From cfedbb660935e72291cbab69c4afdfdb53e37811 Mon Sep 17 00:00:00 2001
From: Shveta Malik <shveta.malik@gmail.com>
Date: Fri, 27 Oct 2023 14:37:30 +0530
Subject: [PATCH v26 2/3] 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
replication can be resumed after failover. All the failover 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 failover
logical slots information and create/update the slots locally.

GUC 'enable_syncslot' enables a physical standby to synchronize failover
logical replication slots from the primary server.

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

The replication launcher on the physical standby queries primary
to get the list of dbids for failover logical slots. 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.

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 and dropped. Any attempt to perform logical
decoding 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).
---
 doc/src/sgml/config.sgml                      |  56 +-
 doc/src/sgml/system-views.sgml                |  10 +
 src/backend/catalog/system_views.sql          |   3 +-
 src/backend/postmaster/bgworker.c             |   5 +-
 .../libpqwalreceiver/libpqwalreceiver.c       |  89 ++
 src/backend/replication/logical/Makefile      |   1 +
 .../replication/logical/applyparallelworker.c |   3 +-
 src/backend/replication/logical/launcher.c    | 976 ++++++++++++++++--
 src/backend/replication/logical/logical.c     |  12 +
 src/backend/replication/logical/meson.build   |   1 +
 src/backend/replication/logical/slotsync.c    | 963 +++++++++++++++++
 src/backend/replication/logical/tablesync.c   |   5 +-
 src/backend/replication/repl_gram.y           |  14 +-
 src/backend/replication/repl_scanner.l        |   2 +
 src/backend/replication/slot.c                |  16 +-
 src/backend/replication/slotfuncs.c           |  35 +-
 src/backend/replication/walsender.c           |  79 +-
 src/backend/storage/lmgr/lwlock.c             |   2 +
 src/backend/storage/lmgr/lwlocknames.txt      |   1 +
 .../utils/activity/wait_event_names.txt       |   2 +
 src/backend/utils/misc/guc_tables.c           |  25 +
 src/backend/utils/misc/postgresql.conf.sample |   2 +
 src/include/catalog/pg_proc.dat               |  10 +-
 src/include/commands/subscriptioncmds.h       |   4 +
 src/include/nodes/replnodes.h                 |   9 +
 src/include/postmaster/bgworker_internals.h   |   1 +
 src/include/replication/logicallauncher.h     |   7 +-
 src/include/replication/logicalworker.h       |   1 +
 src/include/replication/slot.h                |  12 +-
 src/include/replication/walreceiver.h         |  30 +
 src/include/replication/worker_internal.h     |  60 +-
 src/include/storage/lwlock.h                  |   1 +
 src/test/regress/expected/rules.out           |   5 +-
 src/test/regress/expected/sysviews.out        |   3 +-
 src/tools/pgindent/typedefs.list              |   5 +
 35 files changed, 2305 insertions(+), 145 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 7604c7cb85..a81528e34b 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4556,10 +4556,13 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
           A password needs to be provided too, if the sender demands password
           authentication.  It can be provided in the
           <varname>primary_conninfo</varname> string, or in a separate
-          <filename>~/.pgpass</filename> file on the standby server (use
-          <literal>replication</literal> as the database name).
-          Do not specify a database name in the
-          <varname>primary_conninfo</varname> string.
+          <filename>~/.pgpass</filename> file on the standby server.
+         </para>
+         <para>
+          Specify dbname in <varname>primary_conninfo</varname> string
+          to allow synchronization of slots from the primary to standby.
+          This will only be used for slot synchronization. It is ignored
+          for streaming.
          </para>
          <para>
           This parameter can only be set in the <filename>postgresql.conf</filename>
@@ -4884,6 +4887,51 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-enable-syncslot" xreflabel="enable_syncslot">
+      <term><varname>enable_syncslot</varname> (<type>boolean</type>)
+      <indexterm>
+       <primary><varname>enable_syncslot</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        It enables a physical standby to synchronize logical replication failover slots
+        from the primary server so that logical subscribers are not blocked after failover.
+       </para>
+       <para>
+        It is enabled by default. This parameter can only be set in the
+        <filename>postgresql.conf</filename> file or on the server command line.
+       </para>
+      </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.
+       </para>
+      </listitem>
+     </varlistentry>
+
+
      </variablelist>
     </sect2>
 
diff --git a/doc/src/sgml/system-views.sgml b/doc/src/sgml/system-views.sgml
index 8858d47f01..713f993887 100644
--- a/doc/src/sgml/system-views.sgml
+++ b/doc/src/sgml/system-views.sgml
@@ -2543,6 +2543,16 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
        after failover. Always false for physical slots.
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>synced_slot</structfield> <type>bool</type>
+      </para>
+      <para>
+       True if this logical slot is created on the physical standby as part of
+       slot-synchronization from the primary server. Always false for physical slots.
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 04c9d083da..325812ab23 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1003,7 +1003,8 @@ CREATE VIEW pg_replication_slots AS
             L.safe_wal_size,
             L.two_phase,
             L.conflicting,
-            L.failover
+            L.failover,
+            L.synced_slot
     FROM pg_get_replication_slots() AS L
             LEFT JOIN pg_database D ON (L.datoid = D.oid);
 
diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
index 48a9924527..0e039c786f 100644
--- a/src/backend/postmaster/bgworker.c
+++ b/src/backend/postmaster/bgworker.c
@@ -125,11 +125,14 @@ static const struct
 		"ParallelWorkerMain", ParallelWorkerMain
 	},
 	{
-		"ApplyLauncherMain", ApplyLauncherMain
+		"LauncherMain", LauncherMain
 	},
 	{
 		"ApplyWorkerMain", ApplyWorkerMain
 	},
+	{
+		"ReplSlotSyncWorkerMain", ReplSlotSyncWorkerMain
+	},
 	{
 		"ParallelApplyWorkerMain", ParallelApplyWorkerMain
 	},
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3ffcd74698..f33ae53d75 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 +59,8 @@ 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_failover_slots(WalReceiverConn *conn);
+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,
@@ -97,6 +100,8 @@ static WalReceiverFunctionsType PQWalReceiverFunctions = {
 	.walrcv_receive = libpqrcv_receive,
 	.walrcv_send = libpqrcv_send,
 	.walrcv_create_slot = libpqrcv_create_slot,
+	.walrcv_get_dbinfo_for_failover_slots = libpqrcv_get_dbinfo_for_failover_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
@@ -410,6 +415,90 @@ libpqrcv_server_version(WalReceiverConn *conn)
 	return PQserverVersion(conn->streamConn);
 }
 
