Logical replication

- Add PUBLICATION catalogs and DDL - Add SUBSCRIPTION catalog and DDL - Define logical replication protocol and output plugin - Add logical replication workers From: Petr Jelinek <petr@2ndquadrant.com> Reviewed-by: Steve Singer <steve@ssinger.info> Reviewed-by: Andres Freund <andres@anarazel.de> Reviewed-by: Erik Rijkers <er@xs4all.nl> Reviewed-by: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
2025-11-03 09:13:20 +03:00 · 2017-01-19 12:00:00 -05:00
parent ba61a04bc7
commit 665d1fad99
119 changed files with 13354 additions and 95 deletions
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -0,0 +1,759 @@
+/*-------------------------------------------------------------------------
+ * launcher.c
+ *	   PostgreSQL logical replication worker launcher process
+ *
+ * Copyright (c) 2012-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/launcher.c
+ *
+ * NOTES
+ *	  This module contains the logical replication worker launcher which
+ *	  uses the background worker infrastructure to start the logical
+ *	  replication workers for every enabled subscription.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "funcapi.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+
+#include "access/heapam.h"
+#include "access/htup.h"
+#include "access/htup_details.h"
+#include "access/xact.h"
+
+#include "catalog/pg_subscription.h"
+
+#include "libpq/pqsignal.h"
+
+#include "postmaster/bgworker.h"
+#include "postmaster/fork_process.h"
+#include "postmaster/postmaster.h"
+
+#include "replication/logicallauncher.h"
+#include "replication/logicalworker.h"
+#include "replication/slot.h"
+#include "replication/worker_internal.h"
+
+#include "storage/ipc.h"
+#include "storage/proc.h"
+#include "storage/procarray.h"
+#include "storage/procsignal.h"
+
+#include "tcop/tcopprot.h"
+
+#include "utils/memutils.h"
+#include "utils/pg_lsn.h"
+#include "utils/ps_status.h"
+#include "utils/timeout.h"
+#include "utils/snapmgr.h"
+
+/* max sleep time between cycles (3min) */
+#define DEFAULT_NAPTIME_PER_CYCLE 180000L
+
+int	max_logical_replication_workers = 4;
+LogicalRepWorker *MyLogicalRepWorker = NULL;
+
+typedef struct LogicalRepCtxStruct
+{
+	/* Supervisor process. */
+	pid_t		launcher_pid;
+
+	/* Background workers. */
+	LogicalRepWorker	workers[FLEXIBLE_ARRAY_MEMBER];
+} LogicalRepCtxStruct;
+
+LogicalRepCtxStruct *LogicalRepCtx;
+
+static void logicalrep_worker_onexit(int code, Datum arg);
+static void logicalrep_worker_detach(void);
+
+bool		got_SIGTERM = false;
+static bool	on_commit_laucher_wakeup = false;
+
+Datum pg_stat_get_subscription(PG_FUNCTION_ARGS);
+
+
+/*
+ * Load the list of subscriptions.
+ *
+ * Only the fields interesting for worker start/stop functions are filled for
+ * each subscription.
+ */
+static List *
+get_subscription_list(void)
+{
+	List	   *res = NIL;
+	Relation	rel;
+	HeapScanDesc scan;
+	HeapTuple	tup;
+	MemoryContext resultcxt;
+
+	/* This is the context that we will allocate our output data in */
+	resultcxt = CurrentMemoryContext;
+
+	/*
+	 * Start a transaction so we can access pg_database, and get a snapshot.
+	 * We don't have a use for the snapshot itself, but we're interested in
+	 * the secondary effect that it sets RecentGlobalXmin.  (This is critical
+	 * for anything that reads heap pages, because HOT may decide to prune
+	 * them even if the process doesn't attempt to modify any tuples.)
