text: /*-------------------------------------------------------------------------
   * logical.c
   *	   PostgreSQL logical decoding coordination
   *
   * Copyright (c) 2012-2021, PostgreSQL Global Development Group
   *
   * IDENTIFICATION
   *	  src/backend/replication/logical/logical.c
   *
   * NOTES
   *	  This file coordinates interaction between the various modules that
   *	  together provide logical decoding, primarily by providing so
   *	  called LogicalDecodingContexts. The goal is to encapsulate most of the
   *	  internal complexity for consumers of logical decoding, so they can
   *	  create and consume a changestream with a low amount of code. Builtin
   *	  consumers are the walsender and SQL SRF interface, but it's possible to
   *	  add further ones without changing core code, e.g. to consume changes in
   *	  a bgworker.
   *
   *	  The idea is that a consumer provides three callbacks, one to read WAL,
   *	  one to prepare a data write, and a final one for actually writing since
   *	  their implementation depends on the type of consumer.  Check
   *	  logicalfuncs.c for an example implementation of a fairly simple consumer
   *	  and an implementation of a WAL reading callback that's suitable for
   *	  simple consumers.
   *-------------------------------------------------------------------------
   */
  
  #include "postgres.h"
  
  #include "access/xact.h"
  #include "access/xlog_internal.h"
  #include "fmgr.h"
  #include "miscadmin.h"
  #include "pgstat.h"
  #include "replication/decode.h"
  #include "replication/logical.h"
  #include "replication/origin.h"
  #include "replication/reorderbuffer.h"
  #include "replication/snapbuild.h"
  #include "storage/proc.h"
  #include "storage/procarray.h"
  #include "utils/builtins.h"
  #include "utils/memutils.h"
  
  /* data for errcontext callback */
  typedef struct LogicalErrorCallbackState
  {
  	LogicalDecodingContext *ctx;
  	const char *callback_name;
  	XLogRecPtr	report_location;
  } LogicalErrorCallbackState;
  
  /* wrappers around output plugin callbacks */
  static void output_plugin_error_callback(void *arg);
  static void startup_cb_wrapper(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
  							   bool is_init);
  static void shutdown_cb_wrapper(LogicalDecodingContext *ctx);
  static void begin_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn);
  static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  							  XLogRecPtr commit_lsn);
  static void begin_prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn);
  static void prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  							   XLogRecPtr prepare_lsn);
  static void commit_prepared_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  									   XLogRecPtr commit_lsn);
  static void rollback_prepared_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  										 XLogRecPtr prepare_end_lsn, TimestampTz prepare_time);
  static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  							  Relation relation, ReorderBufferChange *change);
  static void truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  								int nrelations, Relation relations[], ReorderBufferChange *change);
  static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  							   XLogRecPtr message_lsn, bool transactional,
  							   const char *prefix, Size message_size, const char *message);
  
  /* streaming callbacks */
  static void stream_start_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  									XLogRecPtr first_lsn);
  static void stream_stop_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  								   XLogRecPtr last_lsn);
  static void stream_abort_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  									XLogRecPtr abort_lsn);
  static void stream_prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  									  XLogRecPtr prepare_lsn);
  static void stream_commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  									 XLogRecPtr commit_lsn);
  static void stream_change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  									 Relation relation, ReorderBufferChange *change);
  static void stream_message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  									  XLogRecPtr message_lsn, bool transactional,
  									  const char *prefix, Size message_size, const char *message);
  static void stream_truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  									   int nrelations, Relation relations[], ReorderBufferChange *change);
  
  static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugin);
  
  /*
   * Make sure the current settings & environment are capable of doing logical
   * decoding.
   */
  void
  CheckLogicalDecodingRequirements(void)
  {
  	CheckSlotRequirements();
  
  	/*
  	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
  	 * needs the same check.
  	 */
  
  	if (wal_level < WAL_LEVEL_LOGICAL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical decoding requires wal_level >= logical")));
  
  	if (MyDatabaseId == InvalidOid)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical decoding requires a database connection")));
  
  	/* ----
  	 * TODO: We got to change that someday soon...
  	 *
  	 * There's basically three things missing to allow this:
  	 * 1) We need to be able to correctly and quickly identify the timeline a
  	 *	  LSN belongs to
  	 * 2) We need to force hot_standby_feedback to be enabled at all times so
  	 *	  the primary cannot remove rows we need.
  	 * 3) support dropping replication slots referring to a database, in
  	 *	  dbase_redo. There can't be any active ones due to HS recovery
  	 *	  conflicts, so that should be relatively easy.
  	 * ----
  	 */
  	if (RecoveryInProgress())
  		ereport(ERROR,
  				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
  				 errmsg("logical decoding cannot be used while in recovery")));
  }
  
  /*
   * Helper function for CreateInitDecodingContext() and
   * CreateDecodingContext() performing common tasks.
   */
  static LogicalDecodingContext *
  StartupDecodingContext(List *output_plugin_options,
  					   XLogRecPtr start_lsn,
  					   TransactionId xmin_horizon,
  					   bool need_full_snapshot,
  					   bool fast_forward,
  					   XLogReaderRoutine *xl_routine,
  					   LogicalOutputPluginWriterPrepareWrite prepare_write,
  					   LogicalOutputPluginWriterWrite do_write,
  					   LogicalOutputPluginWriterUpdateProgress update_progress)
  {
  	ReplicationSlot *slot;
  	MemoryContext context,
  				old_context;
  	LogicalDecodingContext *ctx;
  
  	/* shorter lines... */
  	slot = MyReplicationSlot;
  
  	context = AllocSetContextCreate(CurrentMemoryContext,
  									"Logical decoding context",
  									ALLOCSET_DEFAULT_SIZES);
  	old_context = MemoryContextSwitchTo(context);
  	ctx = palloc0(sizeof(LogicalDecodingContext));
  
  	ctx->context = context;
  
  	/*
  	 * (re-)load output plugins, so we detect a bad (removed) output plugin
  	 * now.
  	 */
  	if (!fast_forward)
  		LoadOutputPlugin(&ctx->callbacks, NameStr(slot->data.plugin));
  
