From c9e54ad02bdd1404bfc89b32bbb0f180caab0f98 Mon Sep 17 00:00:00 2001
From: "houzj.fnst" <houzj.fnst@cn.fujitsu.com>
Date: Wed, 20 Apr 2022 16:45:07 +0800
Subject: [PATCH v65 1/7] Perform streaming logical transactions by parallel
 workers

Currently, for large transactions, the publisher sends the data in multiple
streams (changes divided into chunks depending upon logical_decoding_work_mem),
and then on the subscriber-side, the apply worker writes the changes into
temporary files and once it receives the commit, it reads from those files and
applies the entire transaction. To improve the performance of such
transactions, we can instead allow them to be applied via parallel workers.

In this approach, we assign a new parallel apply worker (if available) as soon
as the xact's first stream is received and the leader apply worker will send
changes to this new worker via shared memory. The parallel apply worker will
directly apply the change instead of writing it to temporary files. However, if
the leader apply worker times out while attempting to send a message to the
parallel apply worker, it will switch to "partial serialize" mode -  in this
mode the leader serializes all remaining changes to a file and notifies the
parallel apply workers to read and apply them at the end of the transaction. We
keep this parallel apply assigned till the transaction commit is received and
also wait for the worker to finish at commit. This preserves commit ordering
and avoids writing to and reading from files in most cases. We still need to
spill if there is no worker available.

This patch also extends the SUBSCRIPTION 'streaming' parameter so that the user
can control whether to apply the streaming transaction in a parallel apply
worker or spill the change to disk. The user can set the streaming parameter to
'on/off', 'parallel'. The parameter value 'parallel' means the streaming will
be applied via a parallel apply worker, if available. The parameter value
'on' means the streaming transaction will be spilled to disk. The default value
is 'off' (same as current behaviour).

In addition, the patch extends the logical replication STREAM_ABORT message so
that abort_time and abort_lsn can also be sent which can be used to update the
replication origin in parallel apply worker when the streaming transaction is
aborted. Because this message extension is needed to support parallel
streaming, parallel streaming is not supported for publications on servers <
PG16.

Note: Since the field 'substream' of catalog 'pg_subscription' has been
expanded, we need bump catalog version.
---
 doc/src/sgml/catalogs.sgml                    |   11 +-
 doc/src/sgml/config.sgml                      |   28 +-
 doc/src/sgml/logical-replication.sgml         |   22 +-
 doc/src/sgml/monitoring.sgml                  |    5 +
 doc/src/sgml/protocol.sgml                    |   29 +-
 doc/src/sgml/ref/create_subscription.sgml     |   24 +-
 doc/src/sgml/system-views.sgml                |    5 +-
 src/backend/access/transam/xact.c             |   24 +-
 src/backend/commands/subscriptioncmds.c       |   67 +-
 src/backend/libpq/pqmq.c                      |   18 +-
 src/backend/postmaster/bgworker.c             |    3 +
 src/backend/postmaster/interrupt.c            |    5 +-
 .../libpqwalreceiver/libpqwalreceiver.c       |    6 +-
 src/backend/replication/logical/Makefile      |    1 +
 .../replication/logical/applyparallelworker.c | 1627 +++++++++++++++++
 src/backend/replication/logical/decode.c      |    5 +-
 src/backend/replication/logical/launcher.c    |  220 ++-
 src/backend/replication/logical/meson.build   |    1 +
 src/backend/replication/logical/origin.c      |   26 +-
 src/backend/replication/logical/proto.c       |   37 +-
 .../replication/logical/reorderbuffer.c       |    5 +-
 src/backend/replication/logical/tablesync.c   |   25 +-
 src/backend/replication/logical/worker.c      | 1359 +++++++++++---
 src/backend/replication/pgoutput/pgoutput.c   |   22 +-
 src/backend/storage/ipc/procsignal.c          |    4 +
 src/backend/storage/lmgr/lmgr.c               |   46 +
 src/backend/tcop/postgres.c                   |    3 +
 src/backend/utils/activity/wait_event.c       |    6 +
 src/backend/utils/adt/lockfuncs.c             |    5 +-
 src/backend/utils/misc/guc_tables.c           |   12 +
 src/backend/utils/misc/postgresql.conf.sample |    1 +
 src/bin/pg_dump/pg_dump.c                     |    6 +-
 src/bin/psql/describe.c                       |   21 +-
 src/include/catalog/pg_subscription.h         |   21 +-
 src/include/commands/subscriptioncmds.h       |    2 +
 src/include/replication/logicallauncher.h     |    1 +
 src/include/replication/logicalproto.h        |   28 +-
 src/include/replication/logicalworker.h       |    8 +
 src/include/replication/origin.h              |    2 +-
 src/include/replication/pgoutput.h            |    2 +-
 src/include/replication/reorderbuffer.h       |    4 +-
 src/include/replication/walreceiver.h         |    2 +-
 src/include/replication/worker_internal.h     |  223 ++-
 src/include/storage/lmgr.h                    |    5 +
 src/include/storage/lock.h                    |   17 +-
 src/include/storage/procsignal.h              |    1 +
 src/include/utils/wait_event.h                |    2 +
 src/test/regress/expected/subscription.out    |   46 +-
 src/test/regress/sql/subscription.sql         |    6 +-
 src/tools/pgindent/typedefs.list              |    7 +
 50 files changed, 3665 insertions(+), 391 deletions(-)
 create mode 100644 src/backend/replication/logical/applyparallelworker.c

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 9316b811ac..c1e4048054 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -7913,11 +7913,16 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>substream</structfield> <type>bool</type>
+       <structfield>substream</structfield> <type>char</type>
       </para>
       <para>
-       If true, the subscription will allow streaming of in-progress
-       transactions
+       Controls how to handle the streaming of in-progress transactions:
+       <literal>f</literal> = disallow streaming of in-progress transactions,
+       <literal>t</literal> = spill the changes of in-progress transactions to
+       disk and apply at once after the transaction is committed on the
+       publisher and received by the subscriber,
+       <literal>p</literal> = apply changes directly using a parallel apply
+       worker if available (same as 't' if no worker is available)
       </para></entry>
      </row>
 
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 9eedab652d..104cce71f0 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4968,7 +4968,8 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       <listitem>
        <para>
         Specifies maximum number of logical replication workers. This includes
-        both apply workers and table synchronization workers.
+        leader apply workers, parallel apply workers, and table synchronization
+        workers.
        </para>
        <para>
         Logical replication workers are taken from the pool defined by
@@ -5008,6 +5009,31 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-max-parallel-apply-workers-per-subscription" xreflabel="max_parallel_apply_workers_per_subscription">
+      <term><varname>max_parallel_apply_workers_per_subscription</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>max_parallel_apply_workers_per_subscription</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Maximum number of parallel apply workers per subscription. This
+        parameter controls the amount of parallelism for streaming of
+        in-progress transactions with subscription parameter
+        <literal>streaming = parallel</literal>.
+       </para>
+       <para>
+        The parallel apply workers are taken from the pool defined by
+        <varname>max_logical_replication_workers</varname>.
+       </para>
+       <para>
+        The default value is 2. This parameter can only be set in the
+        <filename>postgresql.conf</filename> file or on the server command
+        line.
+       </para>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
     </sect2>
 
diff --git a/doc/src/sgml/logical-replication.sgml b/doc/src/sgml/logical-replication.sgml
index 7fdf08b59d..649623e83f 100644
--- a/doc/src/sgml/logical-replication.sgml
+++ b/doc/src/sgml/logical-replication.sgml
@@ -1497,6 +1497,16 @@ CONTEXT:  processing remote data for replication origin "pg_16395" during "INSER
    might not violate any constraint.  This can easily make the subscriber
    inconsistent.
   </para>
+
+  <para>
+   When the streaming mode is <literal>parallel</literal>, the finish LSN of
+   failed transactions may not be logged. In that case, it may be necessary to
+   change the streaming mode to <literal>on</literal> or <literal>off</literal> and
+   cause the same conflicts again so the finish LSN of the failed transaction will
+   be written to the server log. For the usage of finish LSN, please refer to <link
+   linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION ...
+   SKIP</command></link>.
+  </para>
  </sect1>
 
  <sect1 id="logical-replication-restrictions">
@@ -1805,8 +1815,9 @@ CONTEXT:  processing remote data for replication origin "pg_16395" during "INSER
 
    <para>
     <link linkend="guc-max-logical-replication-workers"><varname>max_logical_replication_workers</varname></link>
-    must be set to at least the number of subscriptions (for apply workers), plus
-    some reserve for the table synchronization workers.
+    must be set to at least the number of subscriptions (for leader apply
+    workers), plus some reserve for the table synchronization workers and
+    parallel apply workers.
    </para>
 
    <para>
@@ -1823,6 +1834,13 @@ CONTEXT:  processing remote data for replication origin "pg_16395" during "INSER
      subscription initialization or when new tables are added.
    </para>
 
+   <para>
+    <link linkend="guc-max-parallel-apply-workers-per-subscription"><varname>max_parallel_apply_workers_per_subscription</varname></link>
+     controls the amount of parallelism for streaming of in-progress
+     transactions with subscription parameter
+     <literal>streaming = parallel</literal>.
+   </para>
+
    <para>
     Logical replication workers are also affected by
     <link linkend="guc-wal-receiver-timeout"><varname>wal_receiver_timeout</varname></link>,
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 363b183e5f..eafeeadf47 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -1851,6 +1851,11 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
       <entry><literal>advisory</literal></entry>
       <entry>Waiting to acquire an advisory user lock.</entry>
      </row>
+     <row>
+      <entry><literal>applytransaction</literal></entry>
+      <entry>Waiting to acquire a lock on a remote transaction being applied
+      by a logical replication subscriber.</entry>
+     </row>
      <row>
       <entry><literal>extend</literal></entry>
       <entry>Waiting to extend a relation.</entry>
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 03312e07e2..439ef675f3 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -3103,7 +3103,7 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
      <listitem>
       <para>
        Protocol version. Currently versions <literal>1</literal>, <literal>2</literal>,
-       and <literal>3</literal> are supported.
+       <literal>3</literal>, and <literal>4</literal> are supported.
       </para>
       <para>
        Version <literal>2</literal> is supported only for server version 14
@@ -3113,6 +3113,11 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
        Version <literal>3</literal> is supported only for server version 15
        and above, and it allows streaming of two-phase commits.
       </para>
+      <para>
+       Version <literal>4</literal> is supported only for server version 16
+       and above, and it allows streams of large in-progress transactions to
+       be applied in parallel.
+      </para>
      </listitem>
     </varlistentry>
 
@@ -6883,6 +6888,28 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
         </para>
        </listitem>
       </varlistentry>
+
+      <varlistentry>
+       <term>Int64 (XLogRecPtr)</term>
+       <listitem>
+        <para>
+         The LSN of the abort. This field is available since protocol version
+         4.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>Int64 (TimestampTz)</term>
+       <listitem>
+        <para>
+         Abort timestamp of the transaction. The value is in number
+         of microseconds since PostgreSQL epoch (2000-01-01). This field is
+         available since protocol version 4.
+        </para>
+       </listitem>
+      </varlistentry>
+
      </variablelist>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml
index f9a1776380..f173a09037 100644
--- a/doc/src/sgml/ref/create_subscription.sgml
+++ b/doc/src/sgml/ref/create_subscription.sgml
@@ -228,13 +228,29 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
        </varlistentry>
 
        <varlistentry>
-        <term><literal>streaming</literal> (<type>boolean</type>)</term>
+        <term><literal>streaming</literal> (<type>enum</type>)</term>
         <listitem>
          <para>
           Specifies whether to enable streaming of in-progress transactions
-          for this subscription.  By default, all transactions
-          are fully decoded on the publisher and only then sent to the
-          subscriber as a whole.
+          for this subscription.  The default value is <literal>off</literal>,
+          meaning all transactions are fully decoded on the publisher and only
+          then sent to the subscriber as a whole.
+         </para>
+
+         <para>
+          If set to <literal>on</literal>, the incoming changes are written to
+          temporary files and then applied only after the transaction is
+          committed on the publisher and received by the subscriber.
+         </para>
+
+         <para>
+          If set to <literal>parallel</literal>, incoming changes are directly
+          applied via one of the parallel apply workers, if available. If no
+          parallel apply worker is free to handle streaming transactions then
+          the changes are written to temporary files and applied after the
+          transaction is committed. Note that if an error happens in a
+          parallel apply worker, the finish LSN of the remote transaction
+          might not be reported in the server log.
          </para>
         </listitem>
        </varlistentry>
diff --git a/doc/src/sgml/system-views.sgml b/doc/src/sgml/system-views.sgml
index 143ae5b7bb..8428ee7867 100644
--- a/doc/src/sgml/system-views.sgml
+++ b/doc/src/sgml/system-views.sgml
@@ -1379,8 +1379,9 @@
        <literal>virtualxid</literal>,
        <literal>spectoken</literal>,
        <literal>object</literal>,
-       <literal>userlock</literal>, or
-       <literal>advisory</literal>.
+       <literal>userlock</literal>,
+       <literal>advisory</literal>, or
+       <literal>applytransaction</literal>.
        (See also <xref linkend="wait-event-lock-table"/>.)
       </para></entry>
      </row>
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index b7c7fd9f00..d0d9c86448 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -1712,6 +1712,7 @@ RecordTransactionAbort(bool isSubXact)
 	int			nchildren;
 	TransactionId *children;
 	TimestampTz xact_time;
+	bool		replorigin;
 
 	/*
 	 * If we haven't been assigned an XID, nobody will care whether we aborted
@@ -1742,6 +1743,13 @@ RecordTransactionAbort(bool isSubXact)
 		elog(PANIC, "cannot abort transaction %u, it was already committed",
 			 xid);
 
+	/*
+	 * Are we using the replication origins feature?  Or, in other words, are
+	 * we replaying remote actions?
+	 */
+	replorigin = (replorigin_session_origin != InvalidRepOriginId &&
+				  replorigin_session_origin != DoNotReplicateId);
+
 	/* Fetch the data we need for the abort record */
 	nrels = smgrGetPendingDeletes(false, &rels);
 	nchildren = xactGetCommittedChildren(&children);
@@ -1765,6 +1773,11 @@ RecordTransactionAbort(bool isSubXact)
 					   MyXactFlags, InvalidTransactionId,
 					   NULL);
 
+	if (replorigin)
+		/* Move LSNs forward for this replication origin */
+		replorigin_session_advance(replorigin_session_origin_lsn,
+								   XactLastRecEnd);
+
 	/*
 	 * Report the latest async abort LSN, so that the WAL writer knows to
 	 * flush this abort. There's nothing to be gained by delaying this, since
@@ -5867,11 +5880,10 @@ XactLogAbortRecord(TimestampTz abort_time,
 	}
 
 	/*
-	 * Dump transaction origin information only for abort prepared. We need
-	 * this during recovery to update the replication origin progress.
+	 * Dump transaction origin information. We need this during recovery to
+	 * update the replication origin progress.
 	 */
-	if ((replorigin_session_origin != InvalidRepOriginId) &&
-		TransactionIdIsValid(twophase_xid))
+	if (replorigin_session_origin != InvalidRepOriginId)
 	{
 		xl_xinfo.xinfo |= XACT_XINFO_HAS_ORIGIN;
 
@@ -5928,8 +5940,8 @@ XactLogAbortRecord(TimestampTz abort_time,
 	if (xl_xinfo.xinfo & XACT_XINFO_HAS_ORIGIN)
 		XLogRegisterData((char *) (&xl_origin), sizeof(xl_xact_origin));
 
-	if (TransactionIdIsValid(twophase_xid))
-		XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
+	/* Include the replication origin */
+	XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
 
 	return XLogInsert(RM_XACT_ID, info);
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index d673557ea4..9382e619e9 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -84,7 +84,7 @@ typedef struct SubOpts
 	bool		copy_data;
 	bool		refresh;
 	bool		binary;
-	bool		streaming;
+	char		streaming;
 	bool		twophase;
 	bool		disableonerr;
 	char	   *origin;
@@ -138,7 +138,7 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 	if (IsSet(supported_opts, SUBOPT_BINARY))
 		opts->binary = false;
 	if (IsSet(supported_opts, SUBOPT_STREAMING))
-		opts->streaming = false;
+		opts->streaming = LOGICALREP_STREAM_OFF;
 	if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
 		opts->twophase = false;
 	if (IsSet(supported_opts, SUBOPT_DISABLE_ON_ERR))
@@ -241,7 +241,7 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 				errorConflictingDefElem(defel, pstate);
 
 			opts->specified_opts |= SUBOPT_STREAMING;
-			opts->streaming = defGetBoolean(defel);
+			opts->streaming = defGetStreamingMode(defel);
 		}
 		else if (strcmp(defel->defname, "two_phase") == 0)
 		{
@@ -629,7 +629,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	values[Anum_pg_subscription_subowner - 1] = ObjectIdGetDatum(owner);
 	values[Anum_pg_subscription_subenabled - 1] = BoolGetDatum(opts.enabled);
 	values[Anum_pg_subscription_subbinary - 1] = BoolGetDatum(opts.binary);
-	values[Anum_pg_subscription_substream - 1] = BoolGetDatum(opts.streaming);
+	values[Anum_pg_subscription_substream - 1] = CharGetDatum(opts.streaming);
 	values[Anum_pg_subscription_subtwophasestate - 1] =
 		CharGetDatum(opts.twophase ?
 					 LOGICALREP_TWOPHASE_STATE_PENDING :
@@ -1098,7 +1098,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				if (IsSet(opts.specified_opts, SUBOPT_STREAMING))
 				{
 					values[Anum_pg_subscription_substream - 1] =
-						BoolGetDatum(opts.streaming);
+						CharGetDatum(opts.streaming);
 					replaces[Anum_pg_subscription_substream - 1] = true;
 				}
 