+/*
+ * Get DB info for failover slots
+ *
+ * It gets the DBIDs for failover logical slots from primary. The list returned
+ * by LIST_DBID_FOR_FAILOVER_SLOTS has no duplicates.
+ */
+static List *
+libpqrcv_get_dbinfo_for_failover_slots(WalReceiverConn *conn)
+{
+	PGresult   *res;
+	List	   *slotlist = NIL;
+	int			ntuples;
+	WalRcvFailoverSlotsData *slot_data;
+
+	res = libpqrcv_PQexec(conn->streamConn, "LIST_DBID_FOR_FAILOVER_SLOTS");
+
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		PQclear(res);
+		ereport(ERROR,
+				(errmsg("could not receive failover slots dbinfo 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 failover slots dbinfo: got %d fields, "
+						   "expected 1", nfields)));
+	}
+
+	ntuples = PQntuples(res);
+	for (int i = 0; i < ntuples; i++)
+	{
+		slot_data = palloc0(sizeof(WalRcvFailoverSlotsData));
+		if (!PQgetisnull(res, i, 0))
+			slot_data->dboid = atooid(PQgetvalue(res, i, 0));
+
+		slotlist = lappend(slotlist, slot_data);
+	}
+
+	PQclear(res);
+
+	return slotlist;
+}
+
+/*
+ * Get database name from primary conninfo.
+ *
+ * If dbname is not found in connInfo, return 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)
+	{
+		/* If multiple dbnames are used, then the last one will be returned */
+		if (strcmp(opt->keyword, "dbname") == 0 && opt->val && 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 9b37736f8e..192c9e1860 100644
--- a/src/backend/replication/logical/applyparallelworker.c
+++ b/src/backend/replication/logical/applyparallelworker.c
@@ -922,7 +922,8 @@ 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 501910b445..9b9aed5625 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 +58,31 @@
 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;
+bool		enable_syncslot = true;
+
+/*
+ * Local variables to store the current values of slot-sync related GUCs
+ * before each ConfigReload.
+ */
+static char *PrimaryConnInfoPreReload = NULL;
+static char *PrimarySlotNamePreReload = NULL;
+static bool EnableSyncSlotPreReload;
+static bool HotStandbyFeedbackPreReload;
+
+/*
+ * 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 +96,7 @@ 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 +129,7 @@ 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 +206,8 @@ 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 +216,14 @@ 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 +231,32 @@ 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 +299,8 @@ 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 +327,8 @@ 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 +389,7 @@ retry:
 	{
 		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
 
-		if (!w->in_use)
+		if (!w->hdr.in_use)
 		{
 			worker = w;
 			slot = i;
@@ -380,8 +418,8 @@ 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 +475,10 @@ 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 +495,7 @@ 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 +548,7 @@ 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 +560,23 @@ 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 +592,7 @@ 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 +606,7 @@ 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 +633,7 @@ 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 +646,7 @@ logicalrep_worker_stop_internal(LogicalRepWorker *worker, int signo)
 			CHECK_FOR_INTERRUPTS();
 		}
 
-		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		LWLockAcquire(lock, LW_SHARED);
 	}
 }
 
@@ -623,7 +665,9 @@ 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 +713,10 @@ 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 +742,14 @@ 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 +764,7 @@ 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 +773,7 @@ logicalrep_worker_attach(int slot)
 						slot)));
 	}
 
-	if (MyLogicalRepWorker->proc)
+	if (MyLogicalRepWorker->hdr.proc)
 	{
 		LWLockRelease(LogicalRepWorkerLock);
 		ereport(ERROR,
@@ -736,7 +782,7 @@ 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 +817,9 @@ 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 +842,10 @@ 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;
@@ -931,9 +979,18 @@ 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_function_name, BGW_MAXLEN, "LauncherMain");
 	snprintf(bgw.bgw_name, BGW_MAXLEN,
 			 "logical replication launcher");
 	snprintf(bgw.bgw_type, BGW_MAXLEN,
@@ -953,6 +1010,7 @@ void
 ApplyLauncherShmemInit(void)
 {
 	bool		found;
+	Size		ssw_size;
 
 	LogicalRepCtx = (LogicalRepCtxStruct *)
 		ShmemInitStruct("Logical Replication Launcher Data",
@@ -977,6 +1035,14 @@ 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);
 }
 