+	 */
+	StartTransactionCommand();
+	(void) GetTransactionSnapshot();
+
+	rel = heap_open(SubscriptionRelationId, AccessShareLock);
+	scan = heap_beginscan_catalog(rel, 0, NULL);
+
+	while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))
+	{
+		Form_pg_subscription subform = (Form_pg_subscription) GETSTRUCT(tup);
+		Subscription   *sub;
+		MemoryContext	oldcxt;
+
+		/*
+		 * Allocate our results in the caller's context, not the
+		 * transaction's. We do this inside the loop, and restore the original
+		 * context at the end, so that leaky things like heap_getnext() are
+		 * not called in a potentially long-lived context.
+		 */
+		oldcxt = MemoryContextSwitchTo(resultcxt);
+
+		sub = (Subscription *) palloc(sizeof(Subscription));
+		sub->oid = HeapTupleGetOid(tup);
+		sub->dbid = subform->subdbid;
+		sub->owner = subform->subowner;
+		sub->enabled = subform->subenabled;
+		sub->name = pstrdup(NameStr(subform->subname));
+
+		/* We don't fill fields we are not interested in. */
+		sub->conninfo = NULL;
+		sub->slotname = NULL;
+		sub->publications = NIL;
+
+		res = lappend(res, sub);
+		MemoryContextSwitchTo(oldcxt);
+	}
+
+	heap_endscan(scan);
+	heap_close(rel, AccessShareLock);
+
+	CommitTransactionCommand();
+
+	return res;
+}
+
+/*
+ * Wait for a background worker to start up and attach to the shmem context.
+ *
+ * This is like WaitForBackgroundWorkerStartup(), except that we wait for
+ * attaching, not just start and we also just exit if postmaster died.
+ */
+static bool
+WaitForReplicationWorkerAttach(LogicalRepWorker *worker,
+							   BackgroundWorkerHandle *handle)
+{
+	BgwHandleStatus status;
+	int			rc;
+
+	for (;;)
+	{
+		pid_t		pid;
+
+		CHECK_FOR_INTERRUPTS();
+
+		status = GetBackgroundWorkerPid(handle, &pid);
+
+		/*
+		 * Worker started and attached to our shmem. This check is safe
+		 * because only laucher ever starts the workers, so nobody can steal
+		 * the worker slot.
+		 */
+		if (status == BGWH_STARTED && worker->proc)
+			return true;
+		/* Worker didn't start or died before attaching to our shmem. */
+		if (status == BGWH_STOPPED)
+			return false;
+
+		/*
+		 * We need timeout because we generaly don't get notified via latch
+		 * about the worker attach.
+		 */
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+					   1000L, WAIT_EVENT_BGWORKER_STARTUP);
+
+		if (rc & WL_POSTMASTER_DEATH)
+			proc_exit(1);
+
+		ResetLatch(MyLatch);
+	}
+
+	return false;
+}
+
+/*
+ * Walks the workers array and searches for one that matches given
+ * subscription id.
+ */
+LogicalRepWorker *
+logicalrep_worker_find(Oid subid)
+{
+	int	i;
+	LogicalRepWorker   *res = NULL;
+
+	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+	/* Search for attached worker for a given subscription id. */
+	for (i = 0; i < max_logical_replication_workers; i++)
+	{
+		LogicalRepWorker   *w = &LogicalRepCtx->workers[i];
+		if (w->subid == subid && w->proc && IsBackendPid(w->proc->pid))
+		{
+			res = w;
+			break;
+		}
+	}
+
+	return res;
+}
+
+/*
+ * Start new apply background worker.
+ */
+void
+logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname, Oid userid)
+{
+	BackgroundWorker	bgw;
+	BackgroundWorkerHandle *bgw_handle;
+	int					slot;
+	LogicalRepWorker   *worker = NULL;
+
+	ereport(LOG,
+			(errmsg("starting logical replication worker for subscription \"%s\"",
+					subname)));
+
+	/* Report this after the initial starting message for consistency. */
+	if (max_replication_slots == 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+				 errmsg("cannot start logical replication workers when max_replication_slots = 0")));
+
+	/*
+	 * We need to do the modification of the shared memory under lock so that
+	 * we have consistent view.
