spock_apply.c

/*-------------------------------------------------------------------------
 *
 * spock_apply.c
 * 		spock apply logic
 *
 * Copyright (c) 2022-2025, pgEdge, Inc.
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, The Regents of the University of California
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "miscadmin.h"
#include "libpq-fe.h"
#include "pgstat.h"

#include "access/htup_details.h"
#include "access/xact.h"

#include "catalog/namespace.h"
#include "catalog/pg_inherits.h"
#include "catalog/catalog.h"

#include "commands/async.h"
#include "commands/dbcommands.h"
#include "commands/sequence.h"
#include "commands/tablecmds.h"

#include "executor/executor.h"

#include "libpq/pqformat.h"

#include "mb/pg_wchar.h"

#include "nodes/makefuncs.h"
#include "nodes/parsenodes.h"

#include "optimizer/planner.h"

#ifdef XCP
#include "pgxc/pgxcnode.h"
#endif

#include "postmaster/interrupt.h"
#include "replication/origin.h"
#include "replication/reorderbuffer.h"
#include "replication/walsender.h"

#include "rewrite/rewriteHandler.h"

#include "storage/ipc.h"
#include "storage/lmgr.h"
#include "storage/proc.h"

#include "tcop/pquery.h"
#include "tcop/utility.h"

#include "utils/builtins.h"

#if PG_VERSION_NUM < 150000
#include "utils/int8.h"
#else
#include "utils/builtins.h"
#endif

#include "utils/acl.h"
#include "utils/jsonb.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/pg_lsn.h"
#include "utils/snapmgr.h"

#include "spock_common.h"
#include "spock_conflict.h"
#include "spock_executor.h"
#include "spock_node.h"
#include "spock_queue.h"
#include "spock_relcache.h"
#include "spock_repset.h"
#include "spock_rpc.h"
#include "spock_sync.h"
#include "spock_worker.h"
#include "spock_apply.h"
#include "spock_apply_heap.h"
#include "spock_apply_spi.h"
#include "spock_exception_handler.h"
#include "spock_common.h"
#include "spock_readonly.h"
#include "spock.h"


PGDLLEXPORT void spock_apply_main(Datum main_arg);

static bool in_remote_transaction = false;
static bool first_begin_at_startup = true;
static XLogRecPtr remote_origin_lsn = InvalidXLogRecPtr;
static RepOriginId remote_origin_id = InvalidRepOriginId;
static TimeOffset apply_delay = 0;

static Oid	QueueRelid = InvalidOid;

static List *SyncingTables = NIL;

SpockApplyWorker *MyApplyWorker = NULL;
SpockSubscription *MySubscription = NULL;
int			my_exception_log_index = -1;

static PGconn *applyconn = NULL;

typedef struct SpockApplyFunctions
{
	spock_apply_begin_fn on_begin;
	spock_apply_commit_fn on_commit;
	spock_apply_insert_fn do_insert;
	spock_apply_update_fn do_update;
	spock_apply_delete_fn do_delete;
	spock_apply_can_mi_fn can_multi_insert;
	spock_apply_mi_add_tuple_fn multi_insert_add_tuple;
	spock_apply_mi_finish_fn multi_insert_finish;
} SpockApplyFunctions;

static SpockApplyFunctions apply_api =
{
	.on_begin = spock_apply_heap_begin,
	.on_commit = spock_apply_heap_commit,
	.do_insert = spock_apply_heap_insert,
	.do_update = spock_apply_heap_update,
	.do_delete = spock_apply_heap_delete,
	.can_multi_insert = spock_apply_heap_can_mi,
	.multi_insert_add_tuple = spock_apply_heap_mi_add_tuple,
	.multi_insert_finish = spock_apply_heap_mi_finish
};

/* Number of tuples inserted after which we switch to multi-insert. */
#define MIN_MULTI_INSERT_TUPLES 5
static SpockRelation *last_insert_rel = NULL;
static int	last_insert_rel_cnt = 0;
static bool use_multi_insert = false;

/*
 * A message counter for the xact, for debugging. We don't send
 * the remote change LSN with messages, so this aids identification
 * of which change causes an error.
 */
static uint32 xact_action_counter;

/*
 * Flag if trasaction had any exceptions for sub_disable handling
 * at commit time.
 */
static bool xact_had_exception = false;

typedef struct SPKFlushPosition
{
	dlist_node	node;
	XLogRecPtr	local_end;
	XLogRecPtr	remote_end;
} SPKFlushPosition;

dlist_head	lsn_mapping = DLIST_STATIC_INIT(lsn_mapping);

typedef struct ApplyExecState
{
	EState	   *estate;
	EPQState	epqstate;
	ResultRelInfo *resultRelInfo;
	TupleTableSlot *slot;
} ApplyExecState;

struct ActionErrCallbackArg
{
	const char *action_name;
	SpockRelation *rel;
	bool		is_ddl_or_drop;
};

struct ActionErrCallbackArg errcallback_arg;
TransactionId remote_xid;

/*
 * We enable skipping all data modification changes (INSERT, UPDATE, etc.) for
 * the subscription if the remote transaction's finish LSN matches the sub_skip_lsn.
 * Once we start skipping changes, we don't stop it until we skip all changes of
 * the transaction even if spock.subscription is updated and MySubscription->skiplsn
 * gets changed or reset during that. The sub_skip_lsn is cleared after successfully
 * skipping the transaction or applying non-empty transaction. The latter prevents
 * the mistakenly specified sub_skip_lsn from being left.
 */
static XLogRecPtr skip_xact_finish_lsn = InvalidXLogRecPtr;
#define is_skipping_changes() (unlikely(!XLogRecPtrIsInvalid(skip_xact_finish_lsn)))

/* Functions for skipping changes */
static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
static void stop_skipping_changes(void);
static void clear_subscription_skip_lsn(XLogRecPtr finish_lsn);

static void multi_insert_finish(void);

static void handle_queued_message(HeapTuple msgtup, bool tx_just_started);
static void handle_startup_param(const char *key, const char *value);
static bool parse_bool_param(const char *key, const char *value);
static void process_syncing_tables(XLogRecPtr end_lsn);
static void start_sync_worker(Name nspname, Name relname);

static bool should_log_exception(bool failed);

/*
 * This function returns true when:
 * - exception_logging is not equal to LOG_NONE, and
 *   - Subtransaction failed
 *   OR
 *   - Subtransaction succeeded, and
 *   - exception_behaviour is TRANSDISCARD | SUB_DISABLE or
 *     exception_logging is LOG_ALL
 */
static bool
should_log_exception(bool failed)
{
	if (exception_logging != LOG_NONE)
	{
		if (failed)
			return true;
		else if (exception_logging == LOG_ALL ||
			     exception_behaviour == TRANSDISCARD ||
				 exception_behaviour == SUB_DISABLE)
			return true;
	}

	return false;
}

/*
 * Check if given relation is in process of being synchronized.
 *
 * TODO: performance
 */
static bool
should_apply_changes_for_rel(const char *nspname, const char *relname)
{
	if (list_length(SyncingTables) > 0)
	{
		ListCell   *lc;

		foreach(lc, SyncingTables)
		{
			SpockSyncStatus *sync = (SpockSyncStatus *) lfirst(lc);

			if (namestrcmp(&sync->nspname, nspname) == 0 &&
				namestrcmp(&sync->relname, relname) == 0 &&
				(sync->status != SYNC_STATUS_READY &&
				 !(sync->status == SYNC_STATUS_SYNCDONE &&
				   sync->statuslsn <= replorigin_session_origin_lsn)))
				return false;
		}
	}

	return true;
}

/*
 * Prepare apply state details for errcontext or direct logging.
 *
 * This callback could be invoked at all sorts of weird times
 * so it should assume as little as psosible about the invoking
 * context.
 */
static void
format_action_description(
						  StringInfo si,
						  const char *action_name,
						  SpockRelation *rel,
						  bool is_ddl_or_drop)
{
	appendStringInfoString(si, "apply ");
	appendStringInfoString(si,
						   action_name == NULL ? "(unknown action)" : action_name);

	if (rel != NULL &&
		rel->nspname != NULL
		&& rel->relname != NULL
		&& !is_ddl_or_drop)
	{
		appendStringInfo(si, " from remote relation %s.%s",
						 rel->nspname, rel->relname);
	}

	appendStringInfo(si,
					 " in commit before %X/%X, xid %u committed at %s (action #%u)",
					 (uint32) (replorigin_session_origin_lsn >> 32),
					 (uint32) replorigin_session_origin_lsn,
					 remote_xid,
					 timestamptz_to_str(replorigin_session_origin_timestamp),
					 xact_action_counter);

	if (replorigin_session_origin != InvalidRepOriginId)
	{
		appendStringInfo(si, " from node replorigin %u",
						 replorigin_session_origin);
	}

	if (remote_origin_id != InvalidRepOriginId)
	{
		appendStringInfo(si, " forwarded from commit %X/%X on node %u",
						 (uint32) (remote_origin_lsn >> 32),
						 (uint32) remote_origin_lsn,
						 remote_origin_id);
	}
}

static void
action_error_callback(void *arg)
{
	StringInfoData si;

	initStringInfo(&si);

	format_action_description(&si,
							  errcallback_arg.action_name,
							  errcallback_arg.rel,
							  errcallback_arg.is_ddl_or_drop);

	errcontext("%s", si.data);
	pfree(si.data);
}

/*
 * Begin one step (one INSERT, UPDATE, etc) of a replication transaction.
 *
 * Start a transaction, if this is the first step (else we keep using the
 * existing transaction).
 * Also provide a global snapshot and ensure we run in ApplyMessageContext.
 */
static bool
begin_replication_step(void)
{
	bool		result = false;

	/*
	 * spock doesn't have "statements" as such, so we'll report one statement
	 * per applied transaction. We must set the statement start time because
	 * StartTransaction() uses it to initialize the transaction cached
	 * timestamp used by current_timestamp. If we don't set it, every xact
	 * will get the same current_timestamp. See 2ndQuadrant/spock_internal#148
	 */
	SetCurrentStatementStartTimestamp();

	if (!IsTransactionState())
	{
		StartTransactionCommand();
		apply_api.on_begin();
		result = true;
	}

	PushActiveSnapshot(GetTransactionSnapshot());

	return result;
}

/*
 * Finish up one step of a replication transaction.
 * Callers of begin_replication_step() must also call this.
 *
 * We don't close out the transaction here, but we should increment
 * the command counter to make the effects of this step visible.
 */
static void
end_replication_step(void)
{
	PopActiveSnapshot();

	CommandCounterIncrement();

	MemoryContextSwitchTo(MessageContext);
}

static void
handle_begin(StringInfo s)
{
	SpockExceptionLog *exception_log;
	SpockExceptionLog *new_elog_entry;
	XLogRecPtr	commit_lsn;
	TimestampTz commit_time;
	bool		slot_found = false;
	int			sub_name_len = strlen(MySubscription->name);
	char	   *slot_name;

