SLOT_DROP:
  			event_name = "ReplicationSlotDrop";
  			break;
  		case WAIT_EVENT_SAFE_SNAPSHOT:
  			event_name = "SafeSnapshot";
  			break;
  		case WAIT_EVENT_SYNC_REP:
  			event_name = "SyncRep";
  			break;
  		case WAIT_EVENT_WALRCV_EXIT:
  			event_name = "WalrcvExit";
  			break;
  		case WAIT_EVENT_WAL_RECEIVER_WAIT_START:
  			event_name = "WalReceiverWaitStart";
  			break;
  		case WAIT_EVENT_XACT_GROUP_UPDATE:
  			event_name = "XactGroupUpdate";
  			break;
  			/* no default case, so that compiler will warn */
  	}
  
  	return event_name;
  }
  
  /* ----------
   * pgstat_get_wait_timeout() -
   *
   * Convert WaitEventTimeout to string.
   * ----------
   */
  static const char *
  pgstat_get_wait_timeout(WaitEventTimeout w)
  {
  	const char *event_name = "unknown wait event";
  
  	switch (w)
  	{
  		case WAIT_EVENT_BASE_BACKUP_THROTTLE:
  			event_name = "BaseBackupThrottle";
  			break;
  		case WAIT_EVENT_PG_SLEEP:
  			event_name = "PgSleep";
  			break;
  		case WAIT_EVENT_RECOVERY_APPLY_DELAY:
  			event_name = "RecoveryApplyDelay";
  			break;
  		case WAIT_EVENT_RECOVERY_RETRIEVE_RETRY_INTERVAL:
  			event_name = "RecoveryRetrieveRetryInterval";
  			break;
  		case WAIT_EVENT_VACUUM_DELAY:
  			event_name = "VacuumDelay";
  			break;
  			/* no default case, so that compiler will warn */
  	}
  
  	return event_name;
  }
  
  /* ----------
   * pgstat_get_wait_io() -
   *
   * Convert WaitEventIO to string.
   * ----------
   */
  static const char *
  pgstat_get_wait_io(WaitEventIO w)
  {
  	const char *event_name = "unknown wait event";
  
  	switch (w)
  	{
  		case WAIT_EVENT_BASEBACKUP_READ:
  			event_name = "BaseBackupRead";
  			break;
  		case WAIT_EVENT_BUFFILE_READ:
  			event_name = "BufFileRead";
  			break;
  		case WAIT_EVENT_BUFFILE_WRITE:
  			event_name = "BufFileWrite";
  			break;
  		case WAIT_EVENT_BUFFILE_TRUNCATE:
  			event_name = "BufFileTruncate";
  			break;
  		case WAIT_EVENT_CONTROL_FILE_READ:
  			event_name = "ControlFileRead";
  			break;
  		case WAIT_EVENT_CONTROL_FILE_SYNC:
  			event_name = "ControlFileSync";
  			break;
  		case WAIT_EVENT_CONTROL_FILE_SYNC_UPDATE:
  			event_name = "ControlFileSyncUpdate";
  			break;
  		case WAIT_EVENT_CONTROL_FILE_WRITE:
  			event_name = "ControlFileWrite";
  			break;
  		case WAIT_EVENT_CONTROL_FILE_WRITE_UPDATE:
  			event_name = "ControlFileWriteUpdate";
  			break;
  		case WAIT_EVENT_COPY_FILE_READ:
  			event_name = "CopyFileRead";
  			break;
  		case WAIT_EVENT_COPY_FILE_WRITE:
  			event_name = "CopyFileWrite";
  			break;
  		case WAIT_EVENT_DATA_FILE_EXTEND:
  			event_name = "DataFileExtend";
  			break;
  		case WAIT_EVENT_DATA_FILE_FLUSH:
  			event_name = "DataFileFlush";
  			break;
  		case WAIT_EVENT_DATA_FILE_IMMEDIATE_SYNC:
  			event_name = "DataFileImmediateSync";
  			break;
  		case WAIT_EVENT_DATA_FILE_PREFETCH:
  			event_name = "DataFilePrefetch";
  			break;
  		case WAIT_EVENT_DATA_FILE_READ:
  			event_name = "DataFileRead";
  			break;
  		case WAIT_EVENT_DATA_FILE_SYNC:
  			event_name = "DataFileSync";
  			break;
  		case WAIT_EVENT_DATA_FILE_TRUNCATE:
  			event_name = "DataFileTruncate";
  			break;
  		case WAIT_EVENT_DATA_FILE_WRITE:
  			event_name = "DataFileWrite";
  			break;
  		case WAIT_EVENT_DSM_FILL_ZERO_WRITE:
  			event_name = "DSMFillZeroWrite";
  			break;
  		case WAIT_EVENT_LOCK_FILE_ADDTODATADIR_READ:
  			event_name = "LockFileAddToDataDirRead";
  			break;
  		case WAIT_EVENT_LOCK_FILE_ADDTODATADIR_SYNC:
  			event_name = "LockFileAddToDataDirSync";
  			break;
  		case WAIT_EVENT_LOCK_FILE_ADDTODATADIR_WRITE:
  			event_name = "LockFileAddToDataDirWrite";
  			break;
  		case WAIT_EVENT_LOCK_FILE_CREATE_READ:
  			event_name = "LockFileCreateRead";
  			break;
  		case WAIT_EVENT_LOCK_FILE_CREATE_SYNC:
  			event_name = "LockFileCreateSync";
  			break;
  		case WAIT_EVENT_LOCK_FILE_CREATE_WRITE:
  			event_name = "LockFileCreateWrite";
  			break;
  		case WAIT_EVENT_LOCK_FILE_RECHECKDATADIR_READ:
  			event_name = "LockFileReCheckDataDirRead";
  			break;
  		case WAIT_EVENT_LOGICAL_REWRITE_CHECKPOINT_SYNC:
  			event_name = "LogicalRewriteCheckpointSync";
  			break;
  		case WAIT_EVENT_LOGICAL_REWRITE_MAPPING_SYNC:
  			event_name = "LogicalRewriteMappingSync";
  			break;
  		case WAIT_EVENT_LOGICAL_REWRITE_MAPPING_WRITE:
  			event_name = "LogicalRewriteMappingWrite";
  			break;
  		case WAIT_EVENT_LOGICAL_REWRITE_SYNC:
  			event_name = "LogicalRewriteSync";
  			break;
  		case WAIT_EVENT_LOGICAL_REWRITE_TRUNCATE:
  			event_name = "LogicalRewriteTruncate";
  			break;
  		case WAIT_EVENT_LOGICAL_REWRITE_WRITE:
  			event_name = "LogicalRewriteWrite";
  			break;
  		case WAIT_EVENT_RELATION_MAP_READ:
  			event_name = "RelationMapRead";
  			break;
  		case WAIT_EVENT_RELATION_MAP_SYNC:
  			event_name = "RelationMapSync";
  			break;
  		case WAIT_EVENT_RELATION_MAP_WRITE:
  			event_name = "RelationMapWrite";
  			break;
  		case WAIT_EVENT_REORDER_BUFFER_READ:
  			event_name = "ReorderBufferRead";
  			break;
  		case WAIT_EVENT_REORDER_BUFFER_WRITE:
  			event_name = "ReorderBufferWrite";
  			break;
  		case WAIT_EVENT_REORDER_LOGICAL_MAPPING_READ:
  			event_name = "ReorderLogicalMappingRead";
  			break;
  		case WAIT_EVENT_REPLICATION_SLOT_READ:
  			event_name = "ReplicationSlotRead";
  			break;
  		case WAIT_EVENT_REPLICATION_SLOT_RESTORE_SYNC:
  			event_name = "ReplicationSlotRestoreSync";
  			break;
  		case WAIT_EVENT_REPLICATION_SLOT_SYNC:
  			event_name = "ReplicationSlotSync";
  			break;
  		case WAIT_EVENT_REPLICATION_SLOT_WRITE:
  			event_name = "ReplicationSlotWrite";
  			break;
  		case WAIT_EVENT_SLRU_FLUSH_SYNC:
  			event_name = "SLRUFlushSync";
  			break;
  		case WAIT_EVENT_SLRU_READ:
  			event_name = "SLRURead";
  			break;
  		case WAIT_EVENT_SLRU_SYNC:
  			event_name = "SLRUSync";
  			break;
  		case WAIT_EVENT_SLRU_WRITE:
  			event_name = "SLRUWrite";
  			break;
  		case WAIT_EVENT_SNAPBUILD_READ:
  			event_name = "SnapbuildRead";
  			break;
  		case WAIT_EVENT_SNAPBUILD_SYNC:
  			event_name = "SnapbuildSync";
  			break;
  		case WAIT_EVENT_SNAPBUILD_WRITE:
  			event_name = "SnapbuildWrite";
  			break;
  		case WAIT_EVENT_TIMELINE_HISTORY_FILE_SYNC:
  			event_name = "TimelineHistoryFileSync";
  			break;
  		case WAIT_EVENT_TIMELINE_HISTORY_FILE_WRITE:
  			event_name = "TimelineHistoryFileWrite";
  			break;
  		case WAIT_EVENT_TIMELINE_HISTORY_READ:
  			event_name = "TimelineHistoryRead";
  			break;
  		case WAIT_EVENT_TIMELINE_HISTORY_SYNC:
  			event_name = "TimelineHistorySync";
  			break;
  		case WAIT_EVENT_TIMELINE_HISTORY_WRITE:
  			event_name = "TimelineHistoryWrite";
  			break;
  		case WAIT_EVENT_TWOPHASE_FILE_READ:
  			event_name = "TwophaseFileRead";
  			break;
  		case WAIT_EVENT_TWOPHASE_FILE_SYNC:
  			event_name = "TwophaseFileSync";
  			break;
  		case WAIT_EVENT_TWOPHASE_FILE_WRITE:
  			event_name = "TwophaseFileWrite";
  			break;
  		case WAIT_EVENT_WALSENDER_TIMELINE_HISTORY_READ:
  			event_name = "WALSenderTimelineHistoryRead";
  			break;
  		case WAIT_EVENT_WAL_BOOTSTRAP_SYNC:
  			event_name = "WALBootstrapSync";
  			break;
  		case WAIT_EVENT_WAL_BOOTSTRAP_WRITE:
  			event_name = "WALBootstrapWrite";
  			break;
  		case WAIT_EVENT_WAL_COPY_READ:
  			event_name = "WALCopyRead";
  			break;
  		case WAIT_EVENT_WAL_COPY_SYNC:
  			event_name = "WALCopySync";
  			break;
  		case WAIT_EVENT_WAL_COPY_WRITE:
  			event_name = "WALCopyWrite";
  			break;
  		case WAIT_EVENT_WAL_INIT_SYNC:
  			event_name = "WALInitSync";
  			break;
  		case WAIT_EVENT_WAL_INIT_WRITE:
  			event_name = "WALInitWrite";
  			break;
  		case WAIT_EVENT_WAL_READ:
  			event_name = "WALRead";
  			break;
  		case WAIT_EVENT_WAL_SYNC:
  			event_name = "WALSync";
  			break;
  		case WAIT_EVENT_WAL_SYNC_METHOD_ASSIGN:
  			event_name = "WALSyncMethodAssign";
  			break;
  		case WAIT_EVENT_WAL_WRITE:
  			event_name = "WALWrite";
  			break;
  		case WAIT_EVENT_LOGICAL_CHANGES_READ:
  			event_name = "LogicalChangesRead";
  			break;
  		case WAIT_EVENT_LOGICAL_CHANGES_WRITE:
  			event_name = "LogicalChangesWrite";
  			break;
  		case WAIT_EVENT_LOGICAL_SUBXACT_READ:
  			event_name = "LogicalSubxactRead";
  			break;
  		case WAIT_EVENT_LOGICAL_SUBXACT_WRITE:
  			event_name = "LogicalSubxactWrite";
  			break;
  
  			/* no default case, so that compiler will warn */
  	}
  
  	return event_name;
  }
  
  
  /* ----------
   * pgstat_get_backend_current_activity() -
   *
   *	Return a string representing the current activity of the backend with
   *	the specified PID.  This looks directly at the BackendStatusArray,
   *	and so will provide current information regardless of the age of our
   *	transaction's snapshot of the status array.
   *
   *	It is the caller's responsibility to invoke this only for backends whose
   *	state is expected to remain stable while the result is in use.  The
   *	only current use is in deadlock reporting, where we can expect that
   *	the target backend is blocked on a lock.  (There are corner cases
   *	where the target's wait could get aborted while we are looking at it,
   *	but the very worst consequence is to return a pointer to a string
   *	that's been changed, so we won't worry too much.)
   *
   *	Note: return strings for special cases match pg_stat_get_backend_activity.
   * ----------
   */
  const char *
  pgstat_get_backend_current_activity(int pid, bool checkUser)
  {
  	PgBackendStatus *beentry;
  	int			i;
  
  	beentry = BackendStatusArray;
  	for (i = 1; i <= MaxBackends; i++)
  	{
  		/*
  		 * Although we expect the target backend's entry to be stable, that
  		 * doesn't imply that anyone else's is.  To avoid identifying the
  		 * wrong backend, while we check for a match to the desired PID we
  		 * must follow the protocol of retrying if st_changecount changes
  		 * while we examine the entry, or if it's odd.  (This might be
  		 * unnecessary, since fetching or storing an int is almost certainly
  		 * atomic, but let's play it safe.)  We use a volatile pointer here to
  		 * ensure the compiler doesn't try to get cute.
  		 */
  		volatile PgBackendStatus *vbeentry = beentry;
  		bool		found;
  
  		for (;;)
  		{
  			int			before_changecount;
  			int			after_changecount;
  
  			pgstat_begin_read_activity(vbeentry, before_changecount);
  
  			found = (vbeentry->st_procpid == pid);
  
  			pgstat_end_read_activity(vbeentry, after_changecount);
  
  			if (pgstat_read_activity_complete(before_changecount,
  											  after_changecount))
  				break;
  