  	/*
  	 * Now that the slot's xmin has been set, we can announce ourselves as a
  	 * logical decoding backend which doesn't need to be checked individually
  	 * when computing the xmin horizon because the xmin is enforced via
  	 * replication slots.
  	 *
  	 * We can only do so if we're outside of a transaction (i.e. the case when
  	 * streaming changes via walsender), otherwise an already setup
  	 * snapshot/xid would end up being ignored. That's not a particularly
  	 * bothersome restriction since the SQL interface can't be used for
  	 * streaming anyway.
  	 */
  	if (!IsTransactionOrTransactionBlock())
  	{
  		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
  		MyProc->statusFlags |= PROC_IN_LOGICAL_DECODING;
  		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
  		LWLockRelease(ProcArrayLock);
  	}
  
  	ctx->slot = slot;
  
  	ctx->reader = XLogReaderAllocate(wal_segment_size, NULL, xl_routine, ctx);
  	if (!ctx->reader)
  		ereport(ERROR,
  				(errcode(ERRCODE_OUT_OF_MEMORY),
  				 errmsg("out of memory")));
  
  	ctx->reorder = ReorderBufferAllocate();
  	ctx->snapshot_builder =
  		AllocateSnapshotBuilder(ctx->reorder, xmin_horizon, start_lsn,
  								need_full_snapshot, slot->data.two_phase_at);
  
  	ctx->reorder->private_data = ctx;
  
  	/* wrap output plugin callbacks, so we can add error context information */
  	ctx->reorder->begin = begin_cb_wrapper;
  	ctx->reorder->apply_change = change_cb_wrapper;
  	ctx->reorder->apply_truncate = truncate_cb_wrapper;
  	ctx->reorder->commit = commit_cb_wrapper;
  	ctx->reorder->message = message_cb_wrapper;
  
  	/*
  	 * To support streaming, we require start/stop/abort/commit/change
  	 * callbacks. The message and truncate callbacks are optional, similar to
  	 * regular output plugins. We however enable streaming when at least one
  	 * of the methods is enabled so that we can easily identify missing
  	 * methods.
  	 *
  	 * We decide it here, but only check it later in the wrappers.
  	 */
  	ctx->streaming = (ctx->callbacks.stream_start_cb != NULL) ||
  		(ctx->callbacks.stream_stop_cb != NULL) ||
  		(ctx->callbacks.stream_abort_cb != NULL) ||
  		(ctx->callbacks.stream_commit_cb != NULL) ||
  		(ctx->callbacks.stream_change_cb != NULL) ||
  		(ctx->callbacks.stream_message_cb != NULL) ||
  		(ctx->callbacks.stream_truncate_cb != NULL);
  
  	/*
  	 * streaming callbacks
  	 *
  	 * stream_message and stream_truncate callbacks are optional, so we do not
  	 * fail with ERROR when missing, but the wrappers simply do nothing. We
  	 * must set the ReorderBuffer callbacks to something, otherwise the calls
  	 * from there will crash (we don't want to move the checks there).
  	 */
  	ctx->reorder->stream_start = stream_start_cb_wrapper;
  	ctx->reorder->stream_stop = stream_stop_cb_wrapper;
  	ctx->reorder->stream_abort = stream_abort_cb_wrapper;
  	ctx->reorder->stream_prepare = stream_prepare_cb_wrapper;
  	ctx->reorder->stream_commit = stream_commit_cb_wrapper;
  	ctx->reorder->stream_change = stream_change_cb_wrapper;
  	ctx->reorder->stream_message = stream_message_cb_wrapper;
  	ctx->reorder->stream_truncate = stream_truncate_cb_wrapper;
  
  
  	/*
  	 * To support two-phase logical decoding, we require
  	 * begin_prepare/prepare/commit-prepare/abort-prepare callbacks. The
  	 * filter_prepare callback is optional. We however enable two-phase
  	 * logical decoding when at least one of the methods is enabled so that we
  	 * can easily identify missing methods.
  	 *
  	 * We decide it here, but only check it later in the wrappers.
  	 */
  	ctx->twophase = (ctx->callbacks.begin_prepare_cb != NULL) ||
  		(ctx->callbacks.prepare_cb != NULL) ||
  		(ctx->callbacks.commit_prepared_cb != NULL) ||
  		(ctx->callbacks.rollback_prepared_cb != NULL) ||
  		(ctx->callbacks.stream_prepare_cb != NULL) ||
  		(ctx->callbacks.filter_prepare_cb != NULL);
  
  	/*
  	 * Callback to support decoding at prepare time.
  	 */
  	ctx->reorder->begin_prepare = begin_prepare_cb_wrapper;
  	ctx->reorder->prepare = prepare_cb_wrapper;
  	ctx->reorder->commit_prepared = commit_prepared_cb_wrapper;
  	ctx->reorder->rollback_prepared = rollback_prepared_cb_wrapper;
  
  	ctx->out = makeStringInfo();
  	ctx->prepare_write = prepare_write;
  	ctx->write = do_write;
  	ctx->update_progress = update_progress;
  
  	ctx->output_plugin_options = output_plugin_options;
  
  	ctx->fast_forward = fast_forward;
  
  	MemoryContextSwitchTo(old_context);
  
  	return ctx;
  }
  
  /*
   * Create a new decoding context, for a new logical slot.
   *
   * plugin -- contains the name of the output plugin
   * output_plugin_options -- contains options passed to the output plugin
   * need_full_snapshot -- if true, must obtain a snapshot able to read all
   *		tables; if false, one that can read only catalogs is acceptable.
   * restart_lsn -- if given as invalid, it's this routine's responsibility to
   *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
   *		Otherwise, we set for decoding to start from the given LSN without
   *		marking WAL reserved beforehand.  In that scenario, it's up to the
   *		caller to guarantee that WAL remains available.
   * xl_routine -- XLogReaderRoutine for underlying XLogReader
   * prepare_write, do_write, update_progress --
   *		callbacks that perform the use-case dependent, actual, work.
   *
   * Needs to be called while in a memory context that's at least as long lived
   * as the decoding context because further memory contexts will be created
   * inside it.
   *
   * Returns an initialized decoding context after calling the output plugin's
   * startup function.
   */
  LogicalDecodingContext *
  CreateInitDecodingContext(const char *plugin,
  						  List *output_plugin_options,
  						  bool need_full_snapshot,
  						  XLogRecPtr restart_lsn,
  						  XLogReaderRoutine *xl_routine,
  						  LogicalOutputPluginWriterPrepareWrite prepare_write,
  						  LogicalOutputPluginWriterWrite do_write,
  						  LogicalOutputPluginWriterUpdateProgress update_progress)
  {
  	TransactionId xmin_horizon = InvalidTransactionId;
  	ReplicationSlot *slot;
  	NameData	plugin_name;
  	LogicalDecodingContext *ctx;
  	MemoryContext old_context;
  