 /*
@@ -1115,13 +1181,724 @@ ApplyLauncherWakeup(void)
 }
 
 /*
- * Main loop for the apply launcher process.
+ * 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;
+
+	worker->monitoring_info.confirmed_lsn = 0;
+	worker->monitoring_info.last_update_time = 0;
+}
+
+/*
+ * Attach Slot-sync worker to worker-slot assigned by launcher.
  */
 void
-ApplyLauncherMain(Datum main_arg)
+slotsync_worker_attach(int slot)
 {
-	ereport(DEBUG1,
-			(errmsg_internal("logical replication launcher started")));
+	/* 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);
+}
+
+/*
+ * 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.
+ */
+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);
+}
+
+/*
+ * Slot-Sync worker find.
+ *
+ * Searches the slot-sync worker pool for the worker who manages the
+ * specified dbid. Because a worker can manage multiple dbs, also walk
+ * the db array of each worker to find the match.
+ *
+ * Returns NULL if no matching worker is found.
+ */
+static SlotSyncWorker *
+slotsync_worker_find(Oid dbid)
+{
+	Assert(LWLockHeldByMeInMode(SlotSyncWorkerLock, LW_SHARED));
+
+	/* Search for an attached worker for a given dbid */
+	for (int i = 0; i < max_slotsync_workers; i++)
+	{
+		SlotSyncWorker *w = &LogicalRepCtx->ss_workers[i];
+		Oid		   *dbids;
+
+		if (!w->hdr.in_use)
+			continue;
+
+		dbids = (Oid *) dsa_get_address(w->dbids_dsa, w->dbids_dp);
+		for (int dbidx = 0; dbidx < w->dbcount; dbidx++)
+		{
+			if (dbids[dbidx] == dbid)
+				return w;
+		}
+
+	}
+
+	return NULL;
+}
+
+/*
+ * Setup DSA for slot-sync worker.
+ *
+ * DSA is used for the dbids array. Because the maximum number of dbs a
+ * worker can manage is not known, initially enough memory for
+ * 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)
+{
+	dsa_area   *dbids_dsa;
+	dsa_pointer dbids_dp;
+	dsa_handle	dbids_dsa_handle;
+	MemoryContext oldcontext;
+
+	/* Ensure the 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, DB_PER_WORKER_ALLOC_INIT * 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);
+
+	elog(DEBUG1, "allocated dsa for slot-sync worker for dbcount: %d",
+		 DB_PER_WORKER_ALLOC_INIT);
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return dbids_dsa_handle;
+}
+
+/*
+ * Slot-sync worker launch or reuse
+ *
+ * Start new slot-sync background worker from the pool of available workers
+ * limited 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;
+	int			worker_slot = -1;
+	dsa_handle	handle;
+	Oid		   *dbids;
+	bool		attach;
+	uint32		mindbcnt = PG_UINT32_MAX;
+
+	Assert(OidIsValid(dbid));
+
+	/* The shared memory must only be modified under lock. */
+	LWLockAcquire(SlotSyncWorkerLock, LW_EXCLUSIVE);
+
+	/*
+	 * Find unused worker slot. If all the workers are currently in use, find
+	 * the one with minimum number of dbs and use that.
+	 */
+	for (int 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 (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;
+			uint32		alloc_count = 0;
+			uint32		old_dbcnt = 0;
+			Oid		   *old_dbids = NULL;
+
+			/* Be sure any memory allocated by DSA routines is persistent. */
+			oldcontext = MemoryContextSwitchTo(TopMemoryContext);
+
+			/* Remember the old dbids before we reallocate dsa. */
+			old_dbcnt = worker->dbcount;
+			old_dbids = (Oid *) palloc0(worker->dbcount * sizeof(Oid));
+			memcpy(old_dbids, dbids, worker->dbcount * sizeof(Oid));
+
+			alloc_count = old_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 = old_dbcnt;
+			memcpy(dbids, old_dbids, old_dbcnt * sizeof(Oid));
+			pfree(old_dbids);
+
+			/* 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);
+	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 is done, log that the worker is managing dbid, else raise a
+	 * warning
+	 */
+	if (attach)
+		ereport(LOG,
+				(errmsg("Added database %d to replication slot-sync "
+						"worker %d; dbcount now: %d",
+						dbid, worker_slot, worker->dbcount)));
+	else
+		ereport(WARNING,
+				(errmsg("replication slot-sync worker failed to attach to "
+						"worker-pool slot %d", worker_slot)));
+
+	return attach;
+}
+
+/*
+ * Internal function to stop the slot-sync worker and cleanup afterwards.
+ */
+static void
+slotsync_worker_stop_internal(SlotSyncWorker *worker)
+{
+	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);
+}
+
+/*
+ * Stop all the slot-sync workers in use.
+ */
+static void
+slotsync_workers_stop()
+{
+	for (int widx = 0; widx < max_slotsync_workers; widx++)
+	{
+		SlotSyncWorker *worker = &LogicalRepCtx->ss_workers[widx];
+
+		if (worker && worker->hdr.in_use)
+			slotsync_worker_stop_internal(worker);
+	}
+}
+
+
+/*
+ * 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 failover slots are removed on primary or are disabled for failover.
+ */
+static void
+slotsync_remove_obsolete_dbs(List *remote_dbs)
+{
+	LWLockAcquire(SlotSyncWorkerLock, LW_EXCLUSIVE);
+
+	/* Traverse slot-sync-workers to validate the DBs */
+	for (int widx = 0; widx < max_slotsync_workers; widx++)
+	{
+		SlotSyncWorker *worker = &LogicalRepCtx->ss_workers[widx];
+		Oid		   *dbids;
+
+		if (!worker->hdr.in_use)
+			continue;
+
+		dbids = (Oid *) dsa_get_address(worker->dbids_dsa, worker->dbids_dp);
+
+		for (int dbidx = 0; dbidx < worker->dbcount;)
+		{
+			Oid			wdbid = dbids[dbidx];
+			bool		found = false;
+			ListCell   *lc;
+
+			/* Check if current DB is still present in remote-db-list */
+			foreach(lc, remote_dbs)
+			{
+				WalRcvFailoverSlotsData *failover_slot_data = lfirst(lc);
+
+				if (failover_slot_data->dboid == wdbid)
+				{
+					found = true;
+					break;
+				}
+			}
+
+			/* If not found, then delete this db from worker's db-list */
+			if (!found)
+			{
+				if (dbidx < (worker->dbcount - 1))
+				{
+					/* Shift the DBs and get rid of wdbid */
+					memmove(&dbids[dbidx], &dbids[dbidx + 1],
+							(worker->dbcount - dbidx - 1) * sizeof(Oid));
+				}
+
+				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.
+	 *
+	 * XXX: if needed in future, workers can be restarted in such a case to
+	 * distribute the load.
+	 */
+
+	for (int widx = 0; widx < max_slotsync_workers; widx++)
+	{
+		SlotSyncWorker *worker = &LogicalRepCtx->ss_workers[widx];
+
+		if (worker->hdr.in_use && !worker->dbcount)
+			slotsync_worker_stop_internal(worker);
+	}
+
+	/*
+	 * TODO: Take care of of removal of old 'synced' slots for the dbs which
+	 * are no longer eligible for slot-sync.
+	 */
+}
+
+/*
+ * Connect to the primary server for slotsync purpose and return the connection
+ * info.
+ */
+static WalReceiverConn *
+slotsync_remote_connect()
+{
+	WalReceiverConn *wrconn = NULL;
+	char	   *err;
+	char	   *dbname;
+
+	if (!enable_syncslot)
+		return NULL;
+
+	if (max_slotsync_workers == 0)
+		return NULL;
+
+	/* The primary_slot_name is not set */
+	if (!WalRcv || WalRcv->slotname[0] == '\0')
+	{
+		ereport(WARNING,
+				errmsg("skipping slots synchronization as primary_slot_name "
+					   "is not set."));
+		return NULL;
+	}
+
+	/* The hot_standby_feedback must be ON for slot-sync to work */
+	if (!hot_standby_feedback)
+	{
+		ereport(WARNING,
+				errmsg("skipping slots synchronization as hot_standby_feedback "
+					   "is off."));
+		return NULL;
+	}
+
+	/* The dbname must be specified in primary_conninfo for slot-sync to work */
+	dbname = walrcv_get_dbname_from_conninfo(PrimaryConnInfo);
+	if (dbname == NULL)
+	{
+		ereport(WARNING,
+				errmsg("skipping slots synchronization as dbname is not "
+					   "specified in primary_conninfo."));
+		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;
+}
+
+/*
+ * Save current slot-sync configurations.
+ *
+ * This function is invoked prior to each config-reload on receiving SIGHUP.
+ */
+static void
+save_current_slotsync_configs()
+{
+	/* Free the previous allocations */
+	if (PrimaryConnInfoPreReload)
+		pfree(PrimaryConnInfoPreReload);
+
+	if (PrimarySlotNamePreReload)
+		pfree(PrimarySlotNamePreReload);
+
+	PrimaryConnInfoPreReload = pstrdup(PrimaryConnInfo);
+	PrimarySlotNamePreReload = pstrdup(WalRcv->slotname);
+	EnableSyncSlotPreReload = enable_syncslot;
+	HotStandbyFeedbackPreReload = hot_standby_feedback;
+}
+
+/*
+ * Returns true if any of the slot-sync configurations changed.
+ */
+static bool
+slotsync_configs_changed()
+{
+	if ((EnableSyncSlotPreReload != enable_syncslot) ||
+		(HotStandbyFeedbackPreReload != hot_standby_feedback) ||
+		(strcmp(PrimaryConnInfoPreReload, PrimaryConnInfo) != 0) ||
+		(strcmp(PrimarySlotNamePreReload, WalRcv->slotname) != 0))
+	{
+		return true;
+	}
+
+	return false;
+}
+
+/*
+ * Launch slot-sync background workers.
+ *
+ * Connect to the primary, to get the list of DBIDs for failover logical slots.
+ * Then launch slot-sync workers (limited by max_slotsync_workers) where the DBs
+ * are distributed equally among those workers.
+ */
+static void
+LaunchSlotSyncWorkers(long *wait_time, WalReceiverConn *wrconn)
+{
+	List	   *slots_dbs;
+	ListCell   *lc;
+	MemoryContext tmpctx;
+	MemoryContext oldctx;
+
+	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_failover_slots(wrconn);
+
+	slotsync_remove_obsolete_dbs(slots_dbs);
+
+	foreach(lc, slots_dbs)
+	{
+		WalRcvFailoverSlotsData *failover_slot_data = lfirst(lc);
+		SlotSyncWorker *w;
+
+		Assert(OidIsValid(failover_slot_data->dboid));
+
+		LWLockAcquire(SlotSyncWorkerLock, LW_SHARED);
+		w = slotsync_worker_find(failover_slot_data->dboid);
+		LWLockRelease(SlotSyncWorkerLock);
+
+		if (w != NULL)
+			continue;			/* worker is running already */
+
+		/*
+		 * If we failed to launch this slotsync worker, return and try
+		 * launching the failed and remaining workers in next sync-cycle. But
+		 * change launcher's wait time to minimum of
+		 * wal_retrieve_retry_interval and default wait time to try next
+		 * sync-cycle sooner.
+		 */
+		if (!slotsync_worker_launch_or_reuse(failover_slot_data->dboid))
+		{
+			*wait_time = Min(*wait_time, wal_retrieve_retry_interval);
+			break;
+		}
+	}
+
+	/* Switch back to original memory context. */
+	MemoryContextSwitchTo(oldctx);
+	/* Clean the temporary memory. */
+	MemoryContextDelete(tmpctx);
+}
+
+/*
+ * Launch logical replication apply workers for enabled subscriptions.
+ */
+static void
+LaunchSubscriptionApplyWorker(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 launcher process.
+ */
+void
+LauncherMain(Datum main_arg)
+{
+	WalReceiverConn *wrconn = NULL;
+
+	elog(DEBUG1, "logical replication launcher started");
 