  			/* Make sure we can break out of loop if stuck... */
  			CHECK_FOR_INTERRUPTS();
  		}
  
  		if (found)
  		{
  			/* Now it is safe to use the non-volatile pointer */
  			if (checkUser && !superuser() && beentry->st_userid != GetUserId())
  				return "<insufficient privilege>";
  			else if (*(beentry->st_activity_raw) == '\0')
  				return "<command string not enabled>";
  			else
  			{
  				/* this'll leak a bit of memory, but that seems acceptable */
  				return pgstat_clip_activity(beentry->st_activity_raw);
  			}
  		}
  
  		beentry++;
  	}
  
  	/* If we get here, caller is in error ... */
  	return "<backend information not available>";
  }
  
  /* ----------
   * pgstat_get_crashed_backend_activity() -
   *
   *	Return a string representing the current activity of the backend with
   *	the specified PID.  Like the function above, but reads shared memory with
   *	the expectation that it may be corrupt.  On success, copy the string
   *	into the "buffer" argument and return that pointer.  On failure,
   *	return NULL.
   *
   *	This function is only intended to be used by the postmaster to report the
   *	query that crashed a backend.  In particular, no attempt is made to
   *	follow the correct concurrency protocol when accessing the
   *	BackendStatusArray.  But that's OK, in the worst case we'll return a
   *	corrupted message.  We also must take care not to trip on ereport(ERROR).
   * ----------
   */
  const char *
  pgstat_get_crashed_backend_activity(int pid, char *buffer, int buflen)
  {
  	volatile PgBackendStatus *beentry;
  	int			i;
  
  	beentry = BackendStatusArray;
  
  	/*
  	 * We probably shouldn't get here before shared memory has been set up,
  	 * but be safe.
  	 */
  	if (beentry == NULL || BackendActivityBuffer == NULL)
  		return NULL;
  
  	for (i = 1; i <= MaxBackends; i++)
  	{
  		if (beentry->st_procpid == pid)
  		{
  			/* Read pointer just once, so it can't change after validation */
  			const char *activity = beentry->st_activity_raw;
  			const char *activity_last;
  
  			/*
  			 * We mustn't access activity string before we verify that it
  			 * falls within the BackendActivityBuffer. To make sure that the
  			 * entire string including its ending is contained within the
  			 * buffer, subtract one activity length from the buffer size.
  			 */
  			activity_last = BackendActivityBuffer + BackendActivityBufferSize
  				- pgstat_track_activity_query_size;
  
  			if (activity < BackendActivityBuffer ||
  				activity > activity_last)
  				return NULL;
  
  			/* If no string available, no point in a report */
  			if (activity[0] == '\0')
  				return NULL;
  
  			/*
  			 * Copy only ASCII-safe characters so we don't run into encoding
  			 * problems when reporting the message; and be sure not to run off
  			 * the end of memory.  As only ASCII characters are reported, it
  			 * doesn't seem necessary to perform multibyte aware clipping.
  			 */
  			ascii_safe_strlcpy(buffer, activity,
  							   Min(buflen, pgstat_track_activity_query_size));
  
  			return buffer;
  		}
  
  		beentry++;
  	}
  
  	/* PID not found */
  	return NULL;
  }
  
  /* ------------------------------------------------------------
   * Local support functions follow
   * ------------------------------------------------------------
   */
  
  
  /* ----------
   * pgstat_setheader() -
   *
   *		Set common header fields in a statistics message
   * ----------
   */
  static void
  pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype)
  {
  	hdr->m_type = mtype;
  }
  
  
  /* ----------
   * pgstat_send() -
   *
   *		Send out one statistics message to the collector
   * ----------
   */
  static void
  pgstat_send(void *msg, int len)
  {
  	int			rc;
  
  	if (pgStatSock == PGINVALID_SOCKET)
  		return;
  
  	((PgStat_MsgHdr *) msg)->m_size = len;
  
  	/* We'll retry after EINTR, but ignore all other failures */
  	do
  	{
  		rc = send(pgStatSock, msg, len, 0);
  	} while (rc < 0 && errno == EINTR);
  
  #ifdef USE_ASSERT_CHECKING
  	/* In debug builds, log send failures ... */
  	if (rc < 0)
  		elog(LOG, "could not send to statistics collector: %m");
  #endif
  }
  
  /* ----------
   * pgstat_send_archiver() -
   *
   *	Tell the collector about the WAL file that we successfully
   *	archived or failed to archive.
   * ----------
   */
  void
  pgstat_send_archiver(const char *xlog, bool failed)
  {
  	PgStat_MsgArchiver msg;
  
  	/*
  	 * Prepare and send the message
  	 */
  	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_ARCHIVER);
  	msg.m_failed = failed;
  	strlcpy(msg.m_xlog, xlog, sizeof(msg.m_xlog));
  	msg.m_timestamp = GetCurrentTimestamp();
  	pgstat_send(&msg, sizeof(msg));
  }
  
  /* ----------
   * pgstat_send_bgwriter() -
   *
   *		Send bgwriter statistics to the collector
   * ----------
   */
  void
  pgstat_send_bgwriter(void)
  {
  	/* We assume this initializes to zeroes */
  	static const PgStat_MsgBgWriter all_zeroes;
  
  	/*
  	 * This function can be called even if nothing at all has happened. In
  	 * this case, avoid sending a completely empty message to the stats
  	 * collector.
  	 */
  	if (memcmp(&BgWriterStats, &all_zeroes, sizeof(PgStat_MsgBgWriter)) == 0)
  		return;
  
  	/*
  	 * Prepare and send the message
  	 */
  	pgstat_setheader(&BgWriterStats.m_hdr, PGSTAT_MTYPE_BGWRITER);
  	pgstat_send(&BgWriterStats, sizeof(BgWriterStats));
  
  	/*
  	 * Clear out the statistics buffer, so it can be re-used.
  	 */
  	MemSet(&BgWriterStats, 0, sizeof(BgWriterStats));
  }
  
  /* ----------
   * pgstat_report_wal() -
   *
   * Calculate how much WAL usage counters are increased and send
   * WAL statistics to the collector.
   *
   * Must be called by processes that generate WAL.
   * ----------
   */
  void
  pgstat_report_wal(void)
  {
  	WalUsage	walusage;
  
  	/*
  	 * Calculate how much WAL usage counters are increased by substracting the
  	 * previous counters from the current ones. Fill the results in WAL stats
  	 * message.
  	 */
  	MemSet(&walusage, 0, sizeof(WalUsage));
  	WalUsageAccumDiff(&walusage, &pgWalUsage, &prevWalUsage);
  
  	WalStats.m_wal_records = walusage.wal_records;
  	WalStats.m_wal_fpi = walusage.wal_fpi;
  	WalStats.m_wal_bytes = walusage.wal_bytes;
  
  	/*
  	 * Send WAL stats message to the collector.
  	 */
  	if (!pgstat_send_wal(true))
  		return;
  
  	/*
  	 * Save the current counters for the subsequent calculation of WAL usage.
  	 */
  	prevWalUsage = pgWalUsage;
  }
  
  /* ----------
   * pgstat_send_wal() -
   *
   *	Send WAL statistics to the collector.
   *
   * If 'force' is not set, WAL stats message is only sent if enough time has
   * passed since last one was sent to reach PGSTAT_STAT_INTERVAL.
   *
   * Return true if the message is sent, and false otherwise.
   * ----------
   */
  bool
  pgstat_send_wal(bool force)
  {
  	/* We assume this initializes to zeroes */
  	static const PgStat_MsgWal all_zeroes;
  	static TimestampTz sendTime = 0;
  
  	/*
  	 * This function can be called even if nothing at all has happened. In
  	 * this case, avoid sending a completely empty message to the stats
  	 * collector.
  	 */
  	if (memcmp(&WalStats, &all_zeroes, sizeof(PgStat_MsgWal)) == 0)
  		return false;
  
  	if (!force)
  	{
  		TimestampTz now = GetCurrentTimestamp();
  
  		/*
  		 * Don't send a message unless it's been at least PGSTAT_STAT_INTERVAL
  		 * msec since we last sent one.
  		 */
  		if (!TimestampDifferenceExceeds(sendTime, now, PGSTAT_STAT_INTERVAL))
  			return false;
  		sendTime = now;
  	}
  
  	/*
  	 * Prepare and send the message
  	 */
  	pgstat_setheader(&WalStats.m_hdr, PGSTAT_MTYPE_WAL);
  	pgstat_send(&WalStats, sizeof(WalStats));
  
  	/*
  	 * Clear out the statistics buffer, so it can be re-used.
  	 */
  	MemSet(&WalStats, 0, sizeof(WalStats));
  
  	return true;
  }
  
  /* ----------
   * pgstat_send_slru() -
   *
   *		Send SLRU statistics to the collector
   * ----------
   */
  static void
  pgstat_send_slru(void)
  {
  	/* We assume this initializes to zeroes */
  	static const PgStat_MsgSLRU all_zeroes;
  
  	for (int i = 0; i < SLRU_NUM_ELEMENTS; i++)
  	{
  		/*
  		 * This function can be called even if nothing at all has happened. In
  		 * this case, avoid sending a completely empty message to the stats
  		 * collector.
  		 */
  		if (memcmp(&SLRUStats[i], &all_zeroes, sizeof(PgStat_MsgSLRU)) == 0)
  			continue;
  
  		/* set the SLRU type before each send */
  		SLRUStats[i].m_index = i;
  
  		/*
  		 * Prepare and send the message
  		 */
  		pgstat_setheader(&SLRUStats[i].m_hdr, PGSTAT_MTYPE_SLRU);
  		pgstat_send(&SLRUStats[i], sizeof(PgStat_MsgSLRU));
  
  		/*
  		 * Clear out the statistics buffer, so it can be re-used.
  		 */
  		MemSet(&SLRUStats[i], 0, sizeof(PgStat_MsgSLRU));
  	}
  }
  
  
  /* ----------
   * PgstatCollectorMain() -
   *
   *	Start up the statistics collector process.  This is the body of the
   *	postmaster child process.
   *
   *	The argc/argv parameters are valid only in EXEC_BACKEND case.
   * ----------
   */
  NON_EXEC_STATIC void
  PgstatCollectorMain(int argc, char *argv[])
  {
  	int			len;
  	PgStat_Msg	msg;
  	int			wr;
  	WaitEvent	event;
  	WaitEventSet *wes;
  
  	/*
  	 * Ignore all signals usually bound to some action in the postmaster,
  	 * except SIGHUP and SIGQUIT.  Note we don't need a SIGUSR1 handler to
  	 * support latch operations, because we only use a local latch.
  	 */
  	pqsignal(SIGHUP, SignalHandlerForConfigReload);
  	pqsignal(SIGINT, SIG_IGN);
  	pqsignal(SIGTERM, SIG_IGN);
  	pqsignal(SIGQUIT, SignalHandlerForShutdownRequest);
  	pqsignal(SIGALRM, SIG_IGN);
  	pqsignal(SIGPIPE, SIG_IGN);
  	pqsignal(SIGUSR1, SIG_IGN);
  	pqsignal(SIGUSR2, SIG_IGN);
  	/* Reset some signals that are accepted by postmaster but not here */
  	pqsignal(SIGCHLD, SIG_DFL);
  	PG_SETMASK(&UnBlockSig);
  
  	MyBackendType = B_STATS_COLLECTOR;
  	init_ps_display(NULL);
  
  	/*
  	 * Read in existing stats files or initialize the stats to zero.
  	 */
  	pgStatRunningInCollector = true;
  	pgStatDBHash = pgstat_read_statsfiles(InvalidOid, true, true);
  
  	/* Prepare to wait for our latch or data in our socket. */
  	wes = CreateWaitEventSet(CurrentMemoryContext, 3);
  	AddWaitEventToSet(wes, WL_LATCH_SET, PGINVALID_SOCKET, MyLatch, NULL);
  	AddWaitEventToSet(wes, WL_POSTMASTER_DEATH, PGINVALID_SOCKET, NULL, NULL);
  	AddWaitEventToSet(wes, WL_SOCKET_READABLE, pgStatSock, NULL, NULL);
  
  	/*
  	 * Loop to process messages until we get SIGQUIT or detect ungraceful
  	 * death of our parent postmaster.
  	 *
  	 * For performance reasons, we don't want to do ResetLatch/WaitLatch after
  	 * every message; instead, do that only after a recv() fails to obtain a
  	 * message.  (This effectively means that if backends are sending us stuff
  	 * like mad, we won't notice postmaster death until things slack off a
  	 * bit; which seems fine.)	To do that, we have an inner loop that
  	 * iterates as long as recv() succeeds.  We do check ConfigReloadPending
  	 * inside the inner loop, which means that such interrupts will get
  	 * serviced but the latch won't get cleared until next time there is a
  	 * break in the action.
  	 */
  	for (;;)
  	{
  		/* Clear any already-pending wakeups */
  		ResetLatch(MyLatch);
  