@@ -2122,3 +2122,60 @@ merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *
 
 	return oldpublist;
 }
+
+/*
+ * Extract the streaming mode value from a DefElem.  This is like
+ * defGetBoolean() but also accepts the special value of "parallel".
+ */
+char
+defGetStreamingMode(DefElem *def)
+{
+	/*
+	 * If no parameter value given, assume "true" is meant.
+	 */
+	if (!def->arg)
+		return LOGICALREP_STREAM_ON;
+
+	/*
+	 * Allow 0, 1, "false", "true", "off", "on" or "parallel".
+	 */
+	switch (nodeTag(def->arg))
+	{
+		case T_Integer:
+			switch (intVal(def->arg))
+			{
+				case 0:
+					return LOGICALREP_STREAM_OFF;
+				case 1:
+					return LOGICALREP_STREAM_ON;
+				default:
+					/* otherwise, error out below */
+					break;
+			}
+			break;
+		default:
+			{
+				char	   *sval = defGetString(def);
+
+				/*
+				 * The set of strings accepted here should match up with the
+				 * grammar's opt_boolean_or_string production.
+				 */
+				if (pg_strcasecmp(sval, "false") == 0 ||
+					pg_strcasecmp(sval, "off") == 0)
+					return LOGICALREP_STREAM_OFF;
+				if (pg_strcasecmp(sval, "true") == 0 ||
+					pg_strcasecmp(sval, "on") == 0)
+					return LOGICALREP_STREAM_ON;
+				if (pg_strcasecmp(sval, "parallel") == 0)
+					return LOGICALREP_STREAM_PARALLEL;
+			}
+			break;
+	}
+
+	ereport(ERROR,
+			(errcode(ERRCODE_SYNTAX_ERROR),
+			 errmsg("%s requires a Boolean value or \"parallel\"",
+					def->defname)));
+	return LOGICALREP_STREAM_OFF;	/* keep compiler quiet */
+}
diff --git a/src/backend/libpq/pqmq.c b/src/backend/libpq/pqmq.c
index 4d0415e379..639845fd80 100644
--- a/src/backend/libpq/pqmq.c
+++ b/src/backend/libpq/pqmq.c
@@ -13,11 +13,13 @@
 
 #include "postgres.h"
 
+#include "access/parallel.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "libpq/pqmq.h"
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "replication/logicalworker.h"
 #include "tcop/tcopprot.h"
 #include "utils/builtins.h"
 
@@ -162,9 +164,19 @@ mq_putmessage(char msgtype, const char *s, size_t len)
 		result = shm_mq_sendv(pq_mq_handle, iov, 2, true, true);
 
 		if (pq_mq_parallel_leader_pid != 0)
-			SendProcSignal(pq_mq_parallel_leader_pid,
-						   PROCSIG_PARALLEL_MESSAGE,
-						   pq_mq_parallel_leader_backend_id);
+		{
+			if (IsLogicalParallelApplyWorker())
+				SendProcSignal(pq_mq_parallel_leader_pid,
+							   PROCSIG_PARALLEL_APPLY_MESSAGE,
+							   pq_mq_parallel_leader_backend_id);
+			else
+			{
+				Assert(IsParallelWorker());
+				SendProcSignal(pq_mq_parallel_leader_pid,
+							   PROCSIG_PARALLEL_MESSAGE,
+							   pq_mq_parallel_leader_backend_id);
+			}
+		}
 
 		if (result != SHM_MQ_WOULD_BLOCK)
 			break;
diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
index 0d72de24b0..2dfa9ab522 100644
--- a/src/backend/postmaster/bgworker.c
+++ b/src/backend/postmaster/bgworker.c
@@ -128,6 +128,9 @@ static const struct
 	},
 	{
 		"ApplyWorkerMain", ApplyWorkerMain
+	},
+	{
+		"ParallelApplyWorkerMain", ParallelApplyWorkerMain
 	}
 };
 
diff --git a/src/backend/postmaster/interrupt.c b/src/backend/postmaster/interrupt.c
index 1aed2e2e99..e64029fac4 100644
--- a/src/backend/postmaster/interrupt.c
+++ b/src/backend/postmaster/interrupt.c
@@ -98,8 +98,9 @@ SignalHandlerForCrashExit(SIGNAL_ARGS)
  * shut down and exit.
  *
  * Typically, this handler would be used for SIGTERM, but some processes use
- * other signals. In particular, the checkpointer exits on SIGUSR2, and the
- * WAL writer exits on either SIGINT or SIGTERM.
+ * other signals. In particular, the checkpointer exits on SIGUSR2, and the WAL
+ * writer and the logical replication parallel apply worker exits on either
+ * SIGINT or SIGTERM.
  *
  * ShutdownRequestPending should be checked at a convenient place within the
  * main loop, or else the main loop should call HandleMainLoopInterrupts.
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 7f697b0f29..225da81f2e 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -443,9 +443,9 @@ libpqrcv_startstreaming(WalReceiverConn *conn,
 		appendStringInfo(&cmd, "proto_version '%u'",
 						 options->proto.logical.proto_version);
 
-		if (options->proto.logical.streaming &&
-			PQserverVersion(conn->streamConn) >= 140000)
-			appendStringInfoString(&cmd, ", streaming 'on'");
+		if (options->proto.logical.streaming_str)
+			appendStringInfo(&cmd, ", streaming '%s'",
+							 options->proto.logical.streaming_str);
 
