postgres/src/backend/replication/logical/decode.c

/* -------------------------------------------------------------------------
 *
 * decode.c
 *		This module decodes WAL records read using xlogreader.h's APIs for the
 *		purpose of logical decoding by passing information to the
 *		reorderbuffer module (containing the actual changes) and to the
 *		snapbuild module to build a fitting catalog snapshot (to be able to
 *		properly decode the changes in the reorderbuffer).
 *
 * NOTE:
 *		This basically tries to handle all low level xlog stuff for
 *		reorderbuffer.c and snapbuild.c. There's some minor leakage where a
 *		specific record's struct is used to pass data along, but those just
 *		happen to contain the right amount of data in a convenient
 *		format. There isn't and shouldn't be much intelligence about the
 *		contents of records in here except turning them into a more usable
 *		format.
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  src/backend/replication/logical/decode.c
 *
 * -------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "access/heapam_xlog.h"
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog_internal.h"
#include "access/xlogreader.h"
#include "access/xlogrecord.h"
#include "access/xlogutils.h"
#include "catalog/pg_control.h"
#include "replication/decode.h"
#include "replication/logical.h"
#include "replication/message.h"
#include "replication/origin.h"
#include "replication/reorderbuffer.h"
#include "replication/snapbuild.h"
#include "storage/standby.h"

/* individual record(group)'s handlers */
static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
static void DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
static void DecodeDelete(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
static void DecodeTruncate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
static void DecodeMultiInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
static void DecodeSpecConfirm(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);

static void DecodeCommit(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
						 xl_xact_parsed_commit *parsed, TransactionId xid,
						 bool two_phase);
static void DecodeAbort(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
						xl_xact_parsed_abort *parsed, TransactionId xid,
						bool two_phase);
static void DecodePrepare(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
						  xl_xact_parsed_prepare *parsed);


/* common function to decode tuples */
static void DecodeXLogTuple(char *data, Size len, ReorderBufferTupleBuf *tuple);

/* helper functions for decoding transactions */
static inline bool FilterPrepare(LogicalDecodingContext *ctx,
								 TransactionId xid, const char *gid);
static bool DecodeTXNNeedSkip(LogicalDecodingContext *ctx,
							  XLogRecordBuffer *buf, Oid txn_dbid,
							  RepOriginId origin_id);

/*
 * Take every XLogReadRecord()ed record and perform the actions required to
 * decode it using the output plugin already setup in the logical decoding
 * context.
 *
 * NB: Note that every record's xid needs to be processed by reorderbuffer
 * (xids contained in the content of records are not relevant for this rule).
 * That means that for records which'd otherwise not go through the
 * reorderbuffer ReorderBufferProcessXid() has to be called. We don't want to
 * call ReorderBufferProcessXid for each record type by default, because
 * e.g. empty xacts can be handled more efficiently if there's no previous
 * state for them.
 *
 * We also support the ability to fast forward thru records, skipping some
 * record types completely - see individual record types for details.
 */
void
LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *record)
{
	XLogRecordBuffer buf;
	TransactionId txid;
	RmgrData	rmgr;

	buf.origptr = ctx->reader->ReadRecPtr;
	buf.endptr = ctx->reader->EndRecPtr;
	buf.record = record;

	txid = XLogRecGetTopXid(record);

	/*
	 * If the top-level xid is valid, we need to assign the subxact to the
	 * top-level xact. We need to do this for all records, hence we do it
	 * before the switch.
	 */
	if (TransactionIdIsValid(txid))
	{
		ReorderBufferAssignChild(ctx->reorder,
								 txid,
								 XLogRecGetXid(record),
								 buf.origptr);
	}

	rmgr = GetRmgr(XLogRecGetRmid(record));

	if (rmgr.rm_decode != NULL)
		rmgr.rm_decode(ctx, &buf);
	else
	{
		/* just deal with xid, and done */
		ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(record),
								buf.origptr);
	}
}

/*
 * Handle rmgr XLOG_ID records for LogicalDecodingProcessRecord().
 */
void
xlog_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	SnapBuild  *builder = ctx->snapshot_builder;
	uint8		info = XLogRecGetInfo(buf->record) & ~XLR_INFO_MASK;

	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(buf->record),
							buf->origptr);

	switch (info)
	{
			/* this is also used in END_OF_RECOVERY checkpoints */
		case XLOG_CHECKPOINT_SHUTDOWN:
		case XLOG_END_OF_RECOVERY:
			SnapBuildSerializationPoint(builder, buf->origptr);

			break;
		case XLOG_CHECKPOINT_ONLINE:

			/*
			 * a RUNNING_XACTS record will have been logged near to this, we
			 * can restart from there.
			 */
			break;
		case XLOG_NOOP:
		case XLOG_NEXTOID:
		case XLOG_SWITCH:
		case XLOG_BACKUP_END:
		case XLOG_PARAMETER_CHANGE:
		case XLOG_RESTORE_POINT:
		case XLOG_FPW_CHANGE:
		case XLOG_FPI_FOR_HINT:
		case XLOG_FPI:
		case XLOG_OVERWRITE_CONTRECORD:
			break;
		default:
			elog(ERROR, "unexpected RM_XLOG_ID record type: %u", info);
	}
}

