From b7773f7f72a4d7e301834a2d2876dccfe75a45d0 Mon Sep 17 00:00:00 2001
From: Shveta Malik <shveta.malik@gmail.com>
Date: Tue, 19 Sep 2023 09:41:01 +0530
Subject: [PATCH v19 2/2] Add logical slot sync capability to physical standby

This patch implements synchronization of logical replication slots
from the primary server to the physical standby so that logical
subscribers are not blocked after failover. All the logical
replication slots on the primary (assuming configurations are
appropriate) are automatically created on the physical standbys and
are synced periodically. Slot-sync worker(s) on the standby server
ping the primary at regular intervals to get the necessary logical
slot information and create/update the slots locally.

A new GUC 'max_slotsync_workers' defines the maximum number of
slot-sync workers on the standby. This parameter can only be set at
server start.

Now the replication launcher on the physical standby queries primary
to get the list of dbids that belong to the slots mentioned in GUC
'synchronize_slot_names'. Once it gets the dbids, if dbids <
max_slotsync_workers, it starts only that many workers and if
dbids > max_slotsync_workers, it starts max_slotsync_workers and
divides the work equally among them. Each worker is then responsible
to keep on syncing the logical slots belonging to the DBs assigned to it.

For example, let's say the slots mentioned in 'synchronize_slot_names' on
the primary belongs to 4 DBs and say 'max_slotsync_workers' is 4, then a new
worker will be launched for each db. If a new logical slot with a different
DB is found by replication launcher, it will assign this new db to the worker
handling the minimum number of dbs currently (or first worker in case of equal
count).

Each slot-sync worker will have its own dbids list. Since the upper limit
of this dbid-count is not known, it needs to be handled using dsa. We
initially allocate memory to hold 100 dbids for each worker. If this limit
is exhausted, we reallocate this memory with size incremented again by 100.

The nap time of worker is tuned according to the activity on the primary.
Each worker starts with nap time of 10ms and if no activity is observed on
the primary for some time, then nap time is increased to 10sec. And if
activity is observed again, nap time is reduced back to 10ms. Each worker
uses one slot (first one assigned to it) for monitoring purpose. If there
is no change in lsn of that slot for some threshold time, nap time is
increased to 10sec and as soon as a change is observed, nap time is reduced
back to 10ms.

The logical slots created by slot-sync workers on physical standbys are
not allowed to be consumed. Any attempt to do pg_logical_slot_get_changes
on such slots will result in an error.

If a logical slot is invalidated on the primary, slot on the standby is also
invalidated. If a logical slot on the primary is valid but is invalidated
on the standby due to conflict (say required rows removed on the primary),
then that slot is dropped and recreated on the standby in next sync-cycle.
It is okay to recreate such slots as long as these are not consumable on the
standby (which is the case currently).

If there is any change in synchronize_slot_names, then the slots that are
no longer part of it or the ones that no longer exist on the primary will
be dropped by slot-sync workers on the physical standbys.
---
 doc/src/sgml/config.sgml                      |   28 +
 src/backend/postmaster/bgworker.c             |    3 +
 .../libpqwalreceiver/libpqwalreceiver.c       |  119 ++
 src/backend/replication/logical/Makefile      |    1 +
 .../replication/logical/applyparallelworker.c |    3 +-
 src/backend/replication/logical/launcher.c    |  878 ++++++++++++--
 .../replication/logical/logicalfuncs.c        |   13 +
 src/backend/replication/logical/meson.build   |    1 +
 src/backend/replication/logical/slotsync.c    | 1039 +++++++++++++++++
 src/backend/replication/logical/tablesync.c   |    5 +-
 src/backend/replication/repl_gram.y           |   32 +-
 src/backend/replication/repl_scanner.l        |    2 +
 src/backend/replication/slot.c                |    3 +-
 src/backend/replication/slotfuncs.c           |   29 +
 src/backend/replication/walsender.c           |  121 ++
 src/backend/storage/lmgr/lwlock.c             |    2 +
 src/backend/storage/lmgr/lwlocknames.txt      |    1 +
 .../utils/activity/wait_event_names.txt       |    1 +
 src/backend/utils/misc/guc_tables.c           |   16 +
 src/backend/utils/misc/postgresql.conf.sample |    2 +
 src/include/catalog/pg_proc.dat               |    4 +
 src/include/commands/subscriptioncmds.h       |    4 +
 src/include/nodes/replnodes.h                 |    9 +
 src/include/postmaster/bgworker_internals.h   |    1 +
 src/include/replication/logicallauncher.h     |    4 +
 src/include/replication/logicalworker.h       |    1 +
 src/include/replication/slot.h                |    7 +-
 src/include/replication/walreceiver.h         |   33 +
 src/include/replication/worker_internal.h     |   60 +-
 src/include/storage/lwlock.h                  |    1 +
 src/tools/pgindent/typedefs.list              |    5 +
 31 files changed, 2304 insertions(+), 124 deletions(-)
 create mode 100644 src/backend/replication/logical/slotsync.c
 mode change 100644 => 100755 src/backend/replication/walsender.c

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3d81bd308c..8abc685015 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5015,6 +5015,34 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-max-slotsync-workers" xreflabel="max_slotsync_workers">
+      <term><varname>max_slotsync_workers</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>max_slotsync_workers</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies maximum number of slot synchronization workers.
+       </para>
+       <para>
+        Slot synchronization workers are taken from the pool defined by
+        <varname>max_worker_processes</varname>.
+       </para>
+       <para>
+        The default value is 2. This parameter can only be set at server
+        start.
+       </para>
+       <para>
+        The slot-sync workers are needed for synchronization of logical replication
+        slots from the primary server to the physical standby so that logical
+        subscribers are not blocked after failover. Slot-sync workers need
+        <varname>synchronize_slot_names</varname> to be configured correctly in
+        order to synchronize the logical replication slots.
+       </para>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
     </sect2>
 
diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
index 505e38376c..1df23a99c5 100644
--- a/src/backend/postmaster/bgworker.c
+++ b/src/backend/postmaster/bgworker.c
@@ -129,6 +129,9 @@ static const struct
 	{
 		"ApplyWorkerMain", ApplyWorkerMain
 	},
+	{
+		"ReplSlotSyncWorkerMain", ReplSlotSyncWorkerMain
+	},
 	{
 		"ParallelApplyWorkerMain", ParallelApplyWorkerMain
 	},
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 60d5c1fc40..bb943b4331 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -34,6 +34,7 @@
 #include "utils/memutils.h"
 #include "utils/pg_lsn.h"
 #include "utils/tuplestore.h"
+#include "utils/varlena.h"
 
 PG_MODULE_MAGIC;
 
@@ -58,6 +59,9 @@ static void libpqrcv_get_senderinfo(WalReceiverConn *conn,
 									char **sender_host, int *sender_port);
 static char *libpqrcv_identify_system(WalReceiverConn *conn,
 									  TimeLineID *primary_tli);
+static List *libpqrcv_get_dbinfo_for_logical_slots(WalReceiverConn *conn,
+												   const char *slot_names);
+static char *libpqrcv_get_dbname_from_conninfo(const char *conninfo);
 static int	libpqrcv_server_version(WalReceiverConn *conn);
 static void libpqrcv_readtimelinehistoryfile(WalReceiverConn *conn,
 											 TimeLineID tli, char **filename,
@@ -96,6 +100,8 @@ static WalReceiverFunctionsType PQWalReceiverFunctions = {
 	.walrcv_receive = libpqrcv_receive,
 	.walrcv_send = libpqrcv_send,
 	.walrcv_create_slot = libpqrcv_create_slot,
+	.walrcv_get_dbinfo_for_logical_slots = libpqrcv_get_dbinfo_for_logical_slots,
+	.walrcv_get_dbname_from_conninfo = libpqrcv_get_dbname_from_conninfo,
 	.walrcv_get_backend_pid = libpqrcv_get_backend_pid,
 	.walrcv_exec = libpqrcv_exec,
 	.walrcv_disconnect = libpqrcv_disconnect
@@ -409,6 +415,119 @@ libpqrcv_server_version(WalReceiverConn *conn)
 	return PQserverVersion(conn->streamConn);
 }
 
+/*
+ * Get DB info for logical slots
+ *
+ * It gets the DBIDs for slot_names from primary. The list returned
+ * by LIST_DBID_FOR_LOGICAL_SLOTS has no duplicates.
+ */
+static List *
+libpqrcv_get_dbinfo_for_logical_slots(WalReceiverConn *conn,
+									  const char *slot_names)
+{
+	PGresult   *res;
+	List	   *slotlist = NIL;
+	int			ntuples;
+	StringInfoData s;
+	WalRcvRepSlotDbData *slot_data;
+
+	initStringInfo(&s);
+	appendStringInfoString(&s, "LIST_DBID_FOR_LOGICAL_SLOTS");
+
+	if (strcmp(slot_names, "") != 0 && strcmp(slot_names, "*") != 0)
+	{
+		char	   *rawnames;
+		List	   *namelist;
+		ListCell   *lc;
+
+		appendStringInfoChar(&s, ' ');
+		rawnames = pstrdup(slot_names);
+		SplitIdentifierString(rawnames, ',', &namelist);
+		foreach(lc, namelist)
+		{
+			if (lc != list_head(namelist))
+				appendStringInfoChar(&s, ',');
+			appendStringInfo(&s, "%s",
+							 quote_identifier(lfirst(lc)));
+		}
+	}
+
+	res = libpqrcv_PQexec(conn->streamConn, s.data);
+	pfree(s.data);
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		PQclear(res);
+		ereport(ERROR,
+				(errmsg("could not receive list of slots from the primary server: %s",
+						pchomp(PQerrorMessage(conn->streamConn)))));
+	}
+	if (PQnfields(res) != 1)
+	{
+		int			nfields = PQnfields(res);
+
+		PQclear(res);
+		ereport(ERROR,
+				(errmsg("invalid response from primary server"),
+				 errdetail("Could not get list of slots: got %d fields, "
+						   "expected 1", nfields)));
+	}
+
+	ntuples = PQntuples(res);
+	for (int i = 0; i < ntuples; i++)
+	{
+		slot_data = palloc0(sizeof(WalRcvRepSlotDbData));
+		if (!PQgetisnull(res, i, 0))
+			slot_data->database = atooid(PQgetvalue(res, i, 0));
+
+		slotlist = lappend(slotlist, slot_data);
+	}
+
+	PQclear(res);
+
+	return slotlist;
+}
+
+/*
+ * Get database name from primary conninfo.
+ *
+ * If dbanme is not found in connInfo, return NULL value.
+ * The caller should take care of handling NULL value.
+ */
+static char *
+libpqrcv_get_dbname_from_conninfo(const char *connInfo)
+{
+	PQconninfoOption *opts;
+	PQconninfoOption *opt;
+	char	   *dbname = NULL;
+	char	   *err = NULL;
+
+	opts = PQconninfoParse(connInfo, &err);
+	if (opts == NULL)
+	{
+		/* The error string is malloc'd, so we must free it explicitly */
+		char	   *errcopy = err ? pstrdup(err) : "out of memory";
+
+		PQfreemem(err);
+		ereport(ERROR,
+				(errcode(ERRCODE_SYNTAX_ERROR),
+				 errmsg("invalid connection string syntax: %s", errcopy)));
+	}
+
+	for (opt = opts; opt->keyword != NULL; ++opt)
+	{
+		/* Ignore connection options that are not present. */
+		if (opt->val == NULL)
+			continue;
+
+		if (strcmp(opt->keyword, "dbname") == 0 && opt->val[0] != '\0')
+		{
+			dbname = pstrdup(opt->val);
+		}
+	}
+
+	return dbname;
+}
+
 /*
  * Start streaming WAL data from given streaming options.
  *
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 2dc25e37bb..ba03eeff1c 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -25,6 +25,7 @@ OBJS = \
 	proto.o \
 	relation.o \
 	reorderbuffer.o \
+	slotsync.o \
 	snapbuild.o \
 	tablesync.o \
 	worker.o
diff --git a/src/backend/replication/logical/applyparallelworker.c b/src/backend/replication/logical/applyparallelworker.c
index 82f48a488e..ea461e7ef1 100644
--- a/src/backend/replication/logical/applyparallelworker.c
+++ b/src/backend/replication/logical/applyparallelworker.c
@@ -925,7 +925,8 @@ ParallelApplyWorkerMain(Datum main_arg)
 	before_shmem_exit(pa_shutdown, PointerGetDatum(seg));
 
 	SpinLockAcquire(&MyParallelShared->mutex);
-	MyParallelShared->logicalrep_worker_generation = MyLogicalRepWorker->generation;
+	MyParallelShared->logicalrep_worker_generation =
+								MyLogicalRepWorker->hdr.generation;
 	MyParallelShared->logicalrep_worker_slot_no = worker_slot;
 	SpinLockRelease(&MyParallelShared->mutex);
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 7882fc91ce..56c615810e 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -22,6 +22,7 @@
 #include "access/htup_details.h"
 #include "access/tableam.h"
 #include "access/xact.h"
+#include "catalog/pg_authid.h"
 #include "catalog/pg_subscription.h"
 #include "catalog/pg_subscription_rel.h"
 #include "funcapi.h"
@@ -57,6 +58,21 @@
 int			max_logical_replication_workers = 4;
 int			max_sync_workers_per_subscription = 2;
 int			max_parallel_apply_workers_per_subscription = 2;
+int			max_slotsync_workers = 2;
+
+/*
+ * Initial allocation size for dbids array for each SlotSyncWorker in dynamic
+ * shared memory.
+ */
+#define DB_PER_WORKER_ALLOC_INIT 100
+
+/*
+ * Once initially allocated size is exhausted for dbids array, it is extended by
+ * DB_PER_WORKER_ALLOC_EXTRA size.
+ */
+#define DB_PER_WORKER_ALLOC_EXTRA 100
+
+SlotSyncWorker *MySlotSyncWorker = NULL;
 
 LogicalRepWorker *MyLogicalRepWorker = NULL;
 
@@ -70,6 +86,7 @@ typedef struct LogicalRepCtxStruct
 	dshash_table_handle last_start_dsh;
 
 	/* Background workers. */
+	SlotSyncWorker *ss_workers; /* slot-sync workers */
 	LogicalRepWorker workers[FLEXIBLE_ARRAY_MEMBER];
 } LogicalRepCtxStruct;
 
@@ -102,6 +119,7 @@ static void logicalrep_launcher_onexit(int code, Datum arg);
 static void logicalrep_worker_onexit(int code, Datum arg);
 static void logicalrep_worker_detach(void);
 static void logicalrep_worker_cleanup(LogicalRepWorker *worker);
+static void slotsync_worker_cleanup(SlotSyncWorker *worker);
 static int	logicalrep_pa_worker_count(Oid subid);
 static void logicalrep_launcher_attach_dshmem(void);
 static void ApplyLauncherSetWorkerStartTime(Oid subid, TimestampTz start_time);
@@ -178,6 +196,8 @@ get_subscription_list(void)
 }
 