 		if (options->proto.logical.twophase &&
 			PQserverVersion(conn->streamConn) >= 150000)
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index c4e2fdeb71..2dc25e37bb 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -15,6 +15,7 @@ include $(top_builddir)/src/Makefile.global
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
 OBJS = \
+	applyparallelworker.o \
 	decode.o \
 	launcher.o \
 	logical.o \
diff --git a/src/backend/replication/logical/applyparallelworker.c b/src/backend/replication/logical/applyparallelworker.c
new file mode 100644
index 0000000000..f8a0bb462a
--- /dev/null
+++ b/src/backend/replication/logical/applyparallelworker.c
@@ -0,0 +1,1627 @@
+/*-------------------------------------------------------------------------
+ * applyparallelworker.c
+ *	   Support routines for applying xact by parallel apply worker
+ *
+ * Copyright (c) 2022, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/applyparallelworker.c
+ *
+ * This file contains the code to launch, set up, and teardown a parallel apply
+ * worker which receives the changes from the leader worker and invokes routines
+ * to apply those on the subscriber database. Additionally, this file contains
+ * routines that are intended to support setting up, using, and tearing down a
+ * ParallelApplyWorkerInfo which is required so the leader worker and parallel
+ * apply workers can communicate with each other.
+ *
+ * The parallel apply workers are assigned (if available) as soon as xact's
+ * first stream is received for subscriptions that have set their 'streaming'
+ * option as parallel. The leader apply worker will send changes to this new
+ * worker via shared memory. We keep this worker assigned till the transaction
+ * commit is received and also wait for the worker to finish at commit. This
+ * preserves commit ordering and avoid file I/O in most cases, although we
+ * still need to spill to a file if there is no worker available. See comments
+ * atop logical/worker to know more about streamed xacts whose changes are
+ * spilled to disk. It is important to maintain commit order to avoid failures
+ * due to: (a) transaction dependencies - say if we insert a row in the first
+ * transaction and update it in the second transaction on publisher then
+ * allowing the subscriber to apply both in parallel can lead to failure in the
+ * update; (b) deadlocks - allowing transactions that update the same set of
+ * rows/tables in the opposite order to be applied in parallel can lead to
+ * deadlocks.
+ *
+ * A worker pool is used to avoid restarting workers for each streaming
+ * transaction. We maintain each worker's information (ParallelApplyWorkerInfo)
+ * in the ParallelApplyWorkerPool. After successfully launching a new worker,
+ * its information is added to the ParallelApplyWorkerPool. Once the worker
+ * finishes applying the transaction, it is marked as available for re-use.
+ * Now, before starting a new worker to apply the streaming transaction, we
+ * check the list for any available worker. Note that we retain a maximum of
+ * half the max_parallel_apply_workers_per_subscription workers in the pool and
+ * after that, we simply exit the worker after applying the transaction.
+ *
+ * XXX This worker pool threshold is arbitrary and we can provide a GUC
+ * variable for this in the future if required.
+ *
+ * The leader apply worker will create a separate dynamic shared memory segment
+ * when each parallel apply worker starts. The reason for this design is that
+ * we cannot predict how many workers will be needed. It may be possible to
+ * allocate enough shared memory in one segment based on the maximum number of
+ * parallel apply workers (max_parallel_apply_workers_per_subscription), but
+ * this would waste memory if no process is actually started.
+ *
+ * The dynamic shared memory segment contains: (a) a shm_mq that is used to
+ * send changes in the transaction from leader apply worker to parallel apply
+ * worker; (b) another shm_mq that is used to send errors (and other messages
+ * reported via elog/ereport) from the parallel apply worker to leader apply
+ * worker; (c) necessary information to be shared among parallel apply workers
+ * and the leader apply worker (i.e. members of ParallelApplyWorkerShared).
+ *
+ * Locking Considerations
+ * ----------------------
+ * Since the database structure (schema of subscription tables, constraints,
+ * etc.) of the publisher and subscriber could be different, applying
+ * transactions in parallel mode on the subscriber side can cause some
+ * deadlocks that do not occur on the publisher side. This can happen even
+ * without parallel mode when there are concurrent operations on the
+ * subscriber. In order to detect the deadlocks among leader and parallel apply
+ * workers, we need to ensure that we wait using lmgr locks. An alternative
+ * approach could be to not allow parallelism when the schema of tables is
+ * different between the publisher and subscriber but that would be too
+ * restrictive and would require the publisher to send much more information
+ * than it is currently sending.
+ *
+ * Consider a case where the subscribed table does not have a unique key on the
+ * publisher and has a unique key on the subscriber.
+ *
+ * 1) Deadlock between the leader apply worker and a parallel apply worker
+ *
+ * The parallel apply worker (PA) is executing TX-1 and the leader apply worker
+ * (LA) is executing TX-2 concurrently on the subscriber. Now, LA is waiting
+ * for PA because of the unique key of the subscribed table while PA is waiting
+ * for LA to send the next stream of changes or transaction finish command
+ * message.
+ *
+ * In order for lmgr to detect this, we have LA acquire a session lock on the
+ * remote transaction (by pa_lock_stream()) and have PA wait on the lock before
+ * trying to receive the next stream of changes. Specifically, LA will acquire
+ * the lock before sending the STREAM_STOP and will release it if already
+ * acquired before sending the STREAM_START, STREAM_ABORT (for toplevel
+ * transaction), STREAM_PREPARE, and STREAM_COMMIT. The PA will acquire the
+ * lock after processing STREAM_STOP and STREAM_ABORT (for subtransaction) and
+ * then release the lock immediately after acquiring it.
+ *
+ * The lock graph for the above example will look as follows:
+ * LA (waiting to acquire the lock on the unique index) -> PA (waiting to
+ * acquire the stream lock) -> LA
+ *
+ * This way, when PA is waiting for LA for the next stream of changes, we can
+ * have a wait-edge from PA to LA in lmgr, which will make us detect the
+ * deadlock between LA and PA.
+ *
+ * 2) Deadlock between the leader apply worker and parallel apply workers
+ *
+ * This scenario is similar to the first case but TX-1 and TX-2 are executed by
+ * two parallel apply workers (PA-1 and PA-2 respectively). In this scenario,
+ * PA-2 is waiting for PA-1 to complete its transaction while PA-1 is waiting
+ * for subsequent input from LA. Also, LA is waiting for PA-2 to complete its
+ * transaction in order to preserve the commit order. There is a deadlock among
+ * the three processes.
+ *
+ * In order for lmgr to detect this, we have PA acquire a session lock (this is
+ * a different lock than referred in previous case, see
+ * pa_lock_transaction()) on the transaction being applied and have LA wait on
+ * the lock before proceeding in the transaction finish commands. Specifically,
+ * PA will acquire this lock in Share mode before executing the first message
+ * of the transaction and release it at the xact end. LA will acquire this lock
+ * in AccessExclusive mode at transaction finish commands (STREAM_COMMIT and
+ * STREAM_PREPARE) and release it immediately.
+ *
+ * The lock graph for the above example will look as follows:
+ * LA (waiting to acquire the transaction lock) -> PA-2 (waiting to acquire the
+ * lock due to unique index constraint) -> PA-1 (waiting to acquire the stream
+ * lock) -> LA
+ *
+ * This way when LA is waiting to finish the transaction end command to preserve
+ * the commit order, we will be able to detect deadlock, if any.
+ *
+ * One might think we can use XactLockTableWait(), but XactLockTableWait()
+ * considers PREPARED TRANSACTION as still in progress which means the lock
+ * won't be released even after the parallel apply worker has prepared the
+ * transaction.
+ *
+ * 3) Deadlock when the shm_mq buffer is full
+ *
+ * In the previous scenario (ie. PA-1 and PA-2 are executing transactions
+ * concurrently), if the shm_mq buffer between LA and PA-2 is full, LA has to
+ * wait to send messages, and this wait doesn't appear in lmgr.
+ *
+ * To avoid this wait, we use a non-blocking write and wait with a timeout. If
+ * the timeout is exceeded, the LA will serialize all the pending messages to
+ * a file and indicate PA-2 that it needs to read that file for the remaining
+ * messages. Then LA will start waiting for commit as in the previous case
+ * which will detect deadlock if any. See pa_send_data() and
+ * enum TransApplyAction.
+ *
+ * 4) Lock types
+ *
+ * Both the stream lock and the transaction lock mentioned above are
+ * session-level locks because both locks could be acquired outside the
+ * transaction, and the stream lock in the leader needs to persist across
+ * transaction boundaries i.e. until the end of the streaming transaction.
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "libpq/pqformat.h"
+#include "libpq/pqmq.h"
+#include "pgstat.h"
+#include "postmaster/interrupt.h"
+#include "replication/logicallauncher.h"
+#include "replication/logicalworker.h"
+#include "replication/origin.h"
+#include "replication/worker_internal.h"
+#include "storage/ipc.h"
+#include "storage/lmgr.h"
+#include "tcop/tcopprot.h"
+#include "utils/inval.h"
+#include "utils/memutils.h"
+#include "utils/syscache.h"
+
+#define PG_LOGICAL_APPLY_SHM_MAGIC 0x787ca067
+
+/*
+ * DSM keys for parallel apply worker.  Unlike other parallel execution code,
+ * since we don't need to worry about DSM keys conflicting with plan_node_id we
+ * can use small integers.
+ */
+#define PARALLEL_APPLY_KEY_SHARED		1
+#define PARALLEL_APPLY_KEY_MQ			2
+#define PARALLEL_APPLY_KEY_ERROR_QUEUE	3
+
+/* Queue size of DSM, 16 MB for now. */
+#define DSM_QUEUE_SIZE	(16 * 1024 * 1024)
+
+/*
+ * Error queue size of DSM. It is desirable to make it large enough that a
+ * typical ErrorResponse can be sent without blocking.  That way, a worker that
+ * errors out can write the whole message into the queue and terminate without
+ * waiting for the user backend.
+ */
+#define DSM_ERROR_QUEUE_SIZE			(16 * 1024)
+
+/*
+ * There are three fields in each message received by the parallel apply
+ * worker: start_lsn, end_lsn and send_time. Because we have updated these
+ * statistics in the leader apply worker, we can ignore these fields in the
+ * parallel apply worker (see function LogicalRepApplyLoop).
+ */
+#define SIZE_STATS_MESSAGE (2 * sizeof(XLogRecPtr) + sizeof(TimestampTz))
+
+/*
+ * The type of session-level lock on a transaction being applied on a logical
+ * replication subscriber.
+ */
+#define PARALLEL_APPLY_LOCK_STREAM	0
+#define PARALLEL_APPLY_LOCK_XACT	1
+
+/*
+ * Hash table entry to map xid to the parallel apply worker state.
+ */
+typedef struct ParallelApplyWorkerEntry
+{
+	TransactionId xid;			/* Hash key -- must be first */
+	ParallelApplyWorkerInfo *winfo;
+} ParallelApplyWorkerEntry;
+
+/*
+ * A hash table used to cache the state of streaming transactions being applied
+ * by the parallel apply workers.
+ */
+static HTAB *ParallelApplyTxnHash = NULL;
+
+/*
+* A list (pool) of active parallel apply workers. The information for
+* the new worker is added to the list after successfully launching it. The
+* list entry is removed if there are already enough workers in the worker
+* pool either at the end of the transaction or while trying to find a free
+* worker for applying the transaction. For more information about the worker
+* pool, see comments atop this file.
+ */
+static List *ParallelApplyWorkerPool = NIL;
+
+/*
+ * Information shared between leader apply worker and parallel apply worker.
+ */
+ParallelApplyWorkerShared *MyParallelShared = NULL;
+
+/*
+ * Is there a message sent by a parallel apply worker that the leader apply
+ * worker needs to receive?
+ */
+volatile sig_atomic_t ParallelApplyMessagePending = false;
+
+/*
+ * Cache the parallel apply worker information required for applying the
+ * current streaming transaction. It is used to save the cost of searching the
+ * hash table when applying the changes between STREAM_START and STREAM_STOP.
+ */
+static ParallelApplyWorkerInfo *stream_apply_worker = NULL;
+
+/* A list to maintain subtransactions, if any. */
+static List *subxactlist = NIL;
+
+static void pa_free_worker_info(ParallelApplyWorkerInfo *winfo);
+static ParallelTransState pa_get_xact_state(ParallelApplyWorkerShared *wshared);
+static PartialFileSetState pa_get_fileset_state(void);
+
+/*
+ * Returns true if it is OK to start a parallel apply worker, false otherwise.
+ */
+static bool
+pa_can_start(TransactionId xid)
+{
+	Assert(TransactionIdIsValid(xid));
+
+	/*
+	 * Don't start a new parallel apply worker if the subscription is not
+	 * using parallel streaming mode, or if the publisher does not support
+	 * parallel apply.
+	 */
+	if (!MyLogicalRepWorker->parallel_apply)
+		return false;
+
+	/* Only leader apply workers can start parallel apply workers. */
+	if (!am_leader_apply_worker())
+		return false;
+
+	/*
+	 * Don't start a new parallel worker if user has set skiplsn as it's
+	 * possible that they want to skip the streaming transaction. For
+	 * streaming transactions, we need to serialize the transaction to a file
+	 * so that we can get the last LSN of the transaction to judge whether to
+	 * skip before starting to apply the change.
+	 */
+	if (!XLogRecPtrIsInvalid(MySubscription->skiplsn))
+		return false;
+
+	/*
+	 * For streaming transactions that are being applied using a parallel
+	 * apply worker, we cannot decide whether to apply the change for a
+	 * relation that is not in the READY state (see
+	 * should_apply_changes_for_rel) as we won't know remote_final_lsn by that
+	 * time. So, we don't start the new parallel apply worker in this case.
+	 */
+	if (!AllTablesyncsReady())
+		return false;
+
+	return true;
+}
+
+/*
+ * Set up a dynamic shared memory segment.
+ *
+ * We set up a control region that contains a fixed-size worker info
+ * (ParallelApplyWorkerShared), a message queue, and an error queue.
+ *
+ * Returns true on success, false on failure.
+ */
+static bool
+pa_setup_dsm(ParallelApplyWorkerInfo *winfo)
+{
+	shm_toc_estimator e;
+	Size		segsize;
+	dsm_segment *seg;
+	shm_toc    *toc;
+	ParallelApplyWorkerShared *shared;
+	shm_mq	   *mq;
+	Size		queue_size = DSM_QUEUE_SIZE;
+	Size		error_queue_size = DSM_ERROR_QUEUE_SIZE;
+
+	/*
+	 * Estimate how much shared memory we need.
+	 *
+	 * Because the TOC machinery may choose to insert padding of oddly-sized
+	 * requests, we must estimate each chunk separately.
+	 *
+	 * We need one key to register the location of the header, and two other
+	 * keys to track the locations of the message queue and the error message
+	 * queue.
+	 */
+	shm_toc_initialize_estimator(&e);
+	shm_toc_estimate_chunk(&e, sizeof(ParallelApplyWorkerShared));
+	shm_toc_estimate_chunk(&e, queue_size);
+	shm_toc_estimate_chunk(&e, error_queue_size);
+
+	shm_toc_estimate_keys(&e, 3);
+	segsize = shm_toc_estimate(&e);
+
+	/* Create the shared memory segment and establish a table of contents. */
+	seg = dsm_create(shm_toc_estimate(&e), 0);
+	if (!seg)
+		return false;
+
+	toc = shm_toc_create(PG_LOGICAL_APPLY_SHM_MAGIC, dsm_segment_address(seg),
+						 segsize);
+
+	/* Set up the header region. */
+	shared = shm_toc_allocate(toc, sizeof(ParallelApplyWorkerShared));
+	SpinLockInit(&shared->mutex);
+
+	shared->xact_state = PARALLEL_TRANS_UNKNOWN;
+	pg_atomic_init_u32(&(shared->pending_stream_count), 0);
+	shared->last_commit_end = InvalidXLogRecPtr;
+	shared->fileset_state = FS_EMPTY;
+
+	shm_toc_insert(toc, PARALLEL_APPLY_KEY_SHARED, shared);
+
+	/* Set up message queue for the worker. */
+	mq = shm_mq_create(shm_toc_allocate(toc, queue_size), queue_size);
+	shm_toc_insert(toc, PARALLEL_APPLY_KEY_MQ, mq);
+	shm_mq_set_sender(mq, MyProc);
+
+	/* Attach the queue. */
+	winfo->mq_handle = shm_mq_attach(mq, seg, NULL);
+
+	/* Set up error queue for the worker. */
+	mq = shm_mq_create(shm_toc_allocate(toc, error_queue_size),
+					   error_queue_size);
+	shm_toc_insert(toc, PARALLEL_APPLY_KEY_ERROR_QUEUE, mq);
+	shm_mq_set_receiver(mq, MyProc);
+
+	/* Attach the queue. */
+	winfo->error_mq_handle = shm_mq_attach(mq, seg, NULL);
+
+	/* Return results to caller. */
+	winfo->dsm_seg = seg;
+	winfo->shared = shared;
+
+	return true;
+}
+
+/*
+ * Try to get a parallel apply worker from the pool. If none is available then
+ * start a new one.
+ */
+static ParallelApplyWorkerInfo *
+pa_launch_parallel_worker(void)
+{
+	MemoryContext oldcontext;
+	bool		launched;
+	ParallelApplyWorkerInfo *winfo;
+	List	   *active_workers = list_copy(ParallelApplyWorkerPool);
+	ListCell   *lc;
+
+	/* Try to get an available parallel apply worker from the worker pool. */
+	foreach(lc, active_workers)
+	{
+		winfo = (ParallelApplyWorkerInfo *) lfirst(lc);
+
+		/*
+		 * We first try to free the worker to improve our chances of finding
+		 * one that is not in use. Normally, we free the worker after ensuring
+		 * that the transaction is committed by the parallel worker but for
+		 * rollbacks, we don't wait for the transaction to finish so can't
+		 * free the worker information immediately.
+		 */
+		if (pa_free_worker(winfo))
+			continue;
+
+		if (!winfo->in_use)
+			return winfo;
+	}
+
+	/*
+	 * Start a new parallel apply worker.
+	 *
+	 * The worker info can be used for the lifetime of the worker process, so
+	 * create it in a permanent context.
+	 */
+	oldcontext = MemoryContextSwitchTo(ApplyContext);
+
+	winfo = (ParallelApplyWorkerInfo *) palloc0(sizeof(ParallelApplyWorkerInfo));
+
+	/* Setup shared memory. */
+	if (!pa_setup_dsm(winfo))
+	{
+		MemoryContextSwitchTo(oldcontext);
+		pfree(winfo);
+		return NULL;
+	}
+
+	launched = logicalrep_worker_launch(MyLogicalRepWorker->dbid,
+										MySubscription->oid,
+										MySubscription->name,
+										MyLogicalRepWorker->userid,
+										InvalidOid,
+										dsm_segment_handle(winfo->dsm_seg));
+
+	if (launched)
+	{
+		ParallelApplyWorkerPool = lappend(ParallelApplyWorkerPool, winfo);
+	}
+	else
+	{
+		pa_free_worker_info(winfo);
+		winfo = NULL;
+	}
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return winfo;
+}
+
+/*
+ * Allocate a parallel apply worker that will be used for the specified xid.
+ *
+ * We first try to get an available worker from the pool, if any and then try
+ * to launch a new worker. On successful allocation, remember the worker
+ * information in the hash table so that we can get it later for processing the
+ * streaming changes.
+ */
+void
+pa_allocate_worker(TransactionId xid)
+{
+	bool		found;
+	ParallelApplyWorkerInfo *winfo = NULL;
+	ParallelApplyWorkerEntry *entry;
+
+	if (!pa_can_start(xid))
+		return;
+
+	/* First time through, initialize parallel apply worker state hashtable. */
+	if (!ParallelApplyTxnHash)
+	{
+		HASHCTL		ctl;
+
+		MemSet(&ctl, 0, sizeof(ctl));
+		ctl.keysize = sizeof(TransactionId);
+		ctl.entrysize = sizeof(ParallelApplyWorkerEntry);
+		ctl.hcxt = ApplyContext;
+
+		ParallelApplyTxnHash = hash_create("logical replication parallel apply workers hash",
+										   16, &ctl,
+										   HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+	}
+
+	/*
+	 * It's necessary to reread the subscription information before assigning
+	 * the transaction to a parallel apply worker. Otherwise, the leader may
+	 * not be able to reread the subscription information if streaming
+	 * transactions keep coming and are handled by parallel apply workers.
+	 */
+	maybe_reread_subscription();
+
+	winfo = pa_launch_parallel_worker();
+	if (!winfo)
+		return;
+
+	/* Create an entry for the requested transaction. */
+	entry = hash_search(ParallelApplyTxnHash, &xid, HASH_ENTER, &found);
+	if (found)
+		elog(ERROR, "hash table corrupted");
+
+	/* Update the transaction information in shared memory. */
+	SpinLockAcquire(&winfo->shared->mutex);
+	winfo->shared->xact_state = PARALLEL_TRANS_UNKNOWN;
+	winfo->shared->xid = xid;
+	SpinLockRelease(&winfo->shared->mutex);
+
+	winfo->in_use = true;
+	winfo->serialize_changes = false;
+	entry->winfo = winfo;
+	entry->xid = xid;
+}
+
+/*
+ * Find the assigned worker for the given transaction, if any.
+ */
+ParallelApplyWorkerInfo *
+pa_find_worker(TransactionId xid)
+{
+	bool		found;
+	ParallelApplyWorkerEntry *entry;
+
+	if (!TransactionIdIsValid(xid))
+		return NULL;
+
+	if (!ParallelApplyTxnHash)
+		return NULL;
+
+	/* Return the cached parallel apply worker if valid. */
+	if (stream_apply_worker)
+		return stream_apply_worker;
+
+	/* Find an entry for the requested transaction. */
+	entry = hash_search(ParallelApplyTxnHash, &xid, HASH_FIND, &found);
+	if (found)
+	{
+		/* The worker must not have exited.  */
+		Assert(entry->winfo->in_use);
+		return entry->winfo;
+	}
+
+	return NULL;
+}
+
+/*
+ * Makes the worker available for reuse.
+ *
+ * This removes the parallel apply worker entry from the hash table so that it
+ * can't be used. If there are enough workers in the pool, it stops the worker
+ * and frees the corresponding info. Otherwise it just marks the worker as
+ * available for reuse.
+ *
+ * For more information about the worker pool, see comments atop this file.
+ *
+ * Returns true if the worker is stopped, false otherwise.
+ */
+bool
+pa_free_worker(ParallelApplyWorkerInfo *winfo)
+{
+	Assert(!am_parallel_apply_worker());
+
+	/* Worker is already available for reuse. */
+	if (!winfo->in_use)
+		return false;
+
+	/*
+	 * Don't free the worker if the transaction in the worker is still in
+	 * progress. This could happen as we don't wait for the apply of rollback
+	 * to finish.
+	 */
+	if (pa_get_xact_state(winfo->shared) != PARALLEL_TRANS_FINISHED)
+		return false;
+
+	if (!hash_search(ParallelApplyTxnHash, &winfo->shared->xid, HASH_REMOVE, NULL))
+		elog(ERROR, "hash table corrupted");
+
+	/*
+	 * Stop the worker if there are enough workers in the pool.
+	 *
+	 * XXX Additionally, we also stop the worker if the leader apply worker
+	 * serialize part of the transaction data due to a send timeout. This is
+	 * because the message could be partially written to the queue and there
+	 * is no way to clean the queue other than resending the message until it
+	 * succeeds. Instead of trying to send the data which anyway would have
+	 * been serialized and then letting the parallel apply worker deal with
+	 * the spurious message, we stop the worker.
+	 */
+	if (winfo->serialize_changes ||
+		list_length(ParallelApplyWorkerPool) >
+		(max_parallel_apply_workers_per_subscription / 2))
+	{
+		int			slot_no;
+		uint16		generation;
+
+		SpinLockAcquire(&winfo->shared->mutex);
+		generation = winfo->shared->logicalrep_worker_generation;
+		slot_no = winfo->shared->logicalrep_worker_slot_no;
+		SpinLockRelease(&winfo->shared->mutex);
+
+		logicalrep_pa_worker_stop(slot_no, generation);
+
+		pa_free_worker_info(winfo);
+
+		return true;
+	}
+
+	winfo->in_use = false;
+	winfo->serialize_changes = false;
+
+	return false;
+}
+
+/*
+ * Free the parallel apply worker information and unlink the files with
+ * serialized changes if any.
+ */
+static void
+pa_free_worker_info(ParallelApplyWorkerInfo *winfo)
+{
+	Assert(winfo);
+
+	if (winfo->mq_handle)
+		shm_mq_detach(winfo->mq_handle);
+
+	if (winfo->error_mq_handle)
+		shm_mq_detach(winfo->error_mq_handle);
+
+	/* Unlink the files with serialized changes. */
+	if (winfo->serialize_changes)
+		stream_cleanup_files(MyLogicalRepWorker->subid, winfo->shared->xid);
+
+	if (winfo->dsm_seg)
+		dsm_detach(winfo->dsm_seg);
+
+	/* Remove from the worker pool. */
+	ParallelApplyWorkerPool = list_delete_ptr(ParallelApplyWorkerPool, winfo);
+
+	pfree(winfo);
+}
+
+/*
+ * Detach from the error_mq_handle for each parallel apply worker.
+ */
+void
+pa_detach_all_error_mq(void)
+{
+	ListCell   *lc;
+
+	foreach(lc, ParallelApplyWorkerPool)
+	{
+		ParallelApplyWorkerInfo *winfo = (ParallelApplyWorkerInfo *) lfirst(lc);
+
+		shm_mq_detach(winfo->error_mq_handle);
+		winfo->error_mq_handle = NULL;
+	}
+}
+
+/*
+ * Check if there are any pending spooled messages.
+ */
+static bool
+pa_has_spooled_message_pending()
+{
+	PartialFileSetState fileset_state;
+
+	fileset_state = pa_get_fileset_state();
+
+	return (fileset_state != FS_EMPTY);
+}
+
+/*
+ * Replay the spooled messages once the leader apply worker has finished
+ * serializing changes to the file.
+ */
+static void
+pa_spooled_messages(void)
+{
+	PartialFileSetState fileset_state;
+
+	fileset_state = pa_get_fileset_state();
+
+	/*
+	 * If the leader apply worker is busy serializing the partial changes then
+	 * acquire the stream lock now and wait for the leader worker to finish
+	 * serializing the changes. Otherwise, the parallel apply worker won't get
+	 * a chance to receive a STREAM_STOP (and acquire the stream lock) until
+	 * the leader had serialized all changes which can lead to undetected
+	 * deadlock.
+	 *
+	 * Note that the fileset state can be FS_SERIALIZE_DONE once the leader
+	 * worker has finished serializing the changes.
+	 */
+	if (fileset_state == FS_SERIALIZE_IN_PROGRESS)
+	{
+		pa_lock_stream(MyParallelShared->xid, AccessShareLock);
+		pa_unlock_stream(MyParallelShared->xid, AccessShareLock);
+
+		fileset_state = pa_get_fileset_state();
+	}
+
+	/*
+	 * We cannot read the file immediately after the leader has serialized all
+	 * changes to the file because there may still be messages in the memory
+	 * queue. We will apply all spooled messages the next time we call this
+	 * function and that will ensure there are no messages left in the memory