/*
 * Handle rmgr XACT_ID records for LogicalDecodingProcessRecord().
 */
void
xact_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	SnapBuild  *builder = ctx->snapshot_builder;
	ReorderBuffer *reorder = ctx->reorder;
	XLogReaderState *r = buf->record;
	uint8		info = XLogRecGetInfo(r) & XLOG_XACT_OPMASK;

	/*
	 * If the snapshot isn't yet fully built, we cannot decode anything, so
	 * bail out.
	 */
	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
		return;

	switch (info)
	{
		case XLOG_XACT_COMMIT:
		case XLOG_XACT_COMMIT_PREPARED:
			{
				xl_xact_commit *xlrec;
				xl_xact_parsed_commit parsed;
				TransactionId xid;
				bool		two_phase = false;

				xlrec = (xl_xact_commit *) XLogRecGetData(r);
				ParseCommitRecord(XLogRecGetInfo(buf->record), xlrec, &parsed);

				if (!TransactionIdIsValid(parsed.twophase_xid))
					xid = XLogRecGetXid(r);
				else
					xid = parsed.twophase_xid;

				/*
				 * We would like to process the transaction in a two-phase
				 * manner iff output plugin supports two-phase commits and
				 * doesn't filter the transaction at prepare time.
				 */
				if (info == XLOG_XACT_COMMIT_PREPARED)
					two_phase = !(FilterPrepare(ctx, xid,
												parsed.twophase_gid));

				DecodeCommit(ctx, buf, &parsed, xid, two_phase);
				break;
			}
		case XLOG_XACT_ABORT:
		case XLOG_XACT_ABORT_PREPARED:
			{
				xl_xact_abort *xlrec;
				xl_xact_parsed_abort parsed;
				TransactionId xid;
				bool		two_phase = false;

				xlrec = (xl_xact_abort *) XLogRecGetData(r);
				ParseAbortRecord(XLogRecGetInfo(buf->record), xlrec, &parsed);

				if (!TransactionIdIsValid(parsed.twophase_xid))
					xid = XLogRecGetXid(r);
				else
					xid = parsed.twophase_xid;

				/*
				 * We would like to process the transaction in a two-phase
				 * manner iff output plugin supports two-phase commits and
				 * doesn't filter the transaction at prepare time.
				 */
				if (info == XLOG_XACT_ABORT_PREPARED)
					two_phase = !(FilterPrepare(ctx, xid,
												parsed.twophase_gid));

				DecodeAbort(ctx, buf, &parsed, xid, two_phase);
				break;
			}
		case XLOG_XACT_ASSIGNMENT:

			/*
			 * We assign subxact to the toplevel xact while processing each
			 * record if required.  So, we don't need to do anything here. See
			 * LogicalDecodingProcessRecord.
			 */
			break;
		case XLOG_XACT_INVALIDATIONS:
			{
				TransactionId xid;
				xl_xact_invals *invals;

				xid = XLogRecGetXid(r);
				invals = (xl_xact_invals *) XLogRecGetData(r);

				/*
				 * Execute the invalidations for xid-less transactions,
				 * otherwise, accumulate them so that they can be processed at
				 * the commit time.
				 */
				if (TransactionIdIsValid(xid))
				{
					if (!ctx->fast_forward)
						ReorderBufferAddInvalidations(reorder, xid,
													  buf->origptr,
													  invals->nmsgs,
													  invals->msgs);
					ReorderBufferXidSetCatalogChanges(ctx->reorder, xid,
													  buf->origptr);
				}
				else if ((!ctx->fast_forward))
					ReorderBufferImmediateInvalidation(ctx->reorder,
													   invals->nmsgs,
													   invals->msgs);
			}
			break;
		case XLOG_XACT_PREPARE:
			{
				xl_xact_parsed_prepare parsed;
				xl_xact_prepare *xlrec;

				/* ok, parse it */
				xlrec = (xl_xact_prepare *) XLogRecGetData(r);
				ParsePrepareRecord(XLogRecGetInfo(buf->record),
								   xlrec, &parsed);

				/*
				 * We would like to process the transaction in a two-phase
				 * manner iff output plugin supports two-phase commits and
				 * doesn't filter the transaction at prepare time.
				 */
				if (FilterPrepare(ctx, parsed.twophase_xid,
								  parsed.twophase_gid))
				{
					ReorderBufferProcessXid(reorder, parsed.twophase_xid,
											buf->origptr);
					break;
				}

				/*
				 * Note that if the prepared transaction has locked [user]
				 * catalog tables exclusively then decoding prepare can block
				 * till the main transaction is committed because it needs to
				 * lock the catalog tables.
				 *
				 * XXX Now, this can even lead to a deadlock if the prepare
				 * transaction is waiting to get it logically replicated for
				 * distributed 2PC. This can be avoided by disallowing
				 * preparing transactions that have locked [user] catalog
				 * tables exclusively but as of now, we ask users not to do
				 * such an operation.
				 */
				DecodePrepare(ctx, buf, &parsed);
				break;
			}
		default:
			elog(ERROR, "unexpected RM_XACT_ID record type: %u", info);
	}
}