 /*
+ * This is common code for logical workers and slotsync workers.
+ *
  * Wait for a background worker to start up and attach to the shmem context.
  *
  * This is only needed for cleaning up the shared memory in case the worker
@@ -186,12 +206,14 @@ get_subscription_list(void)
  * Returns whether the attach was successful.
  */
 static bool
-WaitForReplicationWorkerAttach(LogicalRepWorker *worker,
+WaitForReplicationWorkerAttach(LogicalWorkerHeader *worker,
 							   uint16 generation,
-							   BackgroundWorkerHandle *handle)
+							   BackgroundWorkerHandle *handle,
+							   LWLock *lock)
 {
 	BgwHandleStatus status;
 	int			rc;
+	bool		is_slotsync_worker = (lock == SlotSyncWorkerLock) ? true : false;
 
 	for (;;)
 	{
@@ -199,27 +221,32 @@ WaitForReplicationWorkerAttach(LogicalRepWorker *worker,
 
 		CHECK_FOR_INTERRUPTS();
 
-		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		LWLockAcquire(lock, LW_SHARED);
 
 		/* Worker either died or has started. Return false if died. */
 		if (!worker->in_use || worker->proc)
 		{
-			LWLockRelease(LogicalRepWorkerLock);
+			LWLockRelease(lock);
 			return worker->in_use;
 		}
 
-		LWLockRelease(LogicalRepWorkerLock);
+		LWLockRelease(lock);
 
 		/* Check if worker has died before attaching, and clean up after it. */
 		status = GetBackgroundWorkerPid(handle, &pid);
 
 		if (status == BGWH_STOPPED)
 		{
-			LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
+			LWLockAcquire(lock, LW_EXCLUSIVE);
 			/* Ensure that this was indeed the worker we waited for. */
 			if (generation == worker->generation)
-				logicalrep_worker_cleanup(worker);
-			LWLockRelease(LogicalRepWorkerLock);
+			{
+				if (is_slotsync_worker)
+					slotsync_worker_cleanup((SlotSyncWorker *) worker);
+				else
+					logicalrep_worker_cleanup((LogicalRepWorker *) worker);
+			}
+			LWLockRelease(lock);
 			return false;
 		}
 
@@ -262,8 +289,8 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
 		if (isParallelApplyWorker(w))
 			continue;
 
-		if (w->in_use && w->subid == subid && w->relid == relid &&
-			(!only_running || w->proc))
+		if (w->hdr.in_use && w->subid == subid && w->relid == relid &&
+			(!only_running || w->hdr.proc))
 		{
 			res = w;
 			break;
@@ -290,7 +317,8 @@ logicalrep_workers_find(Oid subid, bool only_running)
 	{
 		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
 
-		if (w->in_use && w->subid == subid && (!only_running || w->proc))
+		if (w->hdr.in_use && w->subid == subid &&
+			(!only_running || w->hdr.proc))
 			res = lappend(res, w);
 	}
 
@@ -351,7 +379,7 @@ retry:
 	{
 		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
 
-		if (!w->in_use)
+		if (!w->hdr.in_use)
 		{
 			worker = w;
 			slot = i;
@@ -380,8 +408,8 @@ retry:
 			 * If the worker was marked in use but didn't manage to attach in
 			 * time, clean it up.
 			 */
-			if (w->in_use && !w->proc &&
-				TimestampDifferenceExceeds(w->launch_time, now,
+			if (w->hdr.in_use && !w->hdr.proc &&
+				TimestampDifferenceExceeds(w->hdr.launch_time, now,
 										   wal_receiver_timeout))
 			{
 				elog(WARNING,
@@ -437,10 +465,10 @@ retry:
 
 	/* Prepare the worker slot. */
 	worker->type = wtype;
-	worker->launch_time = now;
-	worker->in_use = true;
-	worker->generation++;
-	worker->proc = NULL;
+	worker->hdr.launch_time = now;
+	worker->hdr.in_use = true;
+	worker->hdr.generation++;
+	worker->hdr.proc = NULL;
 	worker->dbid = dbid;
 	worker->userid = userid;
 	worker->subid = subid;
@@ -457,7 +485,7 @@ retry:
 	TIMESTAMP_NOBEGIN(worker->reply_time);
 
 	/* Before releasing lock, remember generation for future identification. */
-	generation = worker->generation;
+	generation = worker->hdr.generation;
 
 	LWLockRelease(LogicalRepWorkerLock);
 
@@ -510,7 +538,7 @@ retry:
 	{
 		/* Failed to start worker, so clean up the worker slot. */
 		LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
-		Assert(generation == worker->generation);
+		Assert(generation == worker->hdr.generation);
 		logicalrep_worker_cleanup(worker);
 		LWLockRelease(LogicalRepWorkerLock);
 
@@ -522,19 +550,23 @@ retry:
 	}
 
 	/* Now wait until it attaches. */
-	return WaitForReplicationWorkerAttach(worker, generation, bgw_handle);
+	return WaitForReplicationWorkerAttach((LogicalWorkerHeader *) worker,
+										  generation,
+										  bgw_handle,
+										  LogicalRepWorkerLock);
 }
 
 /*
  * Internal function to stop the worker and wait until it detaches from the
- * slot.
+ * slot. It is used for both logical rep workers and slot-sync workers.
  */
 static void
-logicalrep_worker_stop_internal(LogicalRepWorker *worker, int signo)
+logicalrep_worker_stop_internal(LogicalWorkerHeader *worker, int signo,
+								LWLock *lock)
 {
 	uint16		generation;
 
-	Assert(LWLockHeldByMeInMode(LogicalRepWorkerLock, LW_SHARED));
+	Assert(LWLockHeldByMeInMode(lock, LW_SHARED));
 
 	/*
 	 * Remember which generation was our worker so we can check if what we see
@@ -550,7 +582,7 @@ logicalrep_worker_stop_internal(LogicalRepWorker *worker, int signo)
 	{
 		int			rc;
 
-		LWLockRelease(LogicalRepWorkerLock);
+		LWLockRelease(lock);
 
 		/* Wait a bit --- we don't expect to have to wait long. */
 		rc = WaitLatch(MyLatch,
@@ -564,7 +596,7 @@ logicalrep_worker_stop_internal(LogicalRepWorker *worker, int signo)
 		}
 
 		/* Recheck worker status. */
-		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		LWLockAcquire(lock, LW_SHARED);
 
 		/*
 		 * Check whether the worker slot is no longer used, which would mean
@@ -591,7 +623,7 @@ logicalrep_worker_stop_internal(LogicalRepWorker *worker, int signo)
 		if (!worker->proc || worker->generation != generation)
 			break;
 
-		LWLockRelease(LogicalRepWorkerLock);
+		LWLockRelease(lock);
 
 		/* Wait a bit --- we don't expect to have to wait long. */
 		rc = WaitLatch(MyLatch,
@@ -604,7 +636,7 @@ logicalrep_worker_stop_internal(LogicalRepWorker *worker, int signo)
 			CHECK_FOR_INTERRUPTS();
 		}
 
-		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		LWLockAcquire(lock, LW_SHARED);
 	}
 }
 
@@ -623,7 +655,9 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	if (worker)
 	{
 		Assert(!isParallelApplyWorker(worker));
-		logicalrep_worker_stop_internal(worker, SIGTERM);
+		logicalrep_worker_stop_internal((LogicalWorkerHeader *) worker,
+										SIGTERM,
+										LogicalRepWorkerLock);
 	}
 
 	LWLockRelease(LogicalRepWorkerLock);
@@ -669,8 +703,10 @@ logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo)
 	/*
 	 * Only stop the worker if the generation matches and the worker is alive.
 	 */
-	if (worker->generation == generation && worker->proc)
-		logicalrep_worker_stop_internal(worker, SIGINT);
+	if (worker->hdr.generation == generation && worker->hdr.proc)
+		logicalrep_worker_stop_internal((LogicalWorkerHeader *) worker,
+										SIGINT,
+										LogicalRepWorkerLock);
 
 	LWLockRelease(LogicalRepWorkerLock);
 }
@@ -696,14 +732,14 @@ logicalrep_worker_wakeup(Oid subid, Oid relid)
 /*
  * Wake up (using latch) the specified logical replication worker.
  *
- * Caller must hold lock, else worker->proc could change under us.
+ * Caller must hold lock, else worker->hdr.proc could change under us.
  */
 void
 logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker)
 {
 	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
-	SetLatch(&worker->proc->procLatch);
+	SetLatch(&worker->hdr.proc->procLatch);
 }
 
 /*
@@ -718,7 +754,7 @@ logicalrep_worker_attach(int slot)
 	Assert(slot >= 0 && slot < max_logical_replication_workers);
 	MyLogicalRepWorker = &LogicalRepCtx->workers[slot];
 
-	if (!MyLogicalRepWorker->in_use)
+	if (!MyLogicalRepWorker->hdr.in_use)
 	{
 		LWLockRelease(LogicalRepWorkerLock);
 		ereport(ERROR,
@@ -727,7 +763,7 @@ logicalrep_worker_attach(int slot)
 						slot)));
 	}
 
-	if (MyLogicalRepWorker->proc)
+	if (MyLogicalRepWorker->hdr.proc)
 	{
 		LWLockRelease(LogicalRepWorkerLock);
 		ereport(ERROR,
@@ -736,7 +772,7 @@ logicalrep_worker_attach(int slot)
 						"another worker, cannot attach", slot)));
 	}
 
-	MyLogicalRepWorker->proc = MyProc;
+	MyLogicalRepWorker->hdr.proc = MyProc;
 	before_shmem_exit(logicalrep_worker_onexit, (Datum) 0);
 
 	LWLockRelease(LogicalRepWorkerLock);
@@ -771,7 +807,9 @@ logicalrep_worker_detach(void)
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
 
 			if (isParallelApplyWorker(w))
-				logicalrep_worker_stop_internal(w, SIGTERM);
+				logicalrep_worker_stop_internal((LogicalWorkerHeader *) w,
+												SIGTERM,
+												LogicalRepWorkerLock);
 		}
 
 		LWLockRelease(LogicalRepWorkerLock);
@@ -794,10 +832,10 @@ logicalrep_worker_cleanup(LogicalRepWorker *worker)
 	Assert(LWLockHeldByMeInMode(LogicalRepWorkerLock, LW_EXCLUSIVE));
 
 	worker->type = WORKERTYPE_UNKNOWN;
-	worker->in_use = false;
-	worker->proc = NULL;
-	worker->dbid = InvalidOid;
+	worker->hdr.in_use = false;
+	worker->hdr.proc = NULL;
 	worker->userid = InvalidOid;
+	worker->dbid = InvalidOid;
 	worker->subid = InvalidOid;
 	worker->relid = InvalidOid;
 	worker->leader_pid = InvalidPid;
@@ -931,7 +969,16 @@ ApplyLauncherRegister(void)
 	memset(&bgw, 0, sizeof(bgw));
 	bgw.bgw_flags = BGWORKER_SHMEM_ACCESS |
 		BGWORKER_BACKEND_DATABASE_CONNECTION;
-	bgw.bgw_start_time = BgWorkerStart_RecoveryFinished;
+
+	/*
+	 * The launcher now takes care of launching both logical apply workers and
+	 * logical slot-sync workers. Thus to cater to the requirements of both,
+	 * start it as soon as a consistent state is reached. This will help
+	 * slot-sync workers to start timely on a physical standby while on a
+	 * non-standby server, it holds same meaning as that of
+	 * BgWorkerStart_RecoveryFinished.
+	 */
+	bgw.bgw_start_time = BgWorkerStart_ConsistentState;
 	snprintf(bgw.bgw_library_name, MAXPGPATH, "postgres");
 	snprintf(bgw.bgw_function_name, BGW_MAXLEN, "ApplyLauncherMain");
 	snprintf(bgw.bgw_name, BGW_MAXLEN,
@@ -953,6 +1000,7 @@ void
 ApplyLauncherShmemInit(void)
 {
 	bool		found;
+	Size		ssw_size;
 
 	LogicalRepCtx = (LogicalRepCtxStruct *)
 		ShmemInitStruct("Logical Replication Launcher Data",
@@ -977,6 +1025,14 @@ ApplyLauncherShmemInit(void)
 			SpinLockInit(&worker->relmutex);
 		}
 	}
+
+	/* Allocate shared-memory for slot-sync workers pool now */
+	ssw_size = mul_size(max_slotsync_workers, sizeof(SlotSyncWorker));
+	LogicalRepCtx->ss_workers = (SlotSyncWorker *)
+		ShmemInitStruct("Replication slot-sync workers", ssw_size, &found);
+
+	if (!found)
+		memset(LogicalRepCtx->ss_workers, 0, ssw_size);
 }
 
 /*
@@ -1114,12 +1170,669 @@ ApplyLauncherWakeup(void)
 		kill(LogicalRepCtx->launcher_pid, SIGUSR1);
 }
 