+	 * queue.
+	 */
+	if (fileset_state == FS_SERIALIZE_DONE)
+	{
+		pa_set_fileset_state(MyParallelShared, FS_READY);
+	}
+	else if (fileset_state == FS_READY)
+	{
+		apply_spooled_messages(&MyParallelShared->fileset,
+							   MyParallelShared->xid,
+							   InvalidXLogRecPtr);
+		pa_set_fileset_state(MyParallelShared, FS_EMPTY);
+	}
+}
+
+/*
+ * Interrupt handler for main loop of parallel apply worker.
+ */
+static void
+ProcessParallelApplyInterrupts(void)
+{
+	CHECK_FOR_INTERRUPTS();
+
+	if (ShutdownRequestPending)
+	{
+		ereport(LOG,
+				(errmsg("logical replication parallel apply worker for subscription \"%s\" has finished",
+						MySubscription->name)));
+
+		proc_exit(0);
+	}
+
+	if (ConfigReloadPending)
+	{
+		ConfigReloadPending = false;
+		ProcessConfigFile(PGC_SIGHUP);
+	}
+}
+
+/* Parallel apply worker main loop. */
+static void
+LogicalParallelApplyLoop(shm_mq_handle *mqh)
+{
+	shm_mq_result shmq_res;
+	ErrorContextCallback errcallback;
+	MemoryContext oldcxt = CurrentMemoryContext;
+
+	/*
+	 * Init the ApplyMessageContext which we clean up after each replication
+	 * protocol message.
+	 */
+	ApplyMessageContext = AllocSetContextCreate(ApplyContext,
+												"ApplyMessageContext",
+												ALLOCSET_DEFAULT_SIZES);
+
+	/*
+	 * Push apply error context callback. Fields will be filled while applying
+	 * a change.
+	 */
+	errcallback.callback = apply_error_callback;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	for (;;)
+	{
+		void	   *data;
+		Size		len;
+
+		ProcessParallelApplyInterrupts();
+
+		/* Ensure we are reading the data into our memory context. */
+		MemoryContextSwitchTo(ApplyMessageContext);
+
+		shmq_res = shm_mq_receive(mqh, &len, &data, true);
+
+		if (shmq_res == SHM_MQ_SUCCESS)
+		{
+			StringInfoData s;
+			int			c;
+
+			if (len == 0)
+				elog(ERROR, "invalid message length");
+
+			s.cursor = 0;
+			s.maxlen = -1;
+			s.data = (char *) data;
+			s.len = len;
+
+			/*
+			 * The first byte of messages sent from leader apply worker to
+			 * parallel apply workers can only be 'w'.
+			 */
+			c = pq_getmsgbyte(&s);
+			if (c != 'w')
+				elog(ERROR, "unexpected message \"%c\"", c);
+
+			/*
+			 * Ignore statistics fields that have been updated by the leader
+			 * apply worker.
+			 *
+			 * XXX We can avoid sending the statistics fields from the leader
+			 * apply worker but for that, it needs to rebuild the entire
+			 * message by removing these fields which could be more work than
+			 * simply ignoring these fields in the parallel apply worker.
+			 */
+			s.cursor += SIZE_STATS_MESSAGE;
+
+			apply_dispatch(&s);
+		}
+		else if (shmq_res == SHM_MQ_WOULD_BLOCK)
+		{
+			/* Replay the changes from the file, if any. */
+			if (pa_has_spooled_message_pending())
+			{
+				pa_spooled_messages();
+			}
+			else
+			{
+				int			rc;
+
+				/* Wait for more work. */
+				rc = WaitLatch(MyLatch,
+							   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+							   1000L,
+							   WAIT_EVENT_LOGICAL_PARALLEL_APPLY_MAIN);
+
+				if (rc & WL_LATCH_SET)
+					ResetLatch(MyLatch);
+			}
+		}
+		else
+		{
+			Assert(shmq_res == SHM_MQ_DETACHED);
+
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("lost connection to the logical replication apply worker")));
+		}
+
+		MemoryContextReset(ApplyMessageContext);
+		MemoryContextSwitchTo(oldcxt);
+	}
+
+	/* Pop the error context stack. */
+	error_context_stack = errcallback.previous;
+
+	MemoryContextSwitchTo(oldcxt);
+}
+
+/*
+ * Make sure the leader apply worker tries to read from our error queue one more
+ * time. This guards against the case where we exit uncleanly without sending
+ * an ErrorResponse, for example because some code calls proc_exit directly.
+ */
+static void
+pa_shutdown(int code, Datum arg)
+{
+	SendProcSignal(MyLogicalRepWorker->apply_leader_pid,
+				   PROCSIG_PARALLEL_APPLY_MESSAGE,
+				   InvalidBackendId);
+
+	dsm_detach((dsm_segment *) DatumGetPointer(arg));
+}
+
+/*
+ * Parallel apply worker entry point.
+ */
+void
+ParallelApplyWorkerMain(Datum main_arg)
+{
+	ParallelApplyWorkerShared *shared;
+	dsm_handle	handle;
+	dsm_segment *seg;
+	shm_toc    *toc;
+	shm_mq	   *mq;
+	shm_mq_handle *mqh;
+	shm_mq_handle *error_mqh;
+	RepOriginId originid;
+	int			worker_slot = DatumGetInt32(main_arg);
+	char		originname[NAMEDATALEN];
+
+	/* Setup signal handling. */
+	pqsignal(SIGHUP, SignalHandlerForConfigReload);
+	pqsignal(SIGINT, SignalHandlerForShutdownRequest);
+	pqsignal(SIGTERM, die);
+	BackgroundWorkerUnblockSignals();
+
+	/*
+	 * Attach to the dynamic shared memory segment for the parallel apply, and
+	 * find its table of contents.
+	 *
+	 * Like parallel query, we don't need resource owner by this time. See
+	 * ParallelWorkerMain.
+	 */
+	memcpy(&handle, MyBgworkerEntry->bgw_extra, sizeof(dsm_handle));
+	seg = dsm_attach(handle);
+	if (!seg)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("unable to map dynamic shared memory segment")));
+
+	toc = shm_toc_attach(PG_LOGICAL_APPLY_SHM_MAGIC, dsm_segment_address(seg));
+	if (!toc)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("bad magic number in dynamic shared memory segment")));
+
+	before_shmem_exit(pa_shutdown, PointerGetDatum(seg));
+
+	/* Look up the shared information. */
+	shared = shm_toc_lookup(toc, PARALLEL_APPLY_KEY_SHARED, false);
+	MyParallelShared = shared;
+
+	/*
+	 * Attach to the message queue.
+	 */
+	mq = shm_toc_lookup(toc, PARALLEL_APPLY_KEY_MQ, false);
+	shm_mq_set_receiver(mq, MyProc);
+	mqh = shm_mq_attach(mq, seg, NULL);
+
+	/*
+	 * Primary initialization is complete. Now, we can attach to our slot.
+	 * This is to ensure that the leader apply worker does not write data to
+	 * the uninitialized memory queue.
+	 */
+	logicalrep_worker_attach(worker_slot);
+
+	SpinLockAcquire(&MyParallelShared->mutex);
+	MyParallelShared->logicalrep_worker_generation = MyLogicalRepWorker->generation;
+	MyParallelShared->logicalrep_worker_slot_no = worker_slot;
+	SpinLockRelease(&MyParallelShared->mutex);
+
+	/*
+	 * Attach to the error queue.
+	 */
+	mq = shm_toc_lookup(toc, PARALLEL_APPLY_KEY_ERROR_QUEUE, false);
+	shm_mq_set_sender(mq, MyProc);
+	error_mqh = shm_mq_attach(mq, seg, NULL);
+
+	pq_redirect_to_shm_mq(seg, error_mqh);
+	pq_set_parallel_leader(MyLogicalRepWorker->apply_leader_pid,
+						   InvalidBackendId);
+
+	MyLogicalRepWorker->last_send_time = MyLogicalRepWorker->last_recv_time =
+		MyLogicalRepWorker->reply_time = 0;
+
+	InitializeApplyWorker();
+
+	/* Setup replication origin tracking. */
+	StartTransactionCommand();
+	ReplicationOriginNameForLogicalRep(MySubscription->oid, InvalidOid,
+									   originname, sizeof(originname));
+	originid = replorigin_by_name(originname, false);
+
+	/*
+	 * The parallel apply worker doesn't need to monopolize this replication
+	 * origin which was already acquired by its leader process.
+	 */
+	replorigin_session_setup(originid, MyLogicalRepWorker->apply_leader_pid);
+	replorigin_session_origin = originid;
+	CommitTransactionCommand();
+
+	/*
+	 * Setup callback for syscache so that we know when something changes in
+	 * the subscription relation state.
+	 */
+	CacheRegisterSyscacheCallback(SUBSCRIPTIONRELMAP,
+								  invalidate_syncing_table_states,
+								  (Datum) 0);
+
+	set_apply_error_context_origin(originname);
+
+	LogicalParallelApplyLoop(mqh);
+
+	/*
+	 * The parallel apply worker must not get here because the parallel apply
+	 * worker will only stop when it receives a SIGTERM or SIGINT from the
+	 * leader, detects a change in subscription information, or when there
+	 * there is an error. None of these cases will allow the code to reach
+	 * here.
+	 */
+	Assert(false);
+}
+
+/*
+ * Handle receipt of an interrupt indicating a parallel apply worker message.
+ *
+ * Note: this is called within a signal handler! All we can do is set a flag
+ * that will cause the next CHECK_FOR_INTERRUPTS() to invoke
+ * HandleParallelApplyMessages().
+ */
+void
+HandleParallelApplyMessageInterrupt(void)
+{
+	InterruptPending = true;
+	ParallelApplyMessagePending = true;
+	SetLatch(MyLatch);
+}
+
+/*
+ * Handle a single protocol message received from a single parallel apply
+ * worker.
+ */
+static void
+HandleParallelApplyMessage(ParallelApplyWorkerInfo *winfo, StringInfo msg)
+{
+	char		msgtype;
+
+	msgtype = pq_getmsgbyte(msg);
+
+	switch (msgtype)
+	{
+		case 'E':				/* ErrorResponse */
+			{
+				ErrorData	edata;
+
+				/* Parse ErrorResponse. */
+				pq_parse_errornotice(msg, &edata);
+
+				/*
+				 * If desired, add a context line to show that this is a
+				 * message propagated from a parallel apply worker. Otherwise,
+				 * it can sometimes be confusing to understand what actually
+				 * happened.
+				 */
+				if (edata.context)
+					edata.context = psprintf("%s\n%s", edata.context,
+											 _("logical replication parallel apply worker"));
+				else
+					edata.context = pstrdup(_("logical replication parallel apply worker"));
+
+				/*
+				 * Context beyond that should use the error context callbacks
+				 * that were in effect in LogicalRepApplyLoop().
+				 */
+				error_context_stack = apply_error_context_stack;
+
+				/*
+				 * The actual error must have been reported by the parallel
+				 * apply worker.
+				 */
+				ereport(ERROR,
+						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+						 errmsg("logical replication parallel apply worker exited due to error"),
+						 errcontext("%s", edata.context)));
+			}
+
+			/*
+			 * Don't need to do anything about NoticeResponse and
+			 * NotifyResponse as the logical replication worker doesn't need
+			 * to send messages to the client.
+			 */
+		case 'N':
+		case 'A':
+			break;
+
+		default:
+			elog(ERROR, "unrecognized message type received from logical replication parallel apply worker: %c (message length %d bytes)",
+				 msgtype, msg->len);
+	}
+}
+
+/*
+ * Handle any queued protocol messages received from parallel apply workers.
+ */
+void
+HandleParallelApplyMessages(void)
+{
+	ListCell   *lc;
+	MemoryContext oldcontext;
+
+	static MemoryContext hpam_context = NULL;
+
+	/*
+	 * This is invoked from ProcessInterrupts(), and since some of the
+	 * functions it calls contain CHECK_FOR_INTERRUPTS(), there is a potential
+	 * for recursive calls if more signals are received while this runs. It's
+	 * unclear that recursive entry would be safe, and it doesn't seem useful
+	 * even if it is safe, so let's block interrupts until done.
+	 */
+	HOLD_INTERRUPTS();
+
+	/*
+	 * Moreover, CurrentMemoryContext might be pointing almost anywhere. We
+	 * don't want to risk leaking data into long-lived contexts, so let's do
+	 * our work here in a private context that we can reset on each use.
+	 */
+	if (!hpam_context)			/* first time through? */
+		hpam_context = AllocSetContextCreate(TopMemoryContext,
+											 "HandleParallelApplyMessages",
+											 ALLOCSET_DEFAULT_SIZES);
+	else
+		MemoryContextReset(hpam_context);
+
+	oldcontext = MemoryContextSwitchTo(hpam_context);
+
+	ParallelApplyMessagePending = false;
+
+	foreach(lc, ParallelApplyWorkerPool)
+	{
+		shm_mq_result res;
+		Size		nbytes;
+		void	   *data;
+		ParallelApplyWorkerInfo *winfo = (ParallelApplyWorkerInfo *) lfirst(lc);
+
+		/*
+		 * The leader will detach from the error queue and set it to NULL
+		 * before preparing to stop all parallel apply workers, so we don't
+		 * need to handle error messages anymore. See
+		 * logicalrep_worker_detach.
+		 */
+		if (!winfo->error_mq_handle)
+			continue;
+
+		res = shm_mq_receive(winfo->error_mq_handle, &nbytes, &data, true);
+
+		if (res == SHM_MQ_WOULD_BLOCK)
+			continue;
+		else if (res == SHM_MQ_SUCCESS)
+		{
+			StringInfoData msg;
+
+			initStringInfo(&msg);
+			appendBinaryStringInfo(&msg, data, nbytes);
+			HandleParallelApplyMessage(winfo, &msg);
+			pfree(msg.data);
+		}
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("lost connection to the logical replication parallel apply worker")));
+	}
+
+	MemoryContextSwitchTo(oldcontext);
+
+	/* Might as well clear the context on our way out */
+	MemoryContextReset(hpam_context);
+
+	RESUME_INTERRUPTS();
+}
+
+/*
+ * Send the data to the specified parallel apply worker via shared-memory
+ * queue.
+ *
+ * Return false if the attempt to send data via shared memory times out, true
+ * otherwise.
+ */
+bool
+pa_send_data(ParallelApplyWorkerInfo *winfo, Size nbytes, const void *data)
+{
+	int			rc;
+	shm_mq_result result;
+	TimestampTz startTime = 0;
+
+	Assert(!IsTransactionState());
+	Assert(!winfo->serialize_changes);
+
+#define SHM_SEND_RETRY_INTERVAL_MS 1000
+#define SHM_SEND_TIMEOUT_MS		(10000 - SHM_SEND_RETRY_INTERVAL_MS)
+
+	for (;;)
+	{
+		result = shm_mq_send(winfo->mq_handle, nbytes, data, true, true);
+
+		if (result == SHM_MQ_SUCCESS)
+			return true;
+		else if (result == SHM_MQ_DETACHED)
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("could not send data to shared-memory queue")));
+
+		Assert(result == SHM_MQ_WOULD_BLOCK);
+
+		/* Wait before retrying. */
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+					   SHM_SEND_RETRY_INTERVAL_MS,
+					   WAIT_EVENT_LOGICAL_PARALLEL_APPLY_STATE_CHANGE);
+
+		if (rc & WL_LATCH_SET)
+		{
+			ResetLatch(MyLatch);
+			CHECK_FOR_INTERRUPTS();
+		}
+
+		if (startTime == 0)
+			startTime = GetCurrentTimestamp();
+		else if (TimestampDifferenceExceeds(startTime, GetCurrentTimestamp(),
+											SHM_SEND_TIMEOUT_MS))
+			return false;
+	}
+}
+
+/*
+ * Switch to PARTIAL_SERIALIZE mode for the current transaction -- this means
+ * that the current data and any subsequent data for this transaction will be
+ * serialized to a file. This is done to prevent possible deadlocks with
+ * another parallel apply worker (refer to the comments atop this file).
+ */
+void
+pa_switch_to_partial_serialize(ParallelApplyWorkerInfo *winfo,
+							   bool stream_locked)
+{
+	/*
+	 * The parallel apply worker could be stuck for some reason (say waiting
+	 * on some lock by other backend), so stop trying to send data directly to
+	 * it and start serializing data to the file instead.
+	 */
+	winfo->serialize_changes = true;
+
+	/* Initialize the stream fileset. */
+	stream_start_internal(winfo->shared->xid, true);
+
+	/*
+	 * Acquires the stream lock if not already to make sure that the parallel
+	 * apply worker will wait for the leader to release the stream lock until
+	 * the end of the transaction.
+	 */
+	if (!stream_locked)
+		pa_lock_stream(winfo->shared->xid, AccessExclusiveLock);
+
+	pa_set_fileset_state(winfo->shared, FS_SERIALIZE_IN_PROGRESS);
+}
+
+/*
+ * Wait until the parallel apply worker's transaction state has reached or
+ * exceeded the given xact_state.
+ */
+static void
+pa_wait_for_xact_state(ParallelApplyWorkerInfo *winfo,
+					   ParallelTransState xact_state)
+{
+	for (;;)
+	{
+		/*
+		 * Stop if the transaction state has reached or exceeded the given
+		 * xact_state.
+		 */
+		if (pa_get_xact_state(winfo->shared) >= xact_state)
+			break;
+
+		/* Wait to be signalled. */
+		(void) WaitLatch(MyLatch,
+						 WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+						 10L,
+						 WAIT_EVENT_LOGICAL_PARALLEL_APPLY_STATE_CHANGE);
+
+		/* Reset the latch so we don't spin. */
+		ResetLatch(MyLatch);
+
+		/* An interrupt may have occurred while we were waiting. */
+		CHECK_FOR_INTERRUPTS();
+	}
+}
+
+/*
+ * Wait until the parallel apply worker's transaction finishes.
+ */
+static void
+pa_wait_for_xact_finish(ParallelApplyWorkerInfo *winfo)
+{
+	/*
+	 * Wait until the parallel apply worker set the state to
+	 * PARALLEL_TRANS_STARTED which means it has acquired the transaction
+	 * lock. This is to prevent leader apply worker from acquiring the
+	 * transaction lock earlier than the parallel apply worker.
+	 */
+	pa_wait_for_xact_state(winfo, PARALLEL_TRANS_STARTED);
+
+	/*
+	 * Wait for the transaction lock to be released. This is required to
+	 * detect deadlock among leader and parallel apply workers. Refer to the
+	 * comments atop this file.
+	 */
+	pa_lock_transaction(winfo->shared->xid, AccessShareLock);
+	pa_unlock_transaction(winfo->shared->xid, AccessShareLock);
+
+	/*
+	 * Check if the state becomes PARALLEL_TRANS_FINISHED in case the parallel
+	 * apply worker failed while applying changes causing the lock to be
+	 * released.
+	 */
+	if (pa_get_xact_state(winfo->shared) != PARALLEL_TRANS_FINISHED)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("lost connection to the logical replication parallel apply worker")));
+}
+
+/*
+ * Set the transaction state for a given parallel apply worker.
+ */
+void
+pa_set_xact_state(ParallelApplyWorkerShared *wshared,
+				  ParallelTransState xact_state)
+{
+	SpinLockAcquire(&wshared->mutex);
+	wshared->xact_state = xact_state;
+	SpinLockRelease(&wshared->mutex);
+}
+
+/*
+ * Get the transaction state for a given parallel apply worker.
+ */
+static ParallelTransState
+pa_get_xact_state(ParallelApplyWorkerShared *wshared)
+{
+	ParallelTransState xact_state;
+
+	SpinLockAcquire(&wshared->mutex);
+	xact_state = wshared->xact_state;
+	SpinLockRelease(&wshared->mutex);
+
+	return xact_state;
+}
+
+/*
+ * Cache the parallel apply worker information.
+ */
+void
+pa_set_stream_apply_worker(ParallelApplyWorkerInfo *winfo)
+{
+	stream_apply_worker = winfo;
+}
+
+/*
+ * Form a unique savepoint name for the streaming transaction.
+ *
+ * Note that different subscriptions for publications on different nodes can
+ * receive same remote xid, so we need to use subscription id along with it.
+ *
+ * Return the name in the supplied buffer.
+ */
+static void
+pa_savepoint_name(Oid suboid, TransactionId xid, char *spname, Size szsp)
+{
+	snprintf(spname, szsp, "pg_sp_%u_%u", suboid, xid);
+}
+
+/*
+ * Define a savepoint for a subxact in parallel apply worker if needed.
+ *
+ * The parallel apply worker can figure out if a new subtransaction was
+ * started by checking if the new change arrived with a different xid. In that
+ * case define a named savepoint, so that we are able to rollback to it
+ * if required.
+ */
+void
+pa_start_subtrans(TransactionId current_xid, TransactionId top_xid)
+{
+	if (current_xid != top_xid &&
+		!list_member_xid(subxactlist, current_xid))
+	{
+		MemoryContext oldctx;
+		char		spname[NAMEDATALEN];
+
+		pa_savepoint_name(MySubscription->oid, current_xid,
+						  spname, sizeof(spname));
+
+		elog(DEBUG1, "defining savepoint %s in logical replication parallel apply worker", spname);
+
+		/* We must be in transaction block to define the SAVEPOINT. */
+		if (!IsTransactionBlock())
+		{
+			if (!IsTransactionState())
+				StartTransactionCommand();
+
+			BeginTransactionBlock();
+			CommitTransactionCommand();
+		}
+
+		DefineSavepoint(spname);
+
+		/*
+		 * CommitTransactionCommand is needed to start a subtransaction after
+		 * issuing a SAVEPOINT inside a transaction block (see
+		 * StartSubTransaction()).
+		 */
+		CommitTransactionCommand();
+
+		oldctx = MemoryContextSwitchTo(TopTransactionContext);
+		subxactlist = lappend_xid(subxactlist, current_xid);
+		MemoryContextSwitchTo(oldctx);
+	}
+}
+
+/* Reset the list that maintains subtransactions. */
+void
+pa_reset_subtrans(void)
+{
+	/*
+	 * We don't need to free this explicitly as the allocated memory will be
+	 * freed at the transaction end.
+	 */
+	subxactlist = NIL;
+}
+
+/*
+ * Handle STREAM ABORT message when the transaction was applied in a parallel
+ * apply worker.
+ */
+void
+pa_stream_abort(LogicalRepStreamAbortData *abort_data)
+{
+	TransactionId xid = abort_data->xid;
+	TransactionId subxid = abort_data->subxid;
+
+	/*
+	 * Update origin state so we can restart streaming from correct position
+	 * in case of crash.
+	 */
+	replorigin_session_origin_lsn = abort_data->abort_lsn;
+	replorigin_session_origin_timestamp = abort_data->abort_time;
+
+	/*
+	 * If the two XIDs are the same, it's in fact abort of toplevel xact, so
+	 * just free the subxactlist.
+	 */
+	if (subxid == xid)
+	{
+		/*
+		 * Release the lock as we might be processing an empty streaming
+		 * transaction in which case the lock won't be released during
+		 * transaction rollback.
+		 */
+		pa_unlock_transaction(xid, AccessExclusiveLock);
+
+		AbortCurrentTransaction();
+
+		if (IsTransactionBlock())
+		{
+			EndTransactionBlock(false);
+			CommitTransactionCommand();
+		}
+
+		pa_reset_subtrans();
+
+		pgstat_report_activity(STATE_IDLE, NULL);
+
+		pa_set_xact_state(MyParallelShared, PARALLEL_TRANS_FINISHED);
+	}
+	else
+	{
+		/* OK, so it's a subxact. Rollback to the savepoint. */
+		int			i;
+		char		spname[NAMEDATALEN];
+
+		pa_savepoint_name(MySubscription->oid, subxid, spname, sizeof(spname));
+
+		elog(DEBUG1, "rolling back to savepoint %s in logical replication parallel apply worker", spname);
+
+		/*
+		 * Search the subxactlist, determine the offset tracked for the
+		 * subxact, and truncate the list.
+		 *
+		 * Note that for an empty sub-transaction we won't find the subxid
+		 * here.
+		 */
+		for (i = list_length(subxactlist) - 1; i >= 0; i--)
+		{
+			TransactionId xid_tmp = lfirst_xid(list_nth_cell(subxactlist, i));
+
+			if (xid_tmp == subxid)
+			{
+				RollbackToSavepoint(spname);
+				CommitTransactionCommand();
+				subxactlist = list_truncate(subxactlist, i);
+				break;
+			}
+		}
+	}
+}
+
+/*
+ * Set the fileset state for a particular parallel apply worker. The fileset
+ * will be set once the leader worker serialized all changes to the file
+ * so that it can be used by parallel apply worker.
+ */
+void
+pa_set_fileset_state(ParallelApplyWorkerShared *wshared,
+					 PartialFileSetState fileset_state)
+{
+	SpinLockAcquire(&wshared->mutex);
+	wshared->fileset_state = fileset_state;
+
+	if (fileset_state == FS_SERIALIZE_DONE)
+	{
+		Assert(am_leader_apply_worker());
+		Assert(MyLogicalRepWorker->stream_fileset);
+		wshared->fileset = *MyLogicalRepWorker->stream_fileset;
+	}
+
+	SpinLockRelease(&wshared->mutex);
+}
+
+/*
+ * Get the fileset state for the current parallel apply worker.
+ */
+static PartialFileSetState
+pa_get_fileset_state(void)
+{
+	PartialFileSetState fileset_state;
+
+	Assert(am_parallel_apply_worker());
+
+	SpinLockAcquire(&MyParallelShared->mutex);
+	fileset_state = MyParallelShared->fileset_state;
+	SpinLockRelease(&MyParallelShared->mutex);
+
+	return fileset_state;
+}
+
+/*
+ * Helper functions to acquire and release a lock for each stream block.
+ *
+ * Set locktag_field4 to PARALLEL_APPLY_LOCK_STREAM to indicate that it's a
+ * stream lock.
+ *
+ * Refer to the comments atop this file to see how the stream lock is used.
+ */
+void
+pa_lock_stream(TransactionId xid, LOCKMODE lockmode)
+{
+	LockApplyTransactionForSession(MyLogicalRepWorker->subid, xid,
+								   PARALLEL_APPLY_LOCK_STREAM, lockmode);
+}
+
+void
+pa_unlock_stream(TransactionId xid, LOCKMODE lockmode)
+{
+	UnlockApplyTransactionForSession(MyLogicalRepWorker->subid, xid,
+									 PARALLEL_APPLY_LOCK_STREAM, lockmode);
+}
+
+/*
+ * Helper functions to acquire and release a lock for each local transaction
+ * apply.
+ *
+ * Set locktag_field4 to PARALLEL_APPLY_LOCK_XACT to indicate that it's a
+ * transaction lock.
+ *
+ * Note that all the callers must pass a remote transaction ID instead of a
+ * local transaction ID as xid. This is because the local transaction ID will
+ * only be assigned while applying the first change in the parallel apply but
+ * it's possible that the first change in the parallel apply worker is blocked
+ * by a concurrently executing transaction in another parallel apply worker. We
+ * can only communicate the local transaction id to the leader after applying
+ * the first change so it won't be able to wait after sending the xact finish
+ * command using this lock.
+ *
+ * Refer to the comments atop this file to see how the transaction lock is
+ * used.
+ */
+void
+pa_lock_transaction(TransactionId xid, LOCKMODE lockmode)
+{
+	LockApplyTransactionForSession(MyLogicalRepWorker->subid, xid,
+								   PARALLEL_APPLY_LOCK_XACT, lockmode);
+}
+
+void
+pa_unlock_transaction(TransactionId xid, LOCKMODE lockmode)
+{
+	UnlockApplyTransactionForSession(MyLogicalRepWorker->subid, xid,
+									 PARALLEL_APPLY_LOCK_XACT, lockmode);
+}
+
+/*
+ * Decrement the number of pending streaming blocks and wait on the stream lock
+ * if there is no pending block available.
+ */
+void
+pa_decr_and_wait_stream_block(void)
+{
+	Assert(am_parallel_apply_worker());
+
+	/*
+	 * It is only possible to not have any pending stream chunks when we are
+	 * applying spooled messages.
+	 */
+	if (pg_atomic_read_u32(&MyParallelShared->pending_stream_count) == 0)
+	{
+		if (pa_has_spooled_message_pending())
+			return;
+
+		elog(ERROR, "invalid pending streaming chunk 0");
+	}
+
+	if (pg_atomic_sub_fetch_u32(&MyParallelShared->pending_stream_count, 1) == 0)
+	{
+		pa_lock_stream(MyParallelShared->xid, AccessShareLock);
+		pa_unlock_stream(MyParallelShared->xid, AccessShareLock);
+	}
+}
+
+/*
+ * Finish processing the streaming transaction in the leader apply worker.
+ */
+void
+pa_xact_finish(ParallelApplyWorkerInfo *winfo, XLogRecPtr remote_lsn)
+{
+	Assert(am_leader_apply_worker());
+
+	/*
+	 * Unlock the shared object lock so that parallel apply worker can
+	 * continue to receive and apply changes.
+	 */
+	pa_unlock_stream(winfo->shared->xid, AccessExclusiveLock);
+
+	/*
+	 * Wait for that worker to finish. This is necessary to maintain commit
+	 * order which avoids failures due to transaction dependencies and
+	 * deadlocks.
+	 */
+	pa_wait_for_xact_finish(winfo);
+
+	store_flush_position(remote_lsn, winfo->shared->last_commit_end);
+	(void) pa_free_worker(winfo);
+}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 2cc0ac9eb0..33fdbdc673 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -822,10 +822,11 @@ DecodeAbort(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
 		for (i = 0; i < parsed->nsubxacts; i++)
 		{
 			ReorderBufferAbort(ctx->reorder, parsed->subxacts[i],
-							   buf->record->EndRecPtr);
+							   buf->record->EndRecPtr, abort_time);
 		}
 