	/*
	 * To get here we must have connected successfully and the
	 * replication stream is delivering the first transaction.
	 * At this point we switch to restart_delay_on_exception
	 * assuming that we are just replicating a transaction without
	 * exception handling.
	 */
	MySpockWorker->restart_delay = restart_delay_on_exception;

	xact_action_counter = 1;
	xact_had_exception = false;
	errcallback_arg.action_name = "BEGIN";

	spock_read_begin(s, &commit_lsn, &commit_time, &remote_xid);
	maybe_start_skipping_changes(commit_lsn);

	replorigin_session_origin_timestamp = commit_time;
	replorigin_session_origin_lsn = commit_lsn;
	remote_origin_id = InvalidRepOriginId;

	/*
	 * We either create a new shared memory struct in the error log for
	 * ourselves if it doesn't exist, or check the commit lsn of the existing
	 * entry. There are four cases here:
	 *
	 * 1. The error log is empty and we need to create a new slot anyway.
	 *
	 * 2. The error log is not empty, but we didn't find ourselves in any of
	 * the entries. We need to create a slot here as well.
	 *
	 * 3. The error log is not empty and we found our entry, but the commit
	 * lsn does not match. We simply update the commit lsn and move on. This
	 * case happens when we have not errored out previously.
	 *
	 * 4. The error log is not empty, we found our entry and the commit lsn.
	 * This would mean that we previously errored and restarted. We set the
	 * MyApplyWorker->use_try_block = true.
	 */

	if (first_begin_at_startup)
	{
		first_begin_at_startup = false;

		for (int i = 0; i <= SpockCtx->total_workers; i++)
		{
			exception_log = &exception_log_ptr[i];
			slot_name = NameStr(exception_log->slot_name);

			if (strncmp(slot_name, MySubscription->name, sub_name_len) == 0)
			{
				/* We found our slot in shared memory. */
				slot_found = true;
				my_exception_log_index = i;

				/*
				 * Break out out of the loop whether we've found the commit
				 * LSN or not since we have already found our slot
				 */
				break;
			}
		}

		if (!slot_found)
		{
			int free_slot_index = -1;

			/*
			 * If we don't find ourselves in shared memory, then we get the
			 * pointer to the first free slot we remembered earlier, and fill
			 * in our slot name, commit_lsn and set local_tuple = NULL
			 */
			MyApplyWorker->use_try_block = false;

			/*
			 * Let's acquire an exclusive lock to ensure no changes are made
			 * by another process while we attempt to check again subscription
			 * name exists, if so, we'll take that. Otherwise, remember the
			 * first free slot index.
			 */
			LWLockAcquire(SpockCtx->lock, LW_EXCLUSIVE);

			for (int i = 0; i <= SpockCtx->total_workers; i++)
			{
				exception_log = &exception_log_ptr[i];
				slot_name = NameStr(exception_log->slot_name);

				if (strncmp(slot_name, MySubscription->name, sub_name_len) == 0)
				{
					/* We found our slot in shared memory. */
					slot_found = true;
					my_exception_log_index = i;

					/*
					 * Break out out of the loop whether we've found the commit
					 * LSN or not since we have already found our slot
					 */
					break;
				}

				if (free_slot_index < 0 && strlen(slot_name) == 0)
				{
					free_slot_index = i;
				}
			}

			/* TODO: What to do if we can't find a free slot? */
			if (free_slot_index == -1)
			{
				/* no free entries found. */
				elog(ERROR, "SPOCK %s: unable to find an empty exception log slot.",
					 MySubscription->name);
			}

			/* We didn't find a slot, but we have a valid index. */
			if (!slot_found)
			{
				/* TODO: What happens if a subscription is dropped? Memory leak */
				new_elog_entry = &exception_log_ptr[free_slot_index];
				namestrcpy(&new_elog_entry->slot_name, MySubscription->name);

				/*
				 * Redundant, since it's happening below. But we'll have it for
				 * now
				 */
				new_elog_entry->commit_lsn = commit_lsn;
				new_elog_entry->local_tuple = NULL;

				my_exception_log_index = free_slot_index;
			}

			/* We've occupied the free slot. Let's release the lock now. */
			LWLockRelease(SpockCtx->lock);
		}
	}

	if (slot_found)
	{
		/*
		 * If we find our slot in shared memory, check for commit LSN
		 */
		if (exception_log->commit_lsn == commit_lsn)
		{
			MyApplyWorker->use_try_block = true;

			elog(DEBUG1, "SPOCK %s: entering exception handling",
				 MySubscription->name);

			/*
			 * If we unexpectedly terminate again with error during
			 * exception handling, don't go into a fast error loop.
			 */
			MySpockWorker->restart_delay = restart_delay_default;
		}
	}

	exception_log = &exception_log_ptr[my_exception_log_index];
	exception_log->commit_lsn = commit_lsn;

	/* don't want the overhead otherwise */
	if (apply_delay > 0)
	{
		TimestampTz current;

		current = GetCurrentIntegerTimestamp();

		/* ensure no weirdness due to clock drift */
		if (current > replorigin_session_origin_timestamp)
		{
			long		sec;
			int			usec;

			current = TimestampTzPlusMilliseconds(current,
												  -apply_delay);

			TimestampDifference(current, replorigin_session_origin_timestamp,
								&sec, &usec);
			/* FIXME: deal with overflow? */
			pg_usleep(usec + (sec * USECS_PER_SEC));
		}
	}

	in_remote_transaction = true;

	pgstat_report_activity(STATE_RUNNING, NULL);
}

/*
 * Handle COMMIT message.
 */
static void
handle_commit(StringInfo s)
{
	XLogRecPtr	commit_lsn;
	XLogRecPtr	end_lsn;
	TimestampTz commit_time;

	errcallback_arg.action_name = "COMMIT";
	xact_action_counter++;

	spock_read_commit(s, &commit_lsn, &end_lsn, &commit_time);

	Assert(commit_time == replorigin_session_origin_timestamp);

	if (is_skipping_changes())
	{
		stop_skipping_changes();

		/*
		 * Start a new transaction to clear the subskiplsn, if not started
		 * yet.
		 */
		if (!IsTransactionState())
			StartTransactionCommand();
	}

	if (IsTransactionState())
	{
		SPKFlushPosition *flushpos;

		/*
		 * The transaction is either non-empty or skipped, so we clear the
		 * subskiplsn.
		 */
		clear_subscription_skip_lsn(end_lsn);

		multi_insert_finish();

		apply_api.on_commit();

		/*
		 * We need to write end_lsn to the commit record if we
		 * either had no exception or if we had one in DISCARD
		 * or TRANSDISCARD mode.
		 */
		if (!xact_had_exception)
		{
			replorigin_session_origin_lsn = end_lsn;
		}
		else {
			if (exception_behaviour == DISCARD ||
				exception_behaviour == TRANSDISCARD)
			{
				replorigin_session_origin_lsn = end_lsn;
			}
			else
			{
				elog(ERROR, "SPOCK %s: Unhandled exception_behaviour %d "
							"in spock_apply.c:handle_commit()",
					 MySubscription->name, exception_behaviour);
			}
		}

		/* Have the commit code adjust our logical clock if needed */
		remoteTransactionStopTimestamp = commit_time;

		CommitTransactionCommand();

		remoteTransactionStopTimestamp = 0;

		MemoryContextSwitchTo(TopMemoryContext);

		if (xact_had_exception)
		{
			/*
			 * If we had exception(s) and are in SUB_DISABLE mode then
			 * the subscription got disabled earlier in the code path.
			 * We need to exit here to disconnect.
			 */
			if (exception_behaviour == SUB_DISABLE)
			{
				SpockExceptionLog *exception_log;

				exception_log = &exception_log_ptr[my_exception_log_index];
				exception_log->commit_lsn = InvalidXLogRecPtr;
				MySpockWorker->restart_delay = 0;
				replorigin_session_reset();
				elog(ERROR, "SPOCK %s: exiting because subscription disabled",
					 MySubscription->name);
			}
		}
		else
		{
			/*
			 * If we had no exception(s) in exception handling mode then
			 * the entire transaction would be silently skipped with no
			 * exception_log entries showing in TRANSDISCARD or SUB_DISABLE
			 * mode. We need to retry this once more without exception
			 * handling.
			 */
			if (MyApplyWorker->use_try_block &&
				(exception_behaviour == TRANSDISCARD ||
				 exception_behaviour == SUB_DISABLE))
			{
				SpockExceptionLog *exception_log;

				exception_log = &exception_log_ptr[my_exception_log_index];
				exception_log->commit_lsn = InvalidXLogRecPtr;
				MySpockWorker->restart_delay = 0;
				replorigin_session_reset();
				elog(ERROR, "SPOCK %s: exception handling had no exception(s) "
					 "during replay in TRANSDISCARD or SUB_DISABLE mode",
					 MySubscription->name);
			}
		}

		/* Track commit lsn  */
		flushpos = (SPKFlushPosition *) palloc(sizeof(SPKFlushPosition));
		flushpos->local_end = XactLastCommitEnd;
		flushpos->remote_end = end_lsn;

		dlist_push_tail(&lsn_mapping, &flushpos->node);
		MemoryContextSwitchTo(MessageContext);
	}

	/*
	 * If the xact isn't from the immediate upstream, advance the slot of the
	 * node it originally came from so we start replay of that node's change
	 * data at the right place.
	 *
	 * This is only necessary when we're streaming data from one peer (A) that
	 * in turn receives from other peers (B, C), and we plan to later switch
	 * to replaying directly from B and/or C, no longer receiving forwarded
	 * xacts from A. When we do the switchover we need to know the right place
	 * at which to start replay from B and C. We don't actually do that yet,
	 * but we'll want to be able to do cascaded initialisation in future, so
	 * it's worth keeping track.
	 *
	 * A failure can occur here (see #79) if there's a cascading replication
	 * configuration like:
	 *
	 * X--> Y -> Z |         ^ |         | \---------/
	 *
	 * where the direct and indirect connections from X to Z use different
	 * replication sets so as not to conflict, and where Y and Z are on the
	 * same PostgreSQL instance. In this case our attempt to advance the
	 * replication identifier here will ERROR because it's already in use for
	 * the direct connection from X to Z. So don't do that.
	 */
#if 0

	/*
	 * XXX: This needs to be redone with Spock style forwarding in mind.
	 */
	if (remote_origin_id != InvalidRepOriginId &&
		remote_origin_id != replorigin_session_origin)
	{
		Relation	replorigin_rel;

		elog(DEBUG3, "SPOCK %s: advancing origin oid %u for forwarded "
			 "row to %X/%X",
			 MySubscription->name,
			 remote_origin_id,
			 (uint32) (XactLastCommitEnd >> 32), (uint32) XactLastCommitEnd);

		replorigin_rel = table_open(ReplicationOriginRelationId, RowExclusiveLock);
		replorigin_advance(remote_origin_id, remote_origin_lsn,
						   XactLastCommitEnd, false, false /* XXX ? */ );
		table_close(replorigin_rel, RowExclusiveLock);
	}
#endif

	in_remote_transaction = false;

	/*
	 * Stop replay if we're doing limited replay and we've replayed up to the
	 * last record we're supposed to process.
	 */
	if (MyApplyWorker->replay_stop_lsn != InvalidXLogRecPtr
		&& MyApplyWorker->replay_stop_lsn <= end_lsn)
	{
		ereport(LOG,
				(errmsg("SPOCK %s: %s finished processing; replayed "
						"to %X/%X of required %X/%X",
						MySubscription->name,
						MySpockWorker->worker_type == SPOCK_WORKER_SYNC ? "sync" : "apply",
						(uint32) (end_lsn >> 32), (uint32) end_lsn,
						(uint32) (MyApplyWorker->replay_stop_lsn >> 32),
						(uint32) MyApplyWorker->replay_stop_lsn)));