/*
 * Handle rmgr STANDBY_ID records for LogicalDecodingProcessRecord().
 */
void
standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	SnapBuild  *builder = ctx->snapshot_builder;
	XLogReaderState *r = buf->record;
	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;

	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(r), buf->origptr);

	switch (info)
	{
		case XLOG_RUNNING_XACTS:
			{
				xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);

				SnapBuildProcessRunningXacts(builder, buf->origptr, running);

				/*
				 * Abort all transactions that we keep track of, that are
				 * older than the record's oldestRunningXid. This is the most
				 * convenient spot for doing so since, in contrast to shutdown
				 * or end-of-recovery checkpoints, we have information about
				 * all running transactions which includes prepared ones,
				 * while shutdown checkpoints just know that no non-prepared
				 * transactions are in progress.
				 */
				ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
			}
			break;
		case XLOG_STANDBY_LOCK:
			break;
		case XLOG_INVALIDATIONS:

			/*
			 * We are processing the invalidations at the command level via
			 * XLOG_XACT_INVALIDATIONS.  So we don't need to do anything here.
			 */
			break;
		default:
			elog(ERROR, "unexpected RM_STANDBY_ID record type: %u", info);
	}
}

/*
 * Handle rmgr HEAP2_ID records for LogicalDecodingProcessRecord().
 */
void
heap2_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	uint8		info = XLogRecGetInfo(buf->record) & XLOG_HEAP_OPMASK;
	TransactionId xid = XLogRecGetXid(buf->record);
	SnapBuild  *builder = ctx->snapshot_builder;

	ReorderBufferProcessXid(ctx->reorder, xid, buf->origptr);

	/*
	 * If we don't have snapshot or we are just fast-forwarding, there is no
	 * point in decoding changes.
	 */
	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT ||
		ctx->fast_forward)
		return;

	switch (info)
	{
		case XLOG_HEAP2_MULTI_INSERT:
			if (!ctx->fast_forward &&
				SnapBuildProcessChange(builder, xid, buf->origptr))
				DecodeMultiInsert(ctx, buf);
			break;
		case XLOG_HEAP2_NEW_CID:
			{
				xl_heap_new_cid *xlrec;

				xlrec = (xl_heap_new_cid *) XLogRecGetData(buf->record);
				SnapBuildProcessNewCid(builder, xid, buf->origptr, xlrec);

				break;
			}
		case XLOG_HEAP2_REWRITE:

			/*
			 * Although these records only exist to serve the needs of logical
			 * decoding, all the work happens as part of crash or archive
			 * recovery, so we don't need to do anything here.
			 */
			break;

			/*
			 * Everything else here is just low level physical stuff we're not
			 * interested in.
			 */
		case XLOG_HEAP2_FREEZE_PAGE:
		case XLOG_HEAP2_PRUNE:
		case XLOG_HEAP2_VACUUM:
		case XLOG_HEAP2_VISIBLE:
		case XLOG_HEAP2_LOCK_UPDATED:
			break;
		default:
			elog(ERROR, "unexpected RM_HEAP2_ID record type: %u", info);
	}
}

/*
 * Handle rmgr HEAP_ID records for LogicalDecodingProcessRecord().
 */
void
heap_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	uint8		info = XLogRecGetInfo(buf->record) & XLOG_HEAP_OPMASK;
	TransactionId xid = XLogRecGetXid(buf->record);
	SnapBuild  *builder = ctx->snapshot_builder;

	ReorderBufferProcessXid(ctx->reorder, xid, buf->origptr);

	/*
	 * If we don't have snapshot or we are just fast-forwarding, there is no
	 * point in decoding data changes.
	 */
	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT ||
		ctx->fast_forward)
		return;

	switch (info)
	{
		case XLOG_HEAP_INSERT:
			if (SnapBuildProcessChange(builder, xid, buf->origptr))
				DecodeInsert(ctx, buf);
			break;

			/*
			 * Treat HOT update as normal updates. There is no useful
			 * information in the fact that we could make it a HOT update
			 * locally and the WAL layout is compatible.
			 */
		case XLOG_HEAP_HOT_UPDATE:
		case XLOG_HEAP_UPDATE:
			if (SnapBuildProcessChange(builder, xid, buf->origptr))
				DecodeUpdate(ctx, buf);
			break;

		case XLOG_HEAP_DELETE:
			if (SnapBuildProcessChange(builder, xid, buf->origptr))
				DecodeDelete(ctx, buf);
			break;

		case XLOG_HEAP_TRUNCATE:
			if (SnapBuildProcessChange(builder, xid, buf->origptr))
				DecodeTruncate(ctx, buf);
			break;

		case XLOG_HEAP_INPLACE:

			/*
			 * Inplace updates are only ever performed on catalog tuples and
			 * can, per definition, not change tuple visibility.  Since we
			 * don't decode catalog tuples, we're not interested in the
			 * record's contents.
			 *
			 * In-place updates can be used either by XID-bearing transactions
			 * (e.g.  in CREATE INDEX CONCURRENTLY) or by XID-less
			 * transactions (e.g.  VACUUM).  In the former case, the commit
			 * record will include cache invalidations, so we mark the
			 * transaction as catalog modifying here. Currently that's
			 * redundant because the commit will do that as well, but once we
			 * support decoding in-progress relations, this will be important.
			 */
			if (!TransactionIdIsValid(xid))
				break;