-		ReorderBufferAbort(ctx->reorder, xid, buf->record->EndRecPtr);
+		ReorderBufferAbort(ctx->reorder, xid, buf->record->EndRecPtr,
+						   abort_time);
 	}
 
 	/* update the decoding stats */
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 73594c698a..759f964fbd 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -55,6 +55,7 @@
 /* GUC variables */
 int			max_logical_replication_workers = 4;
 int			max_sync_workers_per_subscription = 2;
+int			max_parallel_apply_workers_per_subscription = 2;
 
 LogicalRepWorker *MyLogicalRepWorker = NULL;
 
@@ -74,6 +75,7 @@ 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 int	logicalrep_pa_worker_count(Oid subid);
 
 static bool on_commit_launcher_wakeup = false;
 
@@ -152,8 +154,10 @@ get_subscription_list(void)
  *
  * This is only needed for cleaning up the shared memory in case the worker
  * fails to attach.
+ *
+ * Return whether the attach was successful.
  */
-static void
+static bool
 WaitForReplicationWorkerAttach(LogicalRepWorker *worker,
 							   uint16 generation,
 							   BackgroundWorkerHandle *handle)
@@ -169,11 +173,11 @@ WaitForReplicationWorkerAttach(LogicalRepWorker *worker,
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		/* Worker either died or has started; no need to do anything. */
+		/* Worker either died or has started. Return false if died. */
 		if (!worker->in_use || worker->proc)
 		{
 			LWLockRelease(LogicalRepWorkerLock);
-			return;
+			return worker->in_use;
 		}
 
 		LWLockRelease(LogicalRepWorkerLock);
@@ -188,7 +192,7 @@ WaitForReplicationWorkerAttach(LogicalRepWorker *worker,
 			if (generation == worker->generation)
 				logicalrep_worker_cleanup(worker);
 			LWLockRelease(LogicalRepWorkerLock);
-			return;
+			return false;
 		}
 
 		/*
@@ -210,6 +214,8 @@ WaitForReplicationWorkerAttach(LogicalRepWorker *worker,
 /*
  * Walks the workers array and searches for one that matches given
  * subscription id and relid.
+ *
+ * We are only interested in the leader apply worker or table sync worker.
  */
 LogicalRepWorker *
 logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
@@ -224,6 +230,10 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
 	{
 		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
 
+		/* Skip parallel apply workers. */
+		if (isParallelApplyWorker(w))
+			continue;
+
 		if (w->in_use && w->subid == subid && w->relid == relid &&
 			(!only_running || w->proc))
 		{
@@ -260,11 +270,13 @@ logicalrep_workers_find(Oid subid, bool only_running)
 }
 