+	 */
+	LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
+
+	/* Find unused worker slot. */
+	for (slot = 0; slot < max_logical_replication_workers; slot++)
+	{
+		if (!LogicalRepCtx->workers[slot].proc)
+		{
+			worker = &LogicalRepCtx->workers[slot];
+			break;
+		}
+	}
+
+	/* Bail if not found */
+	if (worker == NULL)
+	{
+		ereport(WARNING,
+				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+				 errmsg("out of logical replication workers slots"),
+				 errhint("You might need to increase max_logical_replication_workers.")));
+		return;
+	}
+
+	/* Prepare the worker info. */
+	memset(worker, 0, sizeof(LogicalRepWorker));
+	worker->dbid = dbid;
+	worker->userid = userid;
+	worker->subid = subid;
+
+	LWLockRelease(LogicalRepWorkerLock);
+
+	/* Register the new dynamic worker. */
+	bgw.bgw_flags =	BGWORKER_SHMEM_ACCESS |
+		BGWORKER_BACKEND_DATABASE_CONNECTION;
+	bgw.bgw_start_time = BgWorkerStart_RecoveryFinished;
+	bgw.bgw_main = ApplyWorkerMain;
+	snprintf(bgw.bgw_name, BGW_MAXLEN,
+			 "logical replication worker for subscription %u", subid);
+
+	bgw.bgw_restart_time = BGW_NEVER_RESTART;
+	bgw.bgw_notify_pid = MyProcPid;
+	bgw.bgw_main_arg = slot;
+
+	if (!RegisterDynamicBackgroundWorker(&bgw, &bgw_handle))
+	{
+		ereport(WARNING,
+				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+				 errmsg("out of background workers slots"),
+				 errhint("You might need to increase max_worker_processes.")));
+		return;
+	}
+
+	/* Now wait until it attaches. */
+	WaitForReplicationWorkerAttach(worker, bgw_handle);
+}
+
+/*
+ * Stop the logical replication worker and wait until it detaches from the
+ * slot.
+ *
+ * The caller must hold LogicalRepLauncherLock to ensure that new workers are
+ * not being started during this function call.
+ */
+void
+logicalrep_worker_stop(Oid subid)
+{
+	LogicalRepWorker *worker;
+
+	Assert(LWLockHeldByMe(LogicalRepLauncherLock));
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+	worker = logicalrep_worker_find(subid);
+
+	/* No worker, nothing to do. */
+	if (!worker)
+	{
+		LWLockRelease(LogicalRepWorkerLock);
+		return;
+	}
+
+	/*
+	 * If we found worker but it does not have proc set it is starting up,
+	 * wait for it to finish and then kill it.
+	 */
+	while (worker && !worker->proc)
+	{
+		int	rc;
+
+		LWLockRelease(LogicalRepWorkerLock);
+
+		CHECK_FOR_INTERRUPTS();
+
+		/* Wait for signal. */
+		rc = WaitLatch(&MyProc->procLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+					   1000L, WAIT_EVENT_BGWORKER_STARTUP);
+
+		/* emergency bailout if postmaster has died */
+		if (rc & WL_POSTMASTER_DEATH)
+			proc_exit(1);
+
+		ResetLatch(&MyProc->procLatch);
+
+		/* Check if the worker has started. */
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		worker = logicalrep_worker_find(subid);
+		if (!worker || worker->proc)
+			break;
+	}
+
+	/* Now terminate the worker ... */
+	kill(worker->proc->pid, SIGTERM);
+	LWLockRelease(LogicalRepWorkerLock);
+
+	/* ... and wait for it to die. */
+	for (;;)
+	{
+		int	rc;
+
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		if (!worker->proc)
+		{
+			LWLockRelease(LogicalRepWorkerLock);
+			break;
+		}
+		LWLockRelease(LogicalRepWorkerLock);
+
+		CHECK_FOR_INTERRUPTS();
+
+		/* Wait for more work. */
+		rc = WaitLatch(&MyProc->procLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+					   1000L, WAIT_EVENT_BGWORKER_SHUTDOWN);
+
+		/* emergency bailout if postmaster has died */
+		if (rc & WL_POSTMASTER_DEATH)
+			proc_exit(1);
+
+		ResetLatch(&MyProc->procLatch);
+	}
+}
+
+/*
+ * Attach to a slot.