  	/* shorter lines... */
  	slot = MyReplicationSlot;
  
  	/* first some sanity checks that are unlikely to be violated */
  	if (slot == NULL)
  		elog(ERROR, "cannot perform logical decoding without an acquired slot");
  
  	if (plugin == NULL)
  		elog(ERROR, "cannot initialize logical decoding without a specified plugin");
  
  	/* Make sure the passed slot is suitable. These are user facing errors. */
  	if (SlotIsPhysical(slot))
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("cannot use physical replication slot for logical decoding")));
  
  	if (slot->data.database != MyDatabaseId)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("replication slot \"%s\" was not created in this database",
  						NameStr(slot->data.name))));
  
  	if (IsTransactionState() &&
  		GetTopTransactionIdIfAny() != InvalidTransactionId)
  		ereport(ERROR,
  				(errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
  				 errmsg("cannot create logical replication slot in transaction that has performed writes")));
  
  	/*
  	 * Register output plugin name with slot.  We need the mutex to avoid
  	 * concurrent reading of a partially copied string.  But we don't want any
  	 * complicated code while holding a spinlock, so do namestrcpy() outside.
  	 */
  	namestrcpy(&plugin_name, plugin);
  	SpinLockAcquire(&slot->mutex);
  	slot->data.plugin = plugin_name;
  	SpinLockRelease(&slot->mutex);
  
  	if (XLogRecPtrIsInvalid(restart_lsn))
  		ReplicationSlotReserveWal();
  	else
  	{
  		SpinLockAcquire(&slot->mutex);
  		slot->data.restart_lsn = restart_lsn;
  		SpinLockRelease(&slot->mutex);
  	}
  
  	/* ----
  	 * This is a bit tricky: We need to determine a safe xmin horizon to start
  	 * decoding from, to avoid starting from a running xacts record referring
  	 * to xids whose rows have been vacuumed or pruned
  	 * already. GetOldestSafeDecodingTransactionId() returns such a value, but
  	 * without further interlock its return value might immediately be out of
  	 * date.
  	 *
  	 * So we have to acquire the ProcArrayLock to prevent computation of new
  	 * xmin horizons by other backends, get the safe decoding xid, and inform
  	 * the slot machinery about the new limit. Once that's done the
  	 * ProcArrayLock can be released as the slot machinery now is
  	 * protecting against vacuum.
  	 *
  	 * Note that, temporarily, the data, not just the catalog, xmin has to be
  	 * reserved if a data snapshot is to be exported.  Otherwise the initial
  	 * data snapshot created here is not guaranteed to be valid. After that
  	 * the data xmin doesn't need to be managed anymore and the global xmin
  	 * should be recomputed. As we are fine with losing the pegged data xmin
  	 * after crash - no chance a snapshot would get exported anymore - we can
  	 * get away with just setting the slot's
  	 * effective_xmin. ReplicationSlotRelease will reset it again.
  	 *
  	 * ----
  	 */
  	LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
  
  	xmin_horizon = GetOldestSafeDecodingTransactionId(!need_full_snapshot);
  
  	SpinLockAcquire(&slot->mutex);
  	slot->effective_catalog_xmin = xmin_horizon;
  	slot->data.catalog_xmin = xmin_horizon;
  	if (need_full_snapshot)
  		slot->effective_xmin = xmin_horizon;
  	SpinLockRelease(&slot->mutex);
  
  	ReplicationSlotsComputeRequiredXmin(true);
  
  	LWLockRelease(ProcArrayLock);
  
  	ReplicationSlotMarkDirty();
  	ReplicationSlotSave();
  
  	ctx = StartupDecodingContext(NIL, restart_lsn, xmin_horizon,
  								 need_full_snapshot, false,
  								 xl_routine, prepare_write, do_write,
  								 update_progress);
  
  	/* call output plugin initialization callback */
  	old_context = MemoryContextSwitchTo(ctx->context);
  	if (ctx->callbacks.startup_cb != NULL)
  		startup_cb_wrapper(ctx, &ctx->options, true);
  	MemoryContextSwitchTo(old_context);
  
  	/*
  	 * We allow decoding of prepared transactions when the two_phase is
  	 * enabled at the time of slot creation, or when the two_phase option is
  	 * given at the streaming start, provided the plugin supports all the
  	 * callbacks for two-phase.
  	 */
  	ctx->twophase &= slot->data.two_phase;
  
  	ctx->reorder->output_rewrites = ctx->options.receive_rewrites;
  
  	return ctx;
  }
  
  /*
   * Create a new decoding context, for a logical slot that has previously been
   * used already.
   *
   * start_lsn
   *		The LSN at which to start decoding.  If InvalidXLogRecPtr, restart
   *		from the slot's confirmed_flush; otherwise, start from the specified
   *		location (but move it forwards to confirmed_flush if it's older than
   *		that, see below).
   *
   * output_plugin_options
   *		options passed to the output plugin.
   *
   * fast_forward
   *		bypass the generation of logical changes.
   *
   * xl_routine
   *		XLogReaderRoutine used by underlying xlogreader
   *
   * prepare_write, do_write, update_progress
   *		callbacks that have to be filled to perform the use-case dependent,
   *		actual work.
   *
   * Needs to be called while in a memory context that's at least as long lived
   * as the decoding context because further memory contexts will be created
   * inside it.
   *
   * Returns an initialized decoding context after calling the output plugin's
   * startup function.
   */
  LogicalDecodingContext *
  CreateDecodingContext(XLogRecPtr start_lsn,
  					  List *output_plugin_options,
  					  bool fast_forward,
  					  XLogReaderRoutine *xl_routine,
  					  LogicalOutputPluginWriterPrepareWrite prepare_write,
  					  LogicalOutputPluginWriterWrite do_write,
  					  LogicalOutputPluginWriterUpdateProgress update_progress)
  {
  	LogicalDecodingContext *ctx;
  	ReplicationSlot *slot;
  	MemoryContext old_context;
  
  	/* shorter lines... */
  	slot = MyReplicationSlot;
  
  	/* first some sanity checks that are unlikely to be violated */
  	if (slot == NULL)
  		elog(ERROR, "cannot perform logical decoding without an acquired slot");
  