 /*
- * Start new apply background worker, if possible.
+ * Start new logical replication background worker, if possible.
+ *
+ * Returns true on success, false on failure.
  */
-void
+bool
 logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname, Oid userid,
-						 Oid relid)
+						 Oid relid, dsm_handle subworker_dsm)
 {
 	BackgroundWorker bgw;
 	BackgroundWorkerHandle *bgw_handle;
@@ -273,7 +285,12 @@ logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname, Oid userid,
 	int			slot = 0;
 	LogicalRepWorker *worker = NULL;
 	int			nsyncworkers;
+	int			nparallelapplyworkers;
 	TimestampTz now;
+	bool		is_parallel_apply_worker = (subworker_dsm != DSM_HANDLE_INVALID);
+
+	/* Sanity check - tablesync worker cannot be a subworker */
+	Assert(!(is_parallel_apply_worker && OidIsValid(relid)));
 
 	ereport(DEBUG1,
 			(errmsg_internal("starting logical replication worker for subscription \"%s\"",
@@ -351,7 +368,20 @@ retry:
 	if (OidIsValid(relid) && nsyncworkers >= max_sync_workers_per_subscription)
 	{
 		LWLockRelease(LogicalRepWorkerLock);
-		return;
+		return false;
+	}
+
+	nparallelapplyworkers = logicalrep_pa_worker_count(subid);
+
+	/*
+	 * Return false if the number of parallel apply workers reached the limit
+	 * per subscription.
+	 */
+	if (is_parallel_apply_worker &&
+		nparallelapplyworkers >= max_parallel_apply_workers_per_subscription)
+	{
+		LWLockRelease(LogicalRepWorkerLock);
+		return false;
 	}
 
 	/*
@@ -365,7 +395,7 @@ retry:
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("out of logical replication worker slots"),
 				 errhint("You might need to increase max_logical_replication_workers.")));
-		return;
+		return false;
 	}
 
 	/* Prepare the worker slot. */
@@ -380,6 +410,8 @@ retry:
 	worker->relstate = SUBREL_STATE_UNKNOWN;
 	worker->relstate_lsn = InvalidXLogRecPtr;
 	worker->stream_fileset = NULL;
+	worker->apply_leader_pid = is_parallel_apply_worker ? MyProcPid : InvalidPid;
+	worker->parallel_apply = is_parallel_apply_worker;
 	worker->last_lsn = InvalidXLogRecPtr;
 	TIMESTAMP_NOBEGIN(worker->last_send_time);
 	TIMESTAMP_NOBEGIN(worker->last_recv_time);
@@ -397,19 +429,34 @@ retry:
 		BGWORKER_BACKEND_DATABASE_CONNECTION;
 	bgw.bgw_start_time = BgWorkerStart_RecoveryFinished;
 	snprintf(bgw.bgw_library_name, BGW_MAXLEN, "postgres");
-	snprintf(bgw.bgw_function_name, BGW_MAXLEN, "ApplyWorkerMain");
+
+	if (is_parallel_apply_worker)
+		snprintf(bgw.bgw_function_name, BGW_MAXLEN, "ParallelApplyWorkerMain");
+	else
+		snprintf(bgw.bgw_function_name, BGW_MAXLEN, "ApplyWorkerMain");
+
 	if (OidIsValid(relid))
 		snprintf(bgw.bgw_name, BGW_MAXLEN,
 				 "logical replication worker for subscription %u sync %u", subid, relid);
+	else if (is_parallel_apply_worker)
+		snprintf(bgw.bgw_name, BGW_MAXLEN,
+				 "logical replication parallel apply worker for subscription %u", subid);
 	else
 		snprintf(bgw.bgw_name, BGW_MAXLEN,
-				 "logical replication worker for subscription %u", subid);
-	snprintf(bgw.bgw_type, BGW_MAXLEN, "logical replication worker");
+				 "logical replication apply worker for subscription %u", subid);
+
+	if (is_parallel_apply_worker)
+		snprintf(bgw.bgw_type, BGW_MAXLEN, "logical replication parallel worker");
+	else
+		snprintf(bgw.bgw_type, BGW_MAXLEN, "logical replication worker");
 
 	bgw.bgw_restart_time = BGW_NEVER_RESTART;
 	bgw.bgw_notify_pid = MyProcPid;
 	bgw.bgw_main_arg = Int32GetDatum(slot);
 
+	if (is_parallel_apply_worker)
+		memcpy(bgw.bgw_extra, &subworker_dsm, sizeof(dsm_handle));
+
 	if (!RegisterDynamicBackgroundWorker(&bgw, &bgw_handle))
 	{
 		/* Failed to start worker, so clean up the worker slot. */
@@ -422,33 +469,23 @@ retry:
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("out of background worker slots"),
 				 errhint("You might need to increase max_worker_processes.")));
-		return;
+		return false;
 	}
 
 	/* Now wait until it attaches. */
-	WaitForReplicationWorkerAttach(worker, generation, bgw_handle);
+	return WaitForReplicationWorkerAttach(worker, generation, bgw_handle);
 }
 
 /*
- * Stop the logical replication worker for subid/relid, if any, and wait until
- * it detaches from the slot.
+ * Internal function to stop the worker and wait until it detaches from the
+ * slot.
  */
-void
-logicalrep_worker_stop(Oid subid, Oid relid)
+static void
+logicalrep_worker_stop_internal(LogicalRepWorker *worker, int signo)
 {
-	LogicalRepWorker *worker;
 	uint16		generation;
 
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-
-	worker = logicalrep_worker_find(subid, relid, false);
-
-	/* No worker, nothing to do. */
-	if (!worker)
-	{
-		LWLockRelease(LogicalRepWorkerLock);
-		return;
-	}
+	Assert(LWLockHeldByMeInMode(LogicalRepWorkerLock, LW_SHARED));
 
 	/*
 	 * Remember which generation was our worker so we can check if what we see
@@ -486,10 +523,7 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 		 * different, meaning that a different worker has taken the slot.
 		 */
 		if (!worker->in_use || worker->generation != generation)
-		{
-			LWLockRelease(LogicalRepWorkerLock);
 			return;
-		}
 
 		/* Worker has assigned proc, so it has started. */
 		if (worker->proc)
@@ -497,7 +531,7 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	}
 
 	/* Now terminate the worker ... */
-	kill(worker->proc->pid, SIGTERM);
+	kill(worker->proc->pid, signo);
 
 	/* ... and wait for it to die. */
 	for (;;)
@@ -523,6 +557,53 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 	}
+}
+
+/*
+ * Stop the logical replication worker for subid/relid, if any.
+ */
+void
+logicalrep_worker_stop(Oid subid, Oid relid)
+{
+	LogicalRepWorker *worker;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+	worker = logicalrep_worker_find(subid, relid, false);
+
+	if (worker)
+	{
+		Assert(!isParallelApplyWorker(worker));
+		logicalrep_worker_stop_internal(worker, SIGTERM);
+	}
+
+	LWLockRelease(LogicalRepWorkerLock);
+}
+
+/*
+ * Stop the logical replication parallel apply worker corresponding to the
+ * input slot number.
+ *
+ * Node that the function sends SIGINT instead of SIGTERM to the parallel apply
+ * worker so that the worker exits cleanly.
+ */
+void
+logicalrep_pa_worker_stop(int slot_no, uint16 generation)
+{
+	LogicalRepWorker *worker;
+
+	Assert(slot_no >= 0 && slot_no < max_logical_replication_workers);
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+	worker = &LogicalRepCtx->workers[slot_no];
+	Assert(isParallelApplyWorker(worker));
+
+	/*
+	 * 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);
 
 	LWLockRelease(LogicalRepWorkerLock);
 }
@@ -595,11 +676,40 @@ logicalrep_worker_attach(int slot)
 }
 
 /*
- * Detach the worker (cleans up the worker info).
+ * Stop the parallel apply workers if any, and detach the leader apply worker
+ * (cleans up the worker info).
  */
 static void
 logicalrep_worker_detach(void)
 {
+	/* Stop the parallel apply workers. */
+	if (am_leader_apply_worker())
+	{
+		List	   *workers;
+		ListCell   *lc;
+
+		/*
+		 * Detach from the error_mq_handle for all parallel apply workers
+		 * before terminating them. This prevents the leader apply worker from
+		 * receiving the worker termination message and sending it to logs
+		 * when the same is already done by the parallel worker.
+		 */
+		pa_detach_all_error_mq();
+
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		foreach(lc, workers)
+		{
+			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+			if (isParallelApplyWorker(w))
+				logicalrep_worker_stop_internal(w, SIGTERM);
+		}
+
+		LWLockRelease(LogicalRepWorkerLock);
+	}
+
 	/* Block concurrent access. */
 	LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
 
@@ -622,6 +732,8 @@ logicalrep_worker_cleanup(LogicalRepWorker *worker)
 	worker->userid = InvalidOid;
 	worker->subid = InvalidOid;
 	worker->relid = InvalidOid;
+	worker->apply_leader_pid = InvalidPid;
+	worker->parallel_apply = false;
 }
 
 /*
@@ -653,6 +765,13 @@ logicalrep_worker_onexit(int code, Datum arg)
 	if (MyLogicalRepWorker->stream_fileset != NULL)
 		FileSetDeleteAll(MyLogicalRepWorker->stream_fileset);
 
+	/*
+	 * Session level locks may be acquired outside of a transaction in
+	 * parallel apply mode and will not be released when the worker
+	 * terminates, so manually release all locks before the worker exits.
+	 */
+	LockReleaseAll(DEFAULT_LOCKMETHOD, true);
+
 	ApplyLauncherWakeup();
 }
 
@@ -680,6 +799,33 @@ logicalrep_sync_worker_count(Oid subid)
 	return res;
 }
 
+/*
+ * Count the number of registered (but not necessarily running) parallel apply
+ * workers for a subscription.
+ */
+static int
+logicalrep_pa_worker_count(Oid subid)
+{
+	int			i;
+	int			res = 0;
+
+	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+
+	/*
+	 * Scan all attached parallel apply workers, only counting those which
+	 * have the given subscription id.
+	 */
+	for (i = 0; i < max_logical_replication_workers; i++)
+	{
+		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
+
+		if (w->subid == subid && isParallelApplyWorker(w))
+			res++;
+	}
+
+	return res;
+}
+
 /*
  * ApplyLauncherShmemSize
  *		Compute space needed for replication launcher shared memory
@@ -869,7 +1015,7 @@ ApplyLauncherMain(Datum main_arg)
 					wait_time = wal_retrieve_retry_interval;
 
 					logicalrep_worker_launch(sub->dbid, sub->oid, sub->name,
-											 sub->owner, InvalidOid);
+											 sub->owner, InvalidOid, DSM_HANDLE_INVALID);
 				}
 			}
 
@@ -952,6 +1098,10 @@ pg_stat_get_subscription(PG_FUNCTION_ARGS)
 		if (OidIsValid(subid) && worker.subid != subid)
 			continue;
 
+		/* Skip if this is a parallel apply worker */
+		if (isParallelApplyWorker(&worker))
+			continue;
+
 		worker_pid = worker.proc->pid;
 
 		values[0] = ObjectIdGetDatum(worker.subid);
diff --git a/src/backend/replication/logical/meson.build b/src/backend/replication/logical/meson.build
index 1b9f072edc..b78bfba10c 100644
--- a/src/backend/replication/logical/meson.build
+++ b/src/backend/replication/logical/meson.build
@@ -1,6 +1,7 @@
 # Copyright (c) 2022, PostgreSQL Global Development Group
 
 backend_sources += files(
+  'applyparallelworker.c',
   'decode.c',
   'launcher.c',
   'logical.c',
diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c
index f134e44878..8b08378665 100644
--- a/src/backend/replication/logical/origin.c
+++ b/src/backend/replication/logical/origin.c
@@ -1075,12 +1075,20 @@ ReplicationOriginExitCleanup(int code, Datum arg)
  * array doesn't have to be searched when calling
  * replorigin_session_advance().
  *
- * Obviously only one such cached origin can exist per process and the current
- * cached value can only be set again after the previous value is torn down
- * with replorigin_session_reset().
+ * Normally only one such cached origin can exist per process so the cached
+ * value can only be set again after the previous value is torn down with
+ * replorigin_session_reset(). For this normal case pass acquired_by = 0
+ * (meaning the slot is not allowed to be already acquired by another process).
+ *
+ * However, sometimes multiple processes can safely re-use the same origin slot
+ * (for example, multiple parallel apply processes can safely use the same
+ * origin, provided they maintain commit order by allowing only one process to
+ * commit at a time). For this case the first process must pass acquired_by =
+ * 0, and then the other processes sharing that same origin can pass
+ * acquired_by = PID of the first process.
  */
 void
-replorigin_session_setup(RepOriginId node)
+replorigin_session_setup(RepOriginId node, int acquired_by)
 {
 	static bool registered_cleanup;
 	int			i;
@@ -1122,7 +1130,7 @@ replorigin_session_setup(RepOriginId node)
 		if (curstate->roident != node)
 			continue;
 
-		else if (curstate->acquired_by != 0)
+		else if (curstate->acquired_by != 0 && acquired_by == 0)
 		{
 			ereport(ERROR,
 					(errcode(ERRCODE_OBJECT_IN_USE),
@@ -1153,7 +1161,11 @@ replorigin_session_setup(RepOriginId node)
 
 	Assert(session_replication_state->roident != InvalidRepOriginId);
 
-	session_replication_state->acquired_by = MyProcPid;
+	if (acquired_by == 0)
+		session_replication_state->acquired_by = MyProcPid;
+	else if (session_replication_state->acquired_by != acquired_by)
+		elog(ERROR, "could not find replication state slot for replication origin with OID %u which was acquired by %d",
+			 node, acquired_by);
 
 	LWLockRelease(ReplicationOriginLock);
 
@@ -1337,7 +1349,7 @@ pg_replication_origin_session_setup(PG_FUNCTION_ARGS)
 
 	name = text_to_cstring((text *) DatumGetPointer(PG_GETARG_DATUM(0)));
 	origin = replorigin_by_name(name, false);
-	replorigin_session_setup(origin);
+	replorigin_session_setup(origin, 0);
 
 	replorigin_session_origin = origin;
 
diff --git a/src/backend/replication/logical/proto.c b/src/backend/replication/logical/proto.c
index f5f2bc24d8..723ba4669b 100644
--- a/src/backend/replication/logical/proto.c
+++ b/src/backend/replication/logical/proto.c
@@ -1164,10 +1164,14 @@ logicalrep_read_stream_commit(StringInfo in, LogicalRepCommitData *commit_data)
 /*
  * Write STREAM ABORT to the output stream. Note that xid and subxid will be
  * same for the top-level transaction abort.
+ *
+ * If write_abort_info is true, send the abort_lsn and abort_time fields,
+ * otherwise don't.
  */
 void
 logicalrep_write_stream_abort(StringInfo out, TransactionId xid,
-							  TransactionId subxid)
+							  TransactionId subxid, XLogRecPtr abort_lsn,
+							  TimestampTz abort_time, bool write_abort_info)
 {
 	pq_sendbyte(out, LOGICAL_REP_MSG_STREAM_ABORT);
 
@@ -1176,19 +1180,40 @@ logicalrep_write_stream_abort(StringInfo out, TransactionId xid,
 	/* transaction ID */
 	pq_sendint32(out, xid);
 	pq_sendint32(out, subxid);
+
+	if (write_abort_info)
+	{
+		pq_sendint64(out, abort_lsn);
+		pq_sendint64(out, abort_time);
+	}
 }
 
 /*
  * Read STREAM ABORT from the output stream.
+ *
+ * If read_abort_info is true, read the abort_lsn and abort_time fields,
+ * otherwise don't.
  */
 void
-logicalrep_read_stream_abort(StringInfo in, TransactionId *xid,
-							 TransactionId *subxid)
+logicalrep_read_stream_abort(StringInfo in,
+							 LogicalRepStreamAbortData *abort_data,
+							 bool read_abort_info)
 {
-	Assert(xid && subxid);
+	Assert(abort_data);
+
+	abort_data->xid = pq_getmsgint(in, 4);
+	abort_data->subxid = pq_getmsgint(in, 4);
 
-	*xid = pq_getmsgint(in, 4);
-	*subxid = pq_getmsgint(in, 4);
+	if (read_abort_info)
+	{
+		abort_data->abort_lsn = pq_getmsgint64(in);
+		abort_data->abort_time = pq_getmsgint64(in);
+	}
+	else
+	{
+		abort_data->abort_lsn = InvalidXLogRecPtr;
+		abort_data->abort_time = 0;
+	}
 }
 
 /*
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index b567b8b59e..8d5bbaadb1 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -2870,7 +2870,8 @@ ReorderBufferFinishPrepared(ReorderBuffer *rb, TransactionId xid,
  * disk.
  */
 void
-ReorderBufferAbort(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
+ReorderBufferAbort(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+				   TimestampTz abort_time)
 {
 	ReorderBufferTXN *txn;
 
@@ -2881,6 +2882,8 @@ ReorderBufferAbort(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
 	if (txn == NULL)
 		return;
 
