text: /*-------------------------------------------------------------------------
   *
   * pg_control.h
   *	  The system control file "pg_control" is not a heap relation.
   *	  However, we define it here so that the format is documented.
   *
   *
   * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * src/include/catalog/pg_control.h
   *
   *-------------------------------------------------------------------------
   */
  #ifndef PG_CONTROL_H
  #define PG_CONTROL_H
  
  #include "access/xlogdefs.h"
  #include "pgtime.h"				/* for pg_time_t */
  #include "utils/pg_crc.h"
  
  
  /* Version identifier for this pg_control format */
  #define PG_CONTROL_VERSION	921
  
  /*
   * Body of CheckPoint XLOG records.  This is declared here because we keep
   * a copy of the latest one in pg_control for possible disaster recovery.
   * Changing this struct requires a PG_CONTROL_VERSION bump.
   */
  typedef struct CheckPoint
  {
  	XLogRecPtr	redo;			/* next RecPtr available when we began to
  								 * create CheckPoint (i.e. REDO start point) */
  	TimeLineID	ThisTimeLineID; /* current TLI */
  	uint32		nextXidEpoch;	/* higher-order bits of nextXid */
  	TransactionId nextXid;		/* next free XID */
  	Oid			nextOid;		/* next free OID */
  	MultiXactId nextMulti;		/* next free MultiXactId */
  	MultiXactOffset nextMultiOffset;	/* next free MultiXact offset */
  	TransactionId oldestXid;	/* cluster-wide minimum datfrozenxid */
  	Oid			oldestXidDB;	/* database with minimum datfrozenxid */
  	pg_time_t	time;			/* time stamp of checkpoint */
  
  	/*
  	 * Oldest XID still running. This is only needed to initialize hot standby
  	 * mode from an online checkpoint, so we only bother calculating this for
  	 * online checkpoints and only when wal_level is hot_standby. Otherwise
  	 * it's set to InvalidTransactionId.
  	 */
  	TransactionId oldestActiveXid;
  } CheckPoint;
  
  /* XLOG info values for XLOG rmgr */
  #define XLOG_CHECKPOINT_SHUTDOWN		0x00
  #define XLOG_CHECKPOINT_ONLINE			0x10
  #define XLOG_NOOP						0x20
  #define XLOG_NEXTOID					0x30
  #define XLOG_SWITCH						0x40
  #define XLOG_BACKUP_END					0x50
  #define XLOG_PARAMETER_CHANGE			0x60
  #define XLOG_RESTORE_POINT				0x70
  
  
  /*
   * System status indicator.  Note this is stored in pg_control; if you change
   * it, you must bump PG_CONTROL_VERSION
   */
  typedef enum DBState
  {
  	DB_STARTUP = 0,
  	DB_SHUTDOWNED,
  	DB_SHUTDOWNED_IN_RECOVERY,
  	DB_SHUTDOWNING,
  	DB_IN_CRASH_RECOVERY,
  	DB_IN_ARCHIVE_RECOVERY,
  	DB_IN_PRODUCTION
  } DBState;
  
  /*
   * Contents of pg_control.
   *
   * NOTE: try to keep this under 512 bytes so that it will fit on one physical
   * sector of typical disk drives.  This reduces the odds of corruption due to
   * power failure midway through a write.
   */
  
  typedef struct ControlFileData
  {
  	/*
  	 * Unique system identifier --- to ensure we match up xlog files with the
  	 * installation that produced them.
  	 */
  	uint64		system_identifier;
  
  	/*
  	 * Version identifier information.	Keep these fields at the same offset,
  	 * especially pg_control_version; they won't be real useful if they move
  	 * around.	(For historical reasons they must be 8 bytes into the file
  	 * rather than immediately at the front.)
  	 *
  	 * pg_control_version identifies the format of pg_control itself.
  	 * catalog_version_no identifies the format of the system catalogs.
  	 *
  	 * There are additional version identifiers in individual files; for
  	 * example, WAL logs contain per-page magic numbers that can serve as
  	 * version cues for the WAL log.
  	 */
  	uint32		pg_control_version;		/* PG_CONTROL_VERSION */
  	uint32		catalog_version_no;		/* see catversion.h */
  