+ */
+void
+logicalrep_worker_attach(int slot)
+{
+	/* Block concurrent access. */
+	LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
+
+	Assert(slot >= 0 && slot < max_logical_replication_workers);
+	MyLogicalRepWorker = &LogicalRepCtx->workers[slot];
+
+	if (MyLogicalRepWorker->proc)
+		ereport(ERROR,
+			   (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("logical replication worker slot %d already used by "
+					   "another worker", slot)));
+
+	MyLogicalRepWorker->proc = MyProc;
+	before_shmem_exit(logicalrep_worker_onexit, (Datum) 0);
+
+	LWLockRelease(LogicalRepWorkerLock);
+}
+
+/*
+ * Detach the worker (cleans up the worker info).
+ */
+static void
+logicalrep_worker_detach(void)
+{
+	/* Block concurrent access. */
+	LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
+
+	MyLogicalRepWorker->dbid = InvalidOid;
+	MyLogicalRepWorker->userid = InvalidOid;
+	MyLogicalRepWorker->subid = InvalidOid;
+	MyLogicalRepWorker->proc = NULL;
+
+	LWLockRelease(LogicalRepWorkerLock);
+}
+
+/*
+ * Cleanup function.
+ *
+ * Called on logical replication worker exit.
+ */
+static void
+logicalrep_worker_onexit(int code, Datum arg)
+{
+	logicalrep_worker_detach();
+}
+
+/* SIGTERM: set flag to exit at next convenient time */
+void
+logicalrep_worker_sigterm(SIGNAL_ARGS)
+{
+	got_SIGTERM = true;
+
+	/* Waken anything waiting on the process latch */
+	SetLatch(MyLatch);
+}
+
+/*
+ * ApplyLauncherShmemSize
+ *		Compute space needed for replication launcher shared memory
+ */
+Size
+ApplyLauncherShmemSize(void)
+{
+	Size		size;
+
+	/*
+	 * Need the fixed struct and the array of LogicalRepWorker.
+	 */
+	size = sizeof(LogicalRepCtxStruct);
+	size = MAXALIGN(size);
+	size = add_size(size, mul_size(max_logical_replication_workers,
+								   sizeof(LogicalRepWorker)));
+	return size;
+}
+
+void
+ApplyLauncherRegister(void)
+{
+	BackgroundWorker bgw;
+
+	if (max_logical_replication_workers == 0)
+		return;
+
+	bgw.bgw_flags =	BGWORKER_SHMEM_ACCESS |
+		BGWORKER_BACKEND_DATABASE_CONNECTION;
+	bgw.bgw_start_time = BgWorkerStart_RecoveryFinished;
+	bgw.bgw_main = ApplyLauncherMain;
+	snprintf(bgw.bgw_name, BGW_MAXLEN,
+			 "logical replication launcher");
+	bgw.bgw_restart_time = 5;
+	bgw.bgw_notify_pid = 0;
+	bgw.bgw_main_arg = (Datum) 0;
+
+	RegisterBackgroundWorker(&bgw);
+}
+
+/*
+ * ApplyLauncherShmemInit
+ *		Allocate and initialize replication launcher shared memory
+ */
+void
+ApplyLauncherShmemInit(void)
+{
+	bool		found;
+
+	LogicalRepCtx = (LogicalRepCtxStruct *)
+		ShmemInitStruct("Logical Replication Launcher Data",
+						ApplyLauncherShmemSize(),
+						&found);
+
+	if (!found)
+		memset(LogicalRepCtx, 0, ApplyLauncherShmemSize());
+}
+
+/*
+ * Wakeup the launcher on commit if requested.