+	txn->xact_time.abort_time = abort_time;
+
 	/* For streamed transactions notify the remote node about the abort. */
 	if (rbtxn_is_streamed(txn))
 	{
diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
index 94e813ac53..ef0fe13c14 100644
--- a/src/backend/replication/logical/tablesync.c
+++ b/src/backend/replication/logical/tablesync.c
@@ -14,7 +14,7 @@
  *	  The initial data synchronization is done separately for each table,
  *	  in a separate apply worker that only fetches the initial snapshot data
  *	  from the publisher and then synchronizes the position in the stream with
- *	  the main apply worker.
+ *	  the leader apply worker.
  *
  *	  There are several reasons for doing the synchronization this way:
  *	   - It allows us to parallelize the initial data synchronization
@@ -153,7 +153,7 @@ finish_sync_worker(void)
 					get_rel_name(MyLogicalRepWorker->relid))));
 	CommitTransactionCommand();
 
-	/* Find the main apply worker and signal it. */
+	/* Find the leader apply worker and signal it. */
 	logicalrep_worker_wakeup(MyLogicalRepWorker->subid, InvalidOid);
 
 	/* Stop gracefully */
@@ -609,7 +609,8 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 												 MySubscription->oid,
 												 MySubscription->name,
 												 MyLogicalRepWorker->userid,
-												 rstate->relid);
+												 rstate->relid,
+												 DSM_HANDLE_INVALID);
 						hentry->last_start_time = now;
 					}
 				}
@@ -630,6 +631,14 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 void
 process_syncing_tables(XLogRecPtr current_lsn)
 {
+	/*
+	 * Skip for parallel apply workers because they only operate on tables
+	 * that are in a READY state. See pa_can_start() and
+	 * should_apply_changes_for_rel().
+	 */
+	if (am_parallel_apply_worker())
+		return;
+
 	if (am_tablesync_worker())
 		process_syncing_tables_for_sync(current_lsn);
 	else
@@ -1247,7 +1256,7 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
 
 	/*
 	 * Here we use the slot name instead of the subscription name as the
-	 * application_name, so that it is different from the main apply worker,
+	 * application_name, so that it is different from the leader apply worker,
 	 * so that synchronous replication can distinguish them.
 	 */
 	LogRepWorkerWalRcvConn =
@@ -1295,7 +1304,7 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
 		 * time this tablesync was launched.
 		 */
 		originid = replorigin_by_name(originname, false);
-		replorigin_session_setup(originid);
+		replorigin_session_setup(originid, 0);
 		replorigin_session_origin = originid;
 		*origin_startpos = replorigin_session_get_progress(false);
 
@@ -1406,7 +1415,7 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
 						   true /* go backward */ , true /* WAL log */ );
 		UnlockRelationOid(ReplicationOriginRelationId, RowExclusiveLock);
 
-		replorigin_session_setup(originid);
+		replorigin_session_setup(originid, 0);
 		replorigin_session_origin = originid;
 	}
 	else
@@ -1461,8 +1470,8 @@ copy_table_done:
 	SpinLockRelease(&MyLogicalRepWorker->relmutex);
 
 	/*
-	 * Finally, wait until the main apply worker tells us to catch up and then
-	 * return to let LogicalRepApplyLoop do it.
+	 * Finally, wait until the leader apply worker tells us to catch up and
+	 * then return to let LogicalRepApplyLoop do it.
 	 */
 	wait_for_worker_state_change(SUBREL_STATE_CATCHUP);
 	return slotname;
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 96772e4d73..f9efc18ef7 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -22,8 +22,12 @@
  * STREAMED TRANSACTIONS
  * ---------------------
  * Streamed transactions (large transactions exceeding a memory limit on the
- * upstream) are not applied immediately, but instead, the data is written
- * to temporary files and then applied at once when the final commit arrives.
+ * upstream) are applied using one of two approaches:
+ *
+ * 1) Write to temporary files and apply when the final commit arrives
+ *
+ * This approach is used when the user has set the subscription's streaming
+ * option as on.
  *
  * Unlike the regular (non-streamed) case, handling streamed transactions has
  * to handle aborts of both the toplevel transaction and subtransactions. This
@@ -50,6 +54,12 @@
  * the file we desired across multiple stream-open calls for the same
  * transaction.
  *
+ * 2) Parallel apply workers.
+ *
+ * This approach is used when the user has set the subscription's streaming
+ * option as parallel. See logical/applyparallelworker.c for information about
+ * this approach.
+ *
  * TWO_PHASE TRANSACTIONS
  * ----------------------
  * Two phase transactions are replayed at prepare and then committed or
@@ -150,6 +160,7 @@
 #include "executor/execPartition.h"
 #include "executor/nodeModifyTable.h"
 #include "funcapi.h"
+#include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "libpq/pqsignal.h"
 #include "mb/pg_wchar.h"
@@ -233,7 +244,52 @@ typedef struct ApplyErrorCallbackArg
 	char	   *origin_name;
 } ApplyErrorCallbackArg;
 
-static ApplyErrorCallbackArg apply_error_callback_arg =
+/*
+ * What action to take for the transaction.
+ *
+ * TRANS_LEADER_APPLY:
+ * This action means that we are in the leader apply worker and changes of the
+ * transaction are applied directly by the worker.
+ *
+ * TRANS_LEADER_SERIALIZE:
+ * This action means that we are in the leader apply worker or table sync
+ * worker. Changes are written to temporary files and then applied when the
+ * final commit arrives.
+ *
+ * TRANS_LEADER_SEND_TO_PARALLEL:
+ * This action means that we are in the leader apply worker and need to send
+ * the changes to the parallel apply worker.
+ *
+ * TRANS_LEADER_PARTIAL_SERIALIZE:
+ * This action means that we are in the leader apply worker and have sent some
+ * changes directly to the parallel apply worker and the remaining changes are
+ * serialized to a file, due to timeout while sending data. The parallel apply
+ * worker will apply these serialized changes when the final commit arrives.
+ *
+ * We can't use TRANS_LEADER_SERIALIZE for this case because, in addition to
+ * serializing changes, the leader worker also needs to serialize the
+ * STREAM_XXX message to a file, and wait for the parallel apply worker to
+ * finish the transaction when processing the transaction finish command. So
+ * this new action was introduced to keep the code and logic clear.
+ *
+ * TRANS_PARALLEL_APPLY:
+ * This action means that we are in the parallel apply worker and changes of
+ * the transaction are applied directly by the worker.
+ */
+typedef enum
+{
+	/* The action for non-streaming transactions. */
+	TRANS_LEADER_APPLY,
+
+	/* Actions for streaming transactions. */
+	TRANS_LEADER_SERIALIZE,
+	TRANS_LEADER_SEND_TO_PARALLEL,
+	TRANS_LEADER_PARTIAL_SERIALIZE,
+	TRANS_PARALLEL_APPLY
+} TransApplyAction;
+
+/* errcontext tracker */
+ApplyErrorCallbackArg apply_error_callback_arg =
 {
 	.command = 0,
 	.rel = NULL,
@@ -243,7 +299,9 @@ static ApplyErrorCallbackArg apply_error_callback_arg =
 	.origin_name = NULL,
 };
 
-static MemoryContext ApplyMessageContext = NULL;
+ErrorContextCallback *apply_error_context_stack = NULL;
+
+MemoryContext ApplyMessageContext = NULL;
 MemoryContext ApplyContext = NULL;
 
 /* per stream context for streaming transactions */
@@ -262,17 +320,26 @@ static bool in_streamed_transaction = false;
 
 static TransactionId stream_xid = InvalidTransactionId;
 
+/*
+ * The number of changes applied by parallel apply worker during one streaming
+ * block.
+ */
+static uint32 parallel_stream_nchanges = 0;
+
 /*
  * We enable skipping all data modification changes (INSERT, UPDATE, etc.) for
  * the subscription if the remote transaction's finish LSN matches the subskiplsn.
  * Once we start skipping changes, we don't stop it until we skip all changes of
  * the transaction even if pg_subscription is updated and MySubscription->skiplsn
- * gets changed or reset during that. Also, in streaming transaction cases, we
- * don't skip receiving and spooling the changes since we decide whether or not
+ * gets changed or reset during that. Also, in streaming transaction cases (streaming = on),
+ * we don't skip receiving and spooling the changes since we decide whether or not
  * to skip applying the changes when starting to apply changes. The subskiplsn is
  * cleared after successfully skipping the transaction or applying non-empty
  * transaction. The latter prevents the mistakenly specified subskiplsn from
- * being left.
+ * being left. Note that we cannot skip the streaming transactions when using
+ * parallel apply workers because we cannot get the finish LSN before applying
+ * the changes. So, we don't start parallel apply worker when finish LSN is set
+ * by the user.
  */
 static XLogRecPtr skip_xact_finish_lsn = InvalidXLogRecPtr;
 #define is_skipping_changes() (unlikely(!XLogRecPtrIsInvalid(skip_xact_finish_lsn)))
@@ -312,23 +379,16 @@ static inline void cleanup_subxact_info(void);
 /*
  * Serialize and deserialize changes for a toplevel transaction.
  */
-static void stream_cleanup_files(Oid subid, TransactionId xid);
 static void stream_open_file(Oid subid, TransactionId xid,
 							 bool first_segment);
 static void stream_write_change(char action, StringInfo s);
+static void stream_open_and_write_change(TransactionId xid, char action, StringInfo s);
 static void stream_close_file(void);
 
 static void send_feedback(XLogRecPtr recvpos, bool force, bool requestReply);
 
-static void store_flush_position(XLogRecPtr remote_lsn);
-
-static void maybe_reread_subscription(void);
-
 static void DisableSubscriptionAndExit(void);
 
-/* prototype needed because of stream_commit */
-static void apply_dispatch(StringInfo s);
-
 static void apply_handle_commit_internal(LogicalRepCommitData *commit_data);
 static void apply_handle_insert_internal(ApplyExecutionData *edata,
 										 ResultRelInfo *relinfo,
@@ -352,19 +412,32 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 /* Compute GID for two_phase transactions */
 static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
-/* Common streaming function to apply all the spooled messages */
-static void apply_spooled_messages(TransactionId xid, XLogRecPtr lsn);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
 static void clear_subscription_skip_lsn(XLogRecPtr finish_lsn);
 
 /* Functions for apply error callback */
-static void apply_error_callback(void *arg);
 static inline void set_apply_error_context_xact(TransactionId xid, XLogRecPtr lsn);
 static inline void reset_apply_error_context_info(void);
 
+static TransApplyAction get_transaction_apply_action(TransactionId xid,
+													 ParallelApplyWorkerInfo **winfo);
+
+/*
+ * Return the name of the logical replication worker.
+ */
+static const char *
+get_worker_name(void)
+{
+	if (am_tablesync_worker())
+		return _("logical replication table synchronization worker");
+	else if (am_parallel_apply_worker())
+		return _("logical replication parallel apply worker");
+	else
+		return _("logical replication apply worker");
+}
+
 /*
  * Form the origin name for the subscription.
  *
@@ -394,19 +467,43 @@ ReplicationOriginNameForLogicalRep(Oid suboid, Oid relid,
  *
  * This is mainly needed for initial relation data sync as that runs in
  * separate worker process running in parallel and we need some way to skip
- * changes coming to the main apply worker during the sync of a table.
+ * changes coming to the leader apply worker during the sync of a table.
  *
  * Note we need to do smaller or equals comparison for SYNCDONE state because
  * it might hold position of end of initial slot consistent point WAL
  * record + 1 (ie start of next record) and next record can be COMMIT of
  * transaction we are now processing (which is what we set remote_final_lsn
  * to in apply_handle_begin).
+ *
+ * Note that for streaming transactions that are being applied in the parallel
+ * apply worker, we disallow applying changes if the target table in the
+ * subscription is not in the READY state, because we cannot decide whether to
+ * apply the change as we won't know remote_final_lsn by that time.
+ *
+ * We already checked this in pa_can_start() before assigning the
+ * streaming transaction to the parallel worker, but it also needs to be
+ * checked here because if the user executes ALTER SUBSCRIPTION ... REFRESH
+ * PUBLICATION in parallel, the new table can be added to pg_subscription_rel
+ * while applying this transaction.
  */
 static bool
 should_apply_changes_for_rel(LogicalRepRelMapEntry *rel)
 {
 	if (am_tablesync_worker())
 		return MyLogicalRepWorker->relid == rel->localreloid;
+	else if (am_parallel_apply_worker())
+	{
+		/* We don't synchronize rel's that are in unknown state. */
+		if (rel->state != SUBREL_STATE_READY &&
+			rel->state != SUBREL_STATE_UNKNOWN)
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("logical replication parallel apply worker for subscription \"%s\" will stop",
+							MySubscription->name),
+					 errdetail("Cannot handle streamed replication transactions using parallel apply workers until all tables have been synchronized.")));
+
+		return rel->state == SUBREL_STATE_READY;
+	}
 	else
 		return (rel->state == SUBREL_STATE_READY ||
 				(rel->state == SUBREL_STATE_SYNCDONE &&
@@ -452,43 +549,110 @@ end_replication_step(void)
 }
 
 /*
- * Handle streamed transactions.
+ * Handle streamed transactions for both the leader apply worker and the
+ * parallel apply workers.
  *
- * If in streaming mode (receiving a block of streamed transaction), we
- * simply redirect it to a file for the proper toplevel transaction.
+ * In the streaming case (receiving a block of the streamed transaction), for
+ * serialize mode, simply redirect it to a file for the proper toplevel
+ * transaction, and for parallel mode, the leader apply worker will send the
+ * changes to parallel apply workers and the parallel apply worker will define
+ * savepoints if needed. (LOGICAL_REP_MSG_RELATION or LOGICAL_REP_MSG_TYPE
+ * messages will be applied by both leader apply worker and parallel apply
+ * workers).
  *
- * Returns true for streamed transactions, false otherwise (regular mode).
+ * Returns true for streamed transactions (when the change is either serialized
+ * to file or sent to parallel apply worker), false otherwise (regular mode or
+ * needs to be processed by parallel apply worker).
+ *
+ * Exception: If the message being processed is LOGICAL_REP_MSG_RELATION
+ * or LOGICAL_REP_MSG_TYPE, return false even if the message needs to be sent
+ * to a parallel apply worker.
  */
 static bool
 handle_streamed_transaction(LogicalRepMsgType action, StringInfo s)
 {
-	TransactionId xid;
+	TransactionId current_xid;
+	ParallelApplyWorkerInfo *winfo;
+	TransApplyAction apply_action;
+	StringInfoData original_msg;
+
+	apply_action = get_transaction_apply_action(stream_xid, &winfo);
 
 	/* not in streaming mode */
-	if (!in_streamed_transaction)
+	if (apply_action == TRANS_LEADER_APPLY)
 		return false;
 
-	Assert(stream_fd != NULL);
 	Assert(TransactionIdIsValid(stream_xid));
 
+	/*
+	 * The parallel apply worker needs the xid in this message to decide
+	 * whether to define a savepoint, so save the original message that has
+	 * not moved the cursor after the xid. We will serialize this message to a
+	 * file in PARTIAL_SERIALIZE mode.
+	 */
+	original_msg = *s;
+
 	/*
 	 * We should have received XID of the subxact as the first part of the
 	 * message, so extract it.
 	 */
-	xid = pq_getmsgint(s, 4);
+	current_xid = pq_getmsgint(s, 4);
 
-	if (!TransactionIdIsValid(xid))
+	if (!TransactionIdIsValid(current_xid))
 		ereport(ERROR,
 				(errcode(ERRCODE_PROTOCOL_VIOLATION),
 				 errmsg_internal("invalid transaction ID in streamed replication transaction")));
 
-	/* Add the new subxact to the array (unless already there). */
-	subxact_info_add(xid);
+	switch (apply_action)
+	{
+		case TRANS_LEADER_SERIALIZE:
+			Assert(stream_fd);
 
-	/* write the change to the current file */
-	stream_write_change(action, s);
+			/* Add the new subxact to the array (unless already there). */
+			subxact_info_add(current_xid);
+
+			/* Write the change to the current file */
+			stream_write_change(action, s);
+			return true;
+
+		case TRANS_LEADER_SEND_TO_PARALLEL:
+			Assert(winfo);
+
+			/*
+			 * XXX The publisher side doesn't always send relation/type update
+			 * messages after the streaming transaction, so also update the
+			 * relation/type in leader apply worker. See function
+			 * cleanup_rel_sync_cache.
+			 */
+			if (pa_send_data(winfo, s->len, s->data))
+				return (action != LOGICAL_REP_MSG_RELATION &&
+						action != LOGICAL_REP_MSG_TYPE);
+
+			/*
+			 * It is possible that while sending this change to parallel apply
+			 * worker we need to switch to serialize mode.
+			 */
+			pa_switch_to_partial_serialize(winfo, false);
 