		/*
		 * If this is sync worker, update syncing table state to done.
		 */
		if (MySpockWorker->worker_type == SPOCK_WORKER_SYNC)
		{
			StartTransactionCommand();
			set_table_sync_status(MyApplyWorker->subid,
								  NameStr(MySpockWorker->worker.sync.nspname),
								  NameStr(MySpockWorker->worker.sync.relname),
								  SYNC_STATUS_SYNCDONE, end_lsn);
			CommitTransactionCommand();
		}

		/*
		 * Flush all writes so the latest position can be reported back to the
		 * sender.
		 */
		XLogFlush(GetXLogWriteRecPtr());

		/*
		 * Disconnect.
		 *
		 * This needs to happen before the spock_sync_worker_finish() call
		 * otherwise slot drop will fail.
		 */
		PQfinish(applyconn);

		/*
		 * If this is sync worker, finish it.
		 */
		if (MySpockWorker->worker_type == SPOCK_WORKER_SYNC)
			spock_sync_worker_finish();

		/* Stop gracefully */
		proc_exit(0);
	}

	VALGRIND_PRINTF("SPOCK_APPLY: commit %u\n", remote_xid);

	xact_action_counter = 0;
	remote_xid = InvalidTransactionId;

	/*
	 * This is the only place we can reset the use_try_block = false without
	 * any risk of going into the error deathloop
	 */
	MyApplyWorker->use_try_block = false;

	process_syncing_tables(end_lsn);

	/*
	 * Ensure any pending signals/self-notifies are sent out.
	 *
	 * Note that there is a possibility that this will result in an ERROR,
	 * which will result in the apply worker being killed and restarted. As
	 * the notification queues have already been flushed, the same error won't
	 * occur again, however if errors continue, they will dramatically slow
	 * down - but not stop - replication.
	 *
	 * For PG15 and above, such notifications are sent at transaction commit.
	 * (This is also true of previous version branches that received a fix[1]
	 * but where ProcessCompletedNotifies() was converted to a no-op routine
	 * to avoid breaking ABI.)
	 *
	 * [1] -- Discussion:
	 * https://www.postgresql.org/message-id/flat/153243441449.1404.2274116228506175596@wrigleys.postgresql.org
	 */
#if PG_VERSION_NUM < 150000
	ProcessCompletedNotifies();
#endif

	pgstat_report_activity(STATE_IDLE, NULL);
}

/*
 * Handle ORIGIN message.
 */
static void
handle_origin(StringInfo s)
{
	/*
	 * ORIGIN message can only come inside remote transaction and before any
	 * actual writes.
	 */
	if (!in_remote_transaction || IsTransactionState())
		elog(ERROR, "SPOCK %s: ORIGIN message sent out of order",
			 MySubscription->name);

	/*
	 * Read the message and adjust the replorigin_session_origin to the real
	 * origin_id. PostgreSQL builtin logical replication uses the non-sensical
	 * roident, which is linked to the slot of the provider and has nothing to
	 * do with the actual origin of the original transaction.
	 */
	remote_origin_id = spock_read_origin(s, &remote_origin_lsn);
	replorigin_session_origin = remote_origin_id;
}

/*
 * Handle RELATION message.
 *
 * Note we don't do validation against local schema here. The validation is
 * posponed until first change for given relation comes.
 */
static void
handle_relation(StringInfo s)
{
	multi_insert_finish();

	(void) spock_read_rel(s);
}

static void
handle_insert(StringInfo s)
{
	SpockTupleData newtup;
	SpockTupleData *oldtup = NULL;
	HeapTuple	localtup = NULL;
	SpockRelation *rel;
	ErrorData  *edata;
	bool		started_tx;
	bool		failed = false;
	char	   *action_name = "INSERT";

	/*
	 * Quick return if we are skipping data modification changes.
	 */
	if (is_skipping_changes())
		return;

	started_tx = begin_replication_step();

	errcallback_arg.action_name = "INSERT";
	xact_action_counter++;

	rel = spock_read_insert(s, RowExclusiveLock, &newtup);
	errcallback_arg.rel = rel;

	/* If in list of relations which are being synchronized, skip. */
	if (!should_apply_changes_for_rel(rel->nspname, rel->relname))
	{
		spock_relation_close(rel, NoLock);
		end_replication_step();
		return;
	}

	/*
	 * Handle multi_insert capabilities. TODO: Don't do multi- or
	 * batch-inserts when in use_try_block mode
	 */
	if (use_multi_insert && MyApplyWorker->use_try_block == false)
	{
		if (rel != last_insert_rel)
		{
			multi_insert_finish();
			/* Fall through to normal insert. */
		}
		else
		{
			apply_api.multi_insert_add_tuple(rel, &newtup);
			last_insert_rel_cnt++;
			return;
		}
	}
	else if (spock_batch_inserts &&
			 RelationGetRelid(rel->rel) != QueueRelid &&
			 apply_api.can_multi_insert &&
			 apply_api.can_multi_insert(rel) &&
			 MyApplyWorker->use_try_block == false)
	{
		if (rel != last_insert_rel)
		{
			last_insert_rel = rel;
			last_insert_rel_cnt = 0;
		}
		else if (last_insert_rel_cnt++ >= MIN_MULTI_INSERT_TUPLES)
		{
			use_multi_insert = true;
			last_insert_rel_cnt = 0;
		}
	}

	/* Normal insert. */

	/* TODO: Handle multiple inserts */
	if (MyApplyWorker->use_try_block)
	{
		PG_TRY();
		{
			exception_command_counter++;
			BeginInternalSubTransaction(NULL);
			apply_api.do_insert(rel, &newtup);
		}
		PG_CATCH();
		{
			failed = true;
			RollbackAndReleaseCurrentSubTransaction();
			edata = CopyErrorData();
			xact_had_exception = true;
		}
		PG_END_TRY();

		if (!failed)
		{
			if (exception_behaviour == TRANSDISCARD ||
				exception_behaviour == SUB_DISABLE)
				RollbackAndReleaseCurrentSubTransaction();
			else
				ReleaseCurrentSubTransaction();
		}

		/* Let's create an exception log entry if true. */
		if (should_log_exception(failed))
			add_entry_to_exception_log(remote_origin_id,
									   replorigin_session_origin_timestamp,
									   remote_xid,
									   0, 0,
									   rel, localtup, oldtup, &newtup,
									   NULL, NULL,
									   action_name,
									   (failed) ? edata->message : NULL);
	}
	else
	{
		apply_api.do_insert(rel, &newtup);
	}

	/* if INSERT was into our queue, process the message. */
	if (RelationGetRelid(rel->rel) == QueueRelid)
	{
		HeapTuple	ht;
		LockRelId	lockid = rel->rel->rd_lockInfo.lockRelId;
		Relation	qrel;

		multi_insert_finish();

		MemoryContextSwitchTo(MessageContext);

		ht = heap_form_tuple(RelationGetDescr(rel->rel),
							 newtup.values, newtup.nulls);

		LockRelationIdForSession(&lockid, RowExclusiveLock);
		spock_relation_close(rel, NoLock);

		end_replication_step();

		apply_api.on_commit();

		handle_queued_message(ht, started_tx);

		heap_freetuple(ht);

		qrel = table_open(QueueRelid, RowExclusiveLock);

		UnlockRelationIdForSession(&lockid, RowExclusiveLock);

		table_close(qrel, NoLock);

		apply_api.on_begin();
		MemoryContextSwitchTo(MessageContext);
	}
	else
	{
		spock_relation_close(rel, NoLock);
		end_replication_step();
	}
}

static void
multi_insert_finish(void)
{
	if (use_multi_insert && last_insert_rel_cnt)
	{
		const char *old_action = errcallback_arg.action_name;
		SpockRelation *old_rel = errcallback_arg.rel;

		errcallback_arg.action_name = "multi INSERT";
		errcallback_arg.rel = last_insert_rel;

		apply_api.multi_insert_finish(last_insert_rel);
		spock_relation_close(last_insert_rel, NoLock);
		use_multi_insert = false;
		last_insert_rel = NULL;
		last_insert_rel_cnt = 0;

		errcallback_arg.rel = old_rel;
		errcallback_arg.action_name = old_action;
	}
}

static void
handle_update(StringInfo s)
{
	SpockTupleData oldtup;
	SpockTupleData newtup;
	SpockRelation *rel;
	ErrorData  *edata = NULL;
	HeapTuple	localtup;
	bool		hasoldtup;
	bool		failed = false;

	/*
	 * Quick return if we are skipping data modification changes.
	 */
	if (is_skipping_changes())
		return;

	begin_replication_step();

	errcallback_arg.action_name = "UPDATE";
	xact_action_counter++;

	multi_insert_finish();

	rel = spock_read_update(s, RowExclusiveLock, &hasoldtup, &oldtup,
							&newtup);
	errcallback_arg.rel = rel;

	/* If in list of relations which are being synchronized, skip. */
	if (!should_apply_changes_for_rel(rel->nspname, rel->relname))
	{
		spock_relation_close(rel, NoLock);
		end_replication_step();
		return;
	}

	if (MyApplyWorker->use_try_block == true)
	{
		PG_TRY();
		{
			exception_command_counter++;
			BeginInternalSubTransaction(NULL);
			apply_api.do_update(rel, hasoldtup ? &oldtup : &newtup, &newtup);
		}
		PG_CATCH();
		{
			failed = true;
			RollbackAndReleaseCurrentSubTransaction();
			edata = CopyErrorData();
			xact_had_exception = true;
		}
		PG_END_TRY();

		if (!failed)
		{
			if (exception_behaviour == TRANSDISCARD ||
				exception_behaviour == SUB_DISABLE)
				RollbackAndReleaseCurrentSubTransaction();
			else
				ReleaseCurrentSubTransaction();
		}

		/* Let's create an exception log entry if true. */
		if (should_log_exception(failed))
		{
			RepOriginId		local_origin;
			TimestampTz		local_commit_ts;
			TransactionId	xmin;
			bool			local_origin_found = false;

			localtup = exception_log_ptr[my_exception_log_index].local_tuple;
			if (localtup != NULL)
				local_origin_found = get_tuple_origin(rel, localtup,
													  &(localtup->t_self),
													  &xmin,
													  &local_origin,
													  &local_commit_ts);
			if (!local_origin_found)
			{
				xmin = InvalidTransactionId;
				local_origin = InvalidRepOriginId;
				local_commit_ts = 0;
			}
			else
			{
				if (local_origin == 0)
				{
					SpockLocalNode *local_node;

					local_node = get_local_node(false, false);
					local_origin = local_node->node->id;
				}
			}

			add_entry_to_exception_log(remote_origin_id,
									replorigin_session_origin_timestamp,
									remote_xid,
									local_origin, local_commit_ts,
									rel, localtup,
									hasoldtup ? &oldtup : NULL, &newtup,
									NULL, NULL,
									"UPDATE",
									(failed) ? edata->message : NULL);
		}
	}
	else
	{
		apply_api.do_update(rel, hasoldtup ? &oldtup : &newtup, &newtup);
	}

	spock_relation_close(rel, NoLock);

	end_replication_step();
}

static void
handle_delete(StringInfo s)
{
	SpockTupleData oldtup;
	SpockRelation *rel;
	HeapTuple	localtup;
	ErrorData  *edata;
	bool		failed = false;