 	before_shmem_exit(logicalrep_launcher_onexit, (Datum) 0);
 
@@ -1139,79 +1916,35 @@ ApplyLauncherMain(Datum main_arg)
 	 */
 	BackgroundWorkerInitializeConnection(NULL, NULL, 0);
 
+	load_file("libpqwalreceiver", false);
+
+	/*
+	 * If it is Hot Standby, validate the configurations and make remote
+	 * connection for slot-sync purpose
+	 */
+	if (RecoveryInProgress())
+		wrconn = slotsync_remote_connect();
+
 	/* 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)
+		/*
+		 * If it is Hot standby, then try to launch slot-sync workers else
+		 * launch apply workers.
+		 */
+		if (RecoveryInProgress())
 		{
-			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);
-			}
+			/* Launch only if we have succesfully made the connection */
+			if (wrconn)
+				LaunchSlotSyncWorkers(&wait_time, wrconn);
 		}
-
-		/* Switch back to original memory context. */
-		MemoryContextSwitchTo(oldctx);
-		/* Clean the temporary memory. */
-		MemoryContextDelete(subctx);
+		else
+			LaunchSubscriptionApplyWorker(&wait_time);
 
 		/* Wait for more work. */
 		rc = WaitLatch(MyLatch,
@@ -1227,8 +1960,26 @@ ApplyLauncherMain(Datum main_arg)
 
 		if (ConfigReloadPending)
 		{
+			save_current_slotsync_configs();
+
 			ConfigReloadPending = false;
 			ProcessConfigFile(PGC_SIGHUP);
+
+			/*
+			 * If any of the related GUCs changed, stop the slot-sync workers,
+			 * revalidate the new configurations and reconnect. The workers
+			 * will be relaunched in next sync-cycle using the new GUCs.
+			 */
+			if (slotsync_configs_changed())
+			{
+				slotsync_workers_stop();
+
+				if (wrconn)
+					walrcv_disconnect(wrconn);
+
+				if (RecoveryInProgress())
+					wrconn = slotsync_remote_connect();
+			}
 		}
 	}
 
@@ -1260,7 +2011,8 @@ 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 +2050,13 @@ 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/logical.c b/src/backend/replication/logical/logical.c
index 8288da5277..984adfabeb 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -524,6 +524,18 @@ CreateDecodingContext(XLogRecPtr start_lsn,
 				 errmsg("replication slot \"%s\" was not created in this database",
 						NameStr(slot->data.name))));
 