  		/*
  		 * Quit if we get SIGQUIT from the postmaster.
  		 */
  		if (ShutdownRequestPending)
  			break;
  
  		/*
  		 * Inner loop iterates as long as we keep getting messages, or until
  		 * ShutdownRequestPending becomes set.
  		 */
  		while (!ShutdownRequestPending)
  		{
  			/*
  			 * Reload configuration if we got SIGHUP from the postmaster.
  			 */
  			if (ConfigReloadPending)
  			{
  				ConfigReloadPending = false;
  				ProcessConfigFile(PGC_SIGHUP);
  			}
  
  			/*
  			 * Write the stats file(s) if a new request has arrived that is
  			 * not satisfied by existing file(s).
  			 */
  			if (pgstat_write_statsfile_needed())
  				pgstat_write_statsfiles(false, false);
  
  			/*
  			 * Try to receive and process a message.  This will not block,
  			 * since the socket is set to non-blocking mode.
  			 *
  			 * XXX On Windows, we have to force pgwin32_recv to cooperate,
  			 * despite the previous use of pg_set_noblock() on the socket.
  			 * This is extremely broken and should be fixed someday.
  			 */
  #ifdef WIN32
  			pgwin32_noblock = 1;
  #endif
  
  			len = recv(pgStatSock, (char *) &msg,
  					   sizeof(PgStat_Msg), 0);
  
  #ifdef WIN32
  			pgwin32_noblock = 0;
  #endif
  
  			if (len < 0)
  			{
  				if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
  					break;		/* out of inner loop */
  				ereport(ERROR,
  						(errcode_for_socket_access(),
  						 errmsg("could not read statistics message: %m")));
  			}
  
  			/*
  			 * We ignore messages that are smaller than our common header
  			 */
  			if (len < sizeof(PgStat_MsgHdr))
  				continue;
  
  			/*
  			 * The received length must match the length in the header
  			 */
  			if (msg.msg_hdr.m_size != len)
  				continue;
  
  			/*
  			 * O.K. - we accept this message.  Process it.
  			 */
  			switch (msg.msg_hdr.m_type)
  			{
  				case PGSTAT_MTYPE_DUMMY:
  					break;
  
  				case PGSTAT_MTYPE_INQUIRY:
  					pgstat_recv_inquiry(&msg.msg_inquiry, len);
  					break;
  
  				case PGSTAT_MTYPE_TABSTAT:
  					pgstat_recv_tabstat(&msg.msg_tabstat, len);
  					break;
  
  				case PGSTAT_MTYPE_TABPURGE:
  					pgstat_recv_tabpurge(&msg.msg_tabpurge, len);
  					break;
  
  				case PGSTAT_MTYPE_DROPDB:
  					pgstat_recv_dropdb(&msg.msg_dropdb, len);
  					break;
  
  				case PGSTAT_MTYPE_RESETCOUNTER:
  					pgstat_recv_resetcounter(&msg.msg_resetcounter, len);
  					break;
  
  				case PGSTAT_MTYPE_RESETSHAREDCOUNTER:
  					pgstat_recv_resetsharedcounter(&msg.msg_resetsharedcounter,
  												   len);
  					break;
  
  				case PGSTAT_MTYPE_RESETSINGLECOUNTER:
  					pgstat_recv_resetsinglecounter(&msg.msg_resetsinglecounter,
  												   len);
  					break;
  
  				case PGSTAT_MTYPE_RESETSLRUCOUNTER:
  					pgstat_recv_resetslrucounter(&msg.msg_resetslrucounter,
  												 len);
  					break;
  
  				case PGSTAT_MTYPE_RESETREPLSLOTCOUNTER:
  					pgstat_recv_resetreplslotcounter(&msg.msg_resetreplslotcounter,
  													 len);
  					break;
  
  				case PGSTAT_MTYPE_AUTOVAC_START:
  					pgstat_recv_autovac(&msg.msg_autovacuum_start, len);
  					break;
  
  				case PGSTAT_MTYPE_VACUUM:
  					pgstat_recv_vacuum(&msg.msg_vacuum, len);
  					break;
  
  				case PGSTAT_MTYPE_ANALYZE:
  					pgstat_recv_analyze(&msg.msg_analyze, len);
  					break;
  
  				case PGSTAT_MTYPE_ARCHIVER:
  					pgstat_recv_archiver(&msg.msg_archiver, len);
  					break;
  
  				case PGSTAT_MTYPE_BGWRITER:
  					pgstat_recv_bgwriter(&msg.msg_bgwriter, len);
  					break;
  
  				case PGSTAT_MTYPE_WAL:
  					pgstat_recv_wal(&msg.msg_wal, len);
  					break;
  
  				case PGSTAT_MTYPE_SLRU:
  					pgstat_recv_slru(&msg.msg_slru, len);
  					break;
  
  				case PGSTAT_MTYPE_FUNCSTAT:
  					pgstat_recv_funcstat(&msg.msg_funcstat, len);
  					break;
  
  				case PGSTAT_MTYPE_FUNCPURGE:
  					pgstat_recv_funcpurge(&msg.msg_funcpurge, len);
  					break;
  
  				case PGSTAT_MTYPE_RECOVERYCONFLICT:
  					pgstat_recv_recoveryconflict(&msg.msg_recoveryconflict,
  												 len);
  					break;
  
  				case PGSTAT_MTYPE_DEADLOCK:
  					pgstat_recv_deadlock(&msg.msg_deadlock, len);
  					break;
  
  				case PGSTAT_MTYPE_TEMPFILE:
  					pgstat_recv_tempfile(&msg.msg_tempfile, len);
  					break;
  
  				case PGSTAT_MTYPE_CHECKSUMFAILURE:
  					pgstat_recv_checksum_failure(&msg.msg_checksumfailure,
  												 len);
  					break;
  
  				case PGSTAT_MTYPE_REPLSLOT:
  					pgstat_recv_replslot(&msg.msg_replslot, len);
  					break;
  
  				case PGSTAT_MTYPE_CONNECTION:
  					pgstat_recv_connstat(&msg.msg_conn, len);
  					break;
  
  				default:
  					break;
  			}
  		}						/* end of inner message-processing loop */
  
  		/* Sleep until there's something to do */
  #ifndef WIN32
  		wr = WaitEventSetWait(wes, -1L, &event, 1, WAIT_EVENT_PGSTAT_MAIN);
  #else
  
  		/*
  		 * Windows, at least in its Windows Server 2003 R2 incarnation,
  		 * sometimes loses FD_READ events.  Waking up and retrying the recv()
  		 * fixes that, so don't sleep indefinitely.  This is a crock of the
  		 * first water, but until somebody wants to debug exactly what's
  		 * happening there, this is the best we can do.  The two-second
  		 * timeout matches our pre-9.2 behavior, and needs to be short enough
  		 * to not provoke "using stale statistics" complaints from
  		 * backend_read_statsfile.
  		 */
  		wr = WaitEventSetWait(wes, 2 * 1000L /* msec */ , &event, 1,
  							  WAIT_EVENT_PGSTAT_MAIN);
  #endif
  
  		/*
  		 * Emergency bailout if postmaster has died.  This is to avoid the
  		 * necessity for manual cleanup of all postmaster children.
  		 */
  		if (wr == 1 && event.events == WL_POSTMASTER_DEATH)
  			break;
  	}							/* end of outer loop */
  
  	/*
  	 * Save the final stats to reuse at next startup.
  	 */
  	pgstat_write_statsfiles(true, true);
  
  	FreeWaitEventSet(wes);
  
  	exit(0);
  }
  
  /*
   * Subroutine to clear stats in a database entry
   *
   * Tables and functions hashes are initialized to empty.
   */
  static void
  reset_dbentry_counters(PgStat_StatDBEntry *dbentry)
  {
  	HASHCTL		hash_ctl;
  
  	dbentry->n_xact_commit = 0;
  	dbentry->n_xact_rollback = 0;
  	dbentry->n_blocks_fetched = 0;
  	dbentry->n_blocks_hit = 0;
  	dbentry->n_tuples_returned = 0;
  	dbentry->n_tuples_fetched = 0;
  	dbentry->n_tuples_inserted = 0;
  	dbentry->n_tuples_updated = 0;
  	dbentry->n_tuples_deleted = 0;
  	dbentry->last_autovac_time = 0;
  	dbentry->n_conflict_tablespace = 0;
  	dbentry->n_conflict_lock = 0;
  	dbentry->n_conflict_snapshot = 0;
  	dbentry->n_conflict_bufferpin = 0;
  	dbentry->n_conflict_startup_deadlock = 0;
  	dbentry->n_temp_files = 0;
  	dbentry->n_temp_bytes = 0;
  	dbentry->n_deadlocks = 0;
  	dbentry->n_checksum_failures = 0;
  	dbentry->last_checksum_failure = 0;
  	dbentry->n_block_read_time = 0;
  	dbentry->n_block_write_time = 0;
  	dbentry->n_sessions = 0;
  	dbentry->total_session_time = 0;
  	dbentry->total_active_time = 0;
  	dbentry->total_idle_in_xact_time = 0;
  	dbentry->n_sessions_abandoned = 0;
  	dbentry->n_sessions_fatal = 0;
  	dbentry->n_sessions_killed = 0;
  
  	dbentry->stat_reset_timestamp = GetCurrentTimestamp();
  	dbentry->stats_timestamp = 0;
  
  	hash_ctl.keysize = sizeof(Oid);
  	hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
  	dbentry->tables = hash_create("Per-database table",
  								  PGSTAT_TAB_HASH_SIZE,
  								  &hash_ctl,
  								  HASH_ELEM | HASH_BLOBS);
  
  	hash_ctl.keysize = sizeof(Oid);
  	hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
  	dbentry->functions = hash_create("Per-database function",
  									 PGSTAT_FUNCTION_HASH_SIZE,
  									 &hash_ctl,
  									 HASH_ELEM | HASH_BLOBS);
  }
  
  /*
   * Lookup the hash table entry for the specified database. If no hash
   * table entry exists, initialize it, if the create parameter is true.
   * Else, return NULL.
   */
  static PgStat_StatDBEntry *
  pgstat_get_db_entry(Oid databaseid, bool create)
  {
  	PgStat_StatDBEntry *result;
  	bool		found;
  	HASHACTION	action = (create ? HASH_ENTER : HASH_FIND);
  
  	/* Lookup or create the hash table entry for this database */
  	result = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
  												&databaseid,
  												action, &found);
  
  	if (!create && !found)
  		return NULL;
  
  	/*
  	 * If not found, initialize the new one.  This creates empty hash tables
  	 * for tables and functions, too.
  	 */
  	if (!found)
  		reset_dbentry_counters(result);
  
  	return result;
  }
  
  
  /*
   * Lookup the hash table entry for the specified table. If no hash
   * table entry exists, initialize it, if the create parameter is true.
   * Else, return NULL.
   */
  static PgStat_StatTabEntry *
  pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry, Oid tableoid, bool create)
  {
  	PgStat_StatTabEntry *result;
  	bool		found;
  	HASHACTION	action = (create ? HASH_ENTER : HASH_FIND);
  
  	/* Lookup or create the hash table entry for this table */
  	result = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
  												 &tableoid,
  												 action, &found);
  
  	if (!create && !found)
  		return NULL;
  
  	/* If not found, initialize the new one. */
  	if (!found)
  	{
  		result->numscans = 0;
  		result->tuples_returned = 0;
  		result->tuples_fetched = 0;
  		result->tuples_inserted = 0;
  		result->tuples_updated = 0;
  		result->tuples_deleted = 0;
  		result->tuples_hot_updated = 0;
  		result->n_live_tuples = 0;
  		result->n_dead_tuples = 0;
  		result->changes_since_analyze = 0;
  		result->inserts_since_vacuum = 0;
  		result->blocks_fetched = 0;
  		result->blocks_hit = 0;
  		result->vacuum_timestamp = 0;
  		result->vacuum_count = 0;
  		result->autovac_vacuum_timestamp = 0;
  		result->autovac_vacuum_count = 0;
  		result->analyze_timestamp = 0;
  		result->analyze_count = 0;
  		result->autovac_analyze_timestamp = 0;
  		result->autovac_analyze_count = 0;
  	}
  
  	return result;
  }
  
  
  /* ----------
   * pgstat_write_statsfiles() -
   *		Write the global statistics file, as well as requested DB files.
   *
   *	'permanent' specifies writing to the permanent files not temporary ones.
   *	When true (happens only when the collector is shutting down), also remove
   *	the temporary files so that backends starting up under a new postmaster
   *	can't read old data before the new collector is ready.
   *
   *	When 'allDbs' is false, only the requested databases (listed in
   *	pending_write_requests) will be written; otherwise, all databases
   *	will be written.
   * ----------
   */
  static void
  pgstat_write_statsfiles(bool permanent, bool allDbs)
  {
  	HASH_SEQ_STATUS hstat;
  	PgStat_StatDBEntry *dbentry;
  	FILE	   *fpout;
  	int32		format_id;
  	const char *tmpfile = permanent ? PGSTAT_STAT_PERMANENT_TMPFILE : pgstat_stat_tmpname;
  	const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
  	int			rc;
  	int			i;
  
  	elog(DEBUG2, "writing stats file \"%s\"", statfile);
  