  	/* make sure the passed slot is suitable, these are user facing errors */
  	if (SlotIsPhysical(slot))
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("cannot use physical replication slot for logical decoding")));
  
  	if (slot->data.database != MyDatabaseId)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("replication slot \"%s\" was not created in this database",
  						NameStr(slot->data.name))));
  
  	if (start_lsn == InvalidXLogRecPtr)
  	{
  		/* continue from last position */
  		start_lsn = slot->data.confirmed_flush;
  	}
  	else if (start_lsn < slot->data.confirmed_flush)
  	{
  		/*
  		 * It might seem like we should error out in this case, but it's
  		 * pretty common for a client to acknowledge a LSN it doesn't have to
  		 * do anything for, and thus didn't store persistently, because the
  		 * xlog records didn't result in anything relevant for logical
  		 * decoding. Clients have to be able to do that to support synchronous
  		 * replication.
  		 *
  		 * Starting at a different LSN than requested might not catch certain
  		 * kinds of client errors; so the client may wish to check that
  		 * confirmed_flush_lsn matches its expectations.
  		 */
  		elog(LOG, "%X/%X has been already streamed, forwarding to %X/%X",
  			 LSN_FORMAT_ARGS(start_lsn),
  			 LSN_FORMAT_ARGS(slot->data.confirmed_flush));
  
  		start_lsn = slot->data.confirmed_flush;
  	}
  
  	ctx = StartupDecodingContext(output_plugin_options,
  								 start_lsn, InvalidTransactionId, false,
  								 fast_forward, xl_routine, prepare_write,
  								 do_write, update_progress);
  
  	/* call output plugin initialization callback */
  	old_context = MemoryContextSwitchTo(ctx->context);
  	if (ctx->callbacks.startup_cb != NULL)
  		startup_cb_wrapper(ctx, &ctx->options, false);
  	MemoryContextSwitchTo(old_context);
  
  	/*
  	 * We allow decoding of prepared transactions when the two_phase is
  	 * enabled at the time of slot creation, or when the two_phase option is
  	 * given at the streaming start, provided the plugin supports all the
  	 * callbacks for two-phase.
  	 */
  	ctx->twophase &= (slot->data.two_phase || ctx->twophase_opt_given);
  
  	/* Mark slot to allow two_phase decoding if not already marked */
  	if (ctx->twophase && !slot->data.two_phase)
  	{
  		slot->data.two_phase = true;
  		slot->data.two_phase_at = start_lsn;
  		ReplicationSlotMarkDirty();
  		ReplicationSlotSave();
  		SnapBuildSetTwoPhaseAt(ctx->snapshot_builder, start_lsn);
  	}
  
  	ctx->reorder->output_rewrites = ctx->options.receive_rewrites;
  
  	ereport(LOG,
  			(errmsg("starting logical decoding for slot \"%s\"",
  					NameStr(slot->data.name)),
  			 errdetail("Streaming transactions committing after %X/%X, reading WAL from %X/%X.",
  					   LSN_FORMAT_ARGS(slot->data.confirmed_flush),
  					   LSN_FORMAT_ARGS(slot->data.restart_lsn))));
  
  	return ctx;
  }
  
  /*
   * Returns true if a consistent initial decoding snapshot has been built.
   */
  bool
  DecodingContextReady(LogicalDecodingContext *ctx)
  {
  	return SnapBuildCurrentState(ctx->snapshot_builder) == SNAPBUILD_CONSISTENT;
  }
  
  /*
   * Read from the decoding slot, until it is ready to start extracting changes.
   */
  void
  DecodingContextFindStartpoint(LogicalDecodingContext *ctx)
  {
  	ReplicationSlot *slot = ctx->slot;
  
  	/* Initialize from where to start reading WAL. */
  	XLogBeginRead(ctx->reader, slot->data.restart_lsn);
  
  	elog(DEBUG1, "searching for logical decoding starting point, starting at %X/%X",
  		 LSN_FORMAT_ARGS(slot->data.restart_lsn));
  
  	/* Wait for a consistent starting point */
  	for (;;)
  	{
  		XLogRecord *record;
  		char	   *err = NULL;
  
  		/* the read_page callback waits for new WAL */
  		record = XLogReadRecord(ctx->reader, &err);
  		if (err)
  			elog(ERROR, "could not find logical decoding starting point: %s", err);
  		if (!record)
  			elog(ERROR, "could not find logical decoding starting point");
  
  		LogicalDecodingProcessRecord(ctx, ctx->reader);
  
  		/* only continue till we found a consistent spot */
  		if (DecodingContextReady(ctx))
  			break;
  
  		CHECK_FOR_INTERRUPTS();
  	}
  
  	SpinLockAcquire(&slot->mutex);
  	slot->data.confirmed_flush = ctx->reader->EndRecPtr;
  	if (slot->data.two_phase)
  		slot->data.two_phase_at = ctx->reader->EndRecPtr;
  	SpinLockRelease(&slot->mutex);
  }
  
  /*
   * Free a previously allocated decoding context, invoking the shutdown
   * callback if necessary.
   */
  void
  FreeDecodingContext(LogicalDecodingContext *ctx)
  {
  	if (ctx->callbacks.shutdown_cb != NULL)
  		shutdown_cb_wrapper(ctx);
  
  	ReorderBufferFree(ctx->reorder);
  	FreeSnapshotBuilder(ctx->snapshot_builder);
  	XLogReaderFree(ctx->reader);
  	MemoryContextDelete(ctx->context);
  }
  
  /*
   * Prepare a write using the context's output routine.
   */
  void
  OutputPluginPrepareWrite(struct LogicalDecodingContext *ctx, bool last_write)
  {
  	if (!ctx->accept_writes)
  		elog(ERROR, "writes are only accepted in commit, begin and change callbacks");
  
  	ctx->prepare_write(ctx, ctx->write_location, ctx->write_xid, last_write);
  	ctx->prepared_write = true;
  }
  
  /*
   * Perform a write using the context's output routine.
   */
  void
  OutputPluginWrite(struct LogicalDecodingContext *ctx, bool last_write)
  {
  	if (!ctx->prepared_write)
  		elog(ERROR, "OutputPluginPrepareWrite needs to be called before OutputPluginWrite");
  
  	ctx->write(ctx, ctx->write_location, ctx->write_xid, last_write);
  	ctx->prepared_write = false;
  }
  