			(void) SnapBuildProcessChange(builder, xid, buf->origptr);
			ReorderBufferXidSetCatalogChanges(ctx->reorder, xid, buf->origptr);
			break;

		case XLOG_HEAP_CONFIRM:
			if (SnapBuildProcessChange(builder, xid, buf->origptr))
				DecodeSpecConfirm(ctx, buf);
			break;

		case XLOG_HEAP_LOCK:
			/* we don't care about row level locks for now */
			break;

		default:
			elog(ERROR, "unexpected RM_HEAP_ID record type: %u", info);
			break;
	}
}

/*
 * Ask output plugin whether we want to skip this PREPARE and send
 * this transaction as a regular commit later.
 */
static inline bool
FilterPrepare(LogicalDecodingContext *ctx, TransactionId xid,
			  const char *gid)
{
	/*
	 * Skip if decoding of two-phase transactions at PREPARE time is not
	 * enabled. In that case, all two-phase transactions are considered
	 * filtered out and will be applied as regular transactions at COMMIT
	 * PREPARED.
	 */
	if (!ctx->twophase)
		return true;

	/*
	 * The filter_prepare callback is optional. When not supplied, all
	 * prepared transactions should go through.
	 */
	if (ctx->callbacks.filter_prepare_cb == NULL)
		return false;

	return filter_prepare_cb_wrapper(ctx, xid, gid);
}

static inline bool
FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
{
	if (ctx->callbacks.filter_by_origin_cb == NULL)
		return false;

	return filter_by_origin_cb_wrapper(ctx, origin_id);
}

/*
 * Handle rmgr LOGICALMSG_ID records for LogicalDecodingProcessRecord().
 */
void
logicalmsg_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	SnapBuild  *builder = ctx->snapshot_builder;
	XLogReaderState *r = buf->record;
	TransactionId xid = XLogRecGetXid(r);
	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
	RepOriginId origin_id = XLogRecGetOrigin(r);
	Snapshot	snapshot;
	xl_logical_message *message;

	if (info != XLOG_LOGICAL_MESSAGE)
		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);

	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(r), buf->origptr);

	/*
	 * If we don't have snapshot or we are just fast-forwarding, there is no
	 * point in decoding messages.
	 */
	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT ||
		ctx->fast_forward)
		return;

	message = (xl_logical_message *) XLogRecGetData(r);

	if (message->dbId != ctx->slot->data.database ||
		FilterByOrigin(ctx, origin_id))
		return;

	if (message->transactional &&
		!SnapBuildProcessChange(builder, xid, buf->origptr))
		return;
	else if (!message->transactional &&
			 (SnapBuildCurrentState(builder) != SNAPBUILD_CONSISTENT ||
			  SnapBuildXactNeedsSkip(builder, buf->origptr)))
		return;

	snapshot = SnapBuildGetOrBuildSnapshot(builder);
	ReorderBufferQueueMessage(ctx->reorder, xid, snapshot, buf->endptr,
							  message->transactional,
							  message->message, /* first part of message is
												 * prefix */
							  message->message_size,
							  message->message + message->prefix_size);
}

/*
 * Consolidated commit record handling between the different form of commit
 * records.
 *
 * 'two_phase' indicates that caller wants to process the transaction in two
 * phases, first process prepare if not already done and then process
 * commit_prepared.
 */
static void
DecodeCommit(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
			 xl_xact_parsed_commit *parsed, TransactionId xid,
			 bool two_phase)
{
	XLogRecPtr	origin_lsn = InvalidXLogRecPtr;
	TimestampTz commit_time = parsed->xact_time;
	RepOriginId origin_id = XLogRecGetOrigin(buf->record);
	int			i;

	if (parsed->xinfo & XACT_XINFO_HAS_ORIGIN)
	{
		origin_lsn = parsed->origin_lsn;
		commit_time = parsed->origin_timestamp;
	}

	SnapBuildCommitTxn(ctx->snapshot_builder, buf->origptr, xid,
					   parsed->nsubxacts, parsed->subxacts,
					   parsed->xinfo);

	/* ----
	 * Check whether we are interested in this specific transaction, and tell
	 * the reorderbuffer to forget the content of the (sub-)transactions
	 * if not.
	 *
	 * We can't just use ReorderBufferAbort() here, because we need to execute
	 * the transaction's invalidations.  This currently won't be needed if
	 * we're just skipping over the transaction because currently we only do
	 * so during startup, to get to the first transaction the client needs. As
	 * we have reset the catalog caches before starting to read WAL, and we
	 * haven't yet touched any catalogs, there can't be anything to invalidate.
	 * But if we're "forgetting" this commit because it happened in another
	 * database, the invalidations might be important, because they could be
	 * for shared catalogs and we might have loaded data into the relevant
	 * syscaches.
	 * ---
	 */
	if (DecodeTXNNeedSkip(ctx, buf, parsed->dbId, origin_id))
	{
		for (i = 0; i < parsed->nsubxacts; i++)
		{
			ReorderBufferForget(ctx->reorder, parsed->subxacts[i], buf->origptr);
		}
		ReorderBufferForget(ctx->reorder, xid, buf->origptr);

		return;
	}

	/* tell the reorderbuffer about the surviving subtransactions */
	for (i = 0; i < parsed->nsubxacts; i++)
	{
		ReorderBufferCommitChild(ctx->reorder, xid, parsed->subxacts[i],
								 buf->origptr, buf->endptr);
	}