+	/*
+	 * Do not allow consumption of a "synchronized" slot until the standby
+	 * gets promoted.
+	 */
+	if (RecoveryInProgress() && slot->data.synced)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot use replication slot \"%s\" for logical decoding",
+						NameStr(slot->data.name)),
+				 errdetail("This slot is being synced from the primary."),
+				 errhint("Specify another replication slot.")));
+
 	/*
 	 * Check if slot has been invalidated due to max_slot_wal_keep_size. Avoid
 	 * "cannot get changes" wording in this errmsg because that'd be
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..4764fd4167
--- /dev/null
+++ b/src/backend/replication/logical/slotsync.c
@@ -0,0 +1,963 @@
+/*-------------------------------------------------------------------------
+ * 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 failover slots information from the primary server,
+ * create the slots on the standby and synchronize them periodically.
+ *
+ * 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;
+
+/* 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 */
+
+static char *PrimaryConnInfoPreReload = NULL;
+
+/*
+ * Wait for remote slot to pass locally reserved position.
+ */
+static bool
+wait_for_primary_slot_catchup(WalReceiverConn *wrconn, RemoteSlot *remote_slot)
+
+{
+#define WAIT_OUTPUT_COLUMN_COUNT 4
+	StringInfoData cmd;
+
+	ereport(LOG,
+			errmsg("waiting for remote slot \"%s\" LSN (%X/%X) and catalog xmin"
+				   " (%u) to pass local slot LSN (%X/%X) and and catalog xmin (%u)",
+				   remote_slot->name,
+				   LSN_FORMAT_ARGS(remote_slot->restart_lsn),
+				   remote_slot->catalog_xmin,
+				   LSN_FORMAT_ARGS(MyReplicationSlot->data.restart_lsn),
+				   MyReplicationSlot->data.catalog_xmin));
+
+	initStringInfo(&cmd);
+	appendStringInfo(&cmd,
+					 "SELECT conflicting, restart_lsn, confirmed_flush_lsn,"
+					 " catalog_xmin FROM pg_catalog.pg_replication_slots"
+					 " WHERE slot_name = %s",
+					 quote_literal_cstr(remote_slot->name));
+
+	for (;;)
+	{
+		XLogRecPtr	new_invalidated;
+		XLogRecPtr	new_restart_lsn;
+		XLogRecPtr	new_confirmed_lsn;
+		TransactionId new_catalog_xmin;
+		WalRcvExecResult *res;
+		TupleTableSlot *slot;
+		int			rc;
+		bool		isnull;
+		Oid			slotRow[WAIT_OUTPUT_COLUMN_COUNT] = {BOOLOID, LSNOID, LSNOID,
+		XIDOID};
+
+		CHECK_FOR_INTERRUPTS();
+
+		/* Check if this standby is promoted while we are waiting */
+		if (!RecoveryInProgress())
+		{
+			/*
+			 * The remote slot didn't pass the locally reserved position at
+			 * the time of local promotion, so it's not safe to use.
+			 */
+			ereport(
+					WARNING,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg(
+							"slot-sync wait for slot %s interrupted by promotion, "
+							"slot creation aborted", remote_slot->name)));
+			pfree(cmd.data);
+			return false;
+		}
+
+		res = walrcv_exec(wrconn, cmd.data, WAIT_OUTPUT_COLUMN_COUNT, slotRow);
+
+		if (res->status != WALRCV_OK_TUPLES)
+			ereport(ERROR,
+					(errmsg("could not fetch slot info for slot \"%s\" from"
+							" the primary: %s", remote_slot->name, res->err)));
+
+		slot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
+		if (!tuplestore_gettupleslot(res->tuplestore, true, false, slot))
+		{
+			ereport(WARNING,
+					(errmsg("slot \"%s\" disappeared from the primary, aborting"
+							" slot creation", remote_slot->name)));
+			pfree(cmd.data);
+			walrcv_clear_result(res);
+			return false;
+		}
+
+		/*
+		 * It is possible to get null values for lsns and xmin if slot is
+		 * invalidated on primary, so handle accordingly.
+		 */
+		new_invalidated = DatumGetBool(slot_getattr(slot, 1, &isnull));
+		Assert(!isnull);
+
+		new_restart_lsn = DatumGetLSN(slot_getattr(slot, 2, &isnull));
+		if (new_invalidated || isnull)
+		{
+			ereport(WARNING,
+					(errmsg("slot \"%s\" invalidated on primary, aborting"
+							" slot creation", remote_slot->name)));
+			pfree(cmd.data);
+			ExecClearTuple(slot);
+			walrcv_clear_result(res);
+			return false;
+		}
+
+		/*
+		 * Once we got valid restart_lsn, then confirmed_lsn and catalog_xmin
+		 * are expected to be valid/non-null, so assert if found null.
+		 */
+		new_confirmed_lsn = DatumGetLSN(slot_getattr(slot, 3, &isnull));
+		Assert(!isnull);
+
+		new_catalog_xmin = DatumGetTransactionId(slot_getattr(slot,
+															  4, &isnull));
+		Assert(!isnull);
+
+		ExecClearTuple(slot);
+		walrcv_clear_result(res);
+
+		if (new_restart_lsn >= MyReplicationSlot->data.restart_lsn &&
+			TransactionIdFollowsOrEquals(new_catalog_xmin,
+										 MyReplicationSlot->data.catalog_xmin))
+		{
+			/* Update new values in remote_slot */
+			remote_slot->restart_lsn = new_restart_lsn;
+			remote_slot->confirmed_lsn = new_confirmed_lsn;
+			remote_slot->catalog_xmin = new_catalog_xmin;
+
+			ereport(LOG,
+					errmsg("wait over for remote slot \"%s\" as its LSN (%X/%X)"
+						   " and catalog xmin (%u) has now passed local slot LSN"
+						   " (%X/%X) and catalog xmin (%u)",
+						   remote_slot->name,
+						   LSN_FORMAT_ARGS(new_restart_lsn),
+						   new_catalog_xmin,
+						   LSN_FORMAT_ARGS(MyReplicationSlot->data.restart_lsn),
+						   MyReplicationSlot->data.catalog_xmin));
+			pfree(cmd.data);
+			return true;
+		}
+
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+					   WORKER_DEFAULT_NAPTIME_MS,
+					   WAIT_EVENT_REPL_SLOTSYNC_PRIMARY_CATCHUP);
+
+		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_in_list(ReplicationSlot *local_slot, List *remote_slots,
+					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 &&
+				local_slot->data.invalidated != RS_INVAL_NONE)
+				*locally_invalidated = true;
+
+			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 the regular value of WORKER_DEFAULT_NAPTIME_MS.
+ * When no lsn change is observed within the threshold period
+ * WORKER_INACTIVITY_THRESHOLD_MS, 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
+ * another lsn change is observed.
+ */
+static void
+compute_naptime(RemoteSlot *remote_slot, long *naptime)
+{
+	TimestampTz now = GetCurrentTimestamp();
+
+	Assert(*naptime == WORKER_DEFAULT_NAPTIME_MS || *naptime ==
+		   WORKER_INACTIVITY_NAPTIME_MS);
+
+	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;
+
+		/* Something changed; reset naptime to default. */
+		*naptime = WORKER_DEFAULT_NAPTIME_MS;
+	}
+	else
+	{
+		if (*naptime == WORKER_DEFAULT_NAPTIME_MS)
+		{
+			/*
+			 * If the inactivity time reaches the threshold, increase nap
+			 * time.
+			 */
+			if (TimestampDifferenceExceeds(MySlotSyncWorker->monitoring_info.last_update_time,
+										   now, WORKER_INACTIVITY_THRESHOLD_MS))
+				*naptime = WORKER_INACTIVITY_NAPTIME_MS;
+		}
+	}
+}
+
+/*
+ * This gets invalidation cause of the 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 cause 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)));
+
+	cause = DatumGetInt16(slot_getattr(slot, 1, &isnull));
+	Assert(!isnull);
+
+	ExecClearTuple(slot);
+	walrcv_clear_result(res);
+
+	return cause;
+}
+
+/*
+ * Drop obsolete slots
+ *
+ * Drop the slots that no longer need to be synced i.e. these either
+ * do not exist on primary or are no longer enabled as failover slots.
+ *
+ * Also drop the slots that are valid on primary that got invalidated
+ * on standby due to conflict (say required rows removed on primary).
+ * The assumption is, that 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_in_list(local_slot, remote_slot_list,
+										   &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, false);
+
+			ereport(LOG,
+					(errmsg("Dropped replication slot \"%s\" ",
+							NameStr(local_slot->data.name))));
+		}
+	}
+}
+
+/*
+ * Construct Slot Query
+ *
+ * It constructs the query using dbids array in order to get failover
+ * logical slots information from the primary.
+ */
+static void
+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 failover=true and 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, ')');