  /*
   * Update progress tracking (if supported).
   */
  void
  OutputPluginUpdateProgress(struct LogicalDecodingContext *ctx)
  {
  	if (!ctx->update_progress)
  		return;
  
  	ctx->update_progress(ctx, ctx->write_location, ctx->write_xid);
  }
  
  /*
   * Load the output plugin, lookup its output plugin init function, and check
   * that it provides the required callbacks.
   */
  static void
  LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugin)
  {
  	LogicalOutputPluginInit plugin_init;
  
  	plugin_init = (LogicalOutputPluginInit)
  		load_external_function(plugin, "_PG_output_plugin_init", false, NULL);
  
  	if (plugin_init == NULL)
  		elog(ERROR, "output plugins have to declare the _PG_output_plugin_init symbol");
  
  	/* ask the output plugin to fill the callback struct */
  	plugin_init(callbacks);
  
  	if (callbacks->begin_cb == NULL)
  		elog(ERROR, "output plugins have to register a begin callback");
  	if (callbacks->change_cb == NULL)
  		elog(ERROR, "output plugins have to register a change callback");
  	if (callbacks->commit_cb == NULL)
  		elog(ERROR, "output plugins have to register a commit callback");
  }
  
  static void
  output_plugin_error_callback(void *arg)
  {
  	LogicalErrorCallbackState *state = (LogicalErrorCallbackState *) arg;
  
  	/* not all callbacks have an associated LSN  */
  	if (state->report_location != InvalidXLogRecPtr)
  		errcontext("slot \"%s\", output plugin \"%s\", in the %s callback, associated LSN %X/%X",
  				   NameStr(state->ctx->slot->data.name),
  				   NameStr(state->ctx->slot->data.plugin),
  				   state->callback_name,
  				   LSN_FORMAT_ARGS(state->report_location));
  	else
  		errcontext("slot \"%s\", output plugin \"%s\", in the %s callback",
  				   NameStr(state->ctx->slot->data.name),
  				   NameStr(state->ctx->slot->data.plugin),
  				   state->callback_name);
  }
  
  static void
  startup_cb_wrapper(LogicalDecodingContext *ctx, OutputPluginOptions *opt, bool is_init)
  {
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "startup";
  	state.report_location = InvalidXLogRecPtr;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = false;
  
  	/* do the actual work: call callback */
  	ctx->callbacks.startup_cb(ctx, opt, is_init);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  shutdown_cb_wrapper(LogicalDecodingContext *ctx)
  {
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "shutdown";
  	state.report_location = InvalidXLogRecPtr;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = false;
  
  	/* do the actual work: call callback */
  	ctx->callbacks.shutdown_cb(ctx);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  
  /*
   * Callbacks for ReorderBuffer which add in some more information and then call
   * output_plugin.h plugins.
   */
  static void
  begin_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "begin";
  	state.report_location = txn->first_lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  	ctx->write_location = txn->first_lsn;
  
  	/* do the actual work: call callback */
  	ctx->callbacks.begin_cb(ctx, txn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  				  XLogRecPtr commit_lsn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "commit";
  	state.report_location = txn->final_lsn; /* beginning of commit record */
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  	ctx->write_location = txn->end_lsn; /* points to the end of the record */
  
  	/* do the actual work: call callback */
  	ctx->callbacks.commit_cb(ctx, txn, commit_lsn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  /*
   * The functionality of begin_prepare is quite similar to begin with the
   * exception that this will have gid (global transaction id) information which
   * can be used by plugin. Now, we thought about extending the existing begin
   * but that would break the replication protocol and additionally this looks
   * cleaner.
   */
  static void
  begin_prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when two-phase commits are supported */
  	Assert(ctx->twophase);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "begin_prepare";
  	state.report_location = txn->first_lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  	ctx->write_location = txn->first_lsn;
  
  	/*
  	 * If the plugin supports two-phase commits then begin prepare callback is
  	 * mandatory
  	 */
  	if (ctx->callbacks.begin_prepare_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical replication at prepare time requires a %s callback",
  						"begin_prepare_cb")));
  
  	/* do the actual work: call callback */
  	ctx->callbacks.begin_prepare_cb(ctx, txn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  				   XLogRecPtr prepare_lsn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when two-phase commits are supported */
  	Assert(ctx->twophase);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "prepare";
  	state.report_location = txn->final_lsn; /* beginning of prepare record */
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  	ctx->write_location = txn->end_lsn; /* points to the end of the record */
  
  	/*
  	 * If the plugin supports two-phase commits then prepare callback is
  	 * mandatory
  	 */
  	if (ctx->callbacks.prepare_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical replication at prepare time requires a %s callback",
  						"prepare_cb")));
  
  	/* do the actual work: call callback */
  	ctx->callbacks.prepare_cb(ctx, txn, prepare_lsn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  commit_prepared_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  						   XLogRecPtr commit_lsn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when two-phase commits are supported */
  	Assert(ctx->twophase);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "commit_prepared";
  	state.report_location = txn->final_lsn; /* beginning of commit record */
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  	ctx->write_location = txn->end_lsn; /* points to the end of the record */
  
  	/*
  	 * If the plugin support two-phase commits then commit prepared callback
  	 * is mandatory
  	 */
  	if (ctx->callbacks.commit_prepared_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical replication at prepare time requires a %s callback",
  						"commit_prepared_cb")));
  
  	/* do the actual work: call callback */
  	ctx->callbacks.commit_prepared_cb(ctx, txn, commit_lsn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  rollback_prepared_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  							 XLogRecPtr prepare_end_lsn,
  							 TimestampTz prepare_time)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when two-phase commits are supported */
  	Assert(ctx->twophase);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "rollback_prepared";
  	state.report_location = txn->final_lsn; /* beginning of commit record */
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  	ctx->write_location = txn->end_lsn; /* points to the end of the record */
  
  	/*
  	 * If the plugin support two-phase commits then rollback prepared callback
  	 * is mandatory
  	 */
  	if (ctx->callbacks.rollback_prepared_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical replication at prepare time requires a %s callback",
  						"rollback_prepared_cb")));
  