	/*
	 * Send the final commit record if the transaction data is already
	 * decoded, otherwise, process the entire transaction.
	 */
	if (two_phase)
	{
		ReorderBufferFinishPrepared(ctx->reorder, xid, buf->origptr, buf->endptr,
									SnapBuildGetTwoPhaseAt(ctx->snapshot_builder),
									commit_time, origin_id, origin_lsn,
									parsed->twophase_gid, true);
	}
	else
	{
		ReorderBufferCommit(ctx->reorder, xid, buf->origptr, buf->endptr,
							commit_time, origin_id, origin_lsn);
	}

	/*
	 * Update the decoding stats at transaction prepare/commit/abort.
	 * Additionally we send the stats when we spill or stream the changes to
	 * avoid losing them in case the decoding is interrupted. It is not clear
	 * that sending more or less frequently than this would be better.
	 */
	UpdateDecodingStats(ctx);
}

/*
 * Decode PREPARE record. Similar logic as in DecodeCommit.
 *
 * Note that we don't skip prepare even if have detected concurrent abort
 * because it is quite possible that we had already sent some changes before we
 * detect abort in which case we need to abort those changes in the subscriber.
 * To abort such changes, we do send the prepare and then the rollback prepared
 * which is what happened on the publisher-side as well. Now, we can invent a
 * new abort API wherein in such cases we send abort and skip sending prepared
 * and rollback prepared but then it is not that straightforward because we
 * might have streamed this transaction by that time in which case it is
 * handled when the rollback is encountered. It is not impossible to optimize
 * the concurrent abort case but it can introduce design complexity w.r.t
 * handling different cases so leaving it for now as it doesn't seem worth it.
 */
static void
DecodePrepare(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
			  xl_xact_parsed_prepare *parsed)
{
	SnapBuild  *builder = ctx->snapshot_builder;
	XLogRecPtr	origin_lsn = parsed->origin_lsn;
	TimestampTz prepare_time = parsed->xact_time;
	RepOriginId	origin_id = XLogRecGetOrigin(buf->record);
	int			i;
	TransactionId xid = parsed->twophase_xid;

	if (parsed->origin_timestamp != 0)
		prepare_time = parsed->origin_timestamp;

	/*
	 * Remember the prepare info for a txn so that it can be used later in
	 * commit prepared if required. See ReorderBufferFinishPrepared.
	 */
	if (!ReorderBufferRememberPrepareInfo(ctx->reorder, xid, buf->origptr,
										  buf->endptr, prepare_time, origin_id,
										  origin_lsn))
		return;

	/* We can't start streaming unless a consistent state is reached. */
	if (SnapBuildCurrentState(builder) < SNAPBUILD_CONSISTENT)
	{
		ReorderBufferSkipPrepare(ctx->reorder, xid);
		return;
	}

	/*
	 * Check whether we need to process this transaction. See
	 * DecodeTXNNeedSkip for the reasons why we sometimes want to skip the
	 * transaction.
	 *
	 * We can't call ReorderBufferForget as we did in DecodeCommit as the txn
	 * hasn't yet been committed, removing this txn before a commit might
	 * result in the computation of an incorrect restart_lsn. See
	 * SnapBuildProcessRunningXacts. But we need to process cache
	 * invalidations if there are any for the reasons mentioned in
	 * DecodeCommit.
	 */
	if (DecodeTXNNeedSkip(ctx, buf, parsed->dbId, origin_id))
	{
		ReorderBufferSkipPrepare(ctx->reorder, xid);
		ReorderBufferInvalidate(ctx->reorder, xid, buf->origptr);
		return;
	}

	/* Tell the reorderbuffer about the surviving subtransactions. */
	for (i = 0; i < parsed->nsubxacts; i++)
	{
		ReorderBufferCommitChild(ctx->reorder, xid, parsed->subxacts[i],
								 buf->origptr, buf->endptr);
	}

	/* replay actions of all transaction + subtransactions in order */
	ReorderBufferPrepare(ctx->reorder, xid, parsed->twophase_gid);

	/*
	 * Update the decoding stats at transaction prepare/commit/abort.
	 * Additionally we send the stats when we spill or stream the changes to
	 * avoid losing them in case the decoding is interrupted. It is not clear
	 * that sending more or less frequently than this would be better.
	 */
	UpdateDecodingStats(ctx);
}