+/*
+ * Clean up slot-sync worker info.
+ */
+static void
+slotsync_worker_cleanup(SlotSyncWorker *worker)
+{
+	Assert(LWLockHeldByMeInMode(SlotSyncWorkerLock, LW_EXCLUSIVE));
+
+	worker->hdr.in_use = false;
+	worker->hdr.proc = NULL;
+	worker->slot = -1;
+
+	if (DsaPointerIsValid(worker->dbids_dp))
+	{
+		dsa_free(worker->dbids_dsa, worker->dbids_dp);
+		worker->dbids_dp = InvalidDsaPointer;
+	}
+
+	if (worker->dbids_dsa)
+	{
+		dsa_detach(worker->dbids_dsa);
+		worker->dbids_dsa = NULL;
+	}
+
+	worker->dbcount = 0;
+
+	MemSet(NameStr(worker->monitoring_info.slot_name), 0, NAMEDATALEN);
+	worker->monitoring_info.confirmed_lsn = 0;
+	worker->monitoring_info.last_update_time = 0;
+}
+
+/*
+ * Attach Slot-sync worker to worker-slot assigned by launcher.
+ */
+void
+slotsync_worker_attach(int slot)
+{
+	/* Block concurrent access. */
+	LWLockAcquire(SlotSyncWorkerLock, LW_EXCLUSIVE);
+
+	Assert(slot >= 0 && slot < max_slotsync_workers);
+	MySlotSyncWorker = &LogicalRepCtx->ss_workers[slot];
+	MySlotSyncWorker->slot = slot;
+
+	if (!MySlotSyncWorker->hdr.in_use)
+	{
+		LWLockRelease(SlotSyncWorkerLock);
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("replication slot-sync worker slot %d is "
+						"empty, cannot attach", slot)));
+	}
+
+	if (MySlotSyncWorker->hdr.proc)
+	{
+		LWLockRelease(SlotSyncWorkerLock);
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("replication slot-sync worker slot %d is "
+						"already used by another worker, cannot attach", slot)));
+	}
+
+	MySlotSyncWorker->hdr.proc = MyProc;
+
+	LWLockRelease(SlotSyncWorkerLock);
+}
+
+/*
+ * Slot-Sync worker find.
+ *
+ * Walks the slot-sync workers pool and searches for one that matches given
+ * dbid. Since one worker can manage multiple dbs, so it walks the db array in
+ * each worker to find the match.
+ */
+static SlotSyncWorker *
+slotsync_worker_find(Oid dbid)
+{
+	int			i;
+	SlotSyncWorker *res = NULL;
+	Oid		   *dbids;
+
+	Assert(LWLockHeldByMeInMode(SlotSyncWorkerLock, LW_SHARED));
+
+	/* Search for attached worker for a given dbid */
+	for (i = 0; i < max_slotsync_workers; i++)
+	{
+		SlotSyncWorker *w = &LogicalRepCtx->ss_workers[i];
+		int			cnt;
+
+		if (!w->hdr.in_use)
+			continue;
+
+		dbids = (Oid *) dsa_get_address(w->dbids_dsa, w->dbids_dp);
+		for (cnt = 0; cnt < w->dbcount; cnt++)
+		{
+			Oid			wdbid = dbids[cnt];
+
+			if (wdbid == dbid)
+			{
+				res = w;
+				break;
+			}
+		}
+
+		/* If worker is found, break the outer loop */
+		if (res)
+			break;
+	}
+
+	return res;
+}
+
+/*
+ * Setup DSA for slot-sync worker.
+ *
+ * DSA is needed for dbids array. Since max number of dbs a worker can manage
+ * is not known, so initially fixed size to hold DB_PER_WORKER_ALLOC_INIT
+ * dbs is allocated. If this size is exhausted, it can be extended using
+ * dsa free and allocate routines.
+ */
+static dsa_handle
+slotsync_dsa_setup(SlotSyncWorker *worker, int alloc_db_count)
+{
+	dsa_area   *dbids_dsa;
+	dsa_pointer dbids_dp;
+	dsa_handle	dbids_dsa_handle;
+	MemoryContext oldcontext;
+
+	/* Be sure any memory allocated by DSA routines is persistent. */
+	oldcontext = MemoryContextSwitchTo(TopMemoryContext);
+
+	dbids_dsa = dsa_create(LWTRANCHE_SLOTSYNC_DSA);
+	dsa_pin(dbids_dsa);
+	dsa_pin_mapping(dbids_dsa);
+
+	dbids_dp = dsa_allocate0(dbids_dsa, alloc_db_count * sizeof(Oid));
+
+	/* Set-up worker */
+	worker->dbcount = 0;
+	worker->dbids_dsa = dbids_dsa;
+	worker->dbids_dp = dbids_dp;
+
+	/* Get the handle. This is the one which can be passed to worker processes */
+	dbids_dsa_handle = dsa_get_handle(dbids_dsa);
+
+	ereport(DEBUG1,
+			(errmsg("allocated dsa for slot-sync worker for dbcount: %d",
+					alloc_db_count)));
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return dbids_dsa_handle;
+}
+
+/*
+ * Slot-sync worker launch or reuse
+ *
+ * Start new slot-sync background worker from the pool of available workers
+ * going by max_slotsync_workers count. If the worker pool is exhausted,
+ * reuse the existing worker with minimum number of dbs. The idea is to
+ * always distribute the dbs equally among launched workers.
+ * If initially allocated dbids array is exhausted for the selected worker,
+ * reallocate the dbids array with increased size and copy the existing
+ * dbids to it and assign the new one as well.
+ *
+ * Returns true on success, false on failure.
+ */
+static bool
+slotsync_worker_launch_or_reuse(Oid dbid)
+{
+	BackgroundWorker bgw;
+	BackgroundWorkerHandle *bgw_handle;
+	uint16		generation;
+	SlotSyncWorker *worker = NULL;
+	uint32		mindbcnt = 0;
+	uint32		alloc_count = 0;
+	uint32		copied_dbcnt = 0;
+	Oid		   *copied_dbids = NULL;
+	int			worker_slot = -1;
+	dsa_handle	handle;
+	Oid		   *dbids;
+	int			i;
+	bool		attach;
+
+	Assert(OidIsValid(dbid));
+
+	/*
+	 * We need to do the modification of the shared memory under lock so that
+	 * we have consistent view.
+	 */
+	LWLockAcquire(SlotSyncWorkerLock, LW_EXCLUSIVE);
+
+	/* Find unused worker slot. */
+	for (i = 0; i < max_slotsync_workers; i++)
+	{
+		SlotSyncWorker *w = &LogicalRepCtx->ss_workers[i];
+
+		if (!w->hdr.in_use)
+		{
+			worker = w;
+			worker_slot = i;
+			break;
+		}
+	}
+
+	/*
+	 * If all the workers are currently in use. Find the one with minimum
+	 * number of dbs and use that.
+	 */
+	if (!worker)
+	{
+		for (i = 0; i < max_slotsync_workers; i++)
+		{
+			SlotSyncWorker *w = &LogicalRepCtx->ss_workers[i];
+
+			if (i == 0)
+			{
+				mindbcnt = w->dbcount;
+				worker = w;
+				worker_slot = i;
+			}
+			else if (w->dbcount < mindbcnt)
+			{
+				mindbcnt = w->dbcount;
+				worker = w;
+				worker_slot = i;
+			}
+		}
+	}
+
+	/*
+	 * If worker is being reused, and there is vacancy in dbids array, just
+	 * update dbids array and dbcount and we are done. But if dbids array is
+	 * exhausted, reallocate dbids using dsa and copy the old dbids and assign
+	 * the new one as well.
+	 */
+	if (worker->hdr.in_use)
+	{
+		dbids = (Oid *) dsa_get_address(worker->dbids_dsa, worker->dbids_dp);
+
+		if (worker->dbcount < DB_PER_WORKER_ALLOC_INIT)
+		{
+			dbids[worker->dbcount++] = dbid;
+		}
+		else
+		{
+			MemoryContext oldcontext;
+
+			/* Be sure any memory allocated by DSA routines is persistent. */
+			oldcontext = MemoryContextSwitchTo(TopMemoryContext);
+
+			/* Remember the old dbids before we reallocate dsa. */
+			copied_dbcnt = worker->dbcount;
+			copied_dbids = (Oid *) palloc0(worker->dbcount * sizeof(Oid));
+			memcpy(copied_dbids, dbids, worker->dbcount * sizeof(Oid));
+
+			alloc_count = copied_dbcnt + DB_PER_WORKER_ALLOC_EXTRA;
+
+			/* Free the existing dbids and allocate new with increased size */
+			if (DsaPointerIsValid(worker->dbids_dp))
+				dsa_free(worker->dbids_dsa, worker->dbids_dp);
+
+			worker->dbids_dp = dsa_allocate0(worker->dbids_dsa,
+											 alloc_count * sizeof(Oid));
+
+			dbids = (Oid *) dsa_get_address(worker->dbids_dsa, worker->dbids_dp);
+
+			/* Copy the existing dbids */
+			worker->dbcount = copied_dbcnt;
+			memcpy(dbids, copied_dbids, copied_dbcnt * sizeof(Oid));
+
+			/* Assign new dbid */
+			dbids[worker->dbcount++] = dbid;
+
+			MemoryContextSwitchTo(oldcontext);
+		}
+
+		LWLockRelease(SlotSyncWorkerLock);
+
+		ereport(LOG,
+				(errmsg("Added database %d to replication slot-sync "
+						"worker %d; dbcount now: %d",
+						dbid, worker_slot, worker->dbcount)));
+		return true;
+	}
+
+	/* Prepare the new worker. */
+	worker->hdr.launch_time = GetCurrentTimestamp();
+	worker->hdr.in_use = true;
+
+	/*
+	 * 'proc' and 'slot' will be assigned in ReplSlotSyncWorkerMain when we
+	 * attach this worker to a particular worker-pool slot
+	 */
+	worker->hdr.proc = NULL;
+	worker->slot = -1;
+
+	/* TODO: do we really need 'generation', analyse more here */
+	worker->hdr.generation++;
+
+	/* Initial DSA setup for dbids array to hold DB_PER_WORKER_ALLOC_INIT dbs */
+	handle = slotsync_dsa_setup(worker, DB_PER_WORKER_ALLOC_INIT);
+	dbids = (Oid *) dsa_get_address(worker->dbids_dsa, worker->dbids_dp);
+
+	dbids[worker->dbcount++] = dbid;
+
+	/* Before releasing lock, remember generation for future identification. */
+	generation = worker->hdr.generation;
+
+	LWLockRelease(SlotSyncWorkerLock);
+
+	/* Register the new dynamic worker. */
+	memset(&bgw, 0, sizeof(bgw));
+	bgw.bgw_flags = BGWORKER_SHMEM_ACCESS |
+		BGWORKER_BACKEND_DATABASE_CONNECTION;
+	bgw.bgw_start_time = BgWorkerStart_ConsistentState;
+	snprintf(bgw.bgw_library_name, MAXPGPATH, "postgres");
+
+	snprintf(bgw.bgw_function_name, BGW_MAXLEN, "ReplSlotSyncWorkerMain");
+
+	Assert(worker_slot >= 0);
+	snprintf(bgw.bgw_name, BGW_MAXLEN,
+			 "replication slot-sync worker %d", worker_slot);
+
+	snprintf(bgw.bgw_type, BGW_MAXLEN, "slot-sync worker");
+
+	bgw.bgw_restart_time = BGW_NEVER_RESTART;
+	bgw.bgw_notify_pid = MyProcPid;
+	bgw.bgw_main_arg = Int32GetDatum(worker_slot);
+
+	memcpy(bgw.bgw_extra, &handle, sizeof(dsa_handle));
+
+	if (!RegisterDynamicBackgroundWorker(&bgw, &bgw_handle))
+	{
+		/* Failed to start worker, so clean up the worker slot. */
+		LWLockAcquire(SlotSyncWorkerLock, LW_EXCLUSIVE);
+		Assert(generation == worker->hdr.generation);
+		slotsync_worker_cleanup(worker);
+		LWLockRelease(SlotSyncWorkerLock);
+
+		ereport(WARNING,
+				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+				 errmsg("out of background worker slots"),
+				 errhint("You might need to increase %s.", "max_worker_processes")));
+		return false;
+	}
+
+	/* Now wait until it attaches. */
+	attach = WaitForReplicationWorkerAttach((LogicalWorkerHeader *) worker,
+											generation,
+											bgw_handle,
+											SlotSyncWorkerLock);
+	if (!attach)
+		ereport(WARNING,
+				(errmsg("Replication slot-sync worker failed to attach to "
+						"worker-pool slot %d", worker_slot)));
+
+	/* Attach is done, now safe to log that the worker is managing dbid */
+	if (attach)
+		ereport(LOG,
+				(errmsg("Added database %d to replication slot-sync "
+						"worker %d; dbcount now: %d",
+						dbid, worker_slot, worker->dbcount)));
+	return attach;
+}
+
+/*
+ * Slot-sync workers remove obsolete DBs from db-list
+ *
+ * If the DBIds fetched from the primary are lesser than the ones being managed
+ * by slot-sync workers, remove extra dbs from worker's db-list. This may happen
+ * if some slots are removed on primary or 'synchronize_slot_names' have been
+ * changed by user.
+ */
+static void
+slotsync_remove_obsolete_dbs(List *remote_dbs)
+{
+	ListCell   *lc;
+	Oid		   *dbids;
+	int			widx;
+	int			dbidx;
+	int			i;
+
+	LWLockAcquire(SlotSyncWorkerLock, LW_EXCLUSIVE);
+
+	/* Traverse slot-sync-workers to validate the DBs */
+	for (widx = 0; widx < max_slotsync_workers; widx++)
+	{
+		SlotSyncWorker *worker = &LogicalRepCtx->ss_workers[widx];
+
+		if (!worker->hdr.in_use)
+			continue;
+
+		dbids = (Oid *) dsa_get_address(worker->dbids_dsa, worker->dbids_dp);
+
+		for (dbidx = 0; dbidx < worker->dbcount;)
+		{
+			Oid			wdbid = dbids[dbidx];
+			bool		found = false;
+
+			/* Check if current DB is still present in remote-db-list */
+			foreach(lc, remote_dbs)
+			{
+				WalRcvRepSlotDbData *slot_db_data = lfirst(lc);
+
+				if (slot_db_data->database == wdbid)
+				{
+					found = true;
+					break;
+				}
+			}
+
+			/* If not found, then delete this db from worker's db-list */
+			if (!found)
+			{
+				for (i = dbidx; i < worker->dbcount; i++)
+				{
+					/* Shift the DBs and get rid of wdbid */
+					if (i < (worker->dbcount - 1))
+						dbids[i] = dbids[i + 1];
+				}
+
+				worker->dbcount--;
+
+				ereport(LOG,
+						(errmsg("Removed database %d from replication slot-sync "
+								"worker %d; dbcount now: %d",
+								wdbid, worker->slot, worker->dbcount)));
+			}
+
+			/* Else move to next db-position */
+			else
+			{
+				dbidx++;
+			}
+		}
+	}
+
+	LWLockRelease(SlotSyncWorkerLock);
+
+	/* If dbcount for any worker has become 0, shut it down */
+	for (widx = 0; widx < max_slotsync_workers; widx++)
+	{
+		SlotSyncWorker *worker = &LogicalRepCtx->ss_workers[widx];
+
+		if (worker->hdr.in_use && !worker->dbcount)
+		{
+			int			slot = worker->slot;
+
+			LWLockAcquire(SlotSyncWorkerLock, LW_SHARED);
+			ereport(LOG,
+					(errmsg("Stopping replication slot-sync worker %d",
+							slot)));
+			logicalrep_worker_stop_internal((LogicalWorkerHeader *) worker,
+											SIGINT,
+											SlotSyncWorkerLock);
+			LWLockRelease(SlotSyncWorkerLock);
+
+			LWLockAcquire(SlotSyncWorkerLock, LW_EXCLUSIVE);
+			slotsync_worker_cleanup(worker);
+			LWLockRelease(SlotSyncWorkerLock);
+		}
+	}
+}
+
+/*
+ * Connect to primary server for slotsync purpose and return the connection
+ * info. Disconnect previous connection if provided in wrconn_prev.
+ */
+static WalReceiverConn *
+primary_connect(WalReceiverConn *wrconn_prev)
+{
+	WalReceiverConn *wrconn = NULL;
+	char	   *err;
+
+	if (wrconn_prev)
+		walrcv_disconnect(wrconn_prev);
+
+	if (!RecoveryInProgress())
+		return NULL;
+
+	if (max_slotsync_workers == 0)
+		return NULL;
+
+	if (strcmp(synchronize_slot_names, "") == 0)
+		return NULL;
+
+	wrconn = walrcv_connect(PrimaryConnInfo, false, false,
+							"Logical Replication Launcher", &err);
+	if (!wrconn)
+		ereport(ERROR,
+				(errmsg("could not connect to the primary server: %s", err)));
+
+	return wrconn;
+}
+
+/*
+ * Start slot-sync background workers.
+ *
+ * It connects to primary, get the list of DBIDs for slots configured in
+ * synchronize_slot_names. It then launces the slot-sync workers as per
+ * max_slotsync_workers and then assign the DBs equally to the workers
+ * launched.
+ */
+static void
+ApplyLauncherStartSlotSync(long *wait_time, WalReceiverConn *wrconn)
+{
+	List	   *slots_dbs;
+	ListCell   *lc;
+	MemoryContext tmpctx;
+	MemoryContext oldctx;
+
+	if (max_slotsync_workers == 0)
+		return;
+
+	if (strcmp(synchronize_slot_names, "") == 0)
+		return;
+
+	Assert(wrconn);
+
+	/* Use temporary context for the slot list and worker info. */
+	tmpctx = AllocSetContextCreate(TopMemoryContext,
+								   "Logical Replication Launcher slot-sync ctx",
+								   ALLOCSET_DEFAULT_SIZES);
+	oldctx = MemoryContextSwitchTo(tmpctx);
+
+	slots_dbs = walrcv_get_dbinfo_for_logical_slots(wrconn,
+													synchronize_slot_names);
+
+	slotsync_remove_obsolete_dbs(slots_dbs);
+
+	foreach(lc, slots_dbs)
+	{
+		WalRcvRepSlotDbData *slot_db_data = lfirst(lc);
+		SlotSyncWorker *w;
+		TimestampTz last_launch_tried;
+		TimestampTz now;
+		long		elapsed;
+
+		if (!OidIsValid(slot_db_data->database))
+			continue;
+
+		LWLockAcquire(SlotSyncWorkerLock, LW_SHARED);
+		w = slotsync_worker_find(slot_db_data->database);
+		LWLockRelease(SlotSyncWorkerLock);
+
+		if (w != NULL)
+			continue;			/* worker is running already */
+
+		/*
+		 * If the worker is eligible to start now, launch it. Otherwise,
+		 * adjust wait_time so that we'll wake up as soon as it can be
+		 * started.
+		 *
+		 * Each apply worker can only be restarted once per
+		 * wal_retrieve_retry_interval, so that errors do not cause us to
+		 * repeatedly restart the worker as fast as possible.
+		 */
+		last_launch_tried = slot_db_data->last_launch_time;
+		now = GetCurrentTimestamp();
+		if (last_launch_tried == 0 ||
+			(elapsed = TimestampDifferenceMilliseconds(last_launch_tried, now)) >=
+			wal_retrieve_retry_interval)
+		{
+			slot_db_data->last_launch_time = now;
+
+			slotsync_worker_launch_or_reuse(slot_db_data->database);
+		}
+		else
+		{
+			*wait_time = Min(*wait_time,
+							 wal_retrieve_retry_interval - elapsed);
+		}
+	}
+
+	/* Switch back to original memory context. */
+	MemoryContextSwitchTo(oldctx);
+	/* Clean the temporary memory. */
+	MemoryContextDelete(tmpctx);
+}
+
+/*
+ * Start logical replication apply workers for enabled subscriptions.
+ */
+static void
+ApplyLauncherStartSubs(long *wait_time)
+{
+	List	   *sublist;
+	ListCell   *lc;
+	MemoryContext subctx;
+	MemoryContext oldctx;
+
+	/* Use temporary context to avoid leaking memory across cycles. */
+	subctx = AllocSetContextCreate(TopMemoryContext,
+								   "Logical Replication Launcher sublist",
+								   ALLOCSET_DEFAULT_SIZES);
+	oldctx = MemoryContextSwitchTo(subctx);
+
+	/* Start any missing workers for enabled subscriptions. */
+	sublist = get_subscription_list();
+	foreach(lc, sublist)
+	{
+		Subscription *sub = (Subscription *) lfirst(lc);
+		LogicalRepWorker *w;
+		TimestampTz last_start;
+		TimestampTz now;
+		long		elapsed;
+
+		if (!sub->enabled)
+			continue;
+
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		w = logicalrep_worker_find(sub->oid, InvalidOid, false);
+		LWLockRelease(LogicalRepWorkerLock);
+
+		if (w != NULL)
+			continue;			/* worker is running already */
+
+		/*
+		 * If the worker is eligible to start now, launch it.  Otherwise,
+		 * adjust wait_time so that we'll wake up as soon as it can be
+		 * started.
+		 *
+		 * Each subscription's apply worker can only be restarted once per
+		 * wal_retrieve_retry_interval, so that errors do not cause us to
+		 * repeatedly restart the worker as fast as possible.  In cases where
+		 * a restart is expected (e.g., subscription parameter changes),
+		 * another process should remove the last-start entry for the
+		 * subscription so that the worker can be restarted without waiting
+		 * for wal_retrieve_retry_interval to elapse.
+		 */
+		last_start = ApplyLauncherGetWorkerStartTime(sub->oid);
+		now = GetCurrentTimestamp();
+		if (last_start == 0 ||
+			(elapsed = TimestampDifferenceMilliseconds(last_start, now)) >= wal_retrieve_retry_interval)
+		{
+			ApplyLauncherSetWorkerStartTime(sub->oid, now);
+			logicalrep_worker_launch(WORKERTYPE_APPLY,
+									 sub->dbid, sub->oid, sub->name,
+									 sub->owner, InvalidOid,
+									 DSM_HANDLE_INVALID);
+		}
+		else
+		{
+			*wait_time = Min(*wait_time,
+							 wal_retrieve_retry_interval - elapsed);
+		}
+	}
+
+	/* Switch back to original memory context. */
+	MemoryContextSwitchTo(oldctx);
+	/* Clean the temporary memory. */
+	MemoryContextDelete(subctx);
+}
+
 /*
  * Main loop for the apply launcher process.
  */
 void
 ApplyLauncherMain(Datum main_arg)
 {
+	WalReceiverConn *wrconn = NULL;
+
 	ereport(DEBUG1,
 			(errmsg_internal("logical replication launcher started")));
 