	/*
	 * Quick return if we are skipping data modification changes.
	 */
	if (is_skipping_changes())
		return;

	memset(&errcallback_arg, 0, sizeof(struct ActionErrCallbackArg));
	xact_action_counter++;

	begin_replication_step();

	multi_insert_finish();

	rel = spock_read_delete(s, RowExclusiveLock, &oldtup);
	errcallback_arg.rel = rel;

	/* If in list of relations which are being synchronized, skip. */
	if (!should_apply_changes_for_rel(rel->nspname, rel->relname))
	{
		spock_relation_close(rel, NoLock);
		end_replication_step();
		return;
	}

	if (MyApplyWorker->use_try_block)
	{
		PG_TRY();
		{
			exception_command_counter++;
			BeginInternalSubTransaction(NULL);
			apply_api.do_delete(rel, &oldtup);
		}
		PG_CATCH();
		{
			failed = true;
			RollbackAndReleaseCurrentSubTransaction();
			edata = CopyErrorData();
			xact_had_exception = true;
		}
		PG_END_TRY();

		if (!failed)
		{
			if (exception_behaviour == TRANSDISCARD ||
				exception_behaviour == SUB_DISABLE)
				RollbackAndReleaseCurrentSubTransaction();
			else
				ReleaseCurrentSubTransaction();
		}

		/* Let's create an exception log entry if true. */
		if (should_log_exception(failed))
		{
			RepOriginId		local_origin;
			TimestampTz		local_commit_ts;
			TransactionId	xmin;
			bool			local_origin_found = false;

			localtup = exception_log_ptr[my_exception_log_index].local_tuple;
			if (localtup != NULL)
				local_origin_found = get_tuple_origin(rel, localtup,
													  &(localtup->t_self),
													  &xmin,
													  &local_origin,
													  &local_commit_ts);
			if (!local_origin_found)
			{
				xmin = InvalidTransactionId;
				local_origin = InvalidRepOriginId;
				local_commit_ts = 0;
			}
			else
			{
				if (local_origin == 0)
				{
					SpockLocalNode *local_node;

					local_node = get_local_node(false, false);
					local_origin = local_node->node->id;
				}
			}

			add_entry_to_exception_log(remote_origin_id,
									   replorigin_session_origin_timestamp,
									   remote_xid,
									   local_origin, local_commit_ts,
									   rel, localtup,
									   &oldtup, NULL,
									   NULL, NULL,
									   "DELETE",
									   (failed) ? edata->message : NULL);
		}
	}
	else
	{
		apply_api.do_delete(rel, &oldtup);
	}

	spock_relation_close(rel, NoLock);

	end_replication_step();
}

/*
 * Handle TRUNCATE
 */
static void
handle_truncate(StringInfo s)
{
	bool		cascade = false;
	bool		restart_seqs = false;
	List	   *remote_relids = NIL;
	List	   *remote_rels = NIL;
	List	   *rels = NIL;
	List	   *part_rels = NIL;
	List	   *relids = NIL;
	List	   *relids_logged = NIL;
	ListCell   *lc;
	LOCKMODE	lockmode = AccessExclusiveLock;

	/*
	 * Quick return if we are skipping data modification changes.
	 */
	if (is_skipping_changes())
		return;

	begin_replication_step();

	errcallback_arg.action_name = "TRUNCATE";
	remote_relids = spock_read_truncate(s, &cascade, &restart_seqs);

	foreach(lc, remote_relids)
	{
		SpockRelation *rel;
		Oid			relid = lfirst_oid(lc);

		rel = spock_relation_open(relid, lockmode);
		errcallback_arg.rel = rel;

		/* If in list of relations which are being synchronized, skip. */
		if (!should_apply_changes_for_rel(rel->nspname, rel->relname))
		{
			spock_relation_close(rel, NoLock);
			continue;
		}

		remote_rels = lappend(remote_rels, rel);
		rels = lappend(rels, rel->rel);
		relids = lappend_oid(relids, rel->reloid);
		if (RelationIsLogicallyLogged(rel->rel))
			relids_logged = lappend_oid(relids_logged, rel->reloid);

		/*
		 * Truncate partitions if we got a message to truncate a partitioned
		 * table.
		 */
		if (rel->rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
		{
			ListCell   *child;
			List	   *children = find_all_inheritors(rel->reloid,
													   lockmode,
													   NULL);

			foreach(child, children)
			{
				Oid			childrelid = lfirst_oid(child);
				Relation	childrel;

				if (list_member_oid(relids, childrelid))
					continue;

				/* find_all_inheritors already got lock */
				childrel = table_open(childrelid, NoLock);

				/*
				 * Ignore temp tables of other backends.  See similar code in
				 * ExecuteTruncate().
				 */
				if (RELATION_IS_OTHER_TEMP(childrel))
				{
					table_close(childrel, lockmode);
					continue;
				}

				rels = lappend(rels, childrel);
				part_rels = lappend(part_rels, childrel);
				relids = lappend_oid(relids, childrelid);
				/* Log this relation only if needed for logical decoding */
				if (RelationIsLogicallyLogged(childrel))
					relids_logged = lappend_oid(relids_logged, childrelid);
			}
		}
	}

	/*
	 * Even if we used CASCADE on the upstream primary we explicitly default
	 * to replaying changes without further cascading. This might be later
	 * changeable with a user specified option.
	 */
	ExecuteTruncateGuts(rels,
						relids,
						relids_logged,
						DROP_RESTRICT,
						restart_seqs,
						false);
	foreach(lc, remote_rels)
	{
		SpockRelation *rel = lfirst(lc);

		spock_relation_close(rel, NoLock);
	}
	foreach(lc, part_rels)
	{
		Relation	rel = lfirst(lc);

		table_close(rel, NoLock);
	}

	end_replication_step();
}

inline static bool
getmsgisend(StringInfo msg)
{
	return msg->cursor == msg->len;
}

static void
handle_startup(StringInfo s)
{
	uint8		msgver = pq_getmsgbyte(s);

	if (msgver != 1)
		elog(ERROR, "SPOCK %s: Expected startup message version 1, but got %u",
			 MySubscription->name, msgver);

	/*
	 * The startup message consists of null-terminated strings as key/value
	 * pairs. The first entry is always the format identifier.
	 */
	do
	{
		const char *k,
				   *v;

		k = pq_getmsgstring(s);
		if (strlen(k) == 0)
			ereport(ERROR,
					(errcode(ERRCODE_PROTOCOL_VIOLATION),
					 errmsg("SPOCK %s: invalid startup message: key has "
							"zero length",
							MySubscription->name)));

		if (getmsgisend(s))
			ereport(ERROR,
					(errcode(ERRCODE_PROTOCOL_VIOLATION),
					 errmsg("SPOCK %s: invalid startup message: key '%s' "
							"has no following value",
							MySubscription->name, k)));

		/* It's OK to have a zero length value */
		v = pq_getmsgstring(s);

		handle_startup_param(k, v);
	} while (!getmsgisend(s));
}

static bool
parse_bool_param(const char *key, const char *value)
{
	bool		result;

	if (!parse_bool(value, &result))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("SPOCK %s: couldn't parse value '%s' for key '%s' "
						"as boolean",
						MySubscription->name, value, key)));

	return result;
}

static void
handle_startup_param(const char *key, const char *value)
{
	elog(DEBUG2, "SPOCK %s: apply got spock startup msg param  %s=%s",
		 MySubscription->name, key, value);

	if (strcmp(key, "pg_version") == 0)
		elog(DEBUG1, "SPOCK %s: upstream Pg version is %s",
			 MySubscription->name, value);

	if (strcmp(key, "encoding") == 0)
	{
		int			encoding = pg_char_to_encoding(value);

		if (encoding != GetDatabaseEncoding())
			ereport(ERROR,
					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
					 errmsg("SPOCK %s: expected encoding=%s from upstream "
							"but got %s",
							MySubscription->name,
							GetDatabaseEncodingName(), value)));
	}

	if (strcmp(key, "forward_changeset_origins") == 0)
	{
		bool		fwd = parse_bool_param(key, value);

		/* FIXME: Store this somewhere */
		elog(DEBUG1, "SPOCK %s: changeset origin forwarding enabled: %s",
			 MySubscription->name, fwd ? "t" : "f");
	}

	/*
	 * We just ignore a bunch of parameters here because we specify what we
	 * require when we send our params to the upstream. It's required to ERROR
	 * if it can't match what we asked for. It may send the startup message
	 * first, but it'll be followed by an ERROR if it does. There's no need to
	 * check params we can't do anything about mismatches of, like protocol
	 * versions and type sizes.
	 */
}

static RangeVar *
parse_relation_message(Jsonb *message)
{
	JsonbIterator *it;
	JsonbValue	v;
	int			r;
	int			level = 0;
	char	   *key = NULL;
	char	  **parse_res = NULL;
	char	   *nspname = NULL;
	char	   *relname = NULL;

	/* Parse and validate the json message. */
	if (!JB_ROOT_IS_OBJECT(message))
		elog(ERROR, "SPOCK %s: malformed message in queued message tuple: "
			 "root is not object",
			 MySubscription->name);

	it = JsonbIteratorInit(&message->root);
	while ((r = JsonbIteratorNext(&it, &v, false)) != WJB_DONE)
	{
		if (level == 0 && r != WJB_BEGIN_OBJECT)
			elog(ERROR, "SPOCK %s: root element needs to be an object",
				 MySubscription->name);
		else if (level == 0 && r == WJB_BEGIN_OBJECT)
		{
			level++;
		}
		else if (level == 1 && r == WJB_KEY)
		{
			if (strncmp(v.val.string.val, "schema_name", v.val.string.len) == 0)
				parse_res = &nspname;
			else if (strncmp(v.val.string.val, "table_name", v.val.string.len) == 0)
				parse_res = &relname;
			else
				elog(ERROR, "SPOCK %s: unexpected key: %s",
					 MySubscription->name,
					 pnstrdup(v.val.string.val, v.val.string.len));

			key = v.val.string.val;
		}
		else if (level == 1 && r == WJB_VALUE)
		{
			if (!key)
				elog(ERROR, "SPOCK %s: in wrong state when parsing key",
					 MySubscription->name);

			if (v.type != jbvString)
				elog(ERROR, "SPOCK %s: unexpected type for key '%s': %u",
					 MySubscription->name, key, v.type);

			*parse_res = pnstrdup(v.val.string.val, v.val.string.len);
		}
		else if (level == 1 && r != WJB_END_OBJECT)
		{
			elog(ERROR, "SPOCK %s: unexpected content: %u at level %d",
				 MySubscription->name, r, level);
		}
		else if (r == WJB_END_OBJECT)
		{
			level--;
			parse_res = NULL;
			key = NULL;
		}
		else
			elog(ERROR, "SPOCK %s: unexpected content: %u at level %d",
				 MySubscription->name, r, level);