/*
 * Get the data from the various forms of abort records and pass it on to
 * snapbuild.c and reorderbuffer.c.
 *
 * 'two_phase' indicates to finish prepared transaction.
 */
static void
DecodeAbort(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
			xl_xact_parsed_abort *parsed, TransactionId xid,
			bool two_phase)
{
	int			i;
	XLogRecPtr	origin_lsn = InvalidXLogRecPtr;
	TimestampTz abort_time = parsed->xact_time;
	RepOriginId	origin_id = XLogRecGetOrigin(buf->record);
	bool		skip_xact;

	if (parsed->xinfo & XACT_XINFO_HAS_ORIGIN)
	{
		origin_lsn = parsed->origin_lsn;
		abort_time = parsed->origin_timestamp;
	}

	/*
	 * Check whether we need to process this transaction. See
	 * DecodeTXNNeedSkip for the reasons why we sometimes want to skip the
	 * transaction.
	 */
	skip_xact = DecodeTXNNeedSkip(ctx, buf, parsed->dbId, origin_id);

	/*
	 * Send the final rollback record for a prepared transaction unless we
	 * need to skip it. For non-two-phase xacts, simply forget the xact.
	 */
	if (two_phase && !skip_xact)
	{
		ReorderBufferFinishPrepared(ctx->reorder, xid, buf->origptr, buf->endptr,
									InvalidXLogRecPtr,
									abort_time, origin_id, origin_lsn,
									parsed->twophase_gid, false);
	}
	else
	{
		for (i = 0; i < parsed->nsubxacts; i++)
		{
			ReorderBufferAbort(ctx->reorder, parsed->subxacts[i],
							   buf->record->EndRecPtr, abort_time);
		}

		ReorderBufferAbort(ctx->reorder, xid, buf->record->EndRecPtr,
						   abort_time);
	}

	/* update the decoding stats */
	UpdateDecodingStats(ctx);
}

/*
 * Parse XLOG_HEAP_INSERT (not MULTI_INSERT!) records into tuplebufs.
 *
 * Deletes can contain the new tuple.
 */
static void
DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	Size		datalen;
	char	   *tupledata;
	Size		tuplelen;
	XLogReaderState *r = buf->record;
	xl_heap_insert *xlrec;
	ReorderBufferChange *change;
	RelFileLocator target_locator;

	xlrec = (xl_heap_insert *) XLogRecGetData(r);

	/*
	 * Ignore insert records without new tuples (this does happen when
	 * raw_heap_insert marks the TOAST record as HEAP_INSERT_NO_LOGICAL).
	 */
	if (!(xlrec->flags & XLH_INSERT_CONTAINS_NEW_TUPLE))
		return;

	/* only interested in our database */
	XLogRecGetBlockTag(r, 0, &target_locator, NULL, NULL);
	if (target_locator.dbOid != ctx->slot->data.database)
		return;

	/* output plugin doesn't look for this origin, no need to queue */
	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
		return;

	change = ReorderBufferGetChange(ctx->reorder);
	if (!(xlrec->flags & XLH_INSERT_IS_SPECULATIVE))
		change->action = REORDER_BUFFER_CHANGE_INSERT;
	else
		change->action = REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT;
	change->origin_id = XLogRecGetOrigin(r);

	memcpy(&change->data.tp.rlocator, &target_locator, sizeof(RelFileLocator));

	tupledata = XLogRecGetBlockData(r, 0, &datalen);
	tuplelen = datalen - SizeOfHeapHeader;

	change->data.tp.newtuple =
		ReorderBufferGetTupleBuf(ctx->reorder, tuplelen);

	DecodeXLogTuple(tupledata, datalen, change->data.tp.newtuple);

	change->data.tp.clear_toast_afterwards = true;

	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr,
							 change,
							 xlrec->flags & XLH_INSERT_ON_TOAST_RELATION);
}

/*
 * Parse XLOG_HEAP_UPDATE and XLOG_HEAP_HOT_UPDATE, which have the same layout
 * in the record, from wal into proper tuplebufs.
 *
 * Updates can possibly contain a new tuple and the old primary key.
 */
static void
DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	XLogReaderState *r = buf->record;
	xl_heap_update *xlrec;
	ReorderBufferChange *change;
	char	   *data;
	RelFileLocator target_locator;

	xlrec = (xl_heap_update *) XLogRecGetData(r);

	/* only interested in our database */
	XLogRecGetBlockTag(r, 0, &target_locator, NULL, NULL);
	if (target_locator.dbOid != ctx->slot->data.database)
		return;

	/* output plugin doesn't look for this origin, no need to queue */
	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
		return;

	change = ReorderBufferGetChange(ctx->reorder);
	change->action = REORDER_BUFFER_CHANGE_UPDATE;
	change->origin_id = XLogRecGetOrigin(r);
	memcpy(&change->data.tp.rlocator, &target_locator, sizeof(RelFileLocator));

	if (xlrec->flags & XLH_UPDATE_CONTAINS_NEW_TUPLE)
	{
		Size		datalen;
		Size		tuplelen;

		data = XLogRecGetBlockData(r, 0, &datalen);

		tuplelen = datalen - SizeOfHeapHeader;

		change->data.tp.newtuple =
			ReorderBufferGetTupleBuf(ctx->reorder, tuplelen);

		DecodeXLogTuple(data, datalen, change->data.tp.newtuple);
	}

	if (xlrec->flags & XLH_UPDATE_CONTAINS_OLD)
	{
		Size		datalen;
		Size		tuplelen;