@@ -1139,79 +1852,22 @@ ApplyLauncherMain(Datum main_arg)
 	 */
 	BackgroundWorkerInitializeConnection(NULL, NULL, 0);
 
+	load_file("libpqwalreceiver", false);
+
+	wrconn = primary_connect(NULL);
+
 	/* Enter main loop */
 	for (;;)
 	{
 		int			rc;
-		List	   *sublist;
-		ListCell   *lc;
-		MemoryContext subctx;
-		MemoryContext oldctx;
 		long		wait_time = DEFAULT_NAPTIME_PER_CYCLE;
 
 		CHECK_FOR_INTERRUPTS();
 
-		/* Use temporary context to avoid leaking memory across cycles. */
-		subctx = AllocSetContextCreate(TopMemoryContext,
-									   "Logical Replication Launcher sublist",
-									   ALLOCSET_DEFAULT_SIZES);
-		oldctx = MemoryContextSwitchTo(subctx);
-
-		/* Start any missing workers for enabled subscriptions. */
-		sublist = get_subscription_list();
-		foreach(lc, sublist)
-		{
-			Subscription *sub = (Subscription *) lfirst(lc);
-			LogicalRepWorker *w;
-			TimestampTz last_start;
-			TimestampTz now;
-			long		elapsed;
-
-			if (!sub->enabled)
-				continue;
-
-			LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-			w = logicalrep_worker_find(sub->oid, InvalidOid, false);
-			LWLockRelease(LogicalRepWorkerLock);
-
-			if (w != NULL)
-				continue;		/* worker is running already */
-
-			/*
-			 * If the worker is eligible to start now, launch it.  Otherwise,
-			 * adjust wait_time so that we'll wake up as soon as it can be
-			 * started.
-			 *
-			 * Each subscription's apply worker can only be restarted once per
-			 * wal_retrieve_retry_interval, so that errors do not cause us to
-			 * repeatedly restart the worker as fast as possible.  In cases
-			 * where a restart is expected (e.g., subscription parameter
-			 * changes), another process should remove the last-start entry
-			 * for the subscription so that the worker can be restarted
-			 * without waiting for wal_retrieve_retry_interval to elapse.
-			 */
-			last_start = ApplyLauncherGetWorkerStartTime(sub->oid);
-			now = GetCurrentTimestamp();
-			if (last_start == 0 ||
-				(elapsed = TimestampDifferenceMilliseconds(last_start, now)) >= wal_retrieve_retry_interval)
-			{
-				ApplyLauncherSetWorkerStartTime(sub->oid, now);
-				logicalrep_worker_launch(WORKERTYPE_APPLY,
-										 sub->dbid, sub->oid, sub->name,
-										 sub->owner, InvalidOid,
-										 DSM_HANDLE_INVALID);
-			}
-			else
-			{
-				wait_time = Min(wait_time,
-								wal_retrieve_retry_interval - elapsed);
-			}
-		}
-
-		/* Switch back to original memory context. */
-		MemoryContextSwitchTo(oldctx);
-		/* Clean the temporary memory. */
-		MemoryContextDelete(subctx);
+		if (!RecoveryInProgress())
+			ApplyLauncherStartSubs(&wait_time);
+		else
+			ApplyLauncherStartSlotSync(&wait_time, wrconn);
 
 		/* Wait for more work. */
 		rc = WaitLatch(MyLatch,
@@ -1229,6 +1885,9 @@ ApplyLauncherMain(Datum main_arg)
 		{
 			ConfigReloadPending = false;
 			ProcessConfigFile(PGC_SIGHUP);
+
+			/* Reconnect in case primary_conninfo has changed */
+			wrconn = primary_connect(wrconn);
 		}
 	}
 
@@ -1260,7 +1919,8 @@ GetLeaderApplyWorkerPid(pid_t pid)
 	{
 		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
 
-		if (isParallelApplyWorker(w) && w->proc && pid == w->proc->pid)
+		if (isParallelApplyWorker(w) && w->hdr.proc &&
+			pid == w->hdr.proc->pid)
 		{
 			leader_pid = w->leader_pid;
 			break;
@@ -1298,13 +1958,13 @@ pg_stat_get_subscription(PG_FUNCTION_ARGS)
 
 		memcpy(&worker, &LogicalRepCtx->workers[i],
 			   sizeof(LogicalRepWorker));
-		if (!worker.proc || !IsBackendPid(worker.proc->pid))
+		if (!worker.hdr.proc || !IsBackendPid(worker.hdr.proc->pid))
 			continue;
 
 		if (OidIsValid(subid) && worker.subid != subid)
 			continue;
 
-		worker_pid = worker.proc->pid;
+		worker_pid = worker.hdr.proc->pid;
 
 		values[0] = ObjectIdGetDatum(worker.subid);
 		if (isTablesyncWorker(&worker))
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 197169d6b0..de318fb29c 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -202,6 +202,19 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	ReplicationSlotAcquire(NameStr(*name), true);
 