+ */
+void
+AtCommit_ApplyLauncher(void)
+{
+	if (on_commit_laucher_wakeup)
+		ApplyLauncherWakeup();
+}
+
+/*
+ * Request wakeup of the launcher on commit of the transaction.
+ *
+ * This is used to send launcher signal to stop sleeping and proccess the
+ * subscriptions when current transaction commits. Should be used when new
+ * tuple was added to the pg_subscription catalog.
+*/
+void
+ApplyLauncherWakeupAtCommit(void)
+{
+	if (!on_commit_laucher_wakeup)
+		on_commit_laucher_wakeup = true;
+}
+
+void
+ApplyLauncherWakeup(void)
+{
+	if (IsBackendPid(LogicalRepCtx->launcher_pid))
+		kill(LogicalRepCtx->launcher_pid, SIGUSR1);
+}
+
+/*
+ * Main loop for the apply launcher process.
+ */
+void
+ApplyLauncherMain(Datum main_arg)
+{
+	ereport(LOG,
+			(errmsg("logical replication launcher started")));
+
+	/* Establish signal handlers. */
+	pqsignal(SIGTERM, logicalrep_worker_sigterm);
+	BackgroundWorkerUnblockSignals();
+
+	/* Make it easy to identify our processes. */
+	SetConfigOption("application_name", MyBgworkerEntry->bgw_name,
+					PGC_USERSET, PGC_S_SESSION);
+
+	LogicalRepCtx->launcher_pid = MyProcPid;
+
+	/*
+	 * Establish connection to nailed catalogs (we only ever access
+	 * pg_subscription).
+	 */
+	BackgroundWorkerInitializeConnection(NULL, NULL);
+
+	/* Enter main loop */
+	while (!got_SIGTERM)
+	{
+		int			rc;
+		List	   *sublist;
+		ListCell   *lc;
+		MemoryContext	subctx;
+		MemoryContext	oldctx;
+		TimestampTz		now;
+		TimestampTz		last_start_time = 0;
+		long			wait_time = DEFAULT_NAPTIME_PER_CYCLE;
+
+		now = GetCurrentTimestamp();
+
+		/* Limit the start retry to once a wal_retrieve_retry_interval */
+		if (TimestampDifferenceExceeds(last_start_time, now,
+									   wal_retrieve_retry_interval))
+		{
+			/* Use temporary context for the database list and worker info. */
+			subctx = AllocSetContextCreate(TopMemoryContext,
+										   "Logical Replication Launcher sublist",
+										   ALLOCSET_DEFAULT_MINSIZE,
+										   ALLOCSET_DEFAULT_INITSIZE,
+										   ALLOCSET_DEFAULT_MAXSIZE);
+			oldctx = MemoryContextSwitchTo(subctx);
+
+			/* Block any concurrent DROP SUBSCRIPTION. */
+			LWLockAcquire(LogicalRepLauncherLock, LW_EXCLUSIVE);
+
+			/* search for subscriptions to start or stop. */
+			sublist = get_subscription_list();
+
+			/* Start the missing workers for enabled subscriptions. */
+			foreach(lc, sublist)
+			{
+				Subscription	   *sub = (Subscription *) lfirst(lc);
+				LogicalRepWorker   *w;
+
+				LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+				w = logicalrep_worker_find(sub->oid);
+				LWLockRelease(LogicalRepWorkerLock);
+
+				if (sub->enabled && w == NULL)
+				{
+					logicalrep_worker_launch(sub->dbid, sub->oid, sub->name, sub->owner);
+					last_start_time = now;
+					wait_time = wal_retrieve_retry_interval;
+					/* Limit to one worker per mainloop cycle. */
+					break;
+				}
+			}
+
+			LWLockRelease(LogicalRepLauncherLock);
+
+			/* Switch back to original memory context. */
+			MemoryContextSwitchTo(oldctx);
+			/* Clean the temporary memory. */
+			MemoryContextDelete(subctx);
+		}
+		else
+		{
+			/*
+			 * The wait in previous cycle was interruped in less than
+			 * wal_retrieve_retry_interval since last worker was started,
+			 * this usually means crash of the worker, so we should retry
+			 * in wal_retrieve_retry_interval again.