		/* caution, remaining data in record is not aligned */
		data = XLogRecGetData(r) + SizeOfHeapUpdate;
		datalen = XLogRecGetDataLen(r) - SizeOfHeapUpdate;
		tuplelen = datalen - SizeOfHeapHeader;

		change->data.tp.oldtuple =
			ReorderBufferGetTupleBuf(ctx->reorder, tuplelen);

		DecodeXLogTuple(data, datalen, change->data.tp.oldtuple);
	}

	change->data.tp.clear_toast_afterwards = true;

	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr,
							 change, false);
}

/*
 * Parse XLOG_HEAP_DELETE from wal into proper tuplebufs.
 *
 * Deletes can possibly contain the old primary key.
 */
static void
DecodeDelete(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	XLogReaderState *r = buf->record;
	xl_heap_delete *xlrec;
	ReorderBufferChange *change;
	RelFileLocator target_locator;

	xlrec = (xl_heap_delete *) XLogRecGetData(r);

	/* only interested in our database */
	XLogRecGetBlockTag(r, 0, &target_locator, NULL, NULL);
	if (target_locator.dbOid != ctx->slot->data.database)
		return;

	/* output plugin doesn't look for this origin, no need to queue */
	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
		return;

	change = ReorderBufferGetChange(ctx->reorder);

	if (xlrec->flags & XLH_DELETE_IS_SUPER)
		change->action = REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT;
	else
		change->action = REORDER_BUFFER_CHANGE_DELETE;

	change->origin_id = XLogRecGetOrigin(r);

	memcpy(&change->data.tp.rlocator, &target_locator, sizeof(RelFileLocator));

	/* old primary key stored */
	if (xlrec->flags & XLH_DELETE_CONTAINS_OLD)
	{
		Size		datalen = XLogRecGetDataLen(r) - SizeOfHeapDelete;
		Size		tuplelen = datalen - SizeOfHeapHeader;

		Assert(XLogRecGetDataLen(r) > (SizeOfHeapDelete + SizeOfHeapHeader));

		change->data.tp.oldtuple =
			ReorderBufferGetTupleBuf(ctx->reorder, tuplelen);

		DecodeXLogTuple((char *) xlrec + SizeOfHeapDelete,
						datalen, change->data.tp.oldtuple);
	}

	change->data.tp.clear_toast_afterwards = true;

	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr,
							 change, false);
}

/*
 * Parse XLOG_HEAP_TRUNCATE from wal
 */
static void
DecodeTruncate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	XLogReaderState *r = buf->record;
	xl_heap_truncate *xlrec;
	ReorderBufferChange *change;

	xlrec = (xl_heap_truncate *) XLogRecGetData(r);

	/* only interested in our database */
	if (xlrec->dbId != ctx->slot->data.database)
		return;

	/* output plugin doesn't look for this origin, no need to queue */
	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
		return;

	change = ReorderBufferGetChange(ctx->reorder);
	change->action = REORDER_BUFFER_CHANGE_TRUNCATE;
	change->origin_id = XLogRecGetOrigin(r);
	if (xlrec->flags & XLH_TRUNCATE_CASCADE)
		change->data.truncate.cascade = true;
	if (xlrec->flags & XLH_TRUNCATE_RESTART_SEQS)
		change->data.truncate.restart_seqs = true;
	change->data.truncate.nrelids = xlrec->nrelids;
	change->data.truncate.relids = ReorderBufferGetRelids(ctx->reorder,
														  xlrec->nrelids);
	memcpy(change->data.truncate.relids, xlrec->relids,
		   xlrec->nrelids * sizeof(Oid));
	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r),
							 buf->origptr, change, false);
}

/*
 * Decode XLOG_HEAP2_MULTI_INSERT_insert record into multiple tuplebufs.
 *
 * Currently MULTI_INSERT will always contain the full tuples.
 */
static void
DecodeMultiInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	XLogReaderState *r = buf->record;
	xl_heap_multi_insert *xlrec;
	int			i;
	char	   *data;
	char	   *tupledata;
	Size		tuplelen;
	RelFileLocator rlocator;

	xlrec = (xl_heap_multi_insert *) XLogRecGetData(r);

	/*
	 * Ignore insert records without new tuples.  This happens when a
	 * multi_insert is done on a catalog or on a non-persistent relation.
	 */
	if (!(xlrec->flags & XLH_INSERT_CONTAINS_NEW_TUPLE))
		return;

	/* only interested in our database */
	XLogRecGetBlockTag(r, 0, &rlocator, NULL, NULL);
	if (rlocator.dbOid != ctx->slot->data.database)
		return;

	/* output plugin doesn't look for this origin, no need to queue */
	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
		return;