  	/*
  	 * Open the statistics temp file to write out the current values.
  	 */
  	fpout = AllocateFile(tmpfile, PG_BINARY_W);
  	if (fpout == NULL)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not open temporary statistics file \"%s\": %m",
  						tmpfile)));
  		return;
  	}
  
  	/*
  	 * Set the timestamp of the stats file.
  	 */
  	globalStats.stats_timestamp = GetCurrentTimestamp();
  
  	/*
  	 * Write the file header --- currently just a format ID.
  	 */
  	format_id = PGSTAT_FILE_FORMAT_ID;
  	rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
  	(void) rc;					/* we'll check for error with ferror */
  
  	/*
  	 * Write global stats struct
  	 */
  	rc = fwrite(&globalStats, sizeof(globalStats), 1, fpout);
  	(void) rc;					/* we'll check for error with ferror */
  
  	/*
  	 * Write archiver stats struct
  	 */
  	rc = fwrite(&archiverStats, sizeof(archiverStats), 1, fpout);
  	(void) rc;					/* we'll check for error with ferror */
  
  	/*
  	 * Write WAL stats struct
  	 */
  	rc = fwrite(&walStats, sizeof(walStats), 1, fpout);
  	(void) rc;					/* we'll check for error with ferror */
  
  	/*
  	 * Write SLRU stats struct
  	 */
  	rc = fwrite(slruStats, sizeof(slruStats), 1, fpout);
  	(void) rc;					/* we'll check for error with ferror */
  
  	/*
  	 * Walk through the database table.
  	 */
  	hash_seq_init(&hstat, pgStatDBHash);
  	while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
  	{
  		/*
  		 * Write out the table and function stats for this DB into the
  		 * appropriate per-DB stat file, if required.
  		 */
  		if (allDbs || pgstat_db_requested(dbentry->databaseid))
  		{
  			/* Make DB's timestamp consistent with the global stats */
  			dbentry->stats_timestamp = globalStats.stats_timestamp;
  
  			pgstat_write_db_statsfile(dbentry, permanent);
  		}
  
  		/*
  		 * Write out the DB entry. We don't write the tables or functions
  		 * pointers, since they're of no use to any other process.
  		 */
  		fputc('D', fpout);
  		rc = fwrite(dbentry, offsetof(PgStat_StatDBEntry, tables), 1, fpout);
  		(void) rc;				/* we'll check for error with ferror */
  	}
  
  	/*
  	 * Write replication slot stats struct
  	 */
  	for (i = 0; i < nReplSlotStats; i++)
  	{
  		fputc('R', fpout);
  		rc = fwrite(&replSlotStats[i], sizeof(PgStat_ReplSlotStats), 1, fpout);
  		(void) rc;				/* we'll check for error with ferror */
  	}
  
  	/*
  	 * No more output to be done. Close the temp file and replace the old
  	 * pgstat.stat with it.  The ferror() check replaces testing for error
  	 * after each individual fputc or fwrite above.
  	 */
  	fputc('E', fpout);
  
  	if (ferror(fpout))
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not write temporary statistics file \"%s\": %m",
  						tmpfile)));
  		FreeFile(fpout);
  		unlink(tmpfile);
  	}
  	else if (FreeFile(fpout) < 0)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not close temporary statistics file \"%s\": %m",
  						tmpfile)));
  		unlink(tmpfile);
  	}
  	else if (rename(tmpfile, statfile) < 0)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not rename temporary statistics file \"%s\" to \"%s\": %m",
  						tmpfile, statfile)));
  		unlink(tmpfile);
  	}
  
  	if (permanent)
  		unlink(pgstat_stat_filename);
  
  	/*
  	 * Now throw away the list of requests.  Note that requests sent after we
  	 * started the write are still waiting on the network socket.
  	 */
  	list_free(pending_write_requests);
  	pending_write_requests = NIL;
  }
  
  /*
   * return the filename for a DB stat file; filename is the output buffer,
   * of length len.
   */
  static void
  get_dbstat_filename(bool permanent, bool tempname, Oid databaseid,
  					char *filename, int len)
  {
  	int			printed;
  
  	/* NB -- pgstat_reset_remove_files knows about the pattern this uses */
  	printed = snprintf(filename, len, "%s/db_%u.%s",
  					   permanent ? PGSTAT_STAT_PERMANENT_DIRECTORY :
  					   pgstat_stat_directory,
  					   databaseid,
  					   tempname ? "tmp" : "stat");
  	if (printed >= len)
  		elog(ERROR, "overlength pgstat path");
  }
  
  /* ----------
   * pgstat_write_db_statsfile() -
   *		Write the stat file for a single database.
   *
   *	If writing to the permanent file (happens when the collector is
   *	shutting down only), remove the temporary file so that backends
   *	starting up under a new postmaster can't read the old data before
   *	the new collector is ready.
   * ----------
   */
  static void
  pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent)
  {
  	HASH_SEQ_STATUS tstat;
  	HASH_SEQ_STATUS fstat;
  	PgStat_StatTabEntry *tabentry;
  	PgStat_StatFuncEntry *funcentry;
  	FILE	   *fpout;
  	int32		format_id;
  	Oid			dbid = dbentry->databaseid;
  	int			rc;
  	char		tmpfile[MAXPGPATH];
  	char		statfile[MAXPGPATH];
  
  	get_dbstat_filename(permanent, true, dbid, tmpfile, MAXPGPATH);
  	get_dbstat_filename(permanent, false, dbid, statfile, MAXPGPATH);
  
  	elog(DEBUG2, "writing stats file \"%s\"", statfile);
  
  	/*
  	 * Open the statistics temp file to write out the current values.
  	 */
  	fpout = AllocateFile(tmpfile, PG_BINARY_W);
  	if (fpout == NULL)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not open temporary statistics file \"%s\": %m",
  						tmpfile)));
  		return;
  	}
  
  	/*
  	 * Write the file header --- currently just a format ID.
  	 */
  	format_id = PGSTAT_FILE_FORMAT_ID;
  	rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
  	(void) rc;					/* we'll check for error with ferror */
  
  	/*
  	 * Walk through the database's access stats per table.
  	 */
  	hash_seq_init(&tstat, dbentry->tables);
  	while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&tstat)) != NULL)
  	{
  		fputc('T', fpout);
  		rc = fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
  		(void) rc;				/* we'll check for error with ferror */
  	}
  
  	/*
  	 * Walk through the database's function stats table.
  	 */
  	hash_seq_init(&fstat, dbentry->functions);
  	while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&fstat)) != NULL)
  	{
  		fputc('F', fpout);
  		rc = fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
  		(void) rc;				/* we'll check for error with ferror */
  	}
  
  	/*
  	 * No more output to be done. Close the temp file and replace the old
  	 * pgstat.stat with it.  The ferror() check replaces testing for error
  	 * after each individual fputc or fwrite above.
  	 */
  	fputc('E', fpout);
  
  	if (ferror(fpout))
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not write temporary statistics file \"%s\": %m",
  						tmpfile)));
  		FreeFile(fpout);
  		unlink(tmpfile);
  	}
  	else if (FreeFile(fpout) < 0)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not close temporary statistics file \"%s\": %m",
  						tmpfile)));
  		unlink(tmpfile);
  	}
  	else if (rename(tmpfile, statfile) < 0)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
  				 errmsg("could not rename temporary statistics file \"%s\" to \"%s\": %m",
  						tmpfile, statfile)));
  		unlink(tmpfile);
  	}
  
  	if (permanent)
  	{
  		get_dbstat_filename(false, false, dbid, statfile, MAXPGPATH);
  
  		elog(DEBUG2, "removing temporary stats file \"%s\"", statfile);
  		unlink(statfile);
  	}
  }
  
  /* ----------
   * pgstat_read_statsfiles() -
   *
   *	Reads in some existing statistics collector files and returns the
   *	databases hash table that is the top level of the data.
   *
   *	If 'onlydb' is not InvalidOid, it means we only want data for that DB
   *	plus the shared catalogs ("DB 0").  We'll still populate the DB hash
   *	table for all databases, but we don't bother even creating table/function
   *	hash tables for other databases.
   *
   *	'permanent' specifies reading from the permanent files not temporary ones.
   *	When true (happens only when the collector is starting up), remove the
   *	files after reading; the in-memory status is now authoritative, and the
   *	files would be out of date in case somebody else reads them.
   *
   *	If a 'deep' read is requested, table/function stats are read, otherwise
   *	the table/function hash tables remain empty.
   * ----------
   */
  static HTAB *
  pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
  {
  	PgStat_StatDBEntry *dbentry;
  	PgStat_StatDBEntry dbbuf;
  	HASHCTL		hash_ctl;
  	HTAB	   *dbhash;
  	FILE	   *fpin;
  	int32		format_id;
  	bool		found;
  	const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
  	int			i;
  
  	/*
  	 * The tables will live in pgStatLocalContext.
  	 */
  	pgstat_setup_memcxt();
  
  	/*
  	 * Create the DB hashtable
  	 */
  	hash_ctl.keysize = sizeof(Oid);
  	hash_ctl.entrysize = sizeof(PgStat_StatDBEntry);
  	hash_ctl.hcxt = pgStatLocalContext;
  	dbhash = hash_create("Databases hash", PGSTAT_DB_HASH_SIZE, &hash_ctl,
  						 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
  
  	/* Allocate the space for replication slot statistics */
  	replSlotStats = MemoryContextAllocZero(pgStatLocalContext,
  										   max_replication_slots
  										   * sizeof(PgStat_ReplSlotStats));
  	nReplSlotStats = 0;
  
  	/*
  	 * Clear out global, archiver, WAL and SLRU statistics so they start from
  	 * zero in case we can't load an existing statsfile.
  	 */
  	memset(&globalStats, 0, sizeof(globalStats));
  	memset(&archiverStats, 0, sizeof(archiverStats));
  	memset(&walStats, 0, sizeof(walStats));
  	memset(&slruStats, 0, sizeof(slruStats));
  
  	/*
  	 * Set the current timestamp (will be kept only in case we can't load an
  	 * existing statsfile).
  	 */
  	globalStats.stat_reset_timestamp = GetCurrentTimestamp();
  	archiverStats.stat_reset_timestamp = globalStats.stat_reset_timestamp;
  	walStats.stat_reset_timestamp = globalStats.stat_reset_timestamp;
  
  	/*
  	 * Set the same reset timestamp for all SLRU items too.
  	 */
  	for (i = 0; i < SLRU_NUM_ELEMENTS; i++)
  		slruStats[i].stat_reset_timestamp = globalStats.stat_reset_timestamp;
  
  	/*
  	 * Set the same reset timestamp for all replication slots too.
  	 */
  	for (i = 0; i < max_replication_slots; i++)
  		replSlotStats[i].stat_reset_timestamp = globalStats.stat_reset_timestamp;
  
  	/*
  	 * Try to open the stats file. If it doesn't exist, the backends simply
  	 * return zero for anything and the collector simply starts from scratch
  	 * with empty counters.
  	 *
  	 * ENOENT is a possibility if the stats collector is not running or has
  	 * not yet written the stats file the first time.  Any other failure
  	 * condition is suspicious.
  	 */
  	if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
  	{
  		if (errno != ENOENT)
  			ereport(pgStatRunningInCollector ? LOG : WARNING,
  					(errcode_for_file_access(),
  					 errmsg("could not open statistics file \"%s\": %m",
  							statfile)));
  		return dbhash;
  	}
  
  	/*
  	 * Verify it's of the expected format.
  	 */
  	if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
  		format_id != PGSTAT_FILE_FORMAT_ID)
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		goto done;
  	}
  
  	/*
  	 * Read global stats struct
  	 */
  	if (fread(&globalStats, 1, sizeof(globalStats), fpin) != sizeof(globalStats))
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		memset(&globalStats, 0, sizeof(globalStats));
  		goto done;
  	}
  
  	/*
  	 * In the collector, disregard the timestamp we read from the permanent
  	 * stats file; we should be willing to write a temp stats file immediately
  	 * upon the first request from any backend.  This only matters if the old
  	 * file's timestamp is less than PGSTAT_STAT_INTERVAL ago, but that's not
  	 * an unusual scenario.
  	 */
  	if (pgStatRunningInCollector)
  		globalStats.stats_timestamp = 0;
  
  	/*
  	 * Read archiver stats struct
  	 */
  	if (fread(&archiverStats, 1, sizeof(archiverStats), fpin) != sizeof(archiverStats))
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		memset(&archiverStats, 0, sizeof(archiverStats));
  		goto done;
  	}
  
  	/*
  	 * Read WAL stats struct
  	 */
  	if (fread(&walStats, 1, sizeof(walStats), fpin) != sizeof(walStats))
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		memset(&walStats, 0, sizeof(walStats));
  		goto done;
  	}
  
  	/*
  	 * Read SLRU stats struct
  	 */
  	if (fread(slruStats, 1, sizeof(slruStats), fpin) != sizeof(slruStats))
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		memset(&slruStats, 0, sizeof(slruStats));
  		goto done;
  	}
  