	}

	/* Check if we got both schema and table names. */
	if (!nspname)
		elog(ERROR, "SPOCK %s: missing schema_name in relation message",
			 MySubscription->name);

	if (!relname)
		elog(ERROR, "SPOCK %s: missing table_name in relation message",
			 MySubscription->name);

	return makeRangeVar(nspname, relname, -1);
}

/*
 * Handle TABLESYNC message comming via queue table.
 */
static void
handle_table_sync(QueuedMessage *queued_message)
{
	RangeVar   *rv;
	MemoryContext oldcontext;
	SpockSyncStatus *oldsync;
	SpockSyncStatus *newsync;

	rv = parse_relation_message(queued_message->message);

	oldsync = get_table_sync_status(MyApplyWorker->subid, rv->schemaname,
									rv->relname, true);

	if (oldsync)
	{
		elog(INFO, "SPOCK %s: table sync came from queue for table %s.%s "
			 "which already being synchronized, skipping",
			 MySubscription->name,
			 rv->schemaname, rv->relname);

		return;
	}

	/* Keep the lists persistent. */
	oldcontext = MemoryContextSwitchTo(TopMemoryContext);
	newsync = palloc0(sizeof(SpockSyncStatus));
	MemoryContextSwitchTo(oldcontext);

	newsync->kind = SYNC_KIND_DATA;
	newsync->subid = MyApplyWorker->subid;
	newsync->status = SYNC_STATUS_INIT;
	namestrcpy(&newsync->nspname, rv->schemaname);
	namestrcpy(&newsync->relname, rv->relname);
	create_local_sync_status(newsync);

	oldcontext = MemoryContextSwitchTo(TopMemoryContext);
	MemoryContextSwitchTo(oldcontext);

	MyApplyWorker->sync_pending = true;
}

/*
 * Handle SEQUENCE message comming via queue table.
 */
static void
handle_sequence(QueuedMessage *queued_message)
{
	Jsonb	   *message = queued_message->message;
	JsonbIterator *it;
	JsonbValue	v;
	int			r;
	int			level = 0;
	char	   *key = NULL;
	char	  **parse_res = NULL;
	char	   *nspname = NULL;
	char	   *relname = NULL;
	char	   *last_value_raw = NULL;
	int64		last_value;
	Oid			nspoid;
	Oid			reloid;

	/* Parse and validate the json message. */
	if (!JB_ROOT_IS_OBJECT(message))
		elog(ERROR, "SPOCK %s: malformed message in queued message tuple: "
			 "root is not object",
			 MySubscription->name);

	it = JsonbIteratorInit(&message->root);
	while ((r = JsonbIteratorNext(&it, &v, false)) != WJB_DONE)
	{
		if (level == 0 && r != WJB_BEGIN_OBJECT)
			elog(ERROR, "SPOCK %s: root element needs to be an object",
				 MySubscription->name);
		else if (level == 0 && r == WJB_BEGIN_OBJECT)
		{
			level++;
		}
		else if (level == 1 && r == WJB_KEY)
		{
			if (strncmp(v.val.string.val, "schema_name", v.val.string.len) == 0)
				parse_res = &nspname;
			else if (strncmp(v.val.string.val, "sequence_name", v.val.string.len) == 0)
				parse_res = &relname;
			else if (strncmp(v.val.string.val, "last_value", v.val.string.len) == 0)
				parse_res = &last_value_raw;
			else
				elog(ERROR, "SPOCK %s: unexpected key: %s",
					 MySubscription->name,
					 pnstrdup(v.val.string.val, v.val.string.len));

			key = v.val.string.val;
		}
		else if (level == 1 && r == WJB_VALUE)
		{
			if (!key)
				elog(ERROR, "SPOCK %s: in wrong state when parsing key",
					 MySubscription->name);

			if (v.type != jbvString)
				elog(ERROR, "SPOCK %s: unexpected type for key '%s': %u",
					 MySubscription->name, key, v.type);

			*parse_res = pnstrdup(v.val.string.val, v.val.string.len);
		}
		else if (level == 1 && r != WJB_END_OBJECT)
		{
			elog(ERROR, "SPOCK %s: unexpected content: %u at level %d",
				 MySubscription->name, r, level);
		}
		else if (r == WJB_END_OBJECT)
		{
			level--;
			parse_res = NULL;
			key = NULL;
		}
		else
			elog(ERROR, "SPOCK %s: unexpected content: %u at level %d",
				 MySubscription->name, r, level);

	}

	/* Check if we got both schema and table names. */
	if (!nspname)
		elog(ERROR, "SPOCK %s: missing schema_name in sequence message",
			 MySubscription->name);

	if (!relname)
		elog(ERROR, "SPOCK %s: missing table_name in sequence message",
			 MySubscription->name);

	if (!last_value_raw)
		elog(ERROR, "SPOCK %s: missing last_value in sequence message",
			 MySubscription->name);

	nspoid = get_namespace_oid(nspname, false);
	reloid = get_relname_relid(relname, nspoid);
#if PG_VERSION_NUM < 150000
	scanint8(last_value_raw, false, &last_value);
#else
	last_value = pg_strtoint64(last_value_raw);
#endif

	DirectFunctionCall2(setval_oid, ObjectIdGetDatum(reloid),
						Int64GetDatum(last_value));
}

/*
 * Handle SQL message comming via queue table.
 */
static void
handle_sql(QueuedMessage *queued_message, bool tx_just_started, char **sql)
{
	JsonbIterator *it;
	JsonbValue	v;
	int			r;

	/* Validate the json and extract the SQL string from it. */
	if (!JB_ROOT_IS_SCALAR(queued_message->message))
		elog(ERROR, "SPOCK %s: malformed message in queued message tuple: "
			 "root is not scalar",
			 MySubscription->name);

	it = JsonbIteratorInit(&queued_message->message->root);
	r = JsonbIteratorNext(&it, &v, false);
	if (r != WJB_BEGIN_ARRAY)
		elog(ERROR, "SPOCK %s: malformed message in queued message tuple, "
			 "item type %d expected %d",
			 MySubscription->name, r, WJB_BEGIN_ARRAY);

	r = JsonbIteratorNext(&it, &v, false);
	if (r != WJB_ELEM)
		elog(ERROR, "SPOCK %s: malformed message in queued message tuple, "
			 "item type %d expected %d",
			 MySubscription->name, r, WJB_ELEM);

	if (v.type != jbvString)
		elog(ERROR, "SPOCK %s: malformed message in queued message tuple, "
			 "expected value type %d got %d",
			 MySubscription->name, jbvString, v.type);

	*sql = pnstrdup(v.val.string.val, v.val.string.len);

	r = JsonbIteratorNext(&it, &v, false);
	if (r != WJB_END_ARRAY)
		elog(ERROR, "SPOCK %s: malformed message in queued message tuple, "
			 "item type %d expected %d",
			 MySubscription->name, r, WJB_END_ARRAY);

	r = JsonbIteratorNext(&it, &v, false);
	if (r != WJB_DONE)
		elog(ERROR, "SPOCK %s: malformed message in queued message tuple, "
			 "item type %d expected %d",
			 MySubscription->name, r, WJB_DONE);

	/* Run the extracted SQL. */
	spock_execute_sql_command(*sql, queued_message->role, tx_just_started);
}

/*
 * Handle SQL message comming via queue table.
 */
static void
handle_sql_or_exception(QueuedMessage *queued_message, bool tx_just_started)
{
	bool		failed = false;
	char	   *sql = NULL;
	ErrorData  *edata;

	errcallback_arg.action_name = "SQL";

	if (MyApplyWorker->use_try_block)
	{
		PG_TRY();
		{
			exception_command_counter++;
			BeginInternalSubTransaction(NULL);
			handle_sql(queued_message, tx_just_started, &sql);
		}
		PG_CATCH();
		{
			failed = true;
			RollbackAndReleaseCurrentSubTransaction();
			edata = CopyErrorData();
			xact_had_exception = true;
		}
		PG_END_TRY();

		if (!failed)
		{
			if (exception_behaviour == TRANSDISCARD ||
				exception_behaviour == SUB_DISABLE)
				RollbackAndReleaseCurrentSubTransaction();
			else
				ReleaseCurrentSubTransaction();
		}

		/* Let's create an exception log entry if true. */
		if (should_log_exception(failed))
			add_entry_to_exception_log(remote_origin_id,
									   replorigin_session_origin_timestamp,
									   remote_xid,
									   0, 0,
									   NULL, NULL, NULL, NULL,
									   sql, queued_message->role,
									   "SQL",
									   (failed) ? edata->message : NULL);
	}
	else
	{
		handle_sql(queued_message, tx_just_started, &sql);
	}
}

/*
 * Handles messages comming from the queue.
 */
static void
handle_queued_message(HeapTuple msgtup, bool tx_just_started)
{
	QueuedMessage *queued_message;
	const char *old_action_name;

	old_action_name = errcallback_arg.action_name;
	errcallback_arg.is_ddl_or_drop = true;

	queued_message = queued_message_from_tuple(msgtup);

	switch (queued_message->message_type)
	{
		case QUEUE_COMMAND_TYPE_DDL:
			in_spock_queue_ddl_command = true;
			/* fallthrough */
		case QUEUE_COMMAND_TYPE_SQL:
			errcallback_arg.action_name = "QUEUED_SQL";
			handle_sql_or_exception(queued_message, tx_just_started);
			in_spock_queue_ddl_command = false;
			break;
		case QUEUE_COMMAND_TYPE_TABLESYNC:
			errcallback_arg.action_name = "QUEUED_TABLESYNC";
			handle_table_sync(queued_message);
			break;
		case QUEUE_COMMAND_TYPE_SEQUENCE:
			errcallback_arg.action_name = "QUEUED_SEQUENCE";
			handle_sequence(queued_message);
			break;
		default:
			elog(ERROR, "SPOCK %s: unknown message type '%c'",
				 MySubscription->name,
				 queued_message->message_type);
	}

	errcallback_arg.action_name = old_action_name;
	errcallback_arg.is_ddl_or_drop = false;
}

static void
replication_handler(StringInfo s)
{
	ErrorContextCallback errcallback;
	char		action = pq_getmsgbyte(s);

	if (spock_readonly == READONLY_ALL)
		elog(ERROR, "SPOCK %s: cluster is in read-only mode, not performing replication",
			 MySubscription->name);

	memset(&errcallback_arg, 0, sizeof(struct ActionErrCallbackArg));
	errcallback.callback = action_error_callback;
	errcallback.arg = &errcallback_arg;
	errcallback.previous = error_context_stack;
	error_context_stack = &errcallback;

	Assert(CurrentMemoryContext == MessageContext);

	switch (action)
	{
			/* BEGIN */
		case 'B':
			handle_begin(s);
			break;
			/* COMMIT */
		case 'C':
			handle_commit(s);
			break;
			/* ORIGIN */
		case 'O':
			handle_origin(s);
			break;
			/* RELATION */
		case 'R':
			handle_relation(s);
			break;
			/* INSERT */
		case 'I':
			handle_insert(s);
			break;
			/* UPDATE */
		case 'U':
			handle_update(s);
			break;
			/* DELETE */
		case 'D':
			handle_delete(s);
			break;
			/* TRUNCATE */
		case 'T':
			handle_truncate(s);
			break;
			/* STARTUP MESSAGE */
		case 'S':
			handle_startup(s);
			break;
		default:
			elog(ERROR, "SPOCK %s: unknown action of type %c",
				 MySubscription->name, action);
	}

