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[pgsql.git] / src / backend / replication / logical / logical.c

/*-------------------------------------------------------------------------
 * logical.c
 *         PostgreSQL logical decoding coordination
 *
 * Copyright (c) 2012-2024, 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/xlogutils.h"
#include "fmgr.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "replication/decode.h"
#include "replication/logical.h"
#include "replication/reorderbuffer.h"
#include "replication/slotsync.h"
#include "replication/snapbuild.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/builtins.h"
#include "utils/inval.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);

/* callback to update txn's progress */
static void update_progress_txn_cb_wrapper(ReorderBuffer *cache,
                                                                                   ReorderBufferTXN *txn,
                                                                                   XLogRecPtr lsn);

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")));

        if (RecoveryInProgress())
        {
                /*
                 * This check may have race conditions, but whenever
                 * XLOG_PARAMETER_CHANGE indicates that wal_level has changed, we
                 * verify that there are no existing logical replication slots. And to
                 * avoid races around creating a new slot,
                 * CheckLogicalDecodingRequirements() is called once before creating
                 * the slot, and once when logical decoding is initially starting up.
                 */
                if (GetActiveWalLevelOnStandby() < WAL_LEVEL_LOGICAL)
                        ereport(ERROR,
                                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                         errmsg("logical decoding on standby requires \"wal_level\" >= \"logical\" on the primary")));
        }
}

/*
 * 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,
                                           bool in_create,
                                           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"),
                                 errdetail("Failed while allocating a WAL reading processor.")));

        ctx->reorder = ReorderBufferAllocate();
        ctx->snapshot_builder =
                AllocateSnapshotBuilder(ctx->reorder, xmin_horizon, start_lsn,
                                                                need_full_snapshot, in_create, 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;

        /*
         * Callback to support updating progress during sending data of a
         * transaction (and its subtransactions) to the output plugin.
         */
        ctx->reorder->update_progress_txn = update_progress_txn_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;

        /*
         * On a standby, this check is also required while creating the slot.
         * Check the comments in the function.
         */
        CheckLogicalDecodingRequirements();

        /* 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, true,
                                                                 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")));

        /*
         * We need to access the system tables during decoding to build the
         * logical changes unless we are in fast_forward mode where no changes are
         * generated.
         */
        if (slot->data.database != MyDatabaseId && !fast_forward)
                ereport(ERROR,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("replication slot \"%s\" was not created in this database",
                                                NameStr(slot->data.name))));

        /*
         * The slots being synced from the primary can't be used for decoding as
         * they are used after failover. However, we do allow advancing the LSNs
         * during the synchronization of slots. See update_local_synced_slot.
         */
        if (RecoveryInProgress() && slot->data.synced && !IsSyncingReplicationSlots())
                ereport(ERROR,
                                errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                errmsg("cannot use replication slot \"%s\" for logical decoding",
                                           NameStr(slot->data.name)),
                                errdetail("This replication slot is being synchronized from the primary server."),
                                errhint("Specify another replication slot."));

        /*
         * Check if slot has been invalidated due to max_slot_wal_keep_size. Avoid
         * "cannot get changes" wording in this errmsg because that'd be
         * confusingly ambiguous about no changes being available when called from
         * pg_logical_slot_get_changes_guts().
         */
        if (MyReplicationSlot->data.invalidated == RS_INVAL_WAL_REMOVED)
                ereport(ERROR,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("can no longer get changes from replication slot \"%s\"",
                                                NameStr(MyReplicationSlot->data.name)),
                                 errdetail("This slot has been invalidated because it exceeded the maximum reserved size.")));

        if (MyReplicationSlot->data.invalidated != RS_INVAL_NONE)
                ereport(ERROR,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("can no longer get changes from replication slot \"%s\"",
                                                NameStr(MyReplicationSlot->data.name)),
                                 errdetail("This slot has been invalidated because it was conflicting with recovery.")));

        Assert(MyReplicationSlot->data.invalidated == RS_INVAL_NONE);
        Assert(MyReplicationSlot->data.restart_lsn != InvalidXLogRecPtr);

        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, 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, 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)
        {
                SpinLockAcquire(&slot->mutex);
                slot->data.two_phase = true;
                slot->data.two_phase_at = start_lsn;
                SpinLockRelease(&slot->mutex);
                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,
                                                   bool skipped_xact)
{
        if (!ctx->update_progress)
                return;

        ctx->update_progress(ctx, ctx->write_location, ctx->write_xid,
                                                 skipped_xact);
}

/*
 * 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 = &state;
        errcallback.previous = error_context_stack;
        error_context_stack = &errcallback;