  	/*
  	 * We found an existing collector stats file. Read it and put all the
  	 * hashtable entries into place.
  	 */
  	for (;;)
  	{
  		switch (fgetc(fpin))
  		{
  				/*
  				 * 'D'	A PgStat_StatDBEntry struct describing a database
  				 * follows.
  				 */
  			case 'D':
  				if (fread(&dbbuf, 1, offsetof(PgStat_StatDBEntry, tables),
  						  fpin) != offsetof(PgStat_StatDBEntry, tables))
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					goto done;
  				}
  
  				/*
  				 * Add to the DB hash
  				 */
  				dbentry = (PgStat_StatDBEntry *) hash_search(dbhash,
  															 (void *) &dbbuf.databaseid,
  															 HASH_ENTER,
  															 &found);
  				if (found)
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					goto done;
  				}
  
  				memcpy(dbentry, &dbbuf, sizeof(PgStat_StatDBEntry));
  				dbentry->tables = NULL;
  				dbentry->functions = NULL;
  
  				/*
  				 * In the collector, disregard the timestamp we read from the
  				 * permanent stats file; we should be willing to write a temp
  				 * stats file immediately upon the first request from any
  				 * backend.
  				 */
  				if (pgStatRunningInCollector)
  					dbentry->stats_timestamp = 0;
  
  				/*
  				 * Don't create tables/functions hashtables for uninteresting
  				 * databases.
  				 */
  				if (onlydb != InvalidOid)
  				{
  					if (dbbuf.databaseid != onlydb &&
  						dbbuf.databaseid != InvalidOid)
  						break;
  				}
  
  				hash_ctl.keysize = sizeof(Oid);
  				hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
  				hash_ctl.hcxt = pgStatLocalContext;
  				dbentry->tables = hash_create("Per-database table",
  											  PGSTAT_TAB_HASH_SIZE,
  											  &hash_ctl,
  											  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
  
  				hash_ctl.keysize = sizeof(Oid);
  				hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
  				hash_ctl.hcxt = pgStatLocalContext;
  				dbentry->functions = hash_create("Per-database function",
  												 PGSTAT_FUNCTION_HASH_SIZE,
  												 &hash_ctl,
  												 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
  
  				/*
  				 * If requested, read the data from the database-specific
  				 * file.  Otherwise we just leave the hashtables empty.
  				 */
  				if (deep)
  					pgstat_read_db_statsfile(dbentry->databaseid,
  											 dbentry->tables,
  											 dbentry->functions,
  											 permanent);
  
  				break;
  
  				/*
  				 * 'R'	A PgStat_ReplSlotStats struct describing a replication
  				 * slot follows.
  				 */
  			case 'R':
  				if (fread(&replSlotStats[nReplSlotStats], 1, sizeof(PgStat_ReplSlotStats), fpin)
  					!= sizeof(PgStat_ReplSlotStats))
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					memset(&replSlotStats[nReplSlotStats], 0, sizeof(PgStat_ReplSlotStats));
  					goto done;
  				}
  				nReplSlotStats++;
  				break;
  
  			case 'E':
  				goto done;
  
  			default:
  				ereport(pgStatRunningInCollector ? LOG : WARNING,
  						(errmsg("corrupted statistics file \"%s\"",
  								statfile)));
  				goto done;
  		}
  	}
  
  done:
  	FreeFile(fpin);
  
  	/* If requested to read the permanent file, also get rid of it. */
  	if (permanent)
  	{
  		elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
  		unlink(statfile);
  	}
  
  	return dbhash;
  }
  
  
  /* ----------
   * pgstat_read_db_statsfile() -
   *
   *	Reads in the existing statistics collector file for the given database,
   *	filling the passed-in tables and functions hash tables.
   *
   *	As in pgstat_read_statsfiles, if the permanent file is requested, it is
   *	removed after reading.
   *
   *	Note: this code has the ability to skip storing per-table or per-function
   *	data, if NULL is passed for the corresponding hashtable.  That's not used
   *	at the moment though.
   * ----------
   */
  static void
  pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
  						 bool permanent)
  {
  	PgStat_StatTabEntry *tabentry;
  	PgStat_StatTabEntry tabbuf;
  	PgStat_StatFuncEntry funcbuf;
  	PgStat_StatFuncEntry *funcentry;
  	FILE	   *fpin;
  	int32		format_id;
  	bool		found;
  	char		statfile[MAXPGPATH];
  
  	get_dbstat_filename(permanent, false, databaseid, statfile, MAXPGPATH);
  
  	/*
  	 * Try to open the stats file. If it doesn't exist, the backends simply
  	 * return zero for anything and the collector simply starts from scratch
  	 * with empty counters.
  	 *
  	 * ENOENT is a possibility if the stats collector is not running or has
  	 * not yet written the stats file the first time.  Any other failure
  	 * condition is suspicious.
  	 */
  	if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
  	{
  		if (errno != ENOENT)
  			ereport(pgStatRunningInCollector ? LOG : WARNING,
  					(errcode_for_file_access(),
  					 errmsg("could not open statistics file \"%s\": %m",
  							statfile)));
  		return;
  	}
  
  	/*
  	 * Verify it's of the expected format.
  	 */
  	if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
  		format_id != PGSTAT_FILE_FORMAT_ID)
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		goto done;
  	}
  
  	/*
  	 * We found an existing collector stats file. Read it and put all the
  	 * hashtable entries into place.
  	 */
  	for (;;)
  	{
  		switch (fgetc(fpin))
  		{
  				/*
  				 * 'T'	A PgStat_StatTabEntry follows.
  				 */
  			case 'T':
  				if (fread(&tabbuf, 1, sizeof(PgStat_StatTabEntry),
  						  fpin) != sizeof(PgStat_StatTabEntry))
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					goto done;
  				}
  
  				/*
  				 * Skip if table data not wanted.
  				 */
  				if (tabhash == NULL)
  					break;
  
  				tabentry = (PgStat_StatTabEntry *) hash_search(tabhash,
  															   (void *) &tabbuf.tableid,
  															   HASH_ENTER, &found);
  
  				if (found)
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					goto done;
  				}
  
  				memcpy(tabentry, &tabbuf, sizeof(tabbuf));
  				break;
  
  				/*
  				 * 'F'	A PgStat_StatFuncEntry follows.
  				 */
  			case 'F':
  				if (fread(&funcbuf, 1, sizeof(PgStat_StatFuncEntry),
  						  fpin) != sizeof(PgStat_StatFuncEntry))
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					goto done;
  				}
  
  				/*
  				 * Skip if function data not wanted.
  				 */
  				if (funchash == NULL)
  					break;
  
  				funcentry = (PgStat_StatFuncEntry *) hash_search(funchash,
  																 (void *) &funcbuf.functionid,
  																 HASH_ENTER, &found);
  
  				if (found)
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					goto done;
  				}
  
  				memcpy(funcentry, &funcbuf, sizeof(funcbuf));
  				break;
  
  				/*
  				 * 'E'	The EOF marker of a complete stats file.
  				 */
  			case 'E':
  				goto done;
  
  			default:
  				ereport(pgStatRunningInCollector ? LOG : WARNING,
  						(errmsg("corrupted statistics file \"%s\"",
  								statfile)));
  				goto done;
  		}
  	}
  
  done:
  	FreeFile(fpin);
  
  	if (permanent)
  	{
  		elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
  		unlink(statfile);
  	}
  }
  
  /* ----------
   * pgstat_read_db_statsfile_timestamp() -
   *
   *	Attempt to determine the timestamp of the last db statfile write.
   *	Returns true if successful; the timestamp is stored in *ts. The caller must
   *	rely on timestamp stored in *ts iff the function returns true.
   *
   *	This needs to be careful about handling databases for which no stats file
   *	exists, such as databases without a stat entry or those not yet written:
   *
   *	- if there's a database entry in the global file, return the corresponding
   *	stats_timestamp value.
   *
   *	- if there's no db stat entry (e.g. for a new or inactive database),
   *	there's no stats_timestamp value, but also nothing to write so we return
   *	the timestamp of the global statfile.
   * ----------
   */
  static bool
  pgstat_read_db_statsfile_timestamp(Oid databaseid, bool permanent,
  								   TimestampTz *ts)
  {
  	PgStat_StatDBEntry dbentry;
  	PgStat_GlobalStats myGlobalStats;
  	PgStat_ArchiverStats myArchiverStats;
  	PgStat_WalStats myWalStats;
  	PgStat_SLRUStats mySLRUStats[SLRU_NUM_ELEMENTS];
  	PgStat_ReplSlotStats myReplSlotStats;
  	FILE	   *fpin;
  	int32		format_id;
  	const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
  
  	/*
  	 * Try to open the stats file.  As above, anything but ENOENT is worthy of
  	 * complaining about.
  	 */
  	if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
  	{
  		if (errno != ENOENT)
  			ereport(pgStatRunningInCollector ? LOG : WARNING,
  					(errcode_for_file_access(),
  					 errmsg("could not open statistics file \"%s\": %m",
  							statfile)));
  		return false;
  	}
  
  	/*
  	 * Verify it's of the expected format.
  	 */
  	if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
  		format_id != PGSTAT_FILE_FORMAT_ID)
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		FreeFile(fpin);
  		return false;
  	}
  
  	/*
  	 * Read global stats struct
  	 */
  	if (fread(&myGlobalStats, 1, sizeof(myGlobalStats),
  			  fpin) != sizeof(myGlobalStats))
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		FreeFile(fpin);
  		return false;
  	}
  
  	/*
  	 * Read archiver stats struct
  	 */
  	if (fread(&myArchiverStats, 1, sizeof(myArchiverStats),
  			  fpin) != sizeof(myArchiverStats))
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		FreeFile(fpin);
  		return false;
  	}
  
  	/*
  	 * Read WAL stats struct
  	 */
  	if (fread(&myWalStats, 1, sizeof(myWalStats), fpin) != sizeof(myWalStats))
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		FreeFile(fpin);
  		return false;
  	}
  
  	/*
  	 * Read SLRU stats struct
  	 */
  	if (fread(mySLRUStats, 1, sizeof(mySLRUStats), fpin) != sizeof(mySLRUStats))
  	{
  		ereport(pgStatRunningInCollector ? LOG : WARNING,
  				(errmsg("corrupted statistics file \"%s\"", statfile)));
  		FreeFile(fpin);
  		return false;
  	}
  
  	/* By default, we're going to return the timestamp of the global file. */
  	*ts = myGlobalStats.stats_timestamp;
  
  	/*
  	 * We found an existing collector stats file.  Read it and look for a
  	 * record for the requested database.  If found, use its timestamp.
  	 */
  	for (;;)
  	{
  		switch (fgetc(fpin))
  		{
  				/*
  				 * 'D'	A PgStat_StatDBEntry struct describing a database
  				 * follows.
  				 */
  			case 'D':
  				if (fread(&dbentry, 1, offsetof(PgStat_StatDBEntry, tables),
  						  fpin) != offsetof(PgStat_StatDBEntry, tables))
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					FreeFile(fpin);
  					return false;
  				}
  
  				/*
  				 * If this is the DB we're looking for, save its timestamp and
  				 * we're done.
  				 */
  				if (dbentry.databaseid == databaseid)
  				{
  					*ts = dbentry.stats_timestamp;
  					goto done;
  				}
  
  				break;
  
  				/*
  				 * 'R'	A PgStat_ReplSlotStats struct describing a replication
  				 * slot follows.
  				 */
  			case 'R':
  				if (fread(&myReplSlotStats, 1, sizeof(PgStat_ReplSlotStats), fpin)
  					!= sizeof(PgStat_ReplSlotStats))
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					FreeFile(fpin);
  					return false;
  				}
  				break;
  
  			case 'E':
  				goto done;
  
  			default:
  				{
  					ereport(pgStatRunningInCollector ? LOG : WARNING,
  							(errmsg("corrupted statistics file \"%s\"",
  									statfile)));
  					FreeFile(fpin);
  					return false;
  				}
  		}
  	}
  
  done:
  	FreeFile(fpin);
  	return true;
  }
  
  /*
   * If not already done, read the statistics collector stats file into
   * some hash tables.  The results will be kept until pgstat_clear_snapshot()
   * is called (typically, at end of transaction).
   */
  static void
  backend_read_statsfile(void)
  {
  	TimestampTz min_ts = 0;
  	TimestampTz ref_ts = 0;
  	Oid			inquiry_db;
  	int			count;
  
  	/* already read it? */
  	if (pgStatDBHash)
  		return;
  	Assert(!pgStatRunningInCollector);
  
  	/*
  	 * In a normal backend, we check staleness of the data for our own DB, and
  	 * so we send MyDatabaseId in inquiry messages.  In the autovac launcher,
  	 * check staleness of the shared-catalog data, and send InvalidOid in
  	 * inquiry messages so as not to force writing unnecessary data.
  	 */
  	if (IsAutoVacuumLauncherProcess())
  		inquiry_db = InvalidOid;
  	else
  		inquiry_db = MyDatabaseId;
  
  	/*
  	 * Loop until fresh enough stats file is available or we ran out of time.
  	 * The stats inquiry message is sent repeatedly in case collector drops
  	 * it; but not every single time, as that just swamps the collector.
  	 */
  	for (count = 0; count < PGSTAT_POLL_LOOP_COUNT; count++)
  	{
  		bool		ok;
  		TimestampTz file_ts = 0;
  		TimestampTz cur_ts;
  