+}
+
+/*
+ * Synchronize single slot to given position.
+ *
+ * This creates a new slot if there is no existing one and updates the
+ * metadata of the slot as per the data received from the primary.
+ */
+static void
+synchronize_one_slot(WalReceiverConn *wrconn, RemoteSlot *remote_slot)
+{
+	bool		found = false;
+
+	/* Good to check again if standby is promoted */
+	if (!RecoveryInProgress())
+	{
+		ereport(
+				WARNING,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg(
+						"slot-sync for slot \"%s\" interrupted by promotion, "
+						"sync not possible", remote_slot->name)));
+		return;
+	}
+
+	/*
+	 * Make sure that concerned WAL is received before syncing slot to target
+	 * lsn received from the primary.
+	 *
+	 * This check should never pass as on the primary, we have waited for
+	 * standby's confirmation before updating the logical slot. But to take
+	 * care of any bug in that flow, we should retain this check.
+	 */
+	if (remote_slot->confirmed_lsn > WalRcv->latestWalEnd)
+	{
+		ereport(LOG,
+				errmsg_internal("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 */
+	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
+	for (int i = 0; i < max_replication_slots && !found; i++)
+	{
+		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
+
+		if (s->in_use)
+			found = (strcmp(NameStr(s->data.name), remote_slot->name) == 0);
+	}
+	LWLockRelease(ReplicationSlotControlLock);
+
+	StartTransactionCommand();
+
+	/* Already existing slot, acquire */
+	if (found)
+	{
+		ReplicationSlotAcquire(remote_slot->name, true);
+
+		if (remote_slot->restart_lsn < MyReplicationSlot->data.restart_lsn)
+		{
+			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, false);
+		slot = MyReplicationSlot;
+
+		SpinLockAcquire(&slot->mutex);
+		slot->data.database = get_database_oid(remote_slot->database, false);
+		slot->data.failover = true;
+		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 the local restart_lsn and/or local catalog_xmin is ahead of
+		 * those on the remote then we cannot create the local slot in sync
+		 * with the primary because that would mean moving the local slot
+		 * backwards and we might not have WALs retained for old lsns. In this
+		 * case we will wait for the primary's restart_lsn and catalog_xmin to
+		 * catch up with the local one before attempting the sync.
+		 */
+		if (remote_slot->restart_lsn < MyReplicationSlot->data.restart_lsn ||
+			TransactionIdPrecedes(remote_slot->catalog_xmin,
+								  MyReplicationSlot->data.catalog_xmin))
+		{
+			if (!wait_for_primary_slot_catchup(wrconn, remote_slot))
+			{
+				/*
+				 * The remote slot didn't catch up to locally reserved
+				 * position
+				 */
+				ReplicationSlotRelease();
+				CommitTransactionCommand();
+				return;
+			}
+
+		}
+
+		/* Update lsns of slot to remote slot's current position */
+		local_slot_update(remote_slot);
+		ReplicationSlotPersist();
+	}
+
+	ReplicationSlotRelease();
+	CommitTransactionCommand();
+}
+
+/*
+ * Synchronize slots.
+ *
+ * It gets the failover logical slots info from the primary server for the dbids
+ * managed by this worker and then updates the slots locally as per the info
+ * received. 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;
+	Oid		   *dbids;
+	int			count = 0;
+
+	/* The primary_slot_name is not set yet or WALs not received yet */
+	if (!WalRcv ||
+		(WalRcv->slotname[0] == '\0') ||
+		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);
+
+	/*
+	 * Check dbcount before starting to sync. There is a possibility that
+	 * dbids managed by this worker are no longer valid due to change in
+	 * failover slots on primary. In that case, launcher will make dbcount=0
+	 * and will send SIGINT to shutdown this worker. Thus check dbcount before
+	 * we proceed further.
+	 */
+	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);
+	construct_slot_query(&s, dbids);
+
+	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 failover logical slots 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;
+			count++;
+		}
+
+		/* Create list of remote slots to be used by drop_obsolete_slots */
+		remote_slot_list = lappend(remote_slot_list, remote_slot);
+
+		synchronize_one_slot(wrconn, remote_slot);
+
+		/*
+		 * Update naptime as required depending on slot activity. Check only
+		 * for the first slot, if one slot has activity then all slots will.
+		 */
+		if (count == 1)
+			compute_naptime(remote_slot, &naptime);
+
+		ExecClearTuple(slot);
+	}
+
+	/* Drop local slots that no longer need to be synced. */
+	drop_obsolete_slots(dbids, remote_slot_list);
+
+	LWLockRelease(SlotSyncWorkerLock);
+
+	/* We are done, free remote_slot_list elements */
+	list_free_deep(remote_slot_list);
+
+	walrcv_clear_result(res);
+
+	return naptime;
+}
+
+/*
+ * Connect to remote (primary) server.
+ *
+ * This uses GUC primary_conninfo in order to connect to the primary.
+ * For slot-sync to work, primary_conninfo is required to specify 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 has changed.
+ */
+static WalReceiverConn *
+reconnect_if_needed(WalReceiverConn *wrconn_prev)
+{
+	WalReceiverConn *wrconn = NULL;
+
+	/* If no change in PrimaryConnInfo, return the previous connection itself */
+	if (strcmp(PrimaryConnInfoPreReload, PrimaryConnInfo) == 0)
+		return wrconn_prev;
+
+	walrcv_disconnect(wrconn_prev);
+	wrconn = remote_connect();
+	return wrconn;
+}
+
+/*
+ * Interrupt handler for main loop of slot-sync worker.
+ */
+static bool
+ProcessSlotSyncInterrupts(WalReceiverConn *wrconn)
+{
+	bool		reload_done = false;
+
+	CHECK_FOR_INTERRUPTS();
+
+	if (ShutdownRequestPending)
+	{
+		ereport(LOG,
+				errmsg("Replication slot-sync worker %d is shutting"
+					   " down on receiving SIGINT", MySlotSyncWorker->slot));
+
+		walrcv_disconnect(wrconn);
+		proc_exit(0);
+	}
+
+	if (ConfigReloadPending)
+	{
+		ConfigReloadPending = false;
+
+		/* Free the previous allocation. */
+		if (PrimaryConnInfoPreReload)
+			pfree(PrimaryConnInfoPreReload);
+
+		/* Save the GUC primary_conninfo before reloading. */
+		PrimaryConnInfoPreReload = pstrdup(PrimaryConnInfo);
+
+		ProcessConfigFile(PGC_SIGHUP);
+		reload_done = true;
+	}
+
+	return reload_done;
+}
+
+/*
+ * 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);
+
+	ereport(LOG,
+			errmsg("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, if dbname not
+	 * provided, skip sync.
+	 */
+	dbname = walrcv_get_dbname_from_conninfo(PrimaryConnInfo);
+	if (dbname == NULL)
+		proc_exit(0);
+
+	/*
+	 * Connect to the database specified by user in PrimaryConnInfo. We need a
+	 * database connection for walrcv_exec to work. Please see comments atop
+	 * libpqrcv_exec.
+	 */
+	BackgroundWorkerInitializeConnection(dbname,
+										 NULL,
+										 0);
+
+	/* Connect to primary node */
+	wrconn = remote_connect();
+
+	/* Main wait loop. */
+	for (;;)
+	{
+		int			rc;
+		long		naptime;
+		bool		config_reloaded = false;
+
+		config_reloaded = ProcessSlotSyncInterrupts(wrconn);
+
+		/* Reconnect if GUC primary_conninfo got changed */
+		if (config_reloaded)
+			wrconn = reconnect_if_needed(wrconn);
+
+		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 can not get here because it will only stop when it
+	 * receives a SIGINT from the logical replication launcher, or when there
+	 * is an error.
+	 */
+	Assert(false);
+}
diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
index 7036096653..3caebd51f4 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..20bb50f88d 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_FAILOVER_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_failover_slots
 %type <list>	generic_option_list
 %type <defelt>	generic_option
 %type <uintval>	opt_timeline
@@ -114,6 +115,7 @@ command:
 			| read_replication_slot
 			| timeline_history
 			| show
+			| list_dbid_for_failover_slots
 			;
 