        /* set output state */
        ctx->accept_writes = false;
        ctx->end_xact = 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 = &state;
        errcallback.previous = error_context_stack;
        error_context_stack = &errcallback;

        /* set output state */
        ctx->accept_writes = false;
        ctx->end_xact = 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 = &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;
        ctx->end_xact = false;

        /* 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 = &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 */
        ctx->end_xact = true;

        /* 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 = &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;
        ctx->end_xact = false;

        /*
         * 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 = &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 */
        ctx->end_xact = true;

        /*
         * 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 = &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 */
        ctx->end_xact = true;

        /*
         * 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 = &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 */
        ctx->end_xact = true;

        /*
         * 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 = &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->end_xact = false;

        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 = &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->end_xact = false;

        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 = &state;
        errcallback.previous = error_context_stack;
        error_context_stack = &errcallback;

        /* set output state */
        ctx->accept_writes = false;
        ctx->end_xact = 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 = &state;
        errcallback.previous = error_context_stack;
        error_context_stack = &errcallback;

        /* set output state */
        ctx->accept_writes = false;
        ctx->end_xact = 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 = &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;
        ctx->end_xact = false;

        /* 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 = &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;

        ctx->end_xact = false;

        /* 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 = &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;

        ctx->end_xact = false;

        /* 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 = &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;
        ctx->end_xact = true;

        /* 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 = &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;
        ctx->end_xact = true;

        /* 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 = &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;
        ctx->end_xact = true;

        /* 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 = &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->end_xact = false;

        /* 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 = &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;
        ctx->end_xact = false;

        /* 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 = &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->end_xact = false;

        ctx->callbacks.stream_truncate_cb(ctx, txn, nrelations, relations, change);

        /* Pop the error context stack */
        error_context_stack = errcallback.previous;
}

static void
update_progress_txn_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
                                                           XLogRecPtr 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 = "update_progress_txn";
        state.report_location = lsn;
        errcallback.callback = output_plugin_error_callback;
        errcallback.arg = &state;
        errcallback.previous = error_context_stack;
        error_context_stack = &errcallback;

        /* set output state */
        ctx->accept_writes = false;
        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 = lsn;

        ctx->end_xact = false;

        OutputPluginUpdateProgress(ctx, false);

        /* 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)
        {
                SpinLockRelease(&slot->mutex);
        }

        /*
         * 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;
                SpinLockRelease(&slot->mutex);

                /* 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.
         */
        else 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);

        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(ctx->slot, &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;
}

/*
 * Read up to the end of WAL starting from the decoding slot's restart_lsn.
 * Return true if any meaningful/decodable WAL records are encountered,
 * otherwise false.
 */
bool
LogicalReplicationSlotHasPendingWal(XLogRecPtr end_of_wal)
{
        bool            has_pending_wal = false;

        Assert(MyReplicationSlot);

        PG_TRY();
        {
                LogicalDecodingContext *ctx;

                /*
                 * Create our decoding context in fast_forward mode, passing start_lsn
                 * as InvalidXLogRecPtr, so that we start processing from the slot's
                 * confirmed_flush.
                 */
                ctx = CreateDecodingContext(InvalidXLogRecPtr,
                                                                        NIL,
                                                                        true,   /* fast_forward */
                                                                        XL_ROUTINE(.page_read = read_local_xlog_page,
                                                                                           .segment_open = wal_segment_open,
                                                                                           .segment_close = wal_segment_close),
                                                                        NULL, NULL, NULL);

                /*
                 * Start reading at the slot's restart_lsn, which we know points to a
                 * valid record.
                 */
                XLogBeginRead(ctx->reader, MyReplicationSlot->data.restart_lsn);

                /* Invalidate non-timetravel entries */
                InvalidateSystemCaches();

                /* Loop until the end of WAL or some changes are processed */
                while (!has_pending_wal && ctx->reader->EndRecPtr < end_of_wal)
                {
                        XLogRecord *record;
                        char       *errm = NULL;

                        record = XLogReadRecord(ctx->reader, &errm);

                        if (errm)
                                elog(ERROR, "could not find record for logical decoding: %s", errm);

                        if (record != NULL)
                                LogicalDecodingProcessRecord(ctx, ctx->reader);

                        has_pending_wal = ctx->processing_required;

                        CHECK_FOR_INTERRUPTS();
                }

                /* Clean up */
                FreeDecodingContext(ctx);
                InvalidateSystemCaches();
        }
        PG_CATCH();
        {
                /* clear all timetravel entries */
                InvalidateSystemCaches();