	Assert(CurrentMemoryContext == MessageContext);

	if (error_context_stack == &errcallback)
		error_context_stack = errcallback.previous;

	if (action == 'C')
	{
		/*
		 * We clobber MessageContext on commit. It doesn't matter much when we
		 * do it so long as we do so periodically, to prevent the context from
		 * growing too much. We might want to clean it up even 'n'th message
		 * too, but that adds testing burden and isn't done for now.
		 */
		MemoryContextReset(MessageContext);
	}
}

/*
 * Figure out which write/flush positions to report to the walsender process.
 *
 * We can't simply report back the last LSN the walsender sent us because the
 * local transaction might not yet be flushed to disk locally. Instead we
 * build a list that associates local with remote LSNs for every commit. When
 * reporting back the flush position to the sender we iterate that list and
 * check which entries on it are already locally flushed. Those we can report
 * as having been flushed.
 *
 * Returns true if there's no outstanding transactions that need to be
 * flushed.
 */
static bool
get_flush_position(XLogRecPtr *write, XLogRecPtr *flush)
{
	dlist_mutable_iter iter;
#if PG_VERSION_NUM < 150000
	XLogRecPtr	local_flush = GetFlushRecPtr();
#else
	XLogRecPtr	local_flush = GetFlushRecPtr(NULL);
#endif
	*write = InvalidXLogRecPtr;
	*flush = InvalidXLogRecPtr;

	dlist_foreach_modify(iter, &lsn_mapping)
	{
		SPKFlushPosition *pos =
			dlist_container(SPKFlushPosition, node, iter.cur);

		*write = pos->remote_end;

		if (pos->local_end <= local_flush)
		{
			*flush = pos->remote_end;
			dlist_delete(iter.cur);
			pfree(pos);
		}
		else
		{
			/*
			 * Don't want to uselessly iterate over the rest of the list which
			 * could potentially be long. Instead get the last element and
			 * grab the write position from there.
			 */
			pos = dlist_tail_element(SPKFlushPosition, node,
									 &lsn_mapping);
			*write = pos->remote_end;
			return false;
		}
	}

	return dlist_is_empty(&lsn_mapping);
}

/*
 * Send a Standby Status Update message to server.
 *
 * 'recvpos' is the latest LSN we've received data to, force is set if we need
 * to send a response to avoid timeouts.
 */
static bool
send_feedback(PGconn *conn, XLogRecPtr recvpos, int64 now, bool force)
{
	static StringInfo reply_message = NULL;

	static XLogRecPtr last_recvpos = InvalidXLogRecPtr;
	static XLogRecPtr last_writepos = InvalidXLogRecPtr;
	static XLogRecPtr last_flushpos = InvalidXLogRecPtr;

	XLogRecPtr	writepos;
	XLogRecPtr	flushpos;

	/* It's legal to not pass a recvpos */
	if (recvpos < last_recvpos)
		recvpos = last_recvpos;

	if (get_flush_position(&writepos, &flushpos))
	{
		/*
		 * No outstanding transactions to flush, we can report the latest
		 * received position. This is important for synchronous replication.
		 */
		flushpos = writepos = recvpos;
	}

	if (writepos < last_writepos)
		writepos = last_writepos;

	if (flushpos < last_flushpos)
		flushpos = last_flushpos;

	/* if we've already reported everything we're good */
	if (!force &&
		writepos == last_writepos &&
		flushpos == last_flushpos)
		return true;

	if (!reply_message)
	{
		MemoryContext oldcontext = MemoryContextSwitchTo(TopMemoryContext);

		reply_message = makeStringInfo();
		MemoryContextSwitchTo(oldcontext);
	}
	else
		resetStringInfo(reply_message);

	pq_sendbyte(reply_message, 'r');
	pq_sendint64(reply_message, recvpos);	/* write */
	pq_sendint64(reply_message, flushpos);	/* flush */
	pq_sendint64(reply_message, writepos);	/* apply */
	pq_sendint64(reply_message, now);	/* sendTime */
	pq_sendbyte(reply_message, false);	/* replyRequested */

	elog(DEBUG2, "SPOCK %s: sending feedback (force %d) to recv %X/%X, "
		 "write %X/%X, flush %X/%X",
		 MySubscription->name, force,
		 (uint32) (recvpos >> 32), (uint32) recvpos,
		 (uint32) (writepos >> 32), (uint32) writepos,
		 (uint32) (flushpos >> 32), (uint32) flushpos
		);

	if (PQputCopyData(conn, reply_message->data, reply_message->len) <= 0 ||
		PQflush(conn))
	{
		ereport(ERROR,
				(errcode(ERRCODE_CONNECTION_FAILURE),
				 errmsg("SPOCK %s: could not send feedback packet: %s",
						MySubscription->name, PQerrorMessage(conn))));
		return false;
	}

	if (recvpos > last_recvpos)
		last_recvpos = recvpos;
	if (writepos > last_writepos)
		last_writepos = writepos;
	if (flushpos > last_flushpos)
		last_flushpos = flushpos;

	return true;
}

/*
 * Apply main loop.
 */
void
apply_work(PGconn *streamConn)
{
	int			fd;
	char	   *copybuf = NULL;
	XLogRecPtr	last_received = InvalidXLogRecPtr;
	TimestampTz last_receive_timestamp = GetCurrentTimestamp();

	applyconn = streamConn;
	fd = PQsocket(applyconn);

	/* Init the MessageContext which we use for easier cleanup. */
	MessageContext = AllocSetContextCreate(TopMemoryContext,
										   "MessageContext",
										   ALLOCSET_DEFAULT_SIZES);

	MemoryContextSwitchTo(MessageContext);

	/* mark as idle, before starting to loop */
	pgstat_report_activity(STATE_IDLE, NULL);
	Assert(CurrentMemoryContext == MessageContext);

	while (!got_SIGTERM)
	{
		int			rc;
		int			r;

		/*
		 * Background workers mustn't call usleep() or any direct equivalent:
		 * instead, they may wait on their process latch, which sleeps as
		 * necessary, but is awakened if postmaster dies.  That way the
		 * background process goes away immediately in an emergency.
		 */
		rc = WaitLatchOrSocket(&MyProc->procLatch,
							   WL_SOCKET_READABLE | WL_LATCH_SET |
							   WL_TIMEOUT | WL_POSTMASTER_DEATH,
							   fd, 1000L);

		ResetLatch(&MyProc->procLatch);

		CHECK_FOR_INTERRUPTS();

		Assert(CurrentMemoryContext == MessageContext);

		if (ConfigReloadPending)
		{
			ConfigReloadPending = false;
			ProcessConfigFile(PGC_SIGHUP);
		}

		/* emergency bailout if postmaster has died */
		if (rc & WL_POSTMASTER_DEATH)
			proc_exit(1);

		if (rc & WL_SOCKET_READABLE)
			PQconsumeInput(applyconn);

		if (PQstatus(applyconn) == CONNECTION_BAD)
		{
			elog(ERROR, "SPOCK %s: connection to other side has died",
				 MySubscription->name);
		}

		/*
		 * The walsender is supposed to ping us for a status update every
		 * wal_sender_timeout / 2 milliseconds. If we don't get those, we
		 * assume that we have lost the connection.
		 *
		 * Note: keepalive configuration is supposed to cover this but is
		 * apparently unreliable.
		 */
		if (rc & WL_TIMEOUT)
		{
			TimestampTz timeout;

			timeout = TimestampTzPlusMilliseconds(last_receive_timestamp,
												  (wal_sender_timeout * 3) / 2);
			if (GetCurrentTimestamp() > timeout)
			{
				elog(ERROR, "SPOCK %s: terminating apply due to missing "
					 "walsender ping",
					 MySubscription->name);
			}
		}

		Assert(CurrentMemoryContext == MessageContext);

		for (;;)
		{
			if (got_SIGTERM)
				break;

			/* We must not have fallen out of MessageContext by accident */
			Assert(CurrentMemoryContext == MessageContext);

			Assert(copybuf == NULL);
			r = PQgetCopyData(applyconn, &copybuf, 1);

			if (r == -1)
			{
				elog(ERROR, "SPOCK %s: data stream ended",
					 MySubscription->name);
			}
			else if (r == -2)
			{
				elog(ERROR, "SPOCK %s: could not read COPY data: %s",
					 MySubscription->name,
					 PQerrorMessage(applyconn));
			}
			else if (r < 0)
				elog(ERROR, "SPOCK %s: invalid COPY status %d",
					 MySubscription->name, r);
			else if (r == 0)
			{
				/* need to wait for new data */
				break;
			}
			else
			{
				int			c;
				StringInfoData s;

				if (ConfigReloadPending)
				{
					ConfigReloadPending = false;
					ProcessConfigFile(PGC_SIGHUP);
				}

				last_receive_timestamp = GetCurrentTimestamp();

				/*
				 * We're using a StringInfo to wrap existing data here, as a
				 * cursor. We init it manually to avoid a redundant
				 * allocation.
				 */
				memset(&s, 0, sizeof(StringInfoData));
				s.data = copybuf;
				s.len = r;
				s.maxlen = -1;
				s.cursor = 0;

				c = pq_getmsgbyte(&s);

				if (c == 'w')
				{
					XLogRecPtr	start_lsn;
					XLogRecPtr	end_lsn;

					start_lsn = pq_getmsgint64(&s);
					end_lsn = pq_getmsgint64(&s);
					pq_getmsgint64(&s); /* sendTime */

					if (last_received < start_lsn)
						last_received = start_lsn;

					if (last_received < end_lsn)
						last_received = end_lsn;

					replication_handler(&s);
				}
				else if (c == 'k')
				{
					XLogRecPtr	endpos;
					bool		reply_requested;

					endpos = pq_getmsgint64(&s);
					 /* timestamp = */ pq_getmsgint64(&s);
					reply_requested = pq_getmsgbyte(&s);

					send_feedback(applyconn, endpos,
								  GetCurrentTimestamp(),
								  reply_requested);

					if (last_received < endpos)
						last_received = endpos;
				}
				/* other message types are purposefully ignored */

				/* copybuf is malloc'd not palloc'd */
				if (copybuf != NULL)
				{
					PQfreemem(copybuf);
					copybuf = NULL;
				}
			}

			/* We must not have fallen out of MessageContext by accident */
			Assert(CurrentMemoryContext == MessageContext);