  		CHECK_FOR_INTERRUPTS();
  
  		ok = pgstat_read_db_statsfile_timestamp(inquiry_db, false, &file_ts);
  
  		cur_ts = GetCurrentTimestamp();
  		/* Calculate min acceptable timestamp, if we didn't already */
  		if (count == 0 || cur_ts < ref_ts)
  		{
  			/*
  			 * We set the minimum acceptable timestamp to PGSTAT_STAT_INTERVAL
  			 * msec before now.  This indirectly ensures that the collector
  			 * needn't write the file more often than PGSTAT_STAT_INTERVAL. In
  			 * an autovacuum worker, however, we want a lower delay to avoid
  			 * using stale data, so we use PGSTAT_RETRY_DELAY (since the
  			 * number of workers is low, this shouldn't be a problem).
  			 *
  			 * We don't recompute min_ts after sleeping, except in the
  			 * unlikely case that cur_ts went backwards.  So we might end up
  			 * accepting a file a bit older than PGSTAT_STAT_INTERVAL.  In
  			 * practice that shouldn't happen, though, as long as the sleep
  			 * time is less than PGSTAT_STAT_INTERVAL; and we don't want to
  			 * tell the collector that our cutoff time is less than what we'd
  			 * actually accept.
  			 */
  			ref_ts = cur_ts;
  			if (IsAutoVacuumWorkerProcess())
  				min_ts = TimestampTzPlusMilliseconds(ref_ts,
  													 -PGSTAT_RETRY_DELAY);
  			else
  				min_ts = TimestampTzPlusMilliseconds(ref_ts,
  													 -PGSTAT_STAT_INTERVAL);
  		}
  
  		/*
  		 * If the file timestamp is actually newer than cur_ts, we must have
  		 * had a clock glitch (system time went backwards) or there is clock
  		 * skew between our processor and the stats collector's processor.
  		 * Accept the file, but send an inquiry message anyway to make
  		 * pgstat_recv_inquiry do a sanity check on the collector's time.
  		 */
  		if (ok && file_ts > cur_ts)
  		{
  			/*
  			 * A small amount of clock skew between processors isn't terribly
  			 * surprising, but a large difference is worth logging.  We
  			 * arbitrarily define "large" as 1000 msec.
  			 */
  			if (file_ts >= TimestampTzPlusMilliseconds(cur_ts, 1000))
  			{
  				char	   *filetime;
  				char	   *mytime;
  
  				/* Copy because timestamptz_to_str returns a static buffer */
  				filetime = pstrdup(timestamptz_to_str(file_ts));
  				mytime = pstrdup(timestamptz_to_str(cur_ts));
  				ereport(LOG,
  						(errmsg("statistics collector's time %s is later than backend local time %s",
  								filetime, mytime)));
  				pfree(filetime);
  				pfree(mytime);
  			}
  
  			pgstat_send_inquiry(cur_ts, min_ts, inquiry_db);
  			break;
  		}
  
  		/* Normal acceptance case: file is not older than cutoff time */
  		if (ok && file_ts >= min_ts)
  			break;
  
  		/* Not there or too old, so kick the collector and wait a bit */
  		if ((count % PGSTAT_INQ_LOOP_COUNT) == 0)
  			pgstat_send_inquiry(cur_ts, min_ts, inquiry_db);
  
  		pg_usleep(PGSTAT_RETRY_DELAY * 1000L);
  	}
  
  	if (count >= PGSTAT_POLL_LOOP_COUNT)
  		ereport(LOG,
  				(errmsg("using stale statistics instead of current ones "
  						"because stats collector is not responding")));
  
  	/*
  	 * Autovacuum launcher wants stats about all databases, but a shallow read
  	 * is sufficient.  Regular backends want a deep read for just the tables
  	 * they can see (MyDatabaseId + shared catalogs).
  	 */
  	if (IsAutoVacuumLauncherProcess())
  		pgStatDBHash = pgstat_read_statsfiles(InvalidOid, false, false);
  	else
  		pgStatDBHash = pgstat_read_statsfiles(MyDatabaseId, false, true);
  }
  
  
  /* ----------
   * pgstat_setup_memcxt() -
   *
   *	Create pgStatLocalContext, if not already done.
   * ----------
   */
  static void
  pgstat_setup_memcxt(void)
  {
  	if (!pgStatLocalContext)
  		pgStatLocalContext = AllocSetContextCreate(TopMemoryContext,
  												   "Statistics snapshot",
  												   ALLOCSET_SMALL_SIZES);
  }
  
  
  /* ----------
   * pgstat_clear_snapshot() -
   *
   *	Discard any data collected in the current transaction.  Any subsequent
   *	request will cause new snapshots to be read.
   *
   *	This is also invoked during transaction commit or abort to discard
   *	the no-longer-wanted snapshot.
   * ----------
   */
  void
  pgstat_clear_snapshot(void)
  {
  	/* Release memory, if any was allocated */
  	if (pgStatLocalContext)
  		MemoryContextDelete(pgStatLocalContext);
  
  	/* Reset variables */
  	pgStatLocalContext = NULL;
  	pgStatDBHash = NULL;
  	localBackendStatusTable = NULL;
  	localNumBackends = 0;
  	replSlotStats = NULL;
  	nReplSlotStats = 0;
  }
  
  
  /* ----------
   * pgstat_recv_inquiry() -
   *
   *	Process stat inquiry requests.
   * ----------
   */
  static void
  pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  
  	elog(DEBUG2, "received inquiry for database %u", msg->databaseid);
  
  	/*
  	 * If there's already a write request for this DB, there's nothing to do.
  	 *
  	 * Note that if a request is found, we return early and skip the below
  	 * check for clock skew.  This is okay, since the only way for a DB
  	 * request to be present in the list is that we have been here since the
  	 * last write round.  It seems sufficient to check for clock skew once per
  	 * write round.
  	 */
  	if (list_member_oid(pending_write_requests, msg->databaseid))
  		return;
  
  	/*
  	 * Check to see if we last wrote this database at a time >= the requested
  	 * cutoff time.  If so, this is a stale request that was generated before
  	 * we updated the DB file, and we don't need to do so again.
  	 *
  	 * If the requestor's local clock time is older than stats_timestamp, we
  	 * should suspect a clock glitch, ie system time going backwards; though
  	 * the more likely explanation is just delayed message receipt.  It is
  	 * worth expending a GetCurrentTimestamp call to be sure, since a large
  	 * retreat in the system clock reading could otherwise cause us to neglect
  	 * to update the stats file for a long time.
  	 */
  	dbentry = pgstat_get_db_entry(msg->databaseid, false);
  	if (dbentry == NULL)
  	{
  		/*
  		 * We have no data for this DB.  Enter a write request anyway so that
  		 * the global stats will get updated.  This is needed to prevent
  		 * backend_read_statsfile from waiting for data that we cannot supply,
  		 * in the case of a new DB that nobody has yet reported any stats for.
  		 * See the behavior of pgstat_read_db_statsfile_timestamp.
  		 */
  	}
  	else if (msg->clock_time < dbentry->stats_timestamp)
  	{
  		TimestampTz cur_ts = GetCurrentTimestamp();
  
  		if (cur_ts < dbentry->stats_timestamp)
  		{
  			/*
  			 * Sure enough, time went backwards.  Force a new stats file write
  			 * to get back in sync; but first, log a complaint.
  			 */
  			char	   *writetime;
  			char	   *mytime;
  
  			/* Copy because timestamptz_to_str returns a static buffer */
  			writetime = pstrdup(timestamptz_to_str(dbentry->stats_timestamp));
  			mytime = pstrdup(timestamptz_to_str(cur_ts));
  			ereport(LOG,
  					(errmsg("stats_timestamp %s is later than collector's time %s for database %u",
  							writetime, mytime, dbentry->databaseid)));
  			pfree(writetime);
  			pfree(mytime);
  		}
  		else
  		{
  			/*
  			 * Nope, it's just an old request.  Assuming msg's clock_time is
  			 * >= its cutoff_time, it must be stale, so we can ignore it.
  			 */
  			return;
  		}
  	}
  	else if (msg->cutoff_time <= dbentry->stats_timestamp)
  	{
  		/* Stale request, ignore it */
  		return;
  	}
  
  	/*
  	 * We need to write this DB, so create a request.
  	 */
  	pending_write_requests = lappend_oid(pending_write_requests,
  										 msg->databaseid);
  }
  
  
  /* ----------
   * pgstat_recv_tabstat() -
   *
   *	Count what the backend has done.
   * ----------
   */
  static void
  pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  	PgStat_StatTabEntry *tabentry;
  	int			i;
  	bool		found;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	/*
  	 * Update database-wide stats.
  	 */
  	dbentry->n_xact_commit += (PgStat_Counter) (msg->m_xact_commit);
  	dbentry->n_xact_rollback += (PgStat_Counter) (msg->m_xact_rollback);
  	dbentry->n_block_read_time += msg->m_block_read_time;
  	dbentry->n_block_write_time += msg->m_block_write_time;
  
  	/*
  	 * Process all table entries in the message.
  	 */
  	for (i = 0; i < msg->m_nentries; i++)
  	{
  		PgStat_TableEntry *tabmsg = &(msg->m_entry[i]);
  
  		tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
  													   (void *) &(tabmsg->t_id),
  													   HASH_ENTER, &found);
  
  		if (!found)
  		{
  			/*
  			 * If it's a new table entry, initialize counters to the values we
  			 * just got.
  			 */
  			tabentry->numscans = tabmsg->t_counts.t_numscans;
  			tabentry->tuples_returned = tabmsg->t_counts.t_tuples_returned;
  			tabentry->tuples_fetched = tabmsg->t_counts.t_tuples_fetched;
  			tabentry->tuples_inserted = tabmsg->t_counts.t_tuples_inserted;
  			tabentry->tuples_updated = tabmsg->t_counts.t_tuples_updated;
  			tabentry->tuples_deleted = tabmsg->t_counts.t_tuples_deleted;
  			tabentry->tuples_hot_updated = tabmsg->t_counts.t_tuples_hot_updated;
  			tabentry->n_live_tuples = tabmsg->t_counts.t_delta_live_tuples;
  			tabentry->n_dead_tuples = tabmsg->t_counts.t_delta_dead_tuples;
  			tabentry->changes_since_analyze = tabmsg->t_counts.t_changed_tuples;
  			tabentry->inserts_since_vacuum = tabmsg->t_counts.t_tuples_inserted;
  			tabentry->blocks_fetched = tabmsg->t_counts.t_blocks_fetched;
  			tabentry->blocks_hit = tabmsg->t_counts.t_blocks_hit;
  
  			tabentry->vacuum_timestamp = 0;
  			tabentry->vacuum_count = 0;
  			tabentry->autovac_vacuum_timestamp = 0;
  			tabentry->autovac_vacuum_count = 0;
  			tabentry->analyze_timestamp = 0;
  			tabentry->analyze_count = 0;
  			tabentry->autovac_analyze_timestamp = 0;
  			tabentry->autovac_analyze_count = 0;
  		}
  		else
  		{
  			/*
  			 * Otherwise add the values to the existing entry.
  			 */
  			tabentry->numscans += tabmsg->t_counts.t_numscans;
  			tabentry->tuples_returned += tabmsg->t_counts.t_tuples_returned;
  			tabentry->tuples_fetched += tabmsg->t_counts.t_tuples_fetched;
  			tabentry->tuples_inserted += tabmsg->t_counts.t_tuples_inserted;
  			tabentry->tuples_updated += tabmsg->t_counts.t_tuples_updated;
  			tabentry->tuples_deleted += tabmsg->t_counts.t_tuples_deleted;
  			tabentry->tuples_hot_updated += tabmsg->t_counts.t_tuples_hot_updated;
  			/* If table was truncated, first reset the live/dead counters */
  			if (tabmsg->t_counts.t_truncated)
  			{
  				tabentry->n_live_tuples = 0;
  				tabentry->n_dead_tuples = 0;
  				tabentry->inserts_since_vacuum = 0;
  			}
  			tabentry->n_live_tuples += tabmsg->t_counts.t_delta_live_tuples;
  			tabentry->n_dead_tuples += tabmsg->t_counts.t_delta_dead_tuples;
  			tabentry->changes_since_analyze += tabmsg->t_counts.t_changed_tuples;
  			tabentry->inserts_since_vacuum += tabmsg->t_counts.t_tuples_inserted;
  			tabentry->blocks_fetched += tabmsg->t_counts.t_blocks_fetched;
  			tabentry->blocks_hit += tabmsg->t_counts.t_blocks_hit;
  		}
  
  		/* Clamp n_live_tuples in case of negative delta_live_tuples */
  		tabentry->n_live_tuples = Max(tabentry->n_live_tuples, 0);
  		/* Likewise for n_dead_tuples */
  		tabentry->n_dead_tuples = Max(tabentry->n_dead_tuples, 0);
  
  		/*
  		 * Add per-table stats to the per-database entry, too.
  		 */
  		dbentry->n_tuples_returned += tabmsg->t_counts.t_tuples_returned;
  		dbentry->n_tuples_fetched += tabmsg->t_counts.t_tuples_fetched;
  		dbentry->n_tuples_inserted += tabmsg->t_counts.t_tuples_inserted;
  		dbentry->n_tuples_updated += tabmsg->t_counts.t_tuples_updated;
  		dbentry->n_tuples_deleted += tabmsg->t_counts.t_tuples_deleted;
  		dbentry->n_blocks_fetched += tabmsg->t_counts.t_blocks_fetched;
  		dbentry->n_blocks_hit += tabmsg->t_counts.t_blocks_hit;
  	}
  }
  