  	/* do the actual work: call callback */
  	ctx->callbacks.rollback_prepared_cb(ctx, txn, prepare_end_lsn,
  										prepare_time);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  				  Relation relation, ReorderBufferChange *change)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "change";
  	state.report_location = change->lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  
  	/*
  	 * Report this change's lsn so replies from clients can give an up-to-date
  	 * answer. This won't ever be enough (and shouldn't be!) to confirm
  	 * receipt of this transaction, but it might allow another transaction's
  	 * commit to be confirmed with one message.
  	 */
  	ctx->write_location = change->lsn;
  
  	ctx->callbacks.change_cb(ctx, txn, relation, change);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  					int nrelations, Relation relations[], ReorderBufferChange *change)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	if (!ctx->callbacks.truncate_cb)
  		return;
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "truncate";
  	state.report_location = change->lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  
  	/*
  	 * Report this change's lsn so replies from clients can give an up-to-date
  	 * answer. This won't ever be enough (and shouldn't be!) to confirm
  	 * receipt of this transaction, but it might allow another transaction's
  	 * commit to be confirmed with one message.
  	 */
  	ctx->write_location = change->lsn;
  
  	ctx->callbacks.truncate_cb(ctx, txn, nrelations, relations, change);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  bool
  filter_prepare_cb_wrapper(LogicalDecodingContext *ctx, TransactionId xid,
  						  const char *gid)
  {
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  	bool		ret;
  
  	Assert(!ctx->fast_forward);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "filter_prepare";
  	state.report_location = InvalidXLogRecPtr;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = false;
  
  	/* do the actual work: call callback */
  	ret = ctx->callbacks.filter_prepare_cb(ctx, xid, gid);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  
  	return ret;
  }
  
  bool
  filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
  {
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  	bool		ret;
  
  	Assert(!ctx->fast_forward);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "filter_by_origin";
  	state.report_location = InvalidXLogRecPtr;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = false;
  
  	/* do the actual work: call callback */
  	ret = ctx->callbacks.filter_by_origin_cb(ctx, origin_id);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  
  	return ret;
  }
  
  static void
  message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  				   XLogRecPtr message_lsn, bool transactional,
  				   const char *prefix, Size message_size, const char *message)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	if (ctx->callbacks.message_cb == NULL)
  		return;
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "message";
  	state.report_location = message_lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
  	ctx->write_location = message_lsn;
  
  	/* do the actual work: call callback */
  	ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional, prefix,
  							  message_size, message);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  stream_start_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  						XLogRecPtr first_lsn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when streaming is supported. */
  	Assert(ctx->streaming);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "stream_start";
  	state.report_location = first_lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  
  	/*
  	 * Report this message's lsn so replies from clients can give an
  	 * up-to-date answer. This won't ever be enough (and shouldn't be!) to
  	 * confirm receipt of this transaction, but it might allow another
  	 * transaction's commit to be confirmed with one message.
  	 */
  	ctx->write_location = first_lsn;
  
  	/* in streaming mode, stream_start_cb is required */
  	if (ctx->callbacks.stream_start_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical streaming requires a %s callback",
  						"stream_start_cb")));
  
  	ctx->callbacks.stream_start_cb(ctx, txn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  stream_stop_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  					   XLogRecPtr last_lsn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when streaming is supported. */
  	Assert(ctx->streaming);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "stream_stop";
  	state.report_location = last_lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  
  	/*
  	 * Report this message's lsn so replies from clients can give an
  	 * up-to-date answer. This won't ever be enough (and shouldn't be!) to
  	 * confirm receipt of this transaction, but it might allow another
  	 * transaction's commit to be confirmed with one message.
  	 */
  	ctx->write_location = last_lsn;
  
  	/* in streaming mode, stream_stop_cb is required */
  	if (ctx->callbacks.stream_stop_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical streaming requires a %s callback",
  						"stream_stop_cb")));
  
  	ctx->callbacks.stream_stop_cb(ctx, txn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  stream_abort_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  						XLogRecPtr abort_lsn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when streaming is supported. */
  	Assert(ctx->streaming);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "stream_abort";
  	state.report_location = abort_lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  	ctx->write_location = abort_lsn;
  
  	/* in streaming mode, stream_abort_cb is required */
  	if (ctx->callbacks.stream_abort_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical streaming requires a %s callback",
  						"stream_abort_cb")));
  
  	ctx->callbacks.stream_abort_cb(ctx, txn, abort_lsn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  stream_prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  						  XLogRecPtr prepare_lsn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/*
  	 * We're only supposed to call this when streaming and two-phase commits
  	 * are supported.
  	 */
  	Assert(ctx->streaming);
  	Assert(ctx->twophase);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "stream_prepare";
  	state.report_location = txn->final_lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  	ctx->write_location = txn->end_lsn;
  
  	/* in streaming mode with two-phase commits, stream_prepare_cb is required */
  	if (ctx->callbacks.stream_prepare_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical streaming at prepare time requires a %s callback",
  						"stream_prepare_cb")));
  
  	ctx->callbacks.stream_prepare_cb(ctx, txn, prepare_lsn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  stream_commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  						 XLogRecPtr commit_lsn)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when streaming is supported. */
  	Assert(ctx->streaming);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "stream_commit";
  	state.report_location = txn->final_lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  	ctx->write_location = txn->end_lsn;
  
  	/* in streaming mode, stream_commit_cb is required */
  	if (ctx->callbacks.stream_commit_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical streaming requires a %s callback",
  						"stream_commit_cb")));
  
  	ctx->callbacks.stream_commit_cb(ctx, txn, commit_lsn);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  stream_change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  						 Relation relation, ReorderBufferChange *change)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when streaming is supported. */
  	Assert(ctx->streaming);
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "stream_change";
  	state.report_location = change->lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  
  	/*
  	 * Report this change's lsn so replies from clients can give an up-to-date
  	 * answer. This won't ever be enough (and shouldn't be!) to confirm
  	 * receipt of this transaction, but it might allow another transaction's
  	 * commit to be confirmed with one message.
  	 */
  	ctx->write_location = change->lsn;
  
  	/* in streaming mode, stream_change_cb is required */
  	if (ctx->callbacks.stream_change_cb == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
  				 errmsg("logical streaming requires a %s callback",
  						"stream_change_cb")));
  
  	ctx->callbacks.stream_change_cb(ctx, txn, relation, change);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  stream_message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  						  XLogRecPtr message_lsn, bool transactional,
  						  const char *prefix, Size message_size, const char *message)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when streaming is supported. */
  	Assert(ctx->streaming);
  
  	/* this callback is optional */
  	if (ctx->callbacks.stream_message_cb == NULL)
  		return;
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "stream_message";
  	state.report_location = message_lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
  	ctx->write_location = message_lsn;
  