			CHECK_FOR_INTERRUPTS();
		}

		if (xact_had_exception)
		{
			/*
			 * xact_had_exception implies that we are running under
			 * use_try_block == true. If this happens in SUB_DISABLE
			 * exception_behaviour, suspend the subscription here
			 * and suppress feedback.
			 */
			if (exception_behaviour == SUB_DISABLE)
			{
				SpockSubscription *sub;
				char errmsg[1024];

				sub = get_subscription_by_name(MySubscription->name, false);
				sub->enabled = false;
				alter_subscription(sub);

				snprintf(errmsg, sizeof(errmsg),
						 "disabling subscription %s due to exception(s) - "
						 "skip_lsn = %X/%X",
						 MySubscription->name,
						 LSN_FORMAT_ARGS(replorigin_session_origin_lsn));
				exception_command_counter++;
				add_entry_to_exception_log(remote_origin_id,
										   replorigin_session_origin_timestamp,
										   remote_xid,
										   0, 0,
										   NULL, NULL, NULL, NULL,
										   NULL, NULL,
										   "SUB_DISABLE",
										   errmsg);
				elog(WARNING, "SPOCK %s: disabling subscription due to"
							  " exceptions - origin_lsn=%X/%X",
					 MySubscription->name,
					 LSN_FORMAT_ARGS(replorigin_session_origin_lsn));
			}
		}
		else
		{
			/*
			 * If we did not encounter any exception only send feedback
			 * if exception_behaviour == DISCARD or we are not using a
			 * try block at all (default transaction mode). The reason
			 * for this is that in TRANSDISCARD or SUB_DISABLE modes this
			 * not having an exception during use_try_block would lead
			 * to silently skipping the transaction altogether.
			 */
			if (!MyApplyWorker->use_try_block ||
				exception_behaviour == DISCARD)
			{
				send_feedback(applyconn, last_received, GetCurrentTimestamp(),
							  false);
			}
		}

		if (!in_remote_transaction)
			process_syncing_tables(last_received);

		/* We must not have switched out of MessageContext by mistake */
		Assert(CurrentMemoryContext == MessageContext);

		/* Cleanup the memory. */
		MemoryContextReset(MessageContext);

		/*
		 * Only do a leak check if we're between txns; we don't want lots of
		 * noise due to resources that only exist in a txn.
		 */
		if (!IsTransactionState())
		{
			VALGRIND_DO_ADDED_LEAK_CHECK;
			pgstat_report_stat(true);
		}
	}
	elog(LOG, "SPOCK %s: falling out of apply_work() sigterm=%s",
		 MySubscription->name, (got_SIGTERM) ? "true" : "false");
}

/*
 * Add context to the errors produced by spock_execute_sql_command().
 */
static void
execute_sql_command_error_cb(void *arg)
{
	errcontext("during execution of queued SQL statement: %s", (char *) arg);
}

/*
 * Start skipping changes of the transaction if the given LSN matches the
 * LSN specified by subscription's skiplsn.
 */
static void
maybe_start_skipping_changes(XLogRecPtr finish_lsn)
{
	Assert(!is_skipping_changes());
	Assert(!in_remote_transaction);

	/*
	 * Quick return if it's not requested to skip this transaction. This
	 * function is called for every remote transaction and we assume that
	 * skipping the transaction is not used often.
	 */
	if (likely(XLogRecPtrIsInvalid(MySubscription->skiplsn) ||
			   MySubscription->skiplsn != finish_lsn))
		return;

	/* Start skipping all changes of this transaction */
	skip_xact_finish_lsn = finish_lsn;

	ereport(LOG,
			errmsg("SPOCK %s: logical replication starts skipping transaction at LSN %X/%X",
				   MySubscription->name, LSN_FORMAT_ARGS(skip_xact_finish_lsn)));
}

/*
 * Stop skipping changes by resetting skip_xact_finish_lsn if enabled.
 */
static void
stop_skipping_changes(void)
{
	if (!is_skipping_changes())
		return;

	ereport(LOG,
		(errmsg("SPOCK %s: logical replication completed skipping transaction at LSN %X/%X",
				MySubscription->name, LSN_FORMAT_ARGS(skip_xact_finish_lsn))));

	/* Stop skipping changes */
	skip_xact_finish_lsn = InvalidXLogRecPtr;
}

/*
 * Clear sub_skip_lsn of spock.subscription catalog.
 *
 * finish_lsn is the transaction's finish LSN that is used to check if the
 * sub_skip_lsn matches it. If not matched, we raise a warning when clearing the
 * sub_skip_lsn in order to inform users for cases e.g., where the user mistakenly
 * specified the wrong sub_skip_lsn.
 */
static void
clear_subscription_skip_lsn(XLogRecPtr finish_lsn)
{
	SpockSubscription *sub;
	XLogRecPtr	myskiplsn = MySubscription->skiplsn;
	bool		started_tx = false;

	if (likely(XLogRecPtrIsInvalid(myskiplsn)))
		return;

	if (!IsTransactionState())
	{
		StartTransactionCommand();
		started_tx = true;
	}

	sub = get_subscription(MySubscription->id);

	/*
	 * Clear the sub_skip_lsn. If the user has already changed sub_skip_lsn
	 * before clearing it we don't update the catalog and the replication origin
	 * state won't get advanced. So in the worst case, if the server crashes
	 * before sending an acknowledgment of the flush position the transaction
	 * will be sent again and the user needs to set subskiplsn again. We can
	 * reduce the possibility by logging a replication origin WAL record to
	 * advance the origin LSN instead but there is no way to advance the
	 * origin timestamp and it doesn't seem to be worth doing anything about
	 * it since it's a very rare case.
	 */
	if (sub->skiplsn == myskiplsn)
	{
		sub->skiplsn = LSNGetDatum(InvalidXLogRecPtr);
		alter_subscription(sub);

		if (myskiplsn != finish_lsn)
			ereport(WARNING,
					errmsg("skip-LSN of subscription \"%s\" cleared", MySubscription->name),
					errdetail("Remote transaction's finish WAL location (LSN) %X/%X did not match skip-LSN %X/%X.",
							  LSN_FORMAT_ARGS(finish_lsn),
							  LSN_FORMAT_ARGS(myskiplsn)));
		else
			ereport(WARNING,
					errmsg("skip-LSN of subscription \"%s\" cleared", MySubscription->name),
					errdetail("Remote transaction's finish WAL location (LSN) %X/%X equals skip-LSN %X/%X.",
							  LSN_FORMAT_ARGS(finish_lsn),
							  LSN_FORMAT_ARGS(myskiplsn)));
	}

	if (started_tx)
		CommitTransactionCommand();
}

/*
 * Execute an SQL command. This can be multiple multiple queries.
 */
void
spock_execute_sql_command(char *cmdstr, char *role, bool isTopLevel)
{
	const char *save_debug_query_string = debug_query_string;
	List	   *commands;
	ListCell   *command_i;
#ifdef PGXC
	List	   *commandSourceQueries;
	ListCell   *commandSourceQuery_i;
#endif
	MemoryContext oldcontext;
	ErrorContextCallback errcallback;

	oldcontext = MemoryContextSwitchTo(MessageContext);

	errcallback.callback = execute_sql_command_error_cb;
	errcallback.arg = cmdstr;
	errcallback.previous = error_context_stack;
	error_context_stack = &errcallback;

	debug_query_string = cmdstr;

	/*
	 * XL distributes individual statements using just executing them as plain
	 * SQL query and can't handle multistatements this way so we need to get
	 * individual statements using API provided by XL itself.
	 */
#ifdef PGXC
	commands = pg_parse_query_get_source(cmdstr, &commandSourceQueries);
#else
	commands = pg_parse_query(cmdstr);
#endif

	MemoryContextSwitchTo(oldcontext);

	/*
	 * Do a limited amount of safety checking against CONCURRENTLY commands
	 * executed in situations where they aren't allowed. The sender side
	 * should provide protection, but better be safe than sorry.
	 */
	isTopLevel = isTopLevel && (list_length(commands) == 1);

#ifdef PGXC
	forboth(command_i, commands, commandSourceQuery_i, commandSourceQueries)
#else
	foreach(command_i, commands)
#endif
	{
		List	   *plantree_list;
		List	   *querytree_list;
		RawStmt    *command = (RawStmt *) lfirst(command_i);
		CommandTag	commandTag;
		Portal		portal;
		int			save_nestlevel;
		DestReceiver *receiver;
		Oid			save_userid;
		int			save_sec_context;


#ifdef PGXC
		cmdstr = (char *) lfirst(commandSourceQuery_i);
		errcallback.arg = cmdstr;
#endif

		/* temporarily push snapshot for parse analysis/planning */
		PushActiveSnapshot(GetTransactionSnapshot());

		oldcontext = MemoryContextSwitchTo(MessageContext);

		/*
		 * Set the current role to the user that executed the command on the
		 * origin server.
		 */
		GetUserIdAndSecContext(&save_userid, &save_sec_context);
		SetUserIdAndSecContext(get_role_oid(role, false),
							   save_sec_context | SECURITY_LOCAL_USERID_CHANGE);
		save_nestlevel = NewGUCNestLevel();
		commandTag = CreateCommandTag(command);

		/*
		 * check if it's a DDL statement. we only do this for
		 * in_spock_replicate_ddl_command
		 */
		if (in_spock_replicate_ddl_command &&
			GetCommandLogLevel(command->stmt) != LOGSTMT_DDL)
		{
			ereport(ERROR,
					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
					 errmsg("spock.replicate_ddl() cannot execute %s statement",
							GetCommandTagName(commandTag))));
		}

		querytree_list = pg_analyze_and_rewrite(
												command,
												cmdstr,
												NULL, 0);

		plantree_list = pg_plan_queries(
										querytree_list, cmdstr, 0, NULL);

		PopActiveSnapshot();

		portal = CreatePortal("spock", true, true);
		PortalDefineQuery(portal, NULL,
						  cmdstr,
						  commandTag,
						  plantree_list, NULL);
		PortalStart(portal, NULL, 0, InvalidSnapshot);

		receiver = CreateDestReceiver(DestNone);

		(void) PortalRun(portal, FETCH_ALL,
						 isTopLevel,
						 receiver, receiver,
						 NULL);
		(*receiver->rDestroy) (receiver);

		PortalDrop(portal, false);

		CommandCounterIncrement();

		/*
		 * Restore the GUC variables we set above.
		 */
		AtEOXact_GUC(true, save_nestlevel);

		/* Restore previous session privileges */
		SetUserIdAndSecContext(save_userid, save_sec_context);

		MemoryContextSwitchTo(oldcontext);
	}

	/* protect against stack resets during CONCURRENTLY processing */
	if (error_context_stack == &errcallback)
		error_context_stack = errcallback.previous;

	debug_query_string = save_debug_query_string;
}

/*
 * Load list of tables currently pending sync.
 *
 * Must be inside transaction.
 */
static void
reread_unsynced_tables(Oid subid)
{
	MemoryContext saved_ctx;
	List	   *unsynced_tables;
	ListCell   *lc;

	/* Cleanup first. */
	list_free_deep(SyncingTables);
	SyncingTables = NIL;

	/* Read new state. */
	unsynced_tables = get_unsynced_tables(subid);
	saved_ctx = MemoryContextSwitchTo(TopMemoryContext);
	foreach(lc, unsynced_tables)
	{
		SpockSyncStatus *sync = palloc(sizeof(SpockSyncStatus));

		memcpy(sync, lfirst(lc), sizeof(SpockSyncStatus));
		SyncingTables = lappend(SyncingTables, sync);
	}

	MemoryContextSwitchTo(saved_ctx);
}

static void
process_syncing_tables(XLogRecPtr end_lsn)
{
	ListCell   *lc;

	Assert(CurrentMemoryContext == MessageContext);
	Assert(!IsTransactionState());

	/* First check if we need to update the cached information. */
	if (MyApplyWorker->sync_pending)
	{
		StartTransactionCommand();
		MyApplyWorker->sync_pending = false;
		reread_unsynced_tables(MyApplyWorker->subid);
		CommitTransactionCommand();
		MemoryContextSwitchTo(MessageContext);
	}