+	/*
+	 * Do not allow consumption of a "synchronized" slot until the standby
+	 * gets promoted.
+	 */
+	if (RecoveryInProgress() && MyReplicationSlot->data.synced)
+	{
+		ReplicationSlotRelease();
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("operation not permitted on replication slots on "
+						"standby which are synchronized from primary")));
+	}
+
 	PG_TRY();
 	{
 		/* restart at slot's confirmed_flush */
diff --git a/src/backend/replication/logical/meson.build b/src/backend/replication/logical/meson.build
index d48cd4c590..9e52ec421f 100644
--- a/src/backend/replication/logical/meson.build
+++ b/src/backend/replication/logical/meson.build
@@ -11,6 +11,7 @@ backend_sources += files(
   'proto.c',
   'relation.c',
   'reorderbuffer.c',
+  'slotsync.c',
   'snapbuild.c',
   'tablesync.c',
   'worker.c',
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
new file mode 100644
index 0000000000..37e91b0d1f
--- /dev/null
+++ b/src/backend/replication/logical/slotsync.c
@@ -0,0 +1,1039 @@
+/*-------------------------------------------------------------------------
+ * slotsync.c
+ *	   PostgreSQL worker for synchronizing slots to a standby from the
+ *         primary
+ *
+ * Copyright (c) 2023, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/slotsync.c
+ *
+ * This file contains the code for slot-sync workers on physical standby
+ * to fetch logical replication slot information from the primary server
+ * (PrimaryConnInfo), create the slots on the standby, and synchronize
+ * them periodically. Slot-sync workers only synchronize slots configured
+ * in 'synchronize_slot_names'.
+ *
+ * It also takes care of dropping the slots which were created by it and are
+ * currently not needed to be synchronized.
+ *
+ * It takes a nap of WORKER_DEFAULT_NAPTIME_MS before every next
+ * synchronization. If there is no activity observed on the primary for some
+ * time, the nap time is increased to WORKER_INACTIVITY_NAPTIME_MS, but if any
+ * activity is observed, the nap time reverts to the default value.
+ *---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "commands/dbcommands.h"
+#include "pgstat.h"
+#include "postmaster/bgworker.h"
+#include "postmaster/interrupt.h"
+#include "replication/logical.h"
+#include "replication/logicallauncher.h"
+#include "replication/logicalworker.h"
+#include "replication/walreceiver.h"
+#include "replication/worker_internal.h"
+#include "storage/ipc.h"
+#include "storage/procarray.h"
+#include "tcop/tcopprot.h"
+#include "utils/builtins.h"
+#include "utils/guc_hooks.h"
+#include "utils/pg_lsn.h"
+#include "utils/varlena.h"
+
+/*
+ * Structure to hold information fetched from the primary server about a logical
+ * replication slot.
+ */
+typedef struct RemoteSlot
+{
+	char	   *name;
+	char	   *plugin;
+	char	   *database;
+	bool		two_phase;
+	bool		conflicting;
+	XLogRecPtr	restart_lsn;
+	XLogRecPtr	confirmed_lsn;
+	TransactionId catalog_xmin;
+
+	/* RS_INVAL_NONE if valid, or the reason of invalidation */
+	ReplicationSlotInvalidationCause invalidated;
+} RemoteSlot;
+
+List	   *sync_slot_names_list = NIL;
+
+/* Worker's nap time in case of regular activity on primary */
+#define WORKER_DEFAULT_NAPTIME_MS                   10L /* 10 ms */
+
+/* Worker's nap time in case of no-activity on primary */
+#define WORKER_INACTIVITY_NAPTIME_MS                10000L	/* 10 sec */
+
+/*
+ * Inactivity Threshold in ms before increasing nap time of worker.
+ *
+ * If the lsn of slot being monitored did not change for this threshold time,
+ * then increase nap time of current worker from WORKER_DEFAULT_NAPTIME_MS to
+ * WORKER_INACTIVITY_NAPTIME_MS.
+ */
+#define WORKER_INACTIVITY_THRESHOLD_MS 1000L	/* 1 sec */
+
+/*
+ * Wait for remote slot to pass locally reserved position.
+ */
+static void
+wait_for_primary_slot_catchup(WalReceiverConn *wrconn, char *slot_name,
+							  XLogRecPtr min_lsn)
+{
+	WalRcvExecResult *res;
+	TupleTableSlot *slot;
+	Oid			slotRow[1] = {LSNOID};
+	StringInfoData cmd;
+	bool		isnull;
+	XLogRecPtr	restart_lsn;
+
+	for (;;)
+	{
+		int			rc;
+
+		CHECK_FOR_INTERRUPTS();
+
+		initStringInfo(&cmd);
+		appendStringInfo(&cmd,
+						 "SELECT restart_lsn"
+						 "  FROM pg_catalog.pg_replication_slots"
+						 " WHERE slot_name = %s",
+						 quote_literal_cstr(slot_name));
+		res = walrcv_exec(wrconn, cmd.data, 1, slotRow);
+		pfree(cmd.data);
+
+		if (res->status != WALRCV_OK_TUPLES)
+			ereport(ERROR,
+					(errmsg("could not fetch slot info for slot \"%s\" from"
+							" primary: %s", slot_name, res->err)));
+
+		slot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
+		if (!tuplestore_gettupleslot(res->tuplestore, true, false, slot))
+			ereport(ERROR,
+					(errmsg("slot \"%s\" disappeared from the primary",
+							slot_name)));
+
+		restart_lsn = DatumGetLSN(slot_getattr(slot, 1, &isnull));
+		Assert(!isnull);
+
+		ExecClearTuple(slot);
+		walrcv_clear_result(res);
+
+		if (restart_lsn >= min_lsn)
+			break;
+
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+					   wal_retrieve_retry_interval,
+					   WAIT_EVENT_REPL_SLOTSYNC_MAIN);
+
+		ResetLatch(MyLatch);
+
+		/* Emergency bailout if postmaster has died */
+		if (rc & WL_POSTMASTER_DEATH)
+			proc_exit(1);
+	}
+}
+
+/*
+ * Update local slot metadata as per remote_slot's positions
+ */
+static void
+local_slot_update(RemoteSlot *remote_slot)
+{
+	LogicalConfirmReceivedLocation(remote_slot->confirmed_lsn);
+	LogicalIncreaseXminForSlot(remote_slot->confirmed_lsn,
+							   remote_slot->catalog_xmin);
+	LogicalIncreaseRestartDecodingForSlot(remote_slot->confirmed_lsn,
+										  remote_slot->restart_lsn);
+	MyReplicationSlot->data.invalidated = remote_slot->invalidated;
+	ReplicationSlotMarkDirty();
+}
+
+/*
+ * Get list of local logical slot names which are synchronized from
+ * primary and belongs to one of the DBs passed in.
+ */
+static List *
+get_local_synced_slot_names(Oid *dbids)
+{
+	List	   *localSyncedSlots = NIL;
+
+	Assert(LWLockHeldByMeInMode(SlotSyncWorkerLock, LW_SHARED));
+
+	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
+
+	for (int i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
+
+		/* Check if it is logical synchronized slot */
+		if (s->in_use && SlotIsLogical(s) && s->data.synced)
+		{
+			for (int j = 0; j < MySlotSyncWorker->dbcount; j++)
+			{
+				/*
+				 * Add it to output list if this belongs to one of the
+				 * worker's dbs.
+				 */
+				if (s->data.database == dbids[j])
+				{
+					localSyncedSlots = lappend(localSyncedSlots, s);
+					break;
+				}
+			}
+		}
+	}
+
+	LWLockRelease(ReplicationSlotControlLock);
+
+	return localSyncedSlots;
+}
+
+/*
+ * Helper function to check if local_slot is present in remote_slots list.
+ *
+ * It also checks if logical slot is locally invalidated i.e. invalided on
+ * standby but valid on primary. If found so, it sets locally_invalidated to
+ * true.
+ */
+static bool
+slot_exists_locally(List *remote_slots, ReplicationSlot *local_slot,
+					bool *locally_invalidated)
+{
+	ListCell   *cell;
+
+	foreach(cell, remote_slots)
+	{
+		RemoteSlot *remote_slot = (RemoteSlot *) lfirst(cell);
+
+		if (strcmp(remote_slot->name, NameStr(local_slot->data.name)) == 0)
+		{
+			/*
+			 * if remote slot is marked as non-conflicting (i.e. not
+			 * invalidated) but local slot is marked as invalidated, then set
+			 * the bool.
+			 */
+			if (!remote_slot->conflicting &&
+				SlotIsLogical(local_slot) &&
+				local_slot->data.invalidated != RS_INVAL_NONE)
+				*locally_invalidated = true;
+
+			return true;
+		}
+	}
+
+	return false;
+}
+
+/*
+ * Use slot_name in query.
+ *
+ * Check the dbid of the slot and if the dbid is one of the dbids managed by
+ * current worker, then use this slot-name in query to get the data from
+ * primary. If the slot is not created yet on standby (first time it is being
+ * queried), then too, use this slot in query.
+ */
+static bool
+use_slot_in_query(char *slot_name, Oid *dbids)
+{
+	bool		slot_found = false;
+	bool		relevant_db = false;
+	ReplicationSlot *slot;
+
+	Assert(LWLockHeldByMeInMode(SlotSyncWorkerLock, LW_SHARED));
+
+	/* Search for the local slot with the same name as slot_name */
+	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
+
+	for (int i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
+
+		if (s->in_use && SlotIsLogical(s) &&
+			(strcmp(NameStr(s->data.name), slot_name) == 0))
+		{
+			slot_found = true;
+			slot = s;
+			break;
+		}
+	}
+
+	/* Check if slot belongs to one of the input dbids */
+	if (slot_found)
+	{
+		for (int j = 0; j < MySlotSyncWorker->dbcount; j++)
+		{
+			if (slot->data.database == dbids[j])
+			{
+				relevant_db = true;
+				break;
+			}
+		}
+	}
+
+	LWLockRelease(ReplicationSlotControlLock);
+
+	/*
+	 * Return TRUE if either slot is not yet created on standby or if it
+	 * belongs to one of the dbs passed in dbids.
+	 */
+	if (!slot_found || relevant_db)
+		return true;
+
+	return false;
+}
+
+
+/*
+ * Compute nap time for MySlotSyncWorker.
+ *
+ * The slot-sync worker takes a nap before it again checks for slots on primary.
+ * The time for each nap is computed here.
+ *
+ * The first slot managed by each worker is chosen for monitoring purpose.
+ * If the lsn of that slot changes during each sync-check time, then the
+ * nap time is kept at regular value of WORKER_DEFAULT_NAPTIME_MS.
+ * When no lsn change is observed for WORKER_INACTIVITY_THRESHOLD_MS
+ * time, then the nap time is increased to WORKER_INACTIVITY_NAPTIME_MS.
+ * This nap time is brought back to WORKER_DEFAULT_NAPTIME_MS as soon as
+ * lsn change is observed.
+ *
+ * The caller is supposed to ignore return-value of 0. The 0 value is returned
+ * for the slots other that slot being monitored.
+ */
+static long
+compute_naptime(RemoteSlot *remote_slot)
+{
+	if (NameStr(MySlotSyncWorker->monitoring_info.slot_name)[0] == '\0')
+	{
+		/*
+		 * First time, just update the name and lsn and return regular
+		 * nap time. Start comparison from next time onward.
+		 */
+		strcpy(NameStr(MySlotSyncWorker->monitoring_info.slot_name),
+			   remote_slot->name);
+		MySlotSyncWorker->monitoring_info.confirmed_lsn =
+			remote_slot->confirmed_lsn;
+
+		MySlotSyncWorker->monitoring_info.last_update_time =
+			GetCurrentTimestamp();
+
+		return WORKER_DEFAULT_NAPTIME_MS;
+	}
+
+	/* If this is the slot being monitored by this worker, compute nap time */
+	if (strcmp(remote_slot->name,
+			   NameStr(MySlotSyncWorker->monitoring_info.slot_name)) == 0)
+	{
+		TimestampTz now = GetCurrentTimestamp();
+
+		/*
+		 * If new received lsn (remote one) is different from what we have in
+		 * our local slot, then update last_update_time.
+		 */
+		if (MySlotSyncWorker->monitoring_info.confirmed_lsn !=
+			remote_slot->confirmed_lsn)
+			MySlotSyncWorker->monitoring_info.last_update_time = now;
+
+		MySlotSyncWorker->monitoring_info.confirmed_lsn =
+			remote_slot->confirmed_lsn;
+
+		/* If the inactivity time reaches the threshold, increase nap time */
+		if (TimestampDifferenceExceeds(MySlotSyncWorker->monitoring_info.last_update_time,
+									   now, WORKER_INACTIVITY_THRESHOLD_MS))
+			return WORKER_INACTIVITY_NAPTIME_MS;
+		else
+			return WORKER_DEFAULT_NAPTIME_MS;
+	}
+
+	/* If it is not the slot being monitored, return 0 */
+	return 0;
+}
+
+/*
+ * Get Remote Slot's invalidation cause.
+ *
+ * This gets invalidation cause of remote slot.
+ */
+static ReplicationSlotInvalidationCause
+get_remote_invalidation_cause(WalReceiverConn *wrconn, char *slot_name)
+{
+	WalRcvExecResult *res;
+	Oid			slotRow[1] = {INT2OID};
+	StringInfoData cmd;
+	bool		isnull;
+	TupleTableSlot *slot;
+	ReplicationSlotInvalidationCause cause;
+	MemoryContext oldctx = CurrentMemoryContext;
+
+	/* Syscache access needs a transaction env. */
+	StartTransactionCommand();
+
+	/* Make things live outside TX context */
+	MemoryContextSwitchTo(oldctx);
+
+	initStringInfo(&cmd);
+	appendStringInfo(&cmd,
+					 "select pg_get_slot_invalidation_cause(%s)",
+					 quote_literal_cstr(slot_name));
+	res = walrcv_exec(wrconn, cmd.data, 1, slotRow);
+	pfree(cmd.data);
+
+	CommitTransactionCommand();
+
+	/* Switch to oldctx we saved */
+	MemoryContextSwitchTo(oldctx);
+
+	if (res->status != WALRCV_OK_TUPLES)
+		ereport(ERROR,
+				(errmsg("could not fetch invalidation cuase for slot \"%s\" from"
+						" primary: %s", slot_name, res->err)));
+
+	slot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
+	if (!tuplestore_gettupleslot(res->tuplestore, true, false, slot))
+		ereport(ERROR,
+				(errmsg("slot \"%s\" disapeared from the primary",
+						slot_name)));
+
+	cause = DatumGetInt16(slot_getattr(slot, 1, &isnull));
+	Assert(!isnull);
+
+	ExecClearTuple(slot);
+	walrcv_clear_result(res);
+
+	return cause;
+}
+
+/*
+ * Drop obsolete slots
+ *
+ * Drop the slots which no longer need to be synced i.e. these either
+ * do not exist on primary or are no longer part of synchronize_slot_names.
+ *
+ * Also drop the slots which are valid on primary and got invalidated
+ * on standby due to conflict (say required rows removed on primary).
+ * The assumption is, these will get recreated in next sync-cycle and
+ * it is okay to drop and recreate such slots as long as these are not
+ * consumable on standby (which is the case currently).
+ */
+static void
+drop_obsolete_slots(Oid *dbids, List *remote_slot_list)
+{
+	List	   *local_slot_list = NIL;
+	ListCell   *lc_slot;
+
+	Assert(LWLockHeldByMeInMode(SlotSyncWorkerLock, LW_SHARED));
+
+	/*
+	 * Get the list of local slots for dbids managed by this worker, so that
+	 * those not on remote could be dropped.
+	 */
+	local_slot_list = get_local_synced_slot_names(dbids);
+
+	foreach(lc_slot, local_slot_list)
+	{
+		ReplicationSlot *local_slot = (ReplicationSlot *) lfirst(lc_slot);
+		bool		local_exists = false;
+		bool		locally_invalidated = false;
+
+		local_exists = slot_exists_locally(remote_slot_list, local_slot,
+										   &locally_invalidated);
+
+		/*
+		 * Drop the local slot either if it is not in the remote slots list or
+		 * is invalidated while remote slot is still valid.
+		 */
+		if (!local_exists || locally_invalidated)
+		{
+			ReplicationSlotDrop(NameStr(local_slot->data.name), true);
+
+			/* If this slot is being monitored, clean-up the monitoring info */
+			if (strcmp(NameStr(local_slot->data.name),
+					   NameStr(MySlotSyncWorker->monitoring_info.slot_name)) == 0)
+			{
+				MemSet(NameStr(MySlotSyncWorker->monitoring_info.slot_name), 0, NAMEDATALEN);
+				MySlotSyncWorker->monitoring_info.confirmed_lsn = 0;
+				MySlotSyncWorker->monitoring_info.last_update_time = 0;
+			}
+
+			elog(LOG, "Dropped replication slot \"%s\" ",
+				 NameStr(local_slot->data.name));
+		}
+	}
+}
+
+/*
+ * Construct Slot Query
+ *
+ * It constructs the query using dbids array and sync_slot_names_list
+ * in order to get slots information from the primary.
+ */
+static bool
+construct_slot_query(StringInfo s, Oid *dbids)
+{
+	Assert(LWLockHeldByMeInMode(SlotSyncWorkerLock, LW_SHARED));
+
+	appendStringInfo(s,
+					 "SELECT slot_name, plugin, confirmed_flush_lsn,"
+					 " restart_lsn, catalog_xmin, two_phase, conflicting, "
+					 " database FROM pg_catalog.pg_replication_slots"
+					 " WHERE database IN ");
+
+	appendStringInfoChar(s, '(');
+	for (int i = 0; i < MySlotSyncWorker->dbcount; i++)
+	{
+		char	   *dbname;
+
+		if (i != 0)
+			appendStringInfoChar(s, ',');
+
+		dbname = get_database_name(dbids[i]);
+		appendStringInfo(s, "%s",
+						 quote_literal_cstr(dbname));
+		pfree(dbname);
+	}
+	appendStringInfoChar(s, ')');
+
+	if (strcmp(synchronize_slot_names, "") != 0 &&
+		strcmp(synchronize_slot_names, "*") != 0)
+	{
+		ListCell   *lc;
+		bool		first_slot = true;
+
+
+		foreach(lc, sync_slot_names_list)
+		{