	/*
	 * We know that this multi_insert isn't for a catalog, so the block should
	 * always have data even if a full-page write of it is taken.
	 */
	tupledata = XLogRecGetBlockData(r, 0, &tuplelen);
	Assert(tupledata != NULL);

	data = tupledata;
	for (i = 0; i < xlrec->ntuples; i++)
	{
		ReorderBufferChange *change;
		xl_multi_insert_tuple *xlhdr;
		int			datalen;
		ReorderBufferTupleBuf *tuple;
		HeapTupleHeader header;

		change = ReorderBufferGetChange(ctx->reorder);
		change->action = REORDER_BUFFER_CHANGE_INSERT;
		change->origin_id = XLogRecGetOrigin(r);

		memcpy(&change->data.tp.rlocator, &rlocator, sizeof(RelFileLocator));

		xlhdr = (xl_multi_insert_tuple *) SHORTALIGN(data);
		data = ((char *) xlhdr) + SizeOfMultiInsertTuple;
		datalen = xlhdr->datalen;

		change->data.tp.newtuple =
			ReorderBufferGetTupleBuf(ctx->reorder, datalen);

		tuple = change->data.tp.newtuple;
		header = tuple->tuple.t_data;

		/* not a disk based tuple */
		ItemPointerSetInvalid(&tuple->tuple.t_self);

		/*
		 * We can only figure this out after reassembling the transactions.
		 */
		tuple->tuple.t_tableOid = InvalidOid;

		tuple->tuple.t_len = datalen + SizeofHeapTupleHeader;

		memset(header, 0, SizeofHeapTupleHeader);

		memcpy((char *) tuple->tuple.t_data + SizeofHeapTupleHeader,
			   (char *) data,
			   datalen);
		header->t_infomask = xlhdr->t_infomask;
		header->t_infomask2 = xlhdr->t_infomask2;
		header->t_hoff = xlhdr->t_hoff;

		/*
		 * Reset toast reassembly state only after the last row in the last
		 * xl_multi_insert_tuple record emitted by one heap_multi_insert()
		 * call.
		 */
		if (xlrec->flags & XLH_INSERT_LAST_IN_MULTI &&
			(i + 1) == xlrec->ntuples)
			change->data.tp.clear_toast_afterwards = true;
		else
			change->data.tp.clear_toast_afterwards = false;

		ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r),
								 buf->origptr, change, false);

		/* move to the next xl_multi_insert_tuple entry */
		data += datalen;
	}
	Assert(data == tupledata + tuplelen);
}

/*
 * Parse XLOG_HEAP_CONFIRM from wal into a confirmation change.
 *
 * This is pretty trivial, all the state essentially already setup by the
 * speculative insertion.
 */
static void
DecodeSpecConfirm(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
	XLogReaderState *r = buf->record;
	ReorderBufferChange *change;
	RelFileLocator target_locator;

	/* only interested in our database */
	XLogRecGetBlockTag(r, 0, &target_locator, NULL, NULL);
	if (target_locator.dbOid != ctx->slot->data.database)
		return;

	/* output plugin doesn't look for this origin, no need to queue */
	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
		return;

	change = ReorderBufferGetChange(ctx->reorder);
	change->action = REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM;
	change->origin_id = XLogRecGetOrigin(r);

	memcpy(&change->data.tp.rlocator, &target_locator, sizeof(RelFileLocator));

	change->data.tp.clear_toast_afterwards = true;

	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr,
							 change, false);
}


/*
 * Read a HeapTuple as WAL logged by heap_insert, heap_update and heap_delete
 * (but not by heap_multi_insert) into a tuplebuf.
 *
 * The size 'len' and the pointer 'data' in the record need to be
 * computed outside as they are record specific.
 */
static void
DecodeXLogTuple(char *data, Size len, ReorderBufferTupleBuf *tuple)
{
	xl_heap_header xlhdr;
	int			datalen = len - SizeOfHeapHeader;
	HeapTupleHeader header;

	Assert(datalen >= 0);

	tuple->tuple.t_len = datalen + SizeofHeapTupleHeader;
	header = tuple->tuple.t_data;

	/* not a disk based tuple */
	ItemPointerSetInvalid(&tuple->tuple.t_self);

	/* we can only figure this out after reassembling the transactions */
	tuple->tuple.t_tableOid = InvalidOid;

	/* data is not stored aligned, copy to aligned storage */
	memcpy((char *) &xlhdr,
		   data,
		   SizeOfHeapHeader);

	memset(header, 0, SizeofHeapTupleHeader);

	memcpy(((char *) tuple->tuple.t_data) + SizeofHeapTupleHeader,
		   data + SizeOfHeapHeader,
		   datalen);

	header->t_infomask = xlhdr.t_infomask;
	header->t_infomask2 = xlhdr.t_infomask2;
	header->t_hoff = xlhdr.t_hoff;
}

/*
 * Check whether we are interested in this specific transaction.
 *
 * There can be several reasons we might not be interested in this
 * transaction:
 * 1) We might not be interested in decoding transactions up to this
 *	  LSN. This can happen because we previously decoded it and now just
 *	  are restarting or if we haven't assembled a consistent snapshot yet.
 * 2) The transaction happened in another database.
 * 3) The output plugin is not interested in the origin.
 * 4) We are doing fast-forwarding
 */
static bool
DecodeTXNNeedSkip(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
				  Oid txn_dbid, RepOriginId origin_id)
{
	return (SnapBuildXactNeedsSkip(ctx->snapshot_builder, buf->origptr) ||
			(txn_dbid != InvalidOid && txn_dbid != ctx->slot->data.database) ||
			ctx->fast_forward || FilterByOrigin(ctx, origin_id));
}