  
  /* ----------
   * pgstat_recv_tabpurge() -
   *
   *	Arrange for dead table removal.
   * ----------
   */
  static void
  pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  	int			i;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
  
  	/*
  	 * No need to purge if we don't even know the database.
  	 */
  	if (!dbentry || !dbentry->tables)
  		return;
  
  	/*
  	 * Process all table entries in the message.
  	 */
  	for (i = 0; i < msg->m_nentries; i++)
  	{
  		/* Remove from hashtable if present; we don't care if it's not. */
  		(void) hash_search(dbentry->tables,
  						   (void *) &(msg->m_tableid[i]),
  						   HASH_REMOVE, NULL);
  	}
  }
  
  
  /* ----------
   * pgstat_recv_dropdb() -
   *
   *	Arrange for dead database removal
   * ----------
   */
  static void
  pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len)
  {
  	Oid			dbid = msg->m_databaseid;
  	PgStat_StatDBEntry *dbentry;
  
  	/*
  	 * Lookup the database in the hashtable.
  	 */
  	dbentry = pgstat_get_db_entry(dbid, false);
  
  	/*
  	 * If found, remove it (along with the db statfile).
  	 */
  	if (dbentry)
  	{
  		char		statfile[MAXPGPATH];
  
  		get_dbstat_filename(false, false, dbid, statfile, MAXPGPATH);
  
  		elog(DEBUG2, "removing stats file \"%s\"", statfile);
  		unlink(statfile);
  
  		if (dbentry->tables != NULL)
  			hash_destroy(dbentry->tables);
  		if (dbentry->functions != NULL)
  			hash_destroy(dbentry->functions);
  
  		if (hash_search(pgStatDBHash,
  						(void *) &dbid,
  						HASH_REMOVE, NULL) == NULL)
  			ereport(ERROR,
  					(errmsg("database hash table corrupted during cleanup --- abort")));
  	}
  }
  
  
  /* ----------
   * pgstat_recv_resetcounter() -
   *
   *	Reset the statistics for the specified database.
   * ----------
   */
  static void
  pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  
  	/*
  	 * Lookup the database in the hashtable.  Nothing to do if not there.
  	 */
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
  
  	if (!dbentry)
  		return;
  
  	/*
  	 * We simply throw away all the database's table entries by recreating a
  	 * new hash table for them.
  	 */
  	if (dbentry->tables != NULL)
  		hash_destroy(dbentry->tables);
  	if (dbentry->functions != NULL)
  		hash_destroy(dbentry->functions);
  
  	dbentry->tables = NULL;
  	dbentry->functions = NULL;
  
  	/*
  	 * Reset database-level stats, too.  This creates empty hash tables for
  	 * tables and functions.
  	 */
  	reset_dbentry_counters(dbentry);
  }
  
  /* ----------
   * pgstat_recv_resetsharedcounter() -
   *
   *	Reset some shared statistics of the cluster.
   * ----------
   */
  static void
  pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len)
  {
  	if (msg->m_resettarget == RESET_BGWRITER)
  	{
  		/* Reset the global background writer statistics for the cluster. */
  		memset(&globalStats, 0, sizeof(globalStats));
  		globalStats.stat_reset_timestamp = GetCurrentTimestamp();
  	}
  	else if (msg->m_resettarget == RESET_ARCHIVER)
  	{
  		/* Reset the archiver statistics for the cluster. */
  		memset(&archiverStats, 0, sizeof(archiverStats));
  		archiverStats.stat_reset_timestamp = GetCurrentTimestamp();
  	}
  	else if (msg->m_resettarget == RESET_WAL)
  	{
  		/* Reset the WAL statistics for the cluster. */
  		memset(&walStats, 0, sizeof(walStats));
  		walStats.stat_reset_timestamp = GetCurrentTimestamp();
  	}
  
  	/*
  	 * Presumably the sender of this message validated the target, don't
  	 * complain here if it's not valid
  	 */
  }
  
  /* ----------
   * pgstat_recv_resetsinglecounter() -
   *
   *	Reset a statistics for a single object
   * ----------
   */
  static void
  pgstat_recv_resetsinglecounter(PgStat_MsgResetsinglecounter *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
  
  	if (!dbentry)
  		return;
  
  	/* Set the reset timestamp for the whole database */
  	dbentry->stat_reset_timestamp = GetCurrentTimestamp();
  
  	/* Remove object if it exists, ignore it if not */
  	if (msg->m_resettype == RESET_TABLE)
  		(void) hash_search(dbentry->tables, (void *) &(msg->m_objectid),
  						   HASH_REMOVE, NULL);
  	else if (msg->m_resettype == RESET_FUNCTION)
  		(void) hash_search(dbentry->functions, (void *) &(msg->m_objectid),
  						   HASH_REMOVE, NULL);
  }
  
  /* ----------
   * pgstat_recv_resetslrucounter() -
   *
   *	Reset some SLRU statistics of the cluster.
   * ----------
   */
  static void
  pgstat_recv_resetslrucounter(PgStat_MsgResetslrucounter *msg, int len)
  {
  	int			i;
  	TimestampTz ts = GetCurrentTimestamp();
  
  	for (i = 0; i < SLRU_NUM_ELEMENTS; i++)
  	{
  		/* reset entry with the given index, or all entries (index is -1) */
  		if ((msg->m_index == -1) || (msg->m_index == i))
  		{
  			memset(&slruStats[i], 0, sizeof(slruStats[i]));
  			slruStats[i].stat_reset_timestamp = ts;
  		}
  	}
  }
  
  /* ----------
   * pgstat_recv_resetreplslotcounter() -
   *
   *	Reset some replication slot statistics of the cluster.
   * ----------
   */
  static void
  pgstat_recv_resetreplslotcounter(PgStat_MsgResetreplslotcounter *msg,
  								 int len)
  {
  	int			i;
  	int			idx = -1;
  	TimestampTz ts;
  
  	ts = GetCurrentTimestamp();
  	if (msg->clearall)
  	{
  		for (i = 0; i < nReplSlotStats; i++)
  			pgstat_reset_replslot(i, ts);
  	}
  	else
  	{
  		/* Get the index of replication slot statistics to reset */
  		idx = pgstat_replslot_index(msg->m_slotname, false);
  
  		/*
  		 * Nothing to do if the given slot entry is not found.  This could
  		 * happen when the slot with the given name is removed and the
  		 * corresponding statistics entry is also removed before receiving the
  		 * reset message.
  		 */
  		if (idx < 0)
  			return;
  
  		/* Reset the stats for the requested replication slot */
  		pgstat_reset_replslot(idx, ts);
  	}
  }
  
  
  /* ----------
   * pgstat_recv_autovac() -
   *
   *	Process an autovacuum signaling message.
   * ----------
   */
  static void
  pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  
  	/*
  	 * Store the last autovacuum time in the database's hashtable entry.
  	 */
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	dbentry->last_autovac_time = msg->m_start_time;
  }
  
  /* ----------
   * pgstat_recv_vacuum() -
   *
   *	Process a VACUUM message.
   * ----------
   */
  static void
  pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  	PgStat_StatTabEntry *tabentry;
  
  	/*
  	 * Store the data in the table's hashtable entry.
  	 */
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);
  
  	tabentry->n_live_tuples = msg->m_live_tuples;
  	tabentry->n_dead_tuples = msg->m_dead_tuples;
  
  	/*
  	 * It is quite possible that a non-aggressive VACUUM ended up skipping
  	 * various pages, however, we'll zero the insert counter here regardless.
  	 * It's currently used only to track when we need to perform an "insert"
  	 * autovacuum, which are mainly intended to freeze newly inserted tuples.
  	 * Zeroing this may just mean we'll not try to vacuum the table again
  	 * until enough tuples have been inserted to trigger another insert
  	 * autovacuum.  An anti-wraparound autovacuum will catch any persistent
  	 * stragglers.
  	 */
  	tabentry->inserts_since_vacuum = 0;
  
  	if (msg->m_autovacuum)
  	{
  		tabentry->autovac_vacuum_timestamp = msg->m_vacuumtime;
  		tabentry->autovac_vacuum_count++;
  	}
  	else
  	{
  		tabentry->vacuum_timestamp = msg->m_vacuumtime;
  		tabentry->vacuum_count++;
  	}
  }
  
  /* ----------
   * pgstat_recv_analyze() -
   *
   *	Process an ANALYZE message.
   * ----------
   */
  static void
  pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  	PgStat_StatTabEntry *tabentry;
  
  	/*
  	 * Store the data in the table's hashtable entry.
  	 */
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);
  
  	tabentry->n_live_tuples = msg->m_live_tuples;
  	tabentry->n_dead_tuples = msg->m_dead_tuples;
  
  	/*
  	 * If commanded, reset changes_since_analyze to zero.  This forgets any
  	 * changes that were committed while the ANALYZE was in progress, but we
  	 * have no good way to estimate how many of those there were.
  	 */
  	if (msg->m_resetcounter)
  		tabentry->changes_since_analyze = 0;
  
  	if (msg->m_autovacuum)
  	{
  		tabentry->autovac_analyze_timestamp = msg->m_analyzetime;
  		tabentry->autovac_analyze_count++;
  	}
  	else
  	{
  		tabentry->analyze_timestamp = msg->m_analyzetime;
  		tabentry->analyze_count++;
  	}
  }
  
  
  /* ----------
   * pgstat_recv_archiver() -
   *
   *	Process a ARCHIVER message.
   * ----------
   */
  static void
  pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len)
  {
  	if (msg->m_failed)
  	{
  		/* Failed archival attempt */
  		++archiverStats.failed_count;
  		memcpy(archiverStats.last_failed_wal, msg->m_xlog,
  			   sizeof(archiverStats.last_failed_wal));
  		archiverStats.last_failed_timestamp = msg->m_timestamp;
  	}
  	else
  	{
  		/* Successful archival operation */
  		++archiverStats.archived_count;
  		memcpy(archiverStats.last_archived_wal, msg->m_xlog,
  			   sizeof(archiverStats.last_archived_wal));
  		archiverStats.last_archived_timestamp = msg->m_timestamp;
  	}
  }
  
  /* ----------
   * pgstat_recv_bgwriter() -
   *
   *	Process a BGWRITER message.
   * ----------
   */
  static void
  pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len)
  {
  	globalStats.timed_checkpoints += msg->m_timed_checkpoints;
  	globalStats.requested_checkpoints += msg->m_requested_checkpoints;
  	globalStats.checkpoint_write_time += msg->m_checkpoint_write_time;
  	globalStats.checkpoint_sync_time += msg->m_checkpoint_sync_time;
  	globalStats.buf_written_checkpoints += msg->m_buf_written_checkpoints;
  	globalStats.buf_written_clean += msg->m_buf_written_clean;
  	globalStats.maxwritten_clean += msg->m_maxwritten_clean;
  	globalStats.buf_written_backend += msg->m_buf_written_backend;
  	globalStats.buf_fsync_backend += msg->m_buf_fsync_backend;
  	globalStats.buf_alloc += msg->m_buf_alloc;
  }
  
  /* ----------
   * pgstat_recv_wal() -
   *
   *	Process a WAL message.
   * ----------
   */
  static void
  pgstat_recv_wal(PgStat_MsgWal *msg, int len)
  {
  	walStats.wal_records += msg->m_wal_records;
  	walStats.wal_fpi += msg->m_wal_fpi;
  	walStats.wal_bytes += msg->m_wal_bytes;
  	walStats.wal_buffers_full += msg->m_wal_buffers_full;
  	walStats.wal_write += msg->m_wal_write;
  	walStats.wal_sync += msg->m_wal_sync;
  	walStats.wal_write_time += msg->m_wal_write_time;
  	walStats.wal_sync_time += msg->m_wal_sync_time;
  }
  
  /* ----------
   * pgstat_recv_slru() -
   *
   *	Process a SLRU message.
   * ----------
   */
  static void
  pgstat_recv_slru(PgStat_MsgSLRU *msg, int len)
  {
  	slruStats[msg->m_index].blocks_zeroed += msg->m_blocks_zeroed;
  	slruStats[msg->m_index].blocks_hit += msg->m_blocks_hit;
  	slruStats[msg->m_index].blocks_read += msg->m_blocks_read;
  	slruStats[msg->m_index].blocks_written += msg->m_blocks_written;
  	slruStats[msg->m_index].blocks_exists += msg->m_blocks_exists;
  	slruStats[msg->m_index].flush += msg->m_flush;
  	slruStats[msg->m_index].truncate += msg->m_truncate;
  }
  
  /* ----------
   * pgstat_recv_recoveryconflict() -
   *
   *	Process a RECOVERYCONFLICT message.
   * ----------
   */
  static void
  pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	switch (msg->m_reason)
  	{
  		case PROCSIG_RECOVERY_CONFLICT_DATABASE:
  