 /*
@@ -126,6 +128,16 @@ identify_system:
 				}
 			;
 
+/*
+ * LIST_DBID_FOR_FAILOVER_SLOTS
+ */
+list_dbid_for_failover_slots:
+			K_LIST_DBID_FOR_FAILOVER_SLOTS
+				{
+					$$ = (Node *) makeNode(ListDBForFailoverSlotsCmd);
+				}
+			;
+
 /*
  * READ_REPLICATION_SLOT %s
  */
diff --git a/src/backend/replication/repl_scanner.l b/src/backend/replication/repl_scanner.l
index 1cc7fb858c..114ef82ee5 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_FAILOVER_SLOTS	{ return K_LIST_DBID_FOR_FAILOVER_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_FAILOVER_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 8416756866..2e0fe1490e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -317,6 +317,7 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	slot->data.two_phase = two_phase;
 	slot->data.two_phase_at = InvalidXLogRecPtr;
 	slot->data.failover = failover;
+	slot->data.synced = false;
 
 	/* and then data only present in shared memory */
 	slot->just_dirtied = false;
@@ -646,12 +647,25 @@ restart:
  * Permanently drop replication slot identified by the passed in name.
  */
 void
-ReplicationSlotDrop(const char *name, bool nowait)
+ReplicationSlotDrop(const char *name, bool nowait, bool user_cmd)
 {
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, nowait);
 
+	/*
+	 * Do not allow users to drop the slots which are currently being synced
+	 * from the primary to the standby.
+	 */
+	if (user_cmd && RecoveryInProgress() && MyReplicationSlot->data.synced)
+	{
+		ReplicationSlotRelease();
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot drop replication slot \"%s\"", name),
+				 errdetail("This slot is being synced from the primary.")));
+	}
+
 	ReplicationSlotDropAcquired();
 }
 
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 3565ca196f..6121442b15 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -226,11 +226,40 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotRequirements();
 
-	ReplicationSlotDrop(NameStr(*name), true);
+	ReplicationSlotDrop(NameStr(*name), true, true);
 
 	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.
@@ -238,7 +267,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 Datum
 pg_get_replication_slots(PG_FUNCTION_ARGS)
 {
-#define PG_GET_REPLICATION_SLOTS_COLS 16
+#define PG_GET_REPLICATION_SLOTS_COLS 17
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 	XLogRecPtr	currlsn;
 	int			slotno;
@@ -420,6 +449,8 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 
 		values[i++] = BoolGetDatum(slot_contents.data.failover);
 
+		values[i++] = BoolGetDatum(slot_contents.data.synced);
+
 		Assert(i == PG_GET_REPLICATION_SLOTS_COLS);
 
 		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
old mode 100644
new mode 100755
index c74bbd4a70..6dcda821ef
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -479,6 +479,76 @@ IdentifySystem(void)
 	end_tup_output(tstate);
 }
 
+/*
+ * Handle the LIST_DBID_FOR_FAILOVER_SLOTS command.
+ *
+ * Return the list of database-ids for failover logical slots.
+ * The returned list has no duplicates.
+ */
+static void
+ListFailoverSlotsDbids(void)
+{
+	DestReceiver *dest;
+	TupOutputState *tstate;
+	TupleDesc	tupdesc;
+	List	   *database_oids_list = NIL;
+
+	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 (int slotno = 0; slotno < max_replication_slots; slotno++)
+	{
+		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
+		Oid			dboid;
+		bool		failover_slot = false;
+		Datum		values[1];
+		bool		nulls[1];
+
+		if (!slot->in_use)
+			continue;
+
+		SpinLockAcquire(&slot->mutex);
+
+		dboid = slot->data.database;
+		failover_slot = slot->data.failover;
+
+		SpinLockRelease(&slot->mutex);
+
+		if (!failover_slot || SlotIsPhysical(slot))
+			continue;
+
+		/*
+		 * Check if the database OID is already in the list, and if so, skip
+		 * this slot.
+		 */
+		if (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)
@@ -1262,7 +1332,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 static void
 DropReplicationSlot(DropReplicationSlotCmd *cmd)
 {
-	ReplicationSlotDrop(cmd->slotname, !cmd->wait);
+	ReplicationSlotDrop(cmd->slotname, !cmd->wait, false);
 }
 
 /*
@@ -2071,6 +2141,13 @@ exec_replication_command(const char *cmd_string)
 			EndReplicationCommand(cmdtag);
 			break;
 
+		case T_ListDBForFailoverSlotsCmd:
+			cmdtag = "LIST_DBID_FOR_FAILOVER_SLOTS";
+			set_ps_display(cmdtag);
+			ListFailoverSlotsDbids();
+			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 f6e2ec82c1..7ba36b06c1 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -53,6 +53,8 @@ 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 slot-sync worker."
+REPL_SLOTSYNC_PRIMARY_CATCHUP	"Waiting for primary to catch-up, in slot-sync worker."
 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 d728e33d5e..9b4c855427 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -65,8 +65,11 @@
 #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"
@@ -2021,6 +2024,15 @@ struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"enable_syncslot", PGC_SIGHUP, REPLICATION_STANDBY,
+			gettext_noop("Enables a physical standby to synchronize logical replication failover slots from the primary server."),
+		},
+		&enable_syncslot,
+		true,
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, false, NULL, NULL, NULL
@@ -3518,6 +3530,19 @@ 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 014491e06f..08df446060 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -355,6 +355,8 @@
 #wal_retrieve_retry_interval = 5s	# time to wait before retrying to
 					# retrieve WAL after a failed attempt
 #recovery_min_apply_delay = 0		# minimum delay for applying changes during recovery
+#enable_syncslot = on			# enables slot synchronization on the physical standby from the primary
+#max_slotsync_workers = 2		# maximum number of slot synchronization workers
 
 # - Subscribers -
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index e54a462a4e..91e973c71e 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -11074,14 +11074,18 @@
   proname => 'pg_drop_replication_slot', provolatile => 'v', proparallel => 'u',
   prorettype => 'void', proargtypes => 'name',
   prosrc => 'pg_drop_replication_slot' },
+{ oid => '8484', 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',
   proretset => 't', provolatile => 's', prorettype => 'record',
   proargtypes => '',
-  proallargtypes => '{name,name,text,oid,bool,bool,int4,xid,xid,pg_lsn,pg_lsn,text,int8,bool,bool,bool}',
-  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
-  proargnames => '{slot_name,plugin,slot_type,datoid,temporary,active,active_pid,xmin,catalog_xmin,restart_lsn,confirmed_flush_lsn,wal_status,safe_wal_size,two_phase,conflicting,failover}',
+  proallargtypes => '{name,name,text,oid,bool,bool,int4,xid,xid,pg_lsn,pg_lsn,text,int8,bool,bool,bool,bool}',
+  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
+  proargnames => '{slot_name,plugin,slot_type,datoid,temporary,active,active_pid,xmin,catalog_xmin,restart_lsn,confirmed_flush_lsn,wal_status,safe_wal_size,two_phase,conflicting,failover,synced_slot}',
   prosrc => 'pg_get_replication_slots' },
 { oid => '3786', descr => 'set up a logical replication slot',
   proname => 'pg_create_logical_replication_slot', provolatile => 'v',
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 5142a08729..c429d84d79 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_FAILOVER_SLOTS command
+ * -------------------------------
+ */
+typedef struct ListDBForFailoverSlotsCmd
+{
+	NodeTag		type;
+	List	   *slot_names;
+}			ListDBForFailoverSlotsCmd;
 