                PG_RE_THROW();
        }
        PG_END_TRY();

        return has_pending_wal;
}

/*
 * Helper function for advancing our logical replication slot forward.
 *
 * The slot's restart_lsn is used as start point for reading records, while
 * confirmed_flush is used as base point for the decoding context.
 *
 * We cannot just do LogicalConfirmReceivedLocation to update confirmed_flush,
 * because we need to digest WAL to advance restart_lsn allowing to recycle
 * WAL and removal of old catalog tuples.  As decoding is done in fast_forward
 * mode, no changes are generated anyway.
 *
 * *found_consistent_snapshot will be true if the initial decoding snapshot has
 * been built; Otherwise, it will be false.
 */
XLogRecPtr
LogicalSlotAdvanceAndCheckSnapState(XLogRecPtr moveto,
                                                                        bool *found_consistent_snapshot)
{
        LogicalDecodingContext *ctx;
        ResourceOwner old_resowner = CurrentResourceOwner;
        XLogRecPtr      retlsn;

        Assert(moveto != InvalidXLogRecPtr);

        if (found_consistent_snapshot)
                *found_consistent_snapshot = false;

        PG_TRY();
        {
                /*
                 * Create our decoding context in fast_forward mode, passing start_lsn
                 * as InvalidXLogRecPtr, so that we start processing from my slot's
                 * confirmed_flush.
                 */
                ctx = CreateDecodingContext(InvalidXLogRecPtr,
                                                                        NIL,
                                                                        true,   /* fast_forward */
                                                                        XL_ROUTINE(.page_read = read_local_xlog_page,
                                                                                           .segment_open = wal_segment_open,
                                                                                           .segment_close = wal_segment_close),
                                                                        NULL, NULL, NULL);

                /*
                 * Wait for specified streaming replication standby servers (if any)
                 * to confirm receipt of WAL up to moveto lsn.
                 */
                WaitForStandbyConfirmation(moveto);

                /*
                 * Start reading at the slot's restart_lsn, which we know to point to
                 * a valid record.
                 */
                XLogBeginRead(ctx->reader, MyReplicationSlot->data.restart_lsn);

                /* invalidate non-timetravel entries */
                InvalidateSystemCaches();

                /* Decode records until we reach the requested target */
                while (ctx->reader->EndRecPtr < moveto)
                {
                        char       *errm = NULL;
                        XLogRecord *record;

                        /*
                         * Read records.  No changes are generated in fast_forward mode,
                         * but snapbuilder/slot statuses are updated properly.
                         */
                        record = XLogReadRecord(ctx->reader, &errm);
                        if (errm)
                                elog(ERROR, "could not find record while advancing replication slot: %s",
                                         errm);

                        /*
                         * Process the record.  Storage-level changes are ignored in
                         * fast_forward mode, but other modules (such as snapbuilder)
                         * might still have critical updates to do.
                         */
                        if (record)
                                LogicalDecodingProcessRecord(ctx, ctx->reader);

                        CHECK_FOR_INTERRUPTS();
                }

                if (found_consistent_snapshot && DecodingContextReady(ctx))
                        *found_consistent_snapshot = true;

                /*
                 * Logical decoding could have clobbered CurrentResourceOwner during
                 * transaction management, so restore the executor's value.  (This is
                 * a kluge, but it's not worth cleaning up right now.)
                 */
                CurrentResourceOwner = old_resowner;

                if (ctx->reader->EndRecPtr != InvalidXLogRecPtr)
                {
                        LogicalConfirmReceivedLocation(moveto);

                        /*
                         * If only the confirmed_flush LSN has changed the slot won't get
                         * marked as dirty by the above. Callers on the walsender
                         * interface are expected to keep track of their own progress and
                         * don't need it written out. But SQL-interface users cannot
                         * specify their own start positions and it's harder for them to
                         * keep track of their progress, so we should make more of an
                         * effort to save it for them.
                         *
                         * Dirty the slot so it is written out at the next checkpoint. The
                         * LSN position advanced to may still be lost on a crash but this
                         * makes the data consistent after a clean shutdown.
                         */
                        ReplicationSlotMarkDirty();
                }

                retlsn = MyReplicationSlot->data.confirmed_flush;

                /* free context, call shutdown callback */
                FreeDecodingContext(ctx);

                InvalidateSystemCaches();
        }
        PG_CATCH();
        {
                /* clear all timetravel entries */
                InvalidateSystemCaches();

                PG_RE_THROW();
        }
        PG_END_TRY();

        return retlsn;
}