+			char	   *slot_name = lfirst(lc);
+
+			if (!use_slot_in_query(slot_name, dbids))
+				continue;
+
+			if (first_slot)
+				appendStringInfoString(s, " AND slot_name IN (");
+			else
+				appendStringInfoChar(s, ',');
+
+			appendStringInfo(s, "%s",
+							 quote_literal_cstr(slot_name));
+			first_slot = false;
+		}
+
+		if (!first_slot)
+			appendStringInfoChar(s, ')');
+	}
+
+	return true;
+}
+
+/*
+ * Synchronize single slot to given position.
+ *
+ * This creates new slot if there is no existing one and updates the
+ * metadata of existing slots as per the data received from the primary.
+ */
+static void
+synchronize_one_slot(WalReceiverConn *wrconn, RemoteSlot *remote_slot)
+{
+	bool		found = false;
+
+	/*
+	 * Make sure that concerned WAL is received before syncing slot to target
+	 * lsn received from the primary.
+	 */
+	if (remote_slot->confirmed_lsn > WalRcv->latestWalEnd)
+	{
+		ereport(WARNING,
+				errmsg("skipping sync of slot \"%s\" as the received slot-sync "
+					   "lsn %X/%X is ahead of the standby position %X/%X",
+					   remote_slot->name,
+					   LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
+					   LSN_FORMAT_ARGS(WalRcv->latestWalEnd)));
+		return;
+	}
+
+	/* Search for the named slot and mark it active if we find it. */
+	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
+	for (int i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
+
+		if (!s->in_use)
+			continue;
+
+		if (strcmp(NameStr(s->data.name), remote_slot->name) == 0)
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(ReplicationSlotControlLock);
+
+	StartTransactionCommand();
+
+	/* Already existing slot, acquire */
+	if (found)
+	{
+		ReplicationSlotAcquire(remote_slot->name, true);
+
+		if (remote_slot->confirmed_lsn < MyReplicationSlot->data.confirmed_flush)
+		{
+			ereport(WARNING,
+					errmsg("not synchronizing slot %s; synchronization would move"
+						   " it backward", remote_slot->name));
+
+			ReplicationSlotRelease();
+			CommitTransactionCommand();
+			return;
+		}
+
+		/* Update lsns of slot to remote slot's current position */
+		local_slot_update(remote_slot);
+		ReplicationSlotSave();
+	}
+	/* Otherwise create the slot first. */
+	else
+	{
+		TransactionId xmin_horizon = InvalidTransactionId;
+		ReplicationSlot *slot;
+
+		ReplicationSlotCreate(remote_slot->name, true, RS_EPHEMERAL,
+							  remote_slot->two_phase);
+		slot = MyReplicationSlot;
+
+		SpinLockAcquire(&slot->mutex);
+		slot->data.database = get_database_oid(remote_slot->database, false);
+		slot->data.synced = true;
+		namestrcpy(&slot->data.plugin, remote_slot->plugin);
+		SpinLockRelease(&slot->mutex);
+
+		ReplicationSlotReserveWal();
+
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		xmin_horizon = GetOldestSafeDecodingTransactionId(true);
+		slot->effective_catalog_xmin = xmin_horizon;
+		slot->data.catalog_xmin = xmin_horizon;
+		ReplicationSlotsComputeRequiredXmin(true);
+		LWLockRelease(ProcArrayLock);
+
+		if (remote_slot->confirmed_lsn < MyReplicationSlot->data.restart_lsn)
+		{
+			ereport(LOG,
+					errmsg("waiting for remote slot \"%s\" LSN (%X/%X) to pass "
+						   "local slot LSN (%X/%X)", remote_slot->name,
+						   LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
+						   LSN_FORMAT_ARGS(MyReplicationSlot->data.restart_lsn)));
+
+			wait_for_primary_slot_catchup(wrconn, remote_slot->name,
+										  MyReplicationSlot->data.restart_lsn);
+		}
+
+		/* Update lsns of slot to remote slot's current position */
+		local_slot_update(remote_slot);
+		ReplicationSlotPersist();
+	}
+
+	ReplicationSlotRelease();
+	CommitTransactionCommand();
+}
+
+/*
+ * Synchronize slots.
+ *
+ * It looks into dbids array maintained in dsa and gets the logical slots info
+ * from the primary for the slots configured in synchronize_slot_names and
+ * belonging to concerned dbids. It then updates the slots locally as per the
+ * data received from the primary. It creates the slots if not present on the
+ * standby.
+ *
+ * It returns nap time for the next sync-cycle.
+ */
+static long
+synchronize_slots(dsa_area *dsa, WalReceiverConn *wrconn)
+{
+#define SLOTSYNC_COLUMN_COUNT 8
+	Oid			slotRow[SLOTSYNC_COLUMN_COUNT] = {TEXTOID, TEXTOID, LSNOID,
+	LSNOID, XIDOID, BOOLOID, BOOLOID, TEXTOID};
+
+	WalRcvExecResult *res;
+	TupleTableSlot *slot;
+	StringInfoData s;
+	List	   *remote_slot_list = NIL;
+	MemoryContext oldctx = CurrentMemoryContext;
+	long		naptime = WORKER_DEFAULT_NAPTIME_MS;
+	long		value;
+	Oid		   *dbids;
+	ListCell   *cell;
+
+	if (strcmp(synchronize_slot_names, "") == 0 || !WalRcv)
+		return naptime;
+
+	/* The primary_slot_name is not set yet */
+	if (WalRcv->slotname[0] == '\0')
+	{
+		ereport(WARNING,
+				errmsg("skipping sync as primary_slot_name not set."));
+		return naptime;
+	}
+
+	/* WALs not received yet */
+	if (XLogRecPtrIsInvalid(WalRcv->latestWalEnd))
+		return naptime;
+
+	/*
+	 * No more writes to dbcount and dbids by launcher after this until we
+	 * release this lock.
+	 */
+	LWLockAcquire(SlotSyncWorkerLock, LW_SHARED);
+
+	/*
+	 * There is a small window between CHECK_FOR_INTERRUPTS done last and
+	 * above lock acquiring, so there is a chance that synchronize_slot_names
+	 * has changed making dbs assigned to this worker as invalid. In that
+	 * case, launcher will make dbcount=0 and will send SIGINT to this worker.
+	 * So check dbcount before proceeding.
+	 */
+	if (!MySlotSyncWorker->dbcount)
+	{
+		/* Return and handle the interrupts in main loop */
+		return false;
+	}
+
+	/* Get dbids from dsa */
+	dbids = (Oid *) dsa_get_address(dsa, MySlotSyncWorker->dbids_dp);
+
+	/* The syscache access needs a transaction env. */
+	StartTransactionCommand();
+
+	/* Make things live outside TX context */
+	MemoryContextSwitchTo(oldctx);
+
+	/* Construct query to get slots info from the primary */
+	initStringInfo(&s);
+	if (!construct_slot_query(&s, dbids))
+	{
+		pfree(s.data);
+		CommitTransactionCommand();
+		LWLockRelease(SlotSyncWorkerLock);
+		return naptime;
+	}
+
+	elog(DEBUG2, "slot-sync worker%d's query:%s \n", MySlotSyncWorker->slot,
+		 s.data);
+
+	/* Execute the query */
+	res = walrcv_exec(wrconn, s.data, SLOTSYNC_COLUMN_COUNT, slotRow);
+	pfree(s.data);
+
+	if (res->status != WALRCV_OK_TUPLES)
+		ereport(ERROR,
+				(errmsg("could not fetch slot info from the primary: %s",
+						res->err)));
+
+	CommitTransactionCommand();
+
+	/* Switch to oldctx we saved */
+	MemoryContextSwitchTo(oldctx);
+
+	/* Construct the remote_slot tuple and synchronize each slot locally */
+	slot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
+	while (tuplestore_gettupleslot(res->tuplestore, true, false, slot))
+	{
+		bool		isnull;
+		RemoteSlot *remote_slot = palloc0(sizeof(RemoteSlot));
+
+		remote_slot->name = TextDatumGetCString(slot_getattr(slot, 1, &isnull));
+		Assert(!isnull);
+
+		remote_slot->plugin = TextDatumGetCString(slot_getattr(slot, 2, &isnull));
+		Assert(!isnull);
+
+		/*
+		 * It is possible to get null values for lsns and xmin if slot is
+		 * invalidated on primary, so handle accordingly.
+		 */
+		remote_slot->confirmed_lsn = DatumGetLSN(slot_getattr(slot, 3, &isnull));
+		if (isnull)
+			remote_slot->confirmed_lsn = InvalidXLogRecPtr;
+
+		remote_slot->restart_lsn = DatumGetLSN(slot_getattr(slot, 4, &isnull));
+		if (isnull)
+			remote_slot->restart_lsn = InvalidXLogRecPtr;
+
+		remote_slot->catalog_xmin = DatumGetTransactionId(slot_getattr(slot,
+																	   5, &isnull));
+		if (isnull)
+			remote_slot->catalog_xmin = InvalidTransactionId;
+
+		remote_slot->two_phase = DatumGetBool(slot_getattr(slot, 6, &isnull));
+		Assert(!isnull);
+
+		remote_slot->conflicting = DatumGetBool(slot_getattr(slot, 7, &isnull));
+		Assert(!isnull);
+
+		remote_slot->database = TextDatumGetCString(slot_getattr(slot,
+																 8, &isnull));
+		Assert(!isnull);
+
+		if (remote_slot->conflicting)
+			remote_slot->invalidated = get_remote_invalidation_cause(wrconn,
+																	 remote_slot->name);
+		else
+			remote_slot->invalidated = RS_INVAL_NONE;
+
+		/* Create list of remote slot names to be used by drop_obsolete_slots */
+		remote_slot_list = lappend(remote_slot_list, remote_slot);
+
+		synchronize_one_slot(wrconn, remote_slot);
+
+		/*
+		 * Update nap time in case of non-zero value returned. The zero value
+		 * is returned if remote_slot is not the one being monitored.
+		 */
+		value = compute_naptime(remote_slot);
+		if (value)
+			naptime = value;
+
+		ExecClearTuple(slot);
+	}
+
+	/*
+	 * Drop local slots which no longer need to be synced i.e. these either do
+	 * not exist on primary or are no longer part of synchronize_slot_names.
+	 */
+	drop_obsolete_slots(dbids, remote_slot_list);
+
+	LWLockRelease(SlotSyncWorkerLock);
+
+	/* We are done, free remot_slot_list elements */
+	foreach(cell, remote_slot_list)
+	{
+		RemoteSlot *remote_slot = (RemoteSlot *) lfirst(cell);
+
+		pfree(remote_slot);
+	}
+
+	walrcv_clear_result(res);
+
+	return naptime;
+}
+
+/*
+ * Initialize the list from raw synchronize_slot_names and cache it, in order
+ * to avoid parsing it repeatedly. Done at slot-sync worker startup and after
+ * each SIGHUP.
+ */
+static void
+SlotSyncInitSlotNamesList()
+{
+	char	   *rawname;
+
+	if (strcmp(synchronize_slot_names, "") != 0 &&
+		strcmp(synchronize_slot_names, "*") != 0)
+	{
+		rawname = pstrdup(synchronize_slot_names);
+		SplitIdentifierString(rawname, ',', &sync_slot_names_list);
+	}
+}
+
+/*
+ * Connect to remote (primary) server.
+ *
+ * This uses primary_conninfo in order to connect to primary. For slot-sync
+ * to work, primary_conninfo is expected to have dbname as well.
+ */
+static WalReceiverConn *
+remote_connect()
+{
+	WalReceiverConn *wrconn = NULL;
+	char	   *err;
+
+	wrconn = walrcv_connect(PrimaryConnInfo, true, false, "slot-sync", &err);
+	if (wrconn == NULL)
+		ereport(ERROR,
+				(errmsg("could not connect to the primary server: %s", err)));
+	return wrconn;
+}
+
+/*
+ * Reconnect to remote (primary) server if PrimaryConnInfo got changed.
+ */
+static WalReceiverConn *
+reconnect_if_needed(WalReceiverConn *wrconn_prev, char *conninfo_prev)
+{
+	WalReceiverConn *wrconn = NULL;
+
+	/* If no change in PrimaryConnInfo, return previous connection itself */
+	if (strcmp(conninfo_prev, PrimaryConnInfo) == 0)
+		return wrconn_prev;
+
+	walrcv_disconnect(wrconn);
+	wrconn = remote_connect();
+	return wrconn;
+}
+
+/*
+ * Interrupt handler for main loop of slot-sync worker.
+ */
+static bool
+ProcessSlotSyncInterrupts(WalReceiverConn *wrconn, char **conninfo_prev)
+{
+	bool		reload_done = false;
+
+	CHECK_FOR_INTERRUPTS();
+
+	if (ShutdownRequestPending)
+	{
+		elog(LOG, "Replication slot-sync worker %d is shutting"
+			 " down on receiving SIGINT", MySlotSyncWorker->slot);
+
+		/*
+		 * TODO: we need to take care of dropping the slots belonging to dbids
+		 * of this worker before exiting, for the case when all the dbids of
+		 * this worker are obsoleted/dropped on primary and that is the reason
+		 * for this worker's exit.
+		 */
+		walrcv_disconnect(wrconn);
+		proc_exit(0);
+	}
+
+	if (ConfigReloadPending)
+	{
+		ConfigReloadPending = false;
+
+		/* Save the PrimaryConnInfo before reloading */
+		*conninfo_prev = pstrdup(PrimaryConnInfo);
+
+		ProcessConfigFile(PGC_SIGHUP);
+		SlotSyncInitSlotNamesList();
+		reload_done = true;
+	}
+
+	return reload_done;
+}
+
+/*
+ * Detach the worker from DSM and update 'proc' and 'in_use'.
+ * Logical replication launcher will come to know using these
+ * that the worker has shutdown.
+ */
+static void
+slotsync_worker_detach(int code, Datum arg)
+{
+	dsa_detach((dsa_area *) DatumGetPointer(arg));
+	LWLockAcquire(SlotSyncWorkerLock, LW_EXCLUSIVE);
+	MySlotSyncWorker->hdr.in_use = false;
+	MySlotSyncWorker->hdr.proc = NULL;
+	LWLockRelease(SlotSyncWorkerLock);
+}
+
+/*
+ * The main loop of our worker process.
+ */
+void
+ReplSlotSyncWorkerMain(Datum main_arg)
+{
+	int			worker_slot = DatumGetInt32(main_arg);
+	dsa_handle	handle;
+	dsa_area   *dsa;
+	WalReceiverConn *wrconn = NULL;
+	char	   *dbname;
+
+	/* Setup signal handling */
+	pqsignal(SIGHUP, SignalHandlerForConfigReload);
+	pqsignal(SIGINT, SignalHandlerForShutdownRequest);
+	pqsignal(SIGTERM, die);
+	BackgroundWorkerUnblockSignals();
+
+	/*
+	 * Attach to the dynamic shared memory segment for the slot-sync worker
+	 * and find its table of contents.
+	 */
+	memcpy(&handle, MyBgworkerEntry->bgw_extra, sizeof(dsa_handle));
+	dsa = dsa_attach(handle);
+	if (!dsa)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("could not map dynamic shared memory "
+						"segment for slot-sync worker")));
+
+	/* Primary initialization is complete. Now attach to our slot. */
+	slotsync_worker_attach(worker_slot);
+
+	elog(LOG, "Replication slot-sync worker %d started", worker_slot);
+
+	before_shmem_exit(slotsync_worker_detach, PointerGetDatum(dsa));
+
+	/* Load the libpq-specific functions */
+	load_file("libpqwalreceiver", false);
+
+	/* Get the user provided dbname from the connection string */
+	dbname = walrcv_get_dbname_from_conninfo(PrimaryConnInfo);
+	if (dbname == NULL)
+		ereport(ERROR,
+				(errmsg("The dbname not specified in primary_conninfo, skipping"
+						" slots synchronization"),
+				 errhint("Specify dbname in primary_conninfo for slots"
+						 " synchronization to proceed")));
+
+	/*
+	 * Connect to the database specified by user in PrimaryConnInfo. We need
+	 * database connection for walrcv_exec to work. Please see comments atop
+	 * libpqrcv_exec.
+	 */
+	BackgroundWorkerInitializeConnection(dbname,
+										 NULL,
+										 0);
+	SlotSyncInitSlotNamesList();
+
+	/* Connect to primary node */
+	wrconn = remote_connect();
+
+	/* Main wait loop. */
+	for (;;)
+	{
+		int			rc;
+		long		naptime;
+		bool		config_reloaded = false;
+		char	   *conninfo_prev;
+
+		config_reloaded = ProcessSlotSyncInterrupts(wrconn, &conninfo_prev);
+
+		/* Reconnect if primary_conninfo got changed */
+		if (config_reloaded)
+			wrconn = reconnect_if_needed(wrconn, conninfo_prev);
+
+		if (!RecoveryInProgress())
+			proc_exit(0);
+
+		naptime = synchronize_slots(dsa, wrconn);
+
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+					   naptime,
+					   WAIT_EVENT_REPL_SLOTSYNC_MAIN);
+
+		ResetLatch(MyLatch);
+
+		/* Emergency bailout if postmaster has died */
+		if (rc & WL_POSTMASTER_DEATH)
+		{
+			walrcv_disconnect(wrconn);
+			proc_exit(1);
+		}
+	}
+
+	/*
+	 * The slot-sync worker must not get here because it will only stop when
+	 * it receives a SIGINT from the logical replication launcher, or when
+	 * there is an error. None of these cases will allow the code to reach
+	 * here.
+	 */
+	Assert(false);
+}
diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
index e2cee92cf2..7ca0b5464b 100644
--- a/src/backend/replication/logical/tablesync.c
+++ b/src/backend/replication/logical/tablesync.c
@@ -100,6 +100,7 @@
 #include "catalog/pg_subscription_rel.h"
 #include "catalog/pg_type.h"
 #include "commands/copy.h"
+#include "commands/subscriptioncmds.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "parser/parse_relation.h"
@@ -246,7 +247,7 @@ wait_for_worker_state_change(char expected_state)
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 		worker = logicalrep_worker_find(MyLogicalRepWorker->subid,
 										InvalidOid, false);
-		if (worker && worker->proc)
+		if (worker && worker->hdr.proc)
 			logicalrep_worker_wakeup_ptr(worker);
 		LWLockRelease(LogicalRepWorkerLock);
 		if (!worker)
@@ -535,7 +536,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 				if (rstate->state == SUBREL_STATE_SYNCWAIT)
 				{
 					/* Signal the sync worker, as it may be waiting for us. */
-					if (syncworker->proc)
+					if (syncworker->hdr.proc)
 						logicalrep_worker_wakeup_ptr(syncworker);
 