  	/*
  	 * System status data
  	 */
  	DBState		state;			/* see enum above */
  	pg_time_t	time;			/* time stamp of last pg_control update */
  	XLogRecPtr	checkPoint;		/* last check point record ptr */
  	XLogRecPtr	prevCheckPoint; /* previous check point record ptr */
  
  	CheckPoint	checkPointCopy; /* copy of last check point record */
  
  	/*
  	 * These two values determine the minimum point we must recover up to
  	 * before starting up:
  	 *
  	 * minRecoveryPoint is updated to the latest replayed LSN whenever we
  	 * flush a data change during archive recovery. That guards against
  	 * starting archive recovery, aborting it, and restarting with an earlier
  	 * stop location. If we've already flushed data changes from WAL record X
  	 * to disk, we mustn't start up until we reach X again. Zero when not
  	 * doing archive recovery.
  	 *
  	 * backupStartPoint is the redo pointer of the backup start checkpoint, if
  	 * we are recovering from an online backup and haven't reached the end of
  	 * backup yet. It is reset to zero when the end of backup is reached, and
  	 * we mustn't start up before that. A boolean would suffice otherwise, but
  	 * we use the redo pointer as a cross-check when we see an end-of-backup
  	 * record, to make sure the end-of-backup record corresponds the base
  	 * backup we're recovering from.
  	 *
  	 * If backupEndRequired is true, we know for sure that we're restoring
  	 * from a backup, and must see a backup-end record before we can safely
  	 * start up. If it's false, but backupStartPoint is set, a backup_label
  	 * file was found at startup but it may have been a leftover from a stray
  	 * pg_start_backup() call, not accompanied by pg_stop_backup().
  	 */
  	XLogRecPtr	minRecoveryPoint;
  	XLogRecPtr	backupStartPoint;
  	bool		backupEndRequired;
  
  	/*
  	 * Parameter settings that determine if the WAL can be used for archival
  	 * or hot standby.
  	 */
  	int			wal_level;
  	int			MaxConnections;
  	int			max_prepared_xacts;
  	int			max_locks_per_xact;
  
  	/*
  	 * This data is used to check for hardware-architecture compatibility of
  	 * the database and the backend executable.  We need not check endianness
  	 * explicitly, since the pg_control version will surely look wrong to a
  	 * machine of different endianness, but we do need to worry about MAXALIGN
  	 * and floating-point format.  (Note: storage layout nominally also
  	 * depends on SHORTALIGN and INTALIGN, but in practice these are the same
  	 * on all architectures of interest.)
  	 *
  	 * Testing just one double value is not a very bulletproof test for
  	 * floating-point compatibility, but it will catch most cases.
  	 */
  	uint32		maxAlign;		/* alignment requirement for tuples */
  	double		floatFormat;	/* constant 1234567.0 */
  #define FLOATFORMAT_VALUE	1234567.0
  
  	/*
  	 * This data is used to make sure that configuration of this database is
  	 * compatible with the backend executable.
  	 */
  	uint32		blcksz;			/* data block size for this DB */
  	uint32		relseg_size;	/* blocks per segment of large relation */
  
  	uint32		xlog_blcksz;	/* block size within WAL files */
  	uint32		xlog_seg_size;	/* size of each WAL segment */
  
  	uint32		nameDataLen;	/* catalog name field width */
  	uint32		indexMaxKeys;	/* max number of columns in an index */
  
  	uint32		toast_max_chunk_size;	/* chunk size in TOAST tables */
  
  	/* flag indicating internal format of timestamp, interval, time */
  	bool		enableIntTimes; /* int64 storage enabled? */
  
  	/* flags indicating pass-by-value status of various types */
  	bool		float4ByVal;	/* float4 pass-by-value? */
  	bool		float8ByVal;	/* float8, int8, etc pass-by-value? */
  
  	/* CRC of all above ... MUST BE LAST! */
  	pg_crc32	crc;
  } ControlFileData;
  
  /*
   * Physical size of the pg_control file.  Note that this is considerably
   * bigger than the actually used size (ie, sizeof(ControlFileData)).
   * The idea is to keep the physical size constant independent of format
   * changes, so that ReadControlFile will deliver a suitable wrong-version
   * message instead of a read error if it's looking at an incompatible file.
   */
  #define PG_CONTROL_SIZE		8192
  
  #endif   /* PG_CONTROL_H */
  