  	/* do the actual work: call callback */
  	ctx->callbacks.stream_message_cb(ctx, txn, message_lsn, transactional, prefix,
  									 message_size, message);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  static void
  stream_truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
  						   int nrelations, Relation relations[],
  						   ReorderBufferChange *change)
  {
  	LogicalDecodingContext *ctx = cache->private_data;
  	LogicalErrorCallbackState state;
  	ErrorContextCallback errcallback;
  
  	Assert(!ctx->fast_forward);
  
  	/* We're only supposed to call this when streaming is supported. */
  	Assert(ctx->streaming);
  
  	/* this callback is optional */
  	if (!ctx->callbacks.stream_truncate_cb)
  		return;
  
  	/* Push callback + info on the error context stack */
  	state.ctx = ctx;
  	state.callback_name = "stream_truncate";
  	state.report_location = change->lsn;
  	errcallback.callback = output_plugin_error_callback;
  	errcallback.arg = (void *) &state;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/* set output state */
  	ctx->accept_writes = true;
  	ctx->write_xid = txn->xid;
  
  	/*
  	 * Report this change's lsn so replies from clients can give an up-to-date
  	 * answer. This won't ever be enough (and shouldn't be!) to confirm
  	 * receipt of this transaction, but it might allow another transaction's
  	 * commit to be confirmed with one message.
  	 */
  	ctx->write_location = change->lsn;
  
  	ctx->callbacks.stream_truncate_cb(ctx, txn, nrelations, relations, change);
  
  	/* Pop the error context stack */
  	error_context_stack = errcallback.previous;
  }
  
  /*
   * Set the required catalog xmin horizon for historic snapshots in the current
   * replication slot.
   *
   * Note that in the most cases, we won't be able to immediately use the xmin
   * to increase the xmin horizon: we need to wait till the client has confirmed
   * receiving current_lsn with LogicalConfirmReceivedLocation().
   */
  void
  LogicalIncreaseXminForSlot(XLogRecPtr current_lsn, TransactionId xmin)
  {
  	bool		updated_xmin = false;
  	ReplicationSlot *slot;
  	bool		got_new_xmin = false;
  
  	slot = MyReplicationSlot;
  
  	Assert(slot != NULL);
  
  	SpinLockAcquire(&slot->mutex);
  
  	/*
  	 * don't overwrite if we already have a newer xmin. This can happen if we
  	 * restart decoding in a slot.
  	 */
  	if (TransactionIdPrecedesOrEquals(xmin, slot->data.catalog_xmin))
  	{
  	}
  
  	/*
  	 * If the client has already confirmed up to this lsn, we directly can
  	 * mark this as accepted. This can happen if we restart decoding in a
  	 * slot.
  	 */
  	else if (current_lsn <= slot->data.confirmed_flush)
  	{
  		slot->candidate_catalog_xmin = xmin;
  		slot->candidate_xmin_lsn = current_lsn;
  
  		/* our candidate can directly be used */
  		updated_xmin = true;
  	}
  
  	/*
  	 * Only increase if the previous values have been applied, otherwise we
  	 * might never end up updating if the receiver acks too slowly.
  	 */
  	else if (slot->candidate_xmin_lsn == InvalidXLogRecPtr)
  	{
  		slot->candidate_catalog_xmin = xmin;
  		slot->candidate_xmin_lsn = current_lsn;
  
  		/*
  		 * Log new xmin at an appropriate log level after releasing the
  		 * spinlock.
  		 */
  		got_new_xmin = true;
  	}
  	SpinLockRelease(&slot->mutex);
  
  	if (got_new_xmin)
  		elog(DEBUG1, "got new catalog xmin %u at %X/%X", xmin,
  			 LSN_FORMAT_ARGS(current_lsn));
  
  	/* candidate already valid with the current flush position, apply */
  	if (updated_xmin)
  		LogicalConfirmReceivedLocation(slot->data.confirmed_flush);
  }
  
  /*
   * Mark the minimal LSN (restart_lsn) we need to read to replay all
   * transactions that have not yet committed at current_lsn.
   *
   * Just like LogicalIncreaseXminForSlot this only takes effect when the
   * client has confirmed to have received current_lsn.
   */
  void
  LogicalIncreaseRestartDecodingForSlot(XLogRecPtr current_lsn, XLogRecPtr restart_lsn)
  {
  	bool		updated_lsn = false;
  	ReplicationSlot *slot;
  
  	slot = MyReplicationSlot;
  
  	Assert(slot != NULL);
  	Assert(restart_lsn != InvalidXLogRecPtr);
  	Assert(current_lsn != InvalidXLogRecPtr);
  
  	SpinLockAcquire(&slot->mutex);
  
  	/* don't overwrite if have a newer restart lsn */
  	if (restart_lsn <= slot->data.restart_lsn)
  	{
  	}
  
  	/*
  	 * We might have already flushed far enough to directly accept this lsn,
  	 * in this case there is no need to check for existing candidate LSNs
  	 */
  	else if (current_lsn <= slot->data.confirmed_flush)
  	{
  		slot->candidate_restart_valid = current_lsn;
  		slot->candidate_restart_lsn = restart_lsn;
  
  		/* our candidate can directly be used */
  		updated_lsn = true;
  	}
  
  	/*
  	 * Only increase if the previous values have been applied, otherwise we
  	 * might never end up updating if the receiver acks too slowly. A missed
  	 * value here will just cause some extra effort after reconnecting.
  	 */
  	if (slot->candidate_restart_valid == InvalidXLogRecPtr)
  	{
  		slot->candidate_restart_valid = current_lsn;
  		slot->candidate_restart_lsn = restart_lsn;
  		SpinLockRelease(&slot->mutex);
  
  		elog(DEBUG1, "got new restart lsn %X/%X at %X/%X",
  			 LSN_FORMAT_ARGS(restart_lsn),
  			 LSN_FORMAT_ARGS(current_lsn));
  	}
  	else
  	{
  		XLogRecPtr	candidate_restart_lsn;
  		XLogRecPtr	candidate_restart_valid;
  		XLogRecPtr	confirmed_flush;
  
  		candidate_restart_lsn = slot->candidate_restart_lsn;
  		candidate_restart_valid = slot->candidate_restart_valid;
  		confirmed_flush = slot->data.confirmed_flush;
  		SpinLockRelease(&slot->mutex);
  
  		elog(DEBUG1, "failed to increase restart lsn: proposed %X/%X, after %X/%X, current candidate %X/%X, current after %X/%X, flushed up to %X/%X",
  			 LSN_FORMAT_ARGS(restart_lsn),
  			 LSN_FORMAT_ARGS(current_lsn),
  			 LSN_FORMAT_ARGS(candidate_restart_lsn),
  			 LSN_FORMAT_ARGS(candidate_restart_valid),
  			 LSN_FORMAT_ARGS(confirmed_flush));
  	}
  