  			/*
  			 * Since we drop the information about the database as soon as it
  			 * replicates, there is no point in counting these conflicts.
  			 */
  			break;
  		case PROCSIG_RECOVERY_CONFLICT_TABLESPACE:
  			dbentry->n_conflict_tablespace++;
  			break;
  		case PROCSIG_RECOVERY_CONFLICT_LOCK:
  			dbentry->n_conflict_lock++;
  			break;
  		case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
  			dbentry->n_conflict_snapshot++;
  			break;
  		case PROCSIG_RECOVERY_CONFLICT_BUFFERPIN:
  			dbentry->n_conflict_bufferpin++;
  			break;
  		case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
  			dbentry->n_conflict_startup_deadlock++;
  			break;
  	}
  }
  
  /* ----------
   * pgstat_recv_deadlock() -
   *
   *	Process a DEADLOCK message.
   * ----------
   */
  static void
  pgstat_recv_deadlock(PgStat_MsgDeadlock *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	dbentry->n_deadlocks++;
  }
  
  /* ----------
   * pgstat_recv_checksum_failure() -
   *
   *	Process a CHECKSUMFAILURE message.
   * ----------
   */
  static void
  pgstat_recv_checksum_failure(PgStat_MsgChecksumFailure *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	dbentry->n_checksum_failures += msg->m_failurecount;
  	dbentry->last_checksum_failure = msg->m_failure_time;
  }
  
  /* ----------
   * pgstat_recv_replslot() -
   *
   *	Process a REPLSLOT message.
   * ----------
   */
  static void
  pgstat_recv_replslot(PgStat_MsgReplSlot *msg, int len)
  {
  	int			idx;
  
  	/*
  	 * Get the index of replication slot statistics.  On dropping, we don't
  	 * create the new statistics.
  	 */
  	idx = pgstat_replslot_index(msg->m_slotname, !msg->m_drop);
  
  	/*
  	 * The slot entry is not found or there is no space to accommodate the new
  	 * entry.  This could happen when the message for the creation of a slot
  	 * reached before the drop message even though the actual operations
  	 * happen in reverse order.  In such a case, the next update of the
  	 * statistics for the same slot will create the required entry.
  	 */
  	if (idx < 0)
  		return;
  
  	/* it must be a valid replication slot index */
  	Assert(idx < nReplSlotStats);
  
  	if (msg->m_drop)
  	{
  		/* Remove the replication slot statistics with the given name */
  		if (idx < nReplSlotStats - 1)
  			memcpy(&replSlotStats[idx], &replSlotStats[nReplSlotStats - 1],
  				   sizeof(PgStat_ReplSlotStats));
  		nReplSlotStats--;
  	}
  	else
  	{
  		/* Update the replication slot statistics */
  		replSlotStats[idx].spill_txns += msg->m_spill_txns;
  		replSlotStats[idx].spill_count += msg->m_spill_count;
  		replSlotStats[idx].spill_bytes += msg->m_spill_bytes;
  		replSlotStats[idx].stream_txns += msg->m_stream_txns;
  		replSlotStats[idx].stream_count += msg->m_stream_count;
  		replSlotStats[idx].stream_bytes += msg->m_stream_bytes;
  	}
  }
  
  /* ----------
   * pgstat_recv_connstat() -
   *
   *  Process connection information.
   * ----------
   */
  static void
  pgstat_recv_connstat(PgStat_MsgConn *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	dbentry->n_sessions += msg->m_count;
  	dbentry->total_session_time += msg->m_session_time;
  	dbentry->total_active_time += msg->m_active_time;
  	dbentry->total_idle_in_xact_time += msg->m_idle_in_xact_time;
  	switch (msg->m_disconnect)
  	{
  		case DISCONNECT_NOT_YET:
  		case DISCONNECT_NORMAL:
  			/* we don't collect these */
  			break;
  		case DISCONNECT_CLIENT_EOF:
  			dbentry->n_sessions_abandoned++;
  			break;
  		case DISCONNECT_FATAL:
  			dbentry->n_sessions_fatal++;
  			break;
  		case DISCONNECT_KILLED:
  			dbentry->n_sessions_killed++;
  			break;
  	}
  }
  
  /* ----------
   * pgstat_recv_tempfile() -
   *
   *	Process a TEMPFILE message.
   * ----------
   */
  static void
  pgstat_recv_tempfile(PgStat_MsgTempFile *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	dbentry->n_temp_bytes += msg->m_filesize;
  	dbentry->n_temp_files += 1;
  }
  
  /* ----------
   * pgstat_recv_funcstat() -
   *
   *	Count what the backend has done.
   * ----------
   */
  static void
  pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len)
  {
  	PgStat_FunctionEntry *funcmsg = &(msg->m_entry[0]);
  	PgStat_StatDBEntry *dbentry;
  	PgStat_StatFuncEntry *funcentry;
  	int			i;
  	bool		found;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
  
  	/*
  	 * Process all function entries in the message.
  	 */
  	for (i = 0; i < msg->m_nentries; i++, funcmsg++)
  	{
  		funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
  														 (void *) &(funcmsg->f_id),
  														 HASH_ENTER, &found);
  
  		if (!found)
  		{
  			/*
  			 * If it's a new function entry, initialize counters to the values
  			 * we just got.
  			 */
  			funcentry->f_numcalls = funcmsg->f_numcalls;
  			funcentry->f_total_time = funcmsg->f_total_time;
  			funcentry->f_self_time = funcmsg->f_self_time;
  		}
  		else
  		{
  			/*
  			 * Otherwise add the values to the existing entry.
  			 */
  			funcentry->f_numcalls += funcmsg->f_numcalls;
  			funcentry->f_total_time += funcmsg->f_total_time;
  			funcentry->f_self_time += funcmsg->f_self_time;
  		}
  	}
  }
  
  /* ----------
   * pgstat_recv_funcpurge() -
   *
   *	Arrange for dead function removal.
   * ----------
   */
  static void
  pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len)
  {
  	PgStat_StatDBEntry *dbentry;
  	int			i;
  
  	dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
  
  	/*
  	 * No need to purge if we don't even know the database.
  	 */
  	if (!dbentry || !dbentry->functions)
  		return;
  
  	/*
  	 * Process all function entries in the message.
  	 */
  	for (i = 0; i < msg->m_nentries; i++)
  	{
  		/* Remove from hashtable if present; we don't care if it's not. */
  		(void) hash_search(dbentry->functions,
  						   (void *) &(msg->m_functionid[i]),
  						   HASH_REMOVE, NULL);
  	}
  }
  
  /* ----------
   * pgstat_write_statsfile_needed() -
   *
   *	Do we need to write out any stats files?
   * ----------
   */
  static bool
  pgstat_write_statsfile_needed(void)
  {
  	if (pending_write_requests != NIL)
  		return true;
  
  	/* Everything was written recently */
  	return false;
  }
  
  /* ----------
   * pgstat_db_requested() -
   *
   *	Checks whether stats for a particular DB need to be written to a file.
   * ----------
   */
  static bool
  pgstat_db_requested(Oid databaseid)
  {
  	/*
  	 * If any requests are outstanding at all, we should write the stats for
  	 * shared catalogs (the "database" with OID 0).  This ensures that
  	 * backends will see up-to-date stats for shared catalogs, even though
  	 * they send inquiry messages mentioning only their own DB.
  	 */
  	if (databaseid == InvalidOid && pending_write_requests != NIL)
  		return true;
  
  	/* Search to see if there's an open request to write this database. */
  	if (list_member_oid(pending_write_requests, databaseid))
  		return true;
  
  	return false;
  }
  
  /*
   * Convert a potentially unsafely truncated activity string (see
   * PgBackendStatus.st_activity_raw's documentation) into a correctly truncated
   * one.
   *
   * The returned string is allocated in the caller's memory context and may be
   * freed.
   */
  char *
  pgstat_clip_activity(const char *raw_activity)
  {
  	char	   *activity;
  	int			rawlen;
  	int			cliplen;
  
  	/*
  	 * Some callers, like pgstat_get_backend_current_activity(), do not
  	 * guarantee that the buffer isn't concurrently modified. We try to take
  	 * care that the buffer is always terminated by a NUL byte regardless, but
  	 * let's still be paranoid about the string's length. In those cases the
  	 * underlying buffer is guaranteed to be pgstat_track_activity_query_size
  	 * large.
  	 */
  	activity = pnstrdup(raw_activity, pgstat_track_activity_query_size - 1);
  
  	/* now double-guaranteed to be NUL terminated */
  	rawlen = strlen(activity);
  
  	/*
  	 * All supported server-encodings make it possible to determine the length
  	 * of a multi-byte character from its first byte (this is not the case for
  	 * client encodings, see GB18030). As st_activity is always stored using
  	 * server encoding, this allows us to perform multi-byte aware truncation,
  	 * even if the string earlier was truncated in the middle of a multi-byte
  	 * character.
  	 */
  	cliplen = pg_mbcliplen(activity, rawlen,
  						   pgstat_track_activity_query_size - 1);
  
  	activity[cliplen] = '\0';
  
  	return activity;
  }
  
  /* ----------
   * pgstat_replslot_index
   *
   * Return the index of entry of a replication slot with the given name, or
   * -1 if the slot is not found.
   *
   * create_it tells whether to create the new slot entry if it is not found.
   * ----------
   */
  static int
  pgstat_replslot_index(const char *name, bool create_it)
  {
  	int			i;
  
  	Assert(nReplSlotStats <= max_replication_slots);
  	for (i = 0; i < nReplSlotStats; i++)
  	{
  		if (strcmp(replSlotStats[i].slotname, name) == 0)
  			return i;			/* found */
  	}
  
  	/*
  	 * The slot is not found.  We don't want to register the new statistics if
  	 * the list is already full or the caller didn't request.
  	 */
  	if (i == max_replication_slots || !create_it)
  		return -1;
  
  	/* Register new slot */
  	memset(&replSlotStats[nReplSlotStats], 0, sizeof(PgStat_ReplSlotStats));
  	strlcpy(replSlotStats[nReplSlotStats].slotname, name, NAMEDATALEN);
  
  	return nReplSlotStats++;
  }
  
  /* ----------
   * pgstat_reset_replslot
   *
   * Reset the replication slot stats at index 'i'.
   * ----------
   */
  static void
  pgstat_reset_replslot(int i, TimestampTz ts)
  {
  	/* reset only counters. Don't clear slot name */
  	replSlotStats[i].spill_txns = 0;
  	replSlotStats[i].spill_count = 0;
  	replSlotStats[i].spill_bytes = 0;
  	replSlotStats[i].stream_txns = 0;
  	replSlotStats[i].stream_count = 0;
  	replSlotStats[i].stream_bytes = 0;
  	replSlotStats[i].stat_reset_timestamp = ts;
  }
  
  /*
   * pgstat_slru_index
   *
   * Determine index of entry for a SLRU with a given name. If there's no exact
   * match, returns index of the last "other" entry used for SLRUs defined in
   * external projects.
   */
  int
  pgstat_slru_index(const char *name)
  {
  	int			i;
  
  	for (i = 0; i < SLRU_NUM_ELEMENTS; i++)
  	{
  		if (strcmp(slru_names[i], name) == 0)
  			return i;
  	}
  
  	/* return index of the last entry (which is the "other" one) */
  	return (SLRU_NUM_ELEMENTS - 1);
  }
  
  /*
   * pgstat_slru_name
   *
   * Returns SLRU name for an index. The index may be above SLRU_NUM_ELEMENTS,
   * in which case this returns NULL. This allows writing code that does not
   * know the number of entries in advance.
   */
  const char *
  pgstat_slru_name(int slru_idx)
  {
  	if (slru_idx < 0 || slru_idx >= SLRU_NUM_ELEMENTS)
  		return NULL;
  
  	return slru_names[slru_idx];
  }
  
  /*
   * slru_entry
   *
   * Returns pointer to entry with counters for given SLRU (based on the name
   * stored in SlruCtl as lwlock tranche name).
   */
  static inline PgStat_MsgSLRU *
  slru_entry(int slru_idx)
  {
  	/*
  	 * The postmaster should never register any SLRU statistics counts; if it
  	 * did, the counts would be duplicated into child processes via fork().
  	 */
  	Assert(IsUnderPostmaster || !IsPostmasterEnvironment);
  
  	Assert((slru_idx >= 0) && (slru_idx < SLRU_NUM_ELEMENTS));
  
  	return &SLRUStats[slru_idx];
  }
  
  /*
   * SLRU statistics count accumulation functions --- called from slru.c
   */
  
  void
  pgstat_count_slru_page_zeroed(int slru_idx)
  {
  	slru_entry(slru_idx)->m_blocks_zeroed += 1;
  }
  
  void
  pgstat_count_slru_page_hit(int slru_idx)
  {
  	slru_entry(slru_idx)->m_blocks_hit += 1;
  }
  
  void
  pgstat_count_slru_page_exists(int slru_idx)
  {
  	slru_entry(slru_idx)->m_blocks_exists += 1;
  }
  
  void
  pgstat_count_slru_page_read(int slru_idx)
  {
  	slru_entry(slru_idx)->m_blocks_read += 1;
  }
  
  void
  pgstat_count_slru_page_written(int slru_idx)
  {
  	slru_entry(slru_idx)->m_blocks_written += 1;
  }
  
  void
  pgstat_count_slru_flush(int slru_idx)
  {
  	slru_entry(slru_idx)->m_flush += 1;
  }
  
  void
  pgstat_count_slru_truncate(int slru_idx)
  {
  	slru_entry(slru_idx)->m_truncate += 1;
  }
  