	/* Process currently pending sync tables. */
	if (list_length(SyncingTables) > 0)
	{
#if PG_VERSION_NUM < 130000
		ListCell   *prev = NULL;
		ListCell   *next;
#endif

#if PG_VERSION_NUM >= 130000
		foreach(lc, SyncingTables)
#else
		for (lc = list_head(SyncingTables); lc; lc = next)
#endif
		{
			SpockSyncStatus *sync = (SpockSyncStatus *) lfirst(lc);
			SpockSyncStatus *newsync;

#if PG_VERSION_NUM < 130000
			/* We might delete the cell so advance it now. */
			next = lnext(lc);
#endif

			StartTransactionCommand();
			newsync = get_table_sync_status(MyApplyWorker->subid,
											NameStr(sync->nspname),
											NameStr(sync->relname), true);

			/*
			 * TODO: what to do here? We don't really want to die, but this
			 * can mean many things, for now we just assume table is not
			 * relevant for us anymore and leave fixing to the user.
			 *
			 * The reason why this part happens in transaction is that the
			 * memory allocated for sync info will get automatically cleaned
			 * afterwards.
			 */
			if (!newsync)
			{
				sync->status = SYNC_STATUS_READY;
				sync->statuslsn = InvalidXLogRecPtr;
			}
			else
				memcpy(sync, newsync, sizeof(SpockSyncStatus));
			CommitTransactionCommand();
			MemoryContextSwitchTo(MessageContext);

			if (sync->status == SYNC_STATUS_SYNCWAIT)
			{
				SpockWorker *worker;

				LWLockAcquire(SpockCtx->lock, LW_EXCLUSIVE);
				worker = spock_sync_find(MyDatabaseId,
										 MyApplyWorker->subid,
										 NameStr(sync->nspname),
										 NameStr(sync->relname));

				if (spock_worker_running(worker) &&
					end_lsn >= worker->worker.apply.replay_stop_lsn)
				{
					worker->worker.apply.replay_stop_lsn = end_lsn;
					sync->status = SYNC_STATUS_CATCHUP;

					StartTransactionCommand();
					set_table_sync_status(MyApplyWorker->subid,
										  NameStr(sync->nspname),
										  NameStr(sync->relname),
										  sync->status,
										  sync->statuslsn);
					CommitTransactionCommand();
					MemoryContextSwitchTo(MessageContext);

					if (spock_worker_running(worker))
						SetLatch(&worker->proc->procLatch);
					LWLockRelease(SpockCtx->lock);

					if (wait_for_sync_status_change(MyApplyWorker->subid,
													NameStr(sync->nspname),
													NameStr(sync->relname),
													SYNC_STATUS_SYNCDONE,
													&sync->statuslsn))
						sync->status = SYNC_STATUS_SYNCDONE;
				}
				else
					LWLockRelease(SpockCtx->lock);
			}

			if (sync->status == SYNC_STATUS_SYNCDONE &&
				end_lsn >= sync->statuslsn)
			{
				sync->status = SYNC_STATUS_READY;
				sync->statuslsn = end_lsn;

				StartTransactionCommand();
				set_table_sync_status(MyApplyWorker->subid,
									  NameStr(sync->nspname),
									  NameStr(sync->relname),
									  sync->status,
									  sync->statuslsn);
				CommitTransactionCommand();
				MemoryContextSwitchTo(MessageContext);
			}

			/* Ready? Remove it from local cache. */
			if (sync->status == SYNC_STATUS_READY)
			{
#if PG_VERSION_NUM >= 130000
				SyncingTables = foreach_delete_current(SyncingTables, lc);
#else
				SyncingTables = list_delete_cell(SyncingTables, lc, prev);
#endif
				pfree(sync);
			}
			else
			{
#if PG_VERSION_NUM < 130000
				prev = lc;
#endif
			}
		}
	}

	/*
	 * If there are still pending tables for synchronization, launch the sync
	 * worker.
	 */
	foreach(lc, SyncingTables)
	{
		List	   *workers;
		ListCell   *wlc;
		int			nworkers = 0;
		SpockSyncStatus *sync = (SpockSyncStatus *) lfirst(lc);

		if (sync->status == SYNC_STATUS_SYNCDONE || sync->status == SYNC_STATUS_READY)
			continue;

		LWLockAcquire(SpockCtx->lock, LW_EXCLUSIVE);
		workers = spock_sync_find_all(MyDatabaseId, MyApplyWorker->subid);
		foreach(wlc, workers)
		{
			SpockWorker *worker = (SpockWorker *) lfirst(wlc);

			if (spock_worker_running(worker))
				nworkers++;
		}
		LWLockRelease(SpockCtx->lock);

		if (nworkers < 1)
		{
			start_sync_worker(&sync->nspname, &sync->relname);
			break;
		}
	}

	Assert(CurrentMemoryContext == MessageContext);
}

static void
start_sync_worker(Name nspname, Name relname)
{
	SpockWorker worker;

	/* Start the sync worker. */
	memset(&worker, 0, sizeof(SpockWorker));
	worker.worker_type = SPOCK_WORKER_SYNC;
	worker.dboid = MySpockWorker->dboid;
	worker.worker.apply.subid = MyApplyWorker->subid;
	worker.worker.apply.sync_pending = false;	/* Makes no sense for sync
												 * worker. */

	/* Tell the worker to stop at current position. */
	worker.worker.sync.apply.replay_stop_lsn = replorigin_session_origin_lsn;
	memcpy(&worker.worker.sync.nspname, nspname, sizeof(NameData));
	memcpy(&worker.worker.sync.relname, relname, sizeof(NameData));

	(void) spock_worker_register(&worker);
}

static inline TimeOffset
interval_to_timeoffset(const Interval *interval)
{
	TimeOffset	span;

	span = interval->time;

#ifdef HAVE_INT64_TIMESTAMP
	span += interval->month * INT64CONST(30) * USECS_PER_DAY;
	span += interval->day * INT64CONST(24) * USECS_PER_HOUR;
#else
	span += interval->month * ((double) DAYS_PER_MONTH * SECS_PER_DAY);
	span += interval->day * ((double) HOURS_PER_DAY * SECS_PER_HOUR);
#endif

	return span;
}

void
spock_apply_main(Datum main_arg)
{
	int			slot = DatumGetInt32(main_arg);
	PGconn	   *streamConn;
	RepOriginId originid;
	XLogRecPtr	origin_startpos;
	MemoryContext saved_ctx;
	char	   *repsets;
	char	   *origins;

	/* Setup shmem. */
	spock_worker_attach(slot, SPOCK_WORKER_APPLY);
	Assert(MySpockWorker->worker_type == SPOCK_WORKER_APPLY);
	MyApplyWorker = &MySpockWorker->worker.apply;

	/* Attach to dsm segment. */
	Assert(CurrentResourceOwner == NULL);
	CurrentResourceOwner = ResourceOwnerCreate(NULL, "spock apply");

	/* Load correct apply API. */
	if (spock_use_spi)
	{
		if (spock_conflict_resolver != SPOCK_RESOLVE_ERROR)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
					 errmsg("SPOCK %s: spock.use_spi can only be used when "
							"spock.conflict_resolution is set to 'error'",
							MySubscription->name)));

		apply_api.on_begin = spock_apply_spi_begin;
		apply_api.on_commit = spock_apply_spi_commit;
		apply_api.do_insert = spock_apply_spi_insert;
		apply_api.do_update = spock_apply_spi_update;
		apply_api.do_delete = spock_apply_spi_delete;
		apply_api.can_multi_insert = spock_apply_spi_can_mi;
		apply_api.multi_insert_add_tuple = spock_apply_spi_mi_add_tuple;
		apply_api.multi_insert_finish = spock_apply_spi_mi_finish;
	}

	/* Setup synchronous commit according to the user's wishes */
	SetConfigOption("synchronous_commit",
					spock_synchronous_commit ? "local" : "off",
					PGC_BACKEND, PGC_S_OVERRIDE);	/* other context? */

	/* Run as replica session replication role. */
	SetConfigOption("session_replication_role", "replica",
					PGC_SUSET, PGC_S_OVERRIDE); /* other context? */

	/*
	 * Disable function body checks during replay. That's necessary because a)
	 * the creator of the function might have had it disabled b) the function
	 * might be search_path dependant and we don't fix the contents of
	 * functions.
	 */
	SetConfigOption("check_function_bodies", "off",
					PGC_INTERNAL, PGC_S_OVERRIDE);

	/* Load the subscription. */
	StartTransactionCommand();
	saved_ctx = MemoryContextSwitchTo(TopMemoryContext);
	MySubscription = get_subscription(MyApplyWorker->subid);
	MemoryContextSwitchTo(saved_ctx);

#ifdef XCP

	/*
	 * When runnin under XL, initialise the XL executor so that the datanode
	 * and coordinator information is initialised properly.
	 */
	InitMultinodeExecutor(false);
#endif
	CommitTransactionCommand();

	elog(DEBUG1, "SPOCK %s: starting apply worker", MySubscription->name);

	/* Set apply delay if any. */
	if (MySubscription->apply_delay)
		apply_delay =
			interval_to_timeoffset(MySubscription->apply_delay) / 1000;

	/* If the subscription isn't initialized yet, initialize it. */
	spock_sync_subscription(MySubscription);

	elog(DEBUG1, "SPOCK %s: connecting to provider %s, dsn %s",
		 MySubscription->name,
		 MySubscription->origin->name, MySubscription->origin_if->dsn);

	/*
	 * Cache the queue relation id. TODO: invalidation
	 */
	StartTransactionCommand();
	QueueRelid = get_queue_table_oid();

	originid = replorigin_by_name(MySubscription->slot_name, false);
	elog(DEBUG2, "SPOCK %s: setting up replication origin %s (oid %u)",
		 MySubscription->name,
		 MySubscription->slot_name, originid);
	replorigin_session_setup(originid);
	replorigin_session_origin = originid;
	origin_startpos = replorigin_session_get_progress(false);

	/* Start the replication. */
	streamConn = spock_connect_replica(MySubscription->origin_if->dsn,
									   MySubscription->slot_name, NULL);

	repsets = stringlist_to_identifierstr(MySubscription->replication_sets);
	origins = stringlist_to_identifierstr(MySubscription->forward_origins);

	/*
	 * IDENTIFY_SYSTEM sets up some internal state on walsender so call it
	 * even if we don't (yet) want to use any of the results.
	 */
	spock_identify_system(streamConn, NULL, NULL, NULL, NULL);

	spock_start_replication(streamConn, MySubscription->slot_name,
							origin_startpos, origins, repsets, NULL,
							MySubscription->force_text_transfer);
	pfree(repsets);

	CommitTransactionCommand();

	/*
	 * Do an initial leak check with reporting off; we don't want to see these
	 * results, just the later output from ADDED leak checks.
	 */
	VALGRIND_DISABLE_ERROR_REPORTING;
	VALGRIND_DO_LEAK_CHECK;
	VALGRIND_ENABLE_ERROR_REPORTING;

	apply_work(streamConn);

	PQfinish(streamConn);

	/* We should only get here if we received sigTERM */
	proc_exit(0);
}