  	/* candidates are already valid with the current flush position, apply */
  	if (updated_lsn)
  		LogicalConfirmReceivedLocation(slot->data.confirmed_flush);
  }
  
  /*
   * Handle a consumer's confirmation having received all changes up to lsn.
   */
  void
  LogicalConfirmReceivedLocation(XLogRecPtr lsn)
  {
  	Assert(lsn != InvalidXLogRecPtr);
  
  	/* Do an unlocked check for candidate_lsn first. */
  	if (MyReplicationSlot->candidate_xmin_lsn != InvalidXLogRecPtr ||
  		MyReplicationSlot->candidate_restart_valid != InvalidXLogRecPtr)
  	{
  		bool		updated_xmin = false;
  		bool		updated_restart = false;
  
  		SpinLockAcquire(&MyReplicationSlot->mutex);
  
  		MyReplicationSlot->data.confirmed_flush = lsn;
  
  		/* if we're past the location required for bumping xmin, do so */
  		if (MyReplicationSlot->candidate_xmin_lsn != InvalidXLogRecPtr &&
  			MyReplicationSlot->candidate_xmin_lsn <= lsn)
  		{
  			/*
  			 * We have to write the changed xmin to disk *before* we change
  			 * the in-memory value, otherwise after a crash we wouldn't know
  			 * that some catalog tuples might have been removed already.
  			 *
  			 * Ensure that by first writing to ->xmin and only update
  			 * ->effective_xmin once the new state is synced to disk. After a
  			 * crash ->effective_xmin is set to ->xmin.
  			 */
  			if (TransactionIdIsValid(MyReplicationSlot->candidate_catalog_xmin) &&
  				MyReplicationSlot->data.catalog_xmin != MyReplicationSlot->candidate_catalog_xmin)
  			{
  				MyReplicationSlot->data.catalog_xmin = MyReplicationSlot->candidate_catalog_xmin;
  				MyReplicationSlot->candidate_catalog_xmin = InvalidTransactionId;
  				MyReplicationSlot->candidate_xmin_lsn = InvalidXLogRecPtr;
  				updated_xmin = true;
  			}
  		}
  
  		if (MyReplicationSlot->candidate_restart_valid != InvalidXLogRecPtr &&
  			MyReplicationSlot->candidate_restart_valid <= lsn)
  		{
  			Assert(MyReplicationSlot->candidate_restart_lsn != InvalidXLogRecPtr);
  
  			MyReplicationSlot->data.restart_lsn = MyReplicationSlot->candidate_restart_lsn;
  			MyReplicationSlot->candidate_restart_lsn = InvalidXLogRecPtr;
  			MyReplicationSlot->candidate_restart_valid = InvalidXLogRecPtr;
  			updated_restart = true;
  		}
  
  		SpinLockRelease(&MyReplicationSlot->mutex);
  
  		/* first write new xmin to disk, so we know what's up after a crash */
  		if (updated_xmin || updated_restart)
  		{
  			ReplicationSlotMarkDirty();
  			ReplicationSlotSave();
  			elog(DEBUG1, "updated xmin: %u restart: %u", updated_xmin, updated_restart);
  		}
  
  		/*
  		 * Now the new xmin is safely on disk, we can let the global value
  		 * advance. We do not take ProcArrayLock or similar since we only
  		 * advance xmin here and there's not much harm done by a concurrent
  		 * computation missing that.
  		 */
  		if (updated_xmin)
  		{
  			SpinLockAcquire(&MyReplicationSlot->mutex);
  			MyReplicationSlot->effective_catalog_xmin = MyReplicationSlot->data.catalog_xmin;
  			SpinLockRelease(&MyReplicationSlot->mutex);
  
  			ReplicationSlotsComputeRequiredXmin(false);
  			ReplicationSlotsComputeRequiredLSN();
  		}
  	}
  	else
  	{
  		SpinLockAcquire(&MyReplicationSlot->mutex);
  		MyReplicationSlot->data.confirmed_flush = lsn;
  		SpinLockRelease(&MyReplicationSlot->mutex);
  	}
  }
  
  /*
   * Clear logical streaming state during (sub)transaction abort.
   */
  void
  ResetLogicalStreamingState(void)
  {
  	CheckXidAlive = InvalidTransactionId;
  	bsysscan = false;
  }
  
  /*
   * Report stats for a slot.
   */
  void
  UpdateDecodingStats(LogicalDecodingContext *ctx)
  {
  	ReorderBuffer *rb = ctx->reorder;
  	PgStat_StatReplSlotEntry repSlotStat;
  
  	/* Nothing to do if we don't have any replication stats to be sent. */
  	if (rb->spillBytes <= 0 && rb->streamBytes <= 0 && rb->totalBytes <= 0)
  		return;
  
  	elog(DEBUG2, "UpdateDecodingStats: updating stats %p %lld %lld %lld %lld %lld %lld %lld %lld",
  		 rb,
  		 (long long) rb->spillTxns,
  		 (long long) rb->spillCount,
  		 (long long) rb->spillBytes,
  		 (long long) rb->streamTxns,
  		 (long long) rb->streamCount,
  		 (long long) rb->streamBytes,
  		 (long long) rb->totalTxns,
  		 (long long) rb->totalBytes);
  
  	namestrcpy(&repSlotStat.slotname, NameStr(ctx->slot->data.name));
  	repSlotStat.spill_txns = rb->spillTxns;
  	repSlotStat.spill_count = rb->spillCount;
  	repSlotStat.spill_bytes = rb->spillBytes;
  	repSlotStat.stream_txns = rb->streamTxns;
  	repSlotStat.stream_count = rb->streamCount;
  	repSlotStat.stream_bytes = rb->streamBytes;
  	repSlotStat.total_txns = rb->totalTxns;
  	repSlotStat.total_bytes = rb->totalBytes;
  
  	pgstat_report_replslot(&repSlotStat);
  
  	rb->spillTxns = 0;
  	rb->spillCount = 0;
  	rb->spillBytes = 0;
  	rb->streamTxns = 0;
  	rb->streamCount = 0;
  	rb->streamBytes = 0;
  	rb->totalTxns = 0;
  	rb->totalBytes = 0;
  }
  