 /* ----------------------
  *		BASE_BACKUP command
diff --git a/src/include/postmaster/bgworker_internals.h b/src/include/postmaster/bgworker_internals.h
index 09df054fcc..b8fed6031f 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..07cfae7b37 100644
--- a/src/include/replication/logicallauncher.h
+++ b/src/include/replication/logicallauncher.h
@@ -15,9 +15,12 @@
 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 PGDLLIMPORT bool enable_syncslot;
+
 
 extern void ApplyLauncherRegister(void);
-extern void ApplyLauncherMain(Datum main_arg);
+extern void LauncherMain(Datum main_arg);
 
 extern Size ApplyLauncherShmemSize(void);
 extern void ApplyLauncherShmemInit(void);
@@ -31,4 +34,6 @@ 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 7a4fd9e9d7..4af3d19b8c 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.
@@ -112,6 +111,13 @@ typedef struct ReplicationSlotPersistentData
 	/* plugin name */
 	NameData	plugin;
 
+	/*
+	 * Is this a slot created by a sync-slot worker?
+	 *
+	 * Relevant for logical slots on the physical standby.
+	 */
+	bool		synced;
+
 	/*
 	 * Is this a failover slot (sync candidate for physical standbys)?
 	 * Relevant for logical slots on the primary server.
@@ -230,7 +236,7 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
 								  bool two_phase, bool failover);
 extern void ReplicationSlotPersist(void);
-extern void ReplicationSlotDrop(const char *name, bool nowait);
+extern void ReplicationSlotDrop(const char *name, bool nowait, bool user_cmd);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
@@ -255,7 +261,6 @@ 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);
@@ -263,7 +268,6 @@ extern void CheckPointReplicationSlots(bool is_shutdown);
 extern void CheckSlotRequirements(void);
 extern void CheckSlotPermissions(void);
 
-extern void WaitForStandbyLSN(XLogRecPtr wait_for_lsn);
 extern void SlotSyncInitConfig(void);
 extern void SlotSyncFreeConfig(void);
 
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 74f132d586..5c25f7a480 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"
@@ -193,6 +194,14 @@ typedef struct
 	}			proto;
 } WalRcvStreamOptions;
 
+/*
+ * Failover logical slots dbids received from remote.
+ */
+typedef struct WalRcvFailoverSlotsData
+{
+	Oid			dboid;
+}			WalRcvFailoverSlotsData;
+
 struct WalReceiverConn;
 typedef struct WalReceiverConn WalReceiverConn;
 
@@ -282,6 +291,21 @@ typedef void (*walrcv_get_senderinfo_fn) (WalReceiverConn *conn,
 typedef char *(*walrcv_identify_system_fn) (WalReceiverConn *conn,
 											TimeLineID *primary_tli);
 
+/*
+ * walrcv_get_dbinfo_for_failover_slots_fn
+ *
+ * Run LIST_DBID_FOR_FAILOVER_SLOTS on primary server to get the
+ * list of unique DBIDs for failover logical slots
+ */
+typedef List *(*walrcv_get_dbinfo_for_failover_slots_fn) (WalReceiverConn *conn);
+
+/*
+ * 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
  *
@@ -396,6 +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_failover_slots_fn walrcv_get_dbinfo_for_failover_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;
@@ -420,6 +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_failover_slots(conn) \
+	WalReceiverFunctions->walrcv_get_dbinfo_for_failover_slots(conn)
+#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 a9bba11187..1ee3755aff 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 +103,40 @@ 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
+	{
+		XLogRecPtr	confirmed_lsn;
+		TimestampTz last_update_time;
+	}			monitoring_info;
+
+} SlotSyncWorker;
+
 /*
  * State of the transaction in parallel apply worker.
  *
@@ -234,12 +275,15 @@ 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 void slotsync_worker_detach(int code, Datum arg);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
 extern List *logicalrep_workers_find(Oid subid, bool only_running);
@@ -329,9 +373,9 @@ 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
@@ -343,14 +387,14 @@ 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 b038e599c0..0621ee70fc 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/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 5d884e1faa..2b5c54cd3d 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1474,8 +1474,9 @@ pg_replication_slots| SELECT l.slot_name,
     l.safe_wal_size,
     l.two_phase,
     l.conflicting,
-    l.failover
-   FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, temporary, active, active_pid, xmin, catalog_xmin, restart_lsn, confirmed_flush_lsn, wal_status, safe_wal_size, two_phase, conflicting, failover)
+    l.failover,
+    l.synced_slot
+   FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, temporary, active, active_pid, xmin, catalog_xmin, restart_lsn, confirmed_flush_lsn, wal_status, safe_wal_size, two_phase, conflicting, failover, synced_slot)
      LEFT JOIN pg_database d ON ((l.datoid = d.oid)));
 pg_roles| SELECT pg_authid.rolname,
     pg_authid.rolsuper,
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index 271313ebf8..70bd65e2cf 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -132,8 +132,9 @@ select name, setting from pg_settings where name like 'enable%';
  enable_self_join_removal       | on
  enable_seqscan                 | on
  enable_sort                    | on
+ enable_syncslot                | on
  enable_tidscan                 | on
-(22 rows)
+(23 rows)
 
 -- There are always wait event descriptions for various types.
 select type, count(*) > 0 as ok FROM pg_wait_events
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 87c1aee379..71035deef1 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1429,6 +1429,7 @@ LimitState
 LimitStateCond
 List
 ListCell
+ListDBForLogicalSlotsCmd
 ListDictionary
 ListParsedLex
 ListenAction
@@ -1508,6 +1509,7 @@ LogicalSlotInfo
 LogicalSlotInfoArr
 LogicalTape
 LogicalTapeSet
+LogicalWorkerHeader
 LsnReadQueue
 LsnReadQueueNextFun
 LsnReadQueueNextStatus
@@ -2309,6 +2311,7 @@ RelocationBufferInfo
 RelptrFreePageBtree
 RelptrFreePageManager
 RelptrFreePageSpanLeader
+RemoteSlot
 RenameStmt
 ReopenPtrType
 ReorderBuffer
@@ -2565,6 +2568,7 @@ SlabBlock
 SlabContext
 SlabSlot
 SlotNumber
+SlotSyncWorker
 SlruCtl
 SlruCtlData
 SlruErrorCause
@@ -3012,6 +3016,7 @@ WalLevel
 WalRcvData
 WalRcvExecResult
 WalRcvExecStatus
+WalRcvFailoverSlotsData
 WalRcvState
 WalRcvStreamOptions
 WalRcvWakeupReason
-- 
2.34.1