 					/* Now safe to release the LWLock */
diff --git a/src/backend/replication/repl_gram.y b/src/backend/replication/repl_gram.y
index 0c874e33cf..2b00bf845c 100644
--- a/src/backend/replication/repl_gram.y
+++ b/src/backend/replication/repl_gram.y
@@ -76,11 +76,12 @@ Node *replication_parse_result;
 %token K_EXPORT_SNAPSHOT
 %token K_NOEXPORT_SNAPSHOT
 %token K_USE_SNAPSHOT
+%token K_LIST_DBID_FOR_LOGICAL_SLOTS
 
 %type <node>	command
 %type <node>	base_backup start_replication start_logical_replication
 				create_replication_slot drop_replication_slot identify_system
-				read_replication_slot timeline_history show
+				read_replication_slot timeline_history show list_dbid_for_logical_slots
 %type <list>	generic_option_list
 %type <defelt>	generic_option
 %type <uintval>	opt_timeline
@@ -91,6 +92,7 @@ Node *replication_parse_result;
 %type <boolval>	opt_temporary
 %type <list>	create_slot_options create_slot_legacy_opt_list
 %type <defelt>	create_slot_legacy_opt
+%type <list>	slot_name_list slot_name_list_opt
 
 %%
 
@@ -114,6 +116,7 @@ command:
 			| read_replication_slot
 			| timeline_history
 			| show
+			| list_dbid_for_logical_slots
 			;
 
 /*
@@ -126,6 +129,33 @@ identify_system:
 				}
 			;
 
+slot_name_list:
+			IDENT
+				{
+					$$ = list_make1($1);
+				}
+			| slot_name_list ',' IDENT
+				{
+					$$ = lappend($1, $3);
+				}
+
+slot_name_list_opt:
+			slot_name_list			{ $$ = $1; }
+			| /* EMPTY */			{ $$ = NIL; }
+		;
+
+/*
+ * LIST_DBID_FOR_LOGICAL_SLOTS
+ */
+list_dbid_for_logical_slots:
+			K_LIST_DBID_FOR_LOGICAL_SLOTS slot_name_list_opt
+				{
+					ListDBForLogicalSlotsCmd *cmd = makeNode(ListDBForLogicalSlotsCmd);
+					cmd->slot_names = $2;
+					$$ = (Node *) cmd;
+				}
+			;
+
 /*
  * READ_REPLICATION_SLOT %s
  */
diff --git a/src/backend/replication/repl_scanner.l b/src/backend/replication/repl_scanner.l
index 1cc7fb858c..d4ecce6a47 100644
--- a/src/backend/replication/repl_scanner.l
+++ b/src/backend/replication/repl_scanner.l
@@ -128,6 +128,7 @@ DROP_REPLICATION_SLOT		{ return K_DROP_REPLICATION_SLOT; }
 TIMELINE_HISTORY	{ return K_TIMELINE_HISTORY; }
 PHYSICAL			{ return K_PHYSICAL; }
 RESERVE_WAL			{ return K_RESERVE_WAL; }
+LIST_DBID_FOR_LOGICAL_SLOTS	{ return K_LIST_DBID_FOR_LOGICAL_SLOTS; }
 LOGICAL				{ return K_LOGICAL; }
 SLOT				{ return K_SLOT; }
 TEMPORARY			{ return K_TEMPORARY; }
@@ -304,6 +305,7 @@ replication_scanner_is_replication_command(void)
 		case K_READ_REPLICATION_SLOT:
 		case K_TIMELINE_HISTORY:
 		case K_SHOW:
+		case K_LIST_DBID_FOR_LOGICAL_SLOTS:
 			/* Yes; push back the first token so we can parse later. */
 			repl_pushed_back_token = first_token;
 			return true;
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 7370452d3b..364049b93f 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -92,7 +92,7 @@ typedef struct ReplicationSlotOnDisk
 	sizeof(ReplicationSlotOnDisk) - ReplicationSlotOnDiskConstantSize
 
 #define SLOT_MAGIC		0x1051CA1	/* format identifier */
-#define SLOT_VERSION	3		/* version for new files */
+#define SLOT_VERSION	4		/* version for new files */
 
 /* Control array for replication slot management */
 ReplicationSlotCtlData *ReplicationSlotCtl = NULL;
@@ -317,6 +317,7 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	slot->data.persistency = persistency;
 	slot->data.two_phase = two_phase;
 	slot->data.two_phase_at = InvalidXLogRecPtr;
+	slot->data.synced = false;
 
 	/* and then data only present in shared memory */
 	slot->just_dirtied = false;
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 6035cf4816..a1bc090f58 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -225,6 +225,35 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 	PG_RETURN_VOID();
 }
 
+/*
+ * SQL function for getting invalidation cause of a slot.
+ *
+ * Returns ReplicationSlotInvalidationCause enum value for valid slot_name;
+ * returns NULL if slot with given name is not found.
+ *
+ * It return RS_INVAL_NONE if the given slot is not invalidated.
+ */
+Datum
+pg_get_slot_invalidation_cause(PG_FUNCTION_ARGS)
+{
+	Name		name = PG_GETARG_NAME(0);
+	int			slotno;
+
+	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
+	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	{
+		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[slotno];
+
+		if (strcmp(NameStr(s->data.name), NameStr(*name)) == 0)
+		{
+			PG_RETURN_INT16(s->data.invalidated);
+		}
+	}
+	LWLockRelease(ReplicationSlotControlLock);
+
+	PG_RETURN_NULL();
+}
+
 /*
  * pg_get_replication_slots - SQL SRF showing all replication slots
  * that currently exist on the database cluster.
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
old mode 100644
new mode 100755
index 464c278afe..73b01ce34c
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -473,6 +473,120 @@ IdentifySystem(void)
 	end_tup_output(tstate);
 }
 
+static int
+pg_qsort_namecmp(const void *a, const void *b)
+{
+	return strncmp(NameStr(*(Name) a), NameStr(*(Name) b), NAMEDATALEN);
+}
+
+/*
+ * Handle the LIST_DBID_FOR_LOGICAL_SLOTS command.
+ *
+ * Given the slot-names, this function returns the list of database-ids
+ * corresponding to those slots. The returned list has no duplicates.
+ */
+static void
+ListSlotDatabaseOIDs(ListDBForLogicalSlotsCmd *cmd)
+{
+	DestReceiver *dest;
+	TupOutputState *tstate;
+	TupleDesc	tupdesc;
+	NameData   *slot_names = NULL;
+	int			numslot_names;
+	List	   *database_oids_list = NIL;
+	int			slotno;
+
+	numslot_names = list_length(cmd->slot_names);
+	if (numslot_names)
+	{
+		ListCell   *lc;
+		int			i = 0;
+
+		slot_names = palloc(numslot_names * sizeof(NameData));
+		foreach(lc, cmd->slot_names)
+		{
+			char	   *slot_name = lfirst(lc);
+
+			ReplicationSlotValidateName(slot_name, ERROR);
+			namestrcpy(&slot_names[i++], slot_name);
+		}
+
+		qsort(slot_names, numslot_names, sizeof(NameData), pg_qsort_namecmp);
+	}
+
+	dest = CreateDestReceiver(DestRemoteSimple);
+
+	/* Need a tuple descriptor representing a single column */
+	tupdesc = CreateTemplateTupleDesc(1);
+	TupleDescInitBuiltinEntry(tupdesc, (AttrNumber) 1, "database_oid",
+							  INT8OID, -1, 0);
+
+	/* Prepare for projection of tuples */
+	tstate = begin_tup_output_tupdesc(dest, tupdesc, &TTSOpsVirtual);
+
+	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
+	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	{
+		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
+		Oid			dboid;
+		Datum		values[1];
+		bool		nulls[1];
+
+		if (!slot->in_use)
+			continue;
+
+		SpinLockAcquire(&slot->mutex);
+
+		dboid = slot->data.database;
+
+		SpinLockRelease(&slot->mutex);
+
+		if (numslot_names)
+		{
+			/*
+			 * If slot names were provided and the current slot name is not in
+			 * the list, skip it.
+			 */
+			if (!bsearch((void *) &slot->data.name, (void *) slot_names,
+						 numslot_names, sizeof(NameData), pg_qsort_namecmp))
+				continue;
+
+			/*
+			 * If the current slot is a physical slot, error out. We are
+			 * supposed to get only logical slots for sync-slot purpose.
+			 */
+			if (SlotIsPhysical(slot))
+				ereport(ERROR,
+						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+						 errmsg("physical replication slot %s found in "
+								"synchronize_slot_names",
+								NameStr(slot->data.name))));
+		}
+
+		/*
+		 * Check if the database OID is already in the list, and if so, skip
+		 * this slot.
+		 */
+		if (OidIsValid(dboid) && list_member_oid(database_oids_list, dboid))
+			continue;
+
+		/* Add the database OID to the list */
+		database_oids_list = lappend_oid(database_oids_list, dboid);
+
+		values[0] = Int64GetDatum(dboid);
+		nulls[0] = (dboid == InvalidOid);
+
+		/* Send it to dest */
+		do_tup_output(tstate, values, nulls);
+	}
+	LWLockRelease(ReplicationSlotControlLock);
+
+	/* Clean up the list */
+	list_free(database_oids_list);
+
+	end_tup_output(tstate);
+}
+
 /* Handle READ_REPLICATION_SLOT command */
 static void
 ReadReplicationSlot(ReadReplicationSlotCmd *cmd)
@@ -1990,6 +2104,13 @@ exec_replication_command(const char *cmd_string)
 			EndReplicationCommand(cmdtag);
 			break;
 
+		case T_ListDBForLogicalSlotsCmd:
+			cmdtag = "LIST_DBID_FOR_LOGICAL_SLOTS";
+			set_ps_display(cmdtag);
+			ListSlotDatabaseOIDs((ListDBForLogicalSlotsCmd *) cmd_node);
+			EndReplicationCommand(cmdtag);
+			break;
+
 		case T_StartReplicationCmd:
 			{
 				StartReplicationCmd *cmd = (StartReplicationCmd *) cmd_node;
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 315a78cda9..fd9e73a49b 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -190,6 +190,8 @@ static const char *const BuiltinTrancheNames[] = {
 	"LogicalRepLauncherDSA",
 	/* LWTRANCHE_LAUNCHER_HASH: */
 	"LogicalRepLauncherHash",
+	/* LWTRANCHE_SLOTSYNC_DSA: */
+	"SlotSyncWorkerDSA",
 };
 
 StaticAssertDecl(lengthof(BuiltinTrancheNames) ==
diff --git a/src/backend/storage/lmgr/lwlocknames.txt b/src/backend/storage/lmgr/lwlocknames.txt
index f72f2906ce..e62a3f1bc0 100644
--- a/src/backend/storage/lmgr/lwlocknames.txt
+++ b/src/backend/storage/lmgr/lwlocknames.txt
@@ -54,3 +54,4 @@ XactTruncationLock					44
 WrapLimitsVacuumLock				46
 NotifyQueueTailLock					47
 WaitEventExtensionLock				48
+SlotSyncWorkerLock					49
diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt
index daf2d57d3d..adcf879040 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -53,6 +53,7 @@ LOGICAL_APPLY_MAIN	"Waiting in main loop of logical replication apply process."
 LOGICAL_LAUNCHER_MAIN	"Waiting in main loop of logical replication launcher process."
 LOGICAL_PARALLEL_APPLY_MAIN	"Waiting in main loop of logical replication parallel apply process."
 RECOVERY_WAL_STREAM	"Waiting in main loop of startup process for WAL to arrive, during streaming recovery."
+REPL_SLOTSYNC_MAIN	"Waiting in main loop of worker for synchronizing slots to a standby from primary."
 SYSLOGGER_MAIN	"Waiting in main loop of syslogger process."
 WAL_RECEIVER_MAIN	"Waiting in main loop of WAL receiver process."
 WAL_SENDER_MAIN	"Waiting in main loop of WAL sender process."
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 864f80f328..4fae88af75 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -64,8 +64,11 @@
 #include "postmaster/syslogger.h"
 #include "postmaster/walwriter.h"
 #include "replication/logicallauncher.h"
+#include "replication/reorderbuffer.h"
 #include "replication/slot.h"
 #include "replication/syncrep.h"
+#include "replication/walreceiver.h"
+#include "replication/walsender.h"
 #include "storage/bufmgr.h"
 #include "storage/large_object.h"
 #include "storage/pg_shmem.h"
@@ -3497,6 +3500,19 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"max_slotsync_workers",
+			PGC_POSTMASTER,
+			REPLICATION_STANDBY,
+			gettext_noop("Maximum number of slot synchronization workers "
+						 "on a standby."),
+			NULL,
+		},
+		&max_slotsync_workers,
+		2, 0, MAX_SLOTSYNC_WORKER_LIMIT,
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0, 0, 0, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index f1c87bd2d6..4f0bc2df28 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -357,6 +357,8 @@
 #recovery_min_apply_delay = 0		# minimum delay for applying changes during recovery
 #synchronize_slot_names = ''	# replication slot names to synchronize from
 					# primary to streaming replication standby server
+#max_slotsync_workers = 2		# maximum number of slot synchronization workers
+					# on a standby
 