+			 */
+			wait_time = wal_retrieve_retry_interval;
+		}
+
+		/* Wait for more work. */
+		rc = WaitLatch(&MyProc->procLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+					   wait_time,
+					   WAIT_EVENT_LOGICAL_LAUNCHER_MAIN);
+
+		/* emergency bailout if postmaster has died */
+		if (rc & WL_POSTMASTER_DEATH)
+			proc_exit(1);
+
+		ResetLatch(&MyProc->procLatch);
+	}
+
+	LogicalRepCtx->launcher_pid = 0;
+
+	/* ... and if it returns, we're done */
+	ereport(LOG,
+			(errmsg("logical replication launcher shutting down")));
+
+	proc_exit(0);
+}
+
+/*
+ * Returns state of the subscriptions.
+ */
+Datum
+pg_stat_get_subscription(PG_FUNCTION_ARGS)
+{
+#define PG_STAT_GET_SUBSCRIPTION_COLS	7
+	Oid			subid = PG_ARGISNULL(0) ? InvalidOid : PG_GETARG_OID(0);
+	int			i;
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	TupleDesc	tupdesc;
+	Tuplestorestate *tupstore;
+	MemoryContext per_query_ctx;
+	MemoryContext oldcontext;
+
+	/* check to see if caller supports us returning a tuplestore */
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not " \
+						"allowed in this context")));
+
+	/* Build a tuple descriptor for our result type */
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+	oldcontext = MemoryContextSwitchTo(per_query_ctx);
+
+	tupstore = tuplestore_begin_heap(true, false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = tupdesc;
+
+	MemoryContextSwitchTo(oldcontext);
+
+	/* Make sure we get consistent view of the workers. */
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+	for (i = 0; i <= max_logical_replication_workers; i++)
+	{
+		/* for each row */
+		Datum		values[PG_STAT_GET_SUBSCRIPTION_COLS];
+		bool		nulls[PG_STAT_GET_SUBSCRIPTION_COLS];
+		int			worker_pid;
+		LogicalRepWorker	worker;
+
+		memcpy(&worker, &LogicalRepCtx->workers[i],
+			   sizeof(LogicalRepWorker));
+		if (!worker.proc || !IsBackendPid(worker.proc->pid))
+			continue;
+
+		if (OidIsValid(subid) && worker.subid != subid)
+			continue;
+
+		worker_pid = worker.proc->pid;
+
+		MemSet(values, 0, sizeof(values));
+		MemSet(nulls, 0, sizeof(nulls));
+
+		values[0] = ObjectIdGetDatum(worker.subid);
+		values[1] = Int32GetDatum(worker_pid);
+		if (XLogRecPtrIsInvalid(worker.last_lsn))
+			nulls[2] = true;
+		else
+			values[2] = LSNGetDatum(worker.last_lsn);
+		if (worker.last_send_time == 0)
+			nulls[3] = true;
+		else
+			values[3] = TimestampTzGetDatum(worker.last_send_time);
+		if (worker.last_recv_time == 0)
+			nulls[4] = true;
+		else
+			values[4] = TimestampTzGetDatum(worker.last_recv_time);
+		if (XLogRecPtrIsInvalid(worker.reply_lsn))
+			nulls[5] = true;
+		else
+			values[5] = LSNGetDatum(worker.reply_lsn);
+		if (worker.reply_time == 0)
+			nulls[6] = true;
+		else
+			values[6] = TimestampTzGetDatum(worker.reply_time);
+
+		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+
+		/* If only a single subscription was requested, and we found it, break. */
+		if (OidIsValid(subid))
+			break;
+	}
+
+	LWLockRelease(LogicalRepWorkerLock);
+
+	/* clean up and return the tuplestore */
+	tuplestore_donestoring(tupstore);
+
+	return (Datum) 0;
+}