 # - Subscribers -
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 9805bc6118..947785af43 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -11074,6 +11074,10 @@
   proname => 'pg_drop_replication_slot', provolatile => 'v', proparallel => 'u',
   prorettype => 'void', proargtypes => 'name',
   prosrc => 'pg_drop_replication_slot' },
+{ oid => '6312', descr => 'what caused the replication slot to become invalid',
+  proname => 'pg_get_slot_invalidation_cause', provolatile => 's', proisstrict => 't',
+  prorettype => 'int2', proargtypes => 'name',
+  prosrc => 'pg_get_slot_invalidation_cause' },
 { oid => '3781',
   descr => 'information about replication slots currently in use',
   proname => 'pg_get_replication_slots', prorows => '10', proisstrict => 'f',
diff --git a/src/include/commands/subscriptioncmds.h b/src/include/commands/subscriptioncmds.h
index 214dc6c29e..75b4b2040d 100644
--- a/src/include/commands/subscriptioncmds.h
+++ b/src/include/commands/subscriptioncmds.h
@@ -17,6 +17,7 @@
 
 #include "catalog/objectaddress.h"
 #include "parser/parse_node.h"
+#include "replication/walreceiver.h"
 
 extern ObjectAddress CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 										bool isTopLevel);
@@ -28,4 +29,7 @@ extern void AlterSubscriptionOwner_oid(Oid subid, Oid newOwnerId);
 
 extern char defGetStreamingMode(DefElem *def);
 
+extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn,
+										char *slotname, bool missing_ok);
+
 #endif							/* SUBSCRIPTIONCMDS_H */
diff --git a/src/include/nodes/replnodes.h b/src/include/nodes/replnodes.h
index 4321ba8f86..bc9c1baea1 100644
--- a/src/include/nodes/replnodes.h
+++ b/src/include/nodes/replnodes.h
@@ -33,6 +33,15 @@ typedef struct IdentifySystemCmd
 	NodeTag		type;
 } IdentifySystemCmd;
 
+/* -------------------------------
+ *		LIST_DBID_FOR_LOGICAL_SLOTS command
+ * -------------------------------
+ */
+typedef struct ListDBForLogicalSlotsCmd
+{
+	NodeTag		type;
+	List	   *slot_names;
+} ListDBForLogicalSlotsCmd;
 
 /* ----------------------
  *		BASE_BACKUP command
diff --git a/src/include/postmaster/bgworker_internals.h b/src/include/postmaster/bgworker_internals.h
index 4ad63fd9bd..cccc5da8b2 100644
--- a/src/include/postmaster/bgworker_internals.h
+++ b/src/include/postmaster/bgworker_internals.h
@@ -22,6 +22,7 @@
  * Maximum possible value of parallel workers.
  */
 #define MAX_PARALLEL_WORKER_LIMIT 1024
+#define MAX_SLOTSYNC_WORKER_LIMIT 50
 
 /*
  * List of background workers, private to postmaster.
diff --git a/src/include/replication/logicallauncher.h b/src/include/replication/logicallauncher.h
index a07c9cb311..891ce08cf1 100644
--- a/src/include/replication/logicallauncher.h
+++ b/src/include/replication/logicallauncher.h
@@ -15,6 +15,8 @@
 extern PGDLLIMPORT int max_logical_replication_workers;
 extern PGDLLIMPORT int max_sync_workers_per_subscription;
 extern PGDLLIMPORT int max_parallel_apply_workers_per_subscription;
+extern PGDLLIMPORT int max_slotsync_workers;
+
 
 extern void ApplyLauncherRegister(void);
 extern void ApplyLauncherMain(Datum main_arg);
@@ -31,4 +33,6 @@ extern bool IsLogicalLauncher(void);
 
 extern pid_t GetLeaderApplyWorkerPid(pid_t pid);
 
+extern PGDLLIMPORT char *PrimaryConnInfo;
+
 #endif							/* LOGICALLAUNCHER_H */
diff --git a/src/include/replication/logicalworker.h b/src/include/replication/logicalworker.h
index bbd71d0b42..baad5a8f3a 100644
--- a/src/include/replication/logicalworker.h
+++ b/src/include/replication/logicalworker.h
@@ -19,6 +19,7 @@ extern PGDLLIMPORT volatile sig_atomic_t ParallelApplyMessagePending;
 extern void ApplyWorkerMain(Datum main_arg);
 extern void ParallelApplyWorkerMain(Datum main_arg);
 extern void TablesyncWorkerMain(Datum main_arg);
+extern void ReplSlotSyncWorkerMain(Datum main_arg);
 
 extern bool IsLogicalWorker(void);
 extern bool IsLogicalParallelApplyWorker(void);
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 38c0072043..33a92e4879 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -15,7 +15,6 @@
 #include "storage/lwlock.h"
 #include "storage/shmem.h"
 #include "storage/spin.h"
-#include "replication/walreceiver.h"
 
 /*
  * Behaviour of replication slots, upon release or crash.
@@ -111,6 +110,11 @@ typedef struct ReplicationSlotPersistentData
 
 	/* plugin name */
 	NameData	plugin;
+
+	/*
+	 * Is this a slot created by a sync-slot worker?
+	 */
+	bool		synced;
 } ReplicationSlotPersistentData;
 
 /*
@@ -251,7 +255,6 @@ extern ReplicationSlot *SearchNamedReplicationSlot(const char *name, bool need_l
 extern int	ReplicationSlotIndex(ReplicationSlot *slot);
 extern bool ReplicationSlotName(int index, Name name);
 extern void ReplicationSlotNameForTablesync(Oid suboid, Oid relid, char *syncslotname, Size szslot);
-extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname, bool missing_ok);
 
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 281626fa6f..e856a0130a 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -20,6 +20,7 @@
 #include "pgtime.h"
 #include "port/atomics.h"
 #include "replication/logicalproto.h"
+#include "replication/slot.h"
 #include "replication/walsender.h"
 #include "storage/condition_variable.h"
 #include "storage/latch.h"
@@ -191,6 +192,16 @@ typedef struct
 	}			proto;
 } WalRcvStreamOptions;
 
+/*
+ * Slot's DBid related data
+ */
+typedef struct WalRcvRepSlotDbData
+{
+	Oid			database;		/* Slot's DBid received from remote */
+	TimestampTz last_launch_time;	/* The last time we tried to launch sync
+									 * worker for above Dbid */
+} WalRcvRepSlotDbData;
+
 struct WalReceiverConn;
 typedef struct WalReceiverConn WalReceiverConn;
 
@@ -280,6 +291,22 @@ typedef void (*walrcv_get_senderinfo_fn) (WalReceiverConn *conn,
 typedef char *(*walrcv_identify_system_fn) (WalReceiverConn *conn,
 											TimeLineID *primary_tli);
 
+/*
+ * walrcv_get_dbinfo_for_logical_slots_fn
+ *
+ * Run LIST_DBID_FOR_LOGICAL_SLOTS on primary server to get the
+ * list of unique DBIDs for logical slots mentioned in 'slots'
+ */
+typedef List *(*walrcv_get_dbinfo_for_logical_slots_fn) (WalReceiverConn *conn,
+													  const char *slots);
+
+/*
+ * walrcv_get_dbname_from_conninfo_fn
+ *
+ * Returns the dbid from the primary_conninfo
+ */
+typedef char *(*walrcv_get_dbname_from_conninfo_fn) (const char *conninfo);
+
 /*
  * walrcv_server_version_fn
  *
@@ -393,6 +420,8 @@ typedef struct WalReceiverFunctionsType
 	walrcv_get_conninfo_fn walrcv_get_conninfo;
 	walrcv_get_senderinfo_fn walrcv_get_senderinfo;
 	walrcv_identify_system_fn walrcv_identify_system;
+	walrcv_get_dbinfo_for_logical_slots_fn walrcv_get_dbinfo_for_logical_slots;
+	walrcv_get_dbname_from_conninfo_fn walrcv_get_dbname_from_conninfo;
 	walrcv_server_version_fn walrcv_server_version;
 	walrcv_readtimelinehistoryfile_fn walrcv_readtimelinehistoryfile;
 	walrcv_startstreaming_fn walrcv_startstreaming;
@@ -417,6 +446,10 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_get_senderinfo(conn, sender_host, sender_port)
 #define walrcv_identify_system(conn, primary_tli) \
 	WalReceiverFunctions->walrcv_identify_system(conn, primary_tli)
+#define walrcv_get_dbinfo_for_logical_slots(conn, slots) \
+	WalReceiverFunctions->walrcv_get_dbinfo_for_logical_slots(conn, slots)
+#define walrcv_get_dbname_from_conninfo(conninfo) \
+	WalReceiverFunctions->walrcv_get_dbname_from_conninfo(conninfo)
 #define walrcv_server_version(conn) \
 	WalReceiverFunctions->walrcv_server_version(conn)
 #define walrcv_readtimelinehistoryfile(conn, tli, filename, content, size) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 8f4bed0958..b17fb7d5bb 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -36,11 +36,9 @@ typedef enum LogicalRepWorkerType
 	WORKERTYPE_PARALLEL_APPLY
 } LogicalRepWorkerType;
 
-typedef struct LogicalRepWorker
+/* Common data for Slotsync and LogicalRep workers */
+typedef struct LogicalWorkerHeader
 {
-	/* What type of worker is this? */
-	LogicalRepWorkerType type;
-
 	/* Time at which this worker was launched. */
 	TimestampTz launch_time;
 
@@ -53,6 +51,15 @@ typedef struct LogicalRepWorker
 	/* Pointer to proc array. NULL if not running. */
 	PGPROC	   *proc;
 
+} LogicalWorkerHeader;
+
+typedef struct LogicalRepWorker
+{
+	LogicalWorkerHeader hdr;
+
+	/* What type of worker is this? */
+	LogicalRepWorkerType type;
+
 	/* Database id to connect to. */
 	Oid			dbid;
 
@@ -96,6 +103,41 @@ typedef struct LogicalRepWorker
 	TimestampTz reply_time;
 } LogicalRepWorker;
 
+/*
+ * Shared memory structure for Slot-Sync worker. It is allocated by logical
+ * replication launcher and then read by each slot-sync worker.
+ *
+ * It is protected by LWLock (SlotSyncWorkerLock). Each slot-sync worker
+ * reading the structure needs to hold the lock in shared mode, whereas
+ * the logical replication launcher which updates it needs to hold the lock
+ * in exclusive mode.
+ */
+typedef struct SlotSyncWorker
+{
+	LogicalWorkerHeader hdr;
+
+	/* The slot in worker pool to which slot-sync worker is attached */
+	int			slot;
+
+	/* Count of dbids slot-sync worker manages */
+	uint32		dbcount;
+
+	/* DSA for dbids */
+	dsa_area   *dbids_dsa;
+
+	/* dsa_pointer for dbids slot-sync worker manages */
+	dsa_pointer dbids_dp;
+
+	/* Info about slot being monitored for worker's naptime purpose */
+	struct SlotSyncWorkerWatchSlot
+	{
+		NameData	slot_name;
+		XLogRecPtr	confirmed_lsn;
+		TimestampTz last_update_time;
+	}			monitoring_info;
+
+} SlotSyncWorker;
+
 /*
  * State of the transaction in parallel apply worker.
  *
@@ -234,12 +276,14 @@ extern PGDLLIMPORT struct WalReceiverConn *LogRepWorkerWalRcvConn;
 /* Worker and subscription objects. */
 extern PGDLLIMPORT Subscription *MySubscription;
 extern PGDLLIMPORT LogicalRepWorker *MyLogicalRepWorker;
+extern PGDLLIMPORT SlotSyncWorker *MySlotSyncWorker;
 
 extern PGDLLIMPORT bool in_remote_transaction;
 
 extern PGDLLIMPORT bool InitializingApplyWorker;
 
 extern void logicalrep_worker_attach(int slot);
+extern void slotsync_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
 extern List *logicalrep_workers_find(Oid subid, bool only_running);
@@ -327,9 +371,9 @@ extern void pa_decr_and_wait_stream_block(void);
 extern void pa_xact_finish(ParallelApplyWorkerInfo *winfo,
 						   XLogRecPtr remote_lsn);
 
-#define isParallelApplyWorker(worker) ((worker)->in_use && \
+#define isParallelApplyWorker(worker) ((worker)->hdr.in_use && \
 									   (worker)->type == WORKERTYPE_PARALLEL_APPLY)
-#define isTablesyncWorker(worker) ((worker)->in_use && \
+#define isTablesyncWorker(worker) ((worker)->hdr.in_use && \
 								   (worker)->type == WORKERTYPE_TABLESYNC)
 
 static inline bool
@@ -341,14 +385,14 @@ am_tablesync_worker(void)
 static inline bool
 am_leader_apply_worker(void)
 {
-	Assert(MyLogicalRepWorker->in_use);
+	Assert(MyLogicalRepWorker->hdr.in_use);
 	return (MyLogicalRepWorker->type == WORKERTYPE_APPLY);
 }
 
 static inline bool
 am_parallel_apply_worker(void)
 {
-	Assert(MyLogicalRepWorker->in_use);
+	Assert(MyLogicalRepWorker->hdr.in_use);
 	return isParallelApplyWorker(MyLogicalRepWorker);
 }
 
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index d77410bdea..334315acba 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -207,6 +207,7 @@ typedef enum BuiltinTrancheIds
 	LWTRANCHE_PGSTATS_DATA,
 	LWTRANCHE_LAUNCHER_DSA,
 	LWTRANCHE_LAUNCHER_HASH,
+	LWTRANCHE_SLOTSYNC_DSA,
 	LWTRANCHE_FIRST_USER_DEFINED
 }			BuiltinTrancheIds;
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index b5bbdd1608..4dc2ed5304 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1428,6 +1428,7 @@ LimitState
 LimitStateCond
 List
 ListCell
+ListDBForLogicalSlotsCmd
 ListDictionary
 ListParsedLex
 ListenAction
@@ -1505,6 +1506,7 @@ LogicalRepWorkerType
 LogicalRewriteMappingData
 LogicalTape
 LogicalTapeSet
+LogicalWorkerHeader
 LsnReadQueue
 LsnReadQueueNextFun
 LsnReadQueueNextStatus
@@ -2305,6 +2307,7 @@ RelocationBufferInfo
 RelptrFreePageBtree
 RelptrFreePageManager
 RelptrFreePageSpanLeader
+RemoteSlot
 RenameStmt
 ReopenPtrType
 ReorderBuffer
@@ -2560,6 +2563,7 @@ SlabBlock
 SlabContext
 SlabSlot
 SlotNumber
+SlotSyncWorker
 SlruCtl
 SlruCtlData
 SlruErrorCause
@@ -3006,6 +3010,7 @@ WalLevel
 WalRcvData
 WalRcvExecResult
 WalRcvExecStatus
+WalRcvRepSlotDbData
 WalRcvState
 WalRcvStreamOptions
 WalRcvWakeupReason
-- 
2.34.1