-	return true;
+			/* fall through */
+		case TRANS_LEADER_PARTIAL_SERIALIZE:
+			stream_write_change(action, &original_msg);
+
+			/* Same reason as TRANS_LEADER_SEND_TO_PARALLEL case. */
+			return (action != LOGICAL_REP_MSG_RELATION &&
+					action != LOGICAL_REP_MSG_TYPE);
+
+		case TRANS_PARALLEL_APPLY:
+			parallel_stream_nchanges += 1;
+
+			/* Define a savepoint for a subxact if needed. */
+			pa_start_subtrans(current_xid, stream_xid);
+			return false;
+
+		default:
+			Assert(false);
+			return false;		/* silence compiler warning */
+	}
 }
 
 /*
@@ -926,8 +1090,11 @@ apply_handle_prepare_internal(LogicalRepPreparedTxnData *prepare_data)
 	 * BeginTransactionBlock is necessary to balance the EndTransactionBlock
 	 * called within the PrepareTransactionBlock below.
 	 */
-	BeginTransactionBlock();
-	CommitTransactionCommand(); /* Completes the preceding Begin command. */
+	if (!IsTransactionBlock())
+	{
+		BeginTransactionBlock();
+		CommitTransactionCommand(); /* Completes the preceding Begin command. */
+	}
 
 	/*
 	 * Update origin state so we can restart streaming from correct position
@@ -974,7 +1141,7 @@ apply_handle_prepare(StringInfo s)
 	CommitTransactionCommand();
 	pgstat_report_stat(false);
 
-	store_flush_position(prepare_data.end_lsn);
+	store_flush_position(prepare_data.end_lsn, XactLastCommitEnd);
 
 	in_remote_transaction = false;
 
@@ -996,6 +1163,12 @@ apply_handle_prepare(StringInfo s)
 
 /*
  * Handle a COMMIT PREPARED of a previously PREPARED transaction.
+ *
+ * Note that we don't need to wait here if the transaction was prepared in a
+ * parallel apply worker. In that case, we have already waited for the prepare
+ * to finish in apply_handle_stream_prepare() which will ensure all the
+ * operations in that transaction have happened in the subscriber, so no
+ * concurrent transaction can cause deadlock or transaction dependency issues.
  */
 static void
 apply_handle_commit_prepared(StringInfo s)
@@ -1025,7 +1198,7 @@ apply_handle_commit_prepared(StringInfo s)
 	CommitTransactionCommand();
 	pgstat_report_stat(false);
 
-	store_flush_position(prepare_data.end_lsn);
+	store_flush_position(prepare_data.end_lsn, XactLastCommitEnd);
 	in_remote_transaction = false;
 
 	/* Process any tables that are being synchronized in parallel. */
@@ -1039,6 +1212,12 @@ apply_handle_commit_prepared(StringInfo s)
 
 /*
  * Handle a ROLLBACK PREPARED of a previously PREPARED TRANSACTION.
+ *
+ * Note that we don't need to wait here if the transaction was prepared in a
+ * parallel apply worker. In that case, we have already waited for the prepare
+ * to finish in apply_handle_stream_prepare() which will ensure all the
+ * operations in that transaction have happened in the subscriber, so no
+ * concurrent transaction can cause deadlock or transaction dependency issues.
  */
 static void
 apply_handle_rollback_prepared(StringInfo s)
@@ -1080,7 +1259,7 @@ apply_handle_rollback_prepared(StringInfo s)
 
 	pgstat_report_stat(false);
 
-	store_flush_position(rollback_data.rollback_end_lsn);
+	store_flush_position(rollback_data.rollback_end_lsn, XactLastCommitEnd);
 	in_remote_transaction = false;
 
 	/* Process any tables that are being synchronized in parallel. */
@@ -1092,15 +1271,16 @@ apply_handle_rollback_prepared(StringInfo s)
 
 /*
  * Handle STREAM PREPARE.
- *
- * Logic is in two parts:
- * 1. Replay all the spooled operations
- * 2. Mark the transaction as prepared
  */
 static void
 apply_handle_stream_prepare(StringInfo s)
 {
 	LogicalRepPreparedTxnData prepare_data;
+	ParallelApplyWorkerInfo *winfo;
+	TransApplyAction apply_action;
+
+	/* Save the message before it is consumed. */
+	StringInfoData original_msg = *s;
 
 	if (in_streamed_transaction)
 		ereport(ERROR,
@@ -1116,24 +1296,96 @@ apply_handle_stream_prepare(StringInfo s)
 	logicalrep_read_stream_prepare(s, &prepare_data);
 	set_apply_error_context_xact(prepare_data.xid, prepare_data.prepare_lsn);
 
-	elog(DEBUG1, "received prepare for streamed transaction %u", prepare_data.xid);
+	apply_action = get_transaction_apply_action(prepare_data.xid, &winfo);
 
-	/* Replay all the spooled operations. */
-	apply_spooled_messages(prepare_data.xid, prepare_data.prepare_lsn);
+	switch (apply_action)
+	{
+		case TRANS_LEADER_SERIALIZE:
 
-	/* Mark the transaction as prepared. */
-	apply_handle_prepare_internal(&prepare_data);
+			/*
+			 * The transaction has been serialized to file, so replay all the
+			 * spooled operations.
+			 */
+			apply_spooled_messages(MyLogicalRepWorker->stream_fileset,
+								   prepare_data.xid, prepare_data.prepare_lsn);
 
-	CommitTransactionCommand();
+			/* Mark the transaction as prepared. */
+			apply_handle_prepare_internal(&prepare_data);
 
-	pgstat_report_stat(false);
+			CommitTransactionCommand();
 
-	store_flush_position(prepare_data.end_lsn);
+			store_flush_position(prepare_data.end_lsn, XactLastCommitEnd);
 
-	in_remote_transaction = false;
+			in_remote_transaction = false;
+
+			/* Unlink the files with serialized changes and subxact info. */
+			stream_cleanup_files(MyLogicalRepWorker->subid, prepare_data.xid);
+			break;
 
-	/* unlink the files with serialized changes and subxact info. */
-	stream_cleanup_files(MyLogicalRepWorker->subid, prepare_data.xid);
+		case TRANS_LEADER_SEND_TO_PARALLEL:
+			Assert(winfo);
+
+			if (pa_send_data(winfo, s->len, s->data))
+			{
+				/* Finish processing the streaming transaction. */
+				pa_xact_finish(winfo, prepare_data.end_lsn);
+				break;
+			}
+
+			/*
+			 * It is possible that while sending this change to parallel apply
+			 * worker we need to switch to serialize mode.
+			 */
+			pa_switch_to_partial_serialize(winfo, true);
+
+			/* fall through */
+		case TRANS_LEADER_PARTIAL_SERIALIZE:
+			Assert(winfo);
+
+			stream_open_and_write_change(prepare_data.xid,
+										 LOGICAL_REP_MSG_STREAM_PREPARE,
+										 &original_msg);
+
+			pa_set_fileset_state(winfo->shared, FS_SERIALIZE_DONE);
+
+			/* Finish processing the streaming transaction. */
+			pa_xact_finish(winfo, prepare_data.end_lsn);
+			break;
+
+		case TRANS_PARALLEL_APPLY:
+
+			/*
+			 * If the parallel apply worker is applying spooled messages then
+			 * close the file before preparing.
+			 */
+			if (stream_fd)
+				stream_close_file();
+
+			begin_replication_step();
+
+			/* Mark the transaction as prepared. */
+			apply_handle_prepare_internal(&prepare_data);
+
+			end_replication_step();
+
+			CommitTransactionCommand();
+
+			MyParallelShared->last_commit_end = XactLastCommitEnd;
+
+			pa_set_xact_state(MyParallelShared, PARALLEL_TRANS_FINISHED);
+			pa_unlock_transaction(MyParallelShared->xid, AccessExclusiveLock);
+
+			pa_reset_subtrans();
+
+			elog(DEBUG1, "finished processing the STREAM PREPARE command");
+			break;
+
+		default:
+			Assert(false);
+			break;
+	}
+
+	pgstat_report_stat(false);
 
 	/* Process any tables that are being synchronized in parallel. */
 	process_syncing_tables(prepare_data.end_lsn);
@@ -1170,6 +1422,47 @@ apply_handle_origin(StringInfo s)
 				 errmsg_internal("ORIGIN message sent out of order")));
 }
 
+/*
+ * Initialize fileset (if not already done).
+ *
+ * Create a new file when first_segment is true, otherwise open the existing
+ * file.
+ */
+void
+stream_start_internal(TransactionId xid, bool first_segment)
+{
+	begin_replication_step();
+
+	/*
+	 * Initialize the worker's stream_fileset if we haven't yet. This will be
+	 * used for the entire duration of the worker so create it in a permanent
+	 * context. We create this on the very first streaming message from any
+	 * transaction and then use it for this and other streaming transactions.
+	 * Now, we could create a fileset at the start of the worker as well but
+	 * then we won't be sure that it will ever be used.
+	 */
+	if (!MyLogicalRepWorker->stream_fileset)
+	{
+		MemoryContext oldctx;
+
+		oldctx = MemoryContextSwitchTo(ApplyContext);
+
+		MyLogicalRepWorker->stream_fileset = palloc(sizeof(FileSet));
+		FileSetInit(MyLogicalRepWorker->stream_fileset);
+
+		MemoryContextSwitchTo(oldctx);
+	}
+
+	/* Open the spool file for this transaction. */
+	stream_open_file(MyLogicalRepWorker->subid, xid, first_segment);
+
+	/* If this is not the first segment, open existing subxact file. */
+	if (!first_segment)
+		subxact_info_read(MyLogicalRepWorker->subid, xid);
+
+	end_replication_step();
+}
+
 /*
  * Handle STREAM START message.
  */
@@ -1177,21 +1470,17 @@ static void
 apply_handle_stream_start(StringInfo s)
 {
 	bool		first_segment;
+	ParallelApplyWorkerInfo *winfo;
+	TransApplyAction apply_action;
+
+	/* Save the message before it is consumed. */
+	StringInfoData original_msg = *s;
 
 	if (in_streamed_transaction)
 		ereport(ERROR,
 				(errcode(ERRCODE_PROTOCOL_VIOLATION),
 				 errmsg_internal("duplicate STREAM START message")));
 
-	/*
-	 * Start a transaction on stream start, this transaction will be committed
-	 * on the stream stop unless it is a tablesync worker in which case it
-	 * will be committed after processing all the messages. We need the
-	 * transaction for handling the buffile, used for serializing the
-	 * streaming data and subxact info.
-	 */
-	begin_replication_step();
-
 	/* notify handle methods we're processing a remote transaction */
 	in_streamed_transaction = true;
 
@@ -1205,96 +1494,237 @@ apply_handle_stream_start(StringInfo s)
 
 	set_apply_error_context_xact(stream_xid, InvalidXLogRecPtr);
 
-	/*
-	 * Initialize the worker's stream_fileset if we haven't yet. This will be
-	 * used for the entire duration of the worker so create it in a permanent
-	 * context. We create this on the very first streaming message from any
-	 * transaction and then use it for this and other streaming transactions.
-	 * Now, we could create a fileset at the start of the worker as well but
-	 * then we won't be sure that it will ever be used.
-	 */
-	if (MyLogicalRepWorker->stream_fileset == NULL)
+	/* Try to allocate a worker for the streaming transaction. */
+	if (first_segment)
+		pa_allocate_worker(stream_xid);
+
+	apply_action = get_transaction_apply_action(stream_xid, &winfo);
+
+	switch (apply_action)
 	{
-		MemoryContext oldctx;
+		case TRANS_LEADER_SERIALIZE:
 
-		oldctx = MemoryContextSwitchTo(ApplyContext);
+			/*
+			 * Function stream_start_internal starts a transaction. This
+			 * transaction will be committed on the stream stop unless it is a
+			 * tablesync worker in which case it will be committed after
+			 * processing all the messages. We need this transaction for
+			 * handling the BufFile, used for serializing the streaming data
+			 * and subxact info.
+			 */
+			stream_start_internal(stream_xid, first_segment);
+			break;
 
-		MyLogicalRepWorker->stream_fileset = palloc(sizeof(FileSet));
-		FileSetInit(MyLogicalRepWorker->stream_fileset);
+		case TRANS_LEADER_SEND_TO_PARALLEL:
+			Assert(winfo);
 
-		MemoryContextSwitchTo(oldctx);
-	}
+			/*
+			 * Once we start serializing the changes, the parallel apply
+			 * worker will wait for the leader to release the stream lock
+			 * until the end of the transaction. So, we don't need to release
+			 * the lock or increment the stream count in that case.
+			 */
+			if (pa_send_data(winfo, s->len, s->data))
+			{
+				/*
+				 * Unlock the shared object lock so that the parallel apply
+				 * worker can continue to receive changes.
+				 */
+				if (!first_segment)
+					pa_unlock_stream(winfo->shared->xid, AccessExclusiveLock);
+
+				/*
+				 * Increment the number of streaming blocks waiting to be
+				 * processed by parallel apply worker.
+				 */
+				pg_atomic_add_fetch_u32(&winfo->shared->pending_stream_count, 1);
 
-	/* open the spool file for this transaction */
-	stream_open_file(MyLogicalRepWorker->subid, stream_xid, first_segment);
+				/* Cache the parallel apply worker for this transaction. */
+				pa_set_stream_apply_worker(winfo);
+				break;
+			}
 
-	/* if this is not the first segment, open existing subxact file */
-	if (!first_segment)
-		subxact_info_read(MyLogicalRepWorker->subid, stream_xid);
+			/*
+			 * It is possible that while sending this change to parallel apply
+			 * worker we need to switch to serialize mode.
+			 */
+			pa_switch_to_partial_serialize(winfo, !first_segment);
 
-	pgstat_report_activity(STATE_RUNNING, NULL);
+			/* fall through */
+		case TRANS_LEADER_PARTIAL_SERIALIZE:
+			Assert(winfo);
 
-	end_replication_step();
+			/*
+			 * Open the spool file unless it was already opened when switching
+			 * to serialize mode. The transaction started in
+			 * stream_start_internal will be committed on the stream stop.
+			 */
+			if (apply_action != TRANS_LEADER_SEND_TO_PARALLEL)
+				stream_start_internal(stream_xid, first_segment);
+
+			stream_write_change(LOGICAL_REP_MSG_STREAM_START, &original_msg);
+
+			/* Cache the parallel apply worker for this transaction. */
+			pa_set_stream_apply_worker(winfo);
+			break;
+
+		case TRANS_PARALLEL_APPLY:
+			if (first_segment)
+			{
+				/* Hold the lock until the end of the transaction. */
+				pa_lock_transaction(MyParallelShared->xid, AccessExclusiveLock);
+				pa_set_xact_state(MyParallelShared, PARALLEL_TRANS_STARTED);
+			}
+
+			parallel_stream_nchanges = 0;
+			break;
+
+		default:
+			Assert(false);
+			break;
+	}
+
+	pgstat_report_activity(STATE_RUNNING, NULL);
 }
 
 /*
- * Handle STREAM STOP message.
+ * Update the information about subxacts and close the file.
+ *
+ * This function should be called when the stream_start_internal function has
+ * been called.
  */
-static void
-apply_handle_stream_stop(StringInfo s)
+void
+stream_stop_internal(TransactionId xid)
 {
-	if (!in_streamed_transaction)
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("STREAM STOP message without STREAM START")));
-
 	/*
-	 * Close the file with serialized changes, and serialize information about
-	 * subxacts for the toplevel transaction.
+	 * Serialize information about subxacts for the toplevel transaction, then
+	 * close the stream messages spool file.
 	 */
-	subxact_info_write(MyLogicalRepWorker->subid, stream_xid);
+	subxact_info_write(MyLogicalRepWorker->subid, xid);
 	stream_close_file();
 
-	/* We must be in a valid transaction state */
 	Assert(IsTransactionState());
 
 	/* Commit the per-stream transaction */
 	CommitTransactionCommand();
 
-	in_streamed_transaction = false;
-
 	/* Reset per-stream context */
 	MemoryContextReset(LogicalStreamingContext);
-
-	pgstat_report_activity(STATE_IDLE, NULL);
-	reset_apply_error_context_info();
 }
 
 /*
- * Handle STREAM abort message.
+ * Handle STREAM STOP message.
  */
 static void
-apply_handle_stream_abort(StringInfo s)
+apply_handle_stream_stop(StringInfo s)
 {
-	TransactionId xid;
-	TransactionId subxid;
+	ParallelApplyWorkerInfo *winfo;
+	TransApplyAction apply_action;
 
-	if (in_streamed_transaction)
+	if (!in_streamed_transaction)
 		ereport(ERROR,
 				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("STREAM ABORT message without STREAM STOP")));
+				 errmsg_internal("STREAM STOP message without STREAM START")));
+
+	apply_action = get_transaction_apply_action(stream_xid, &winfo);
+
+	switch (apply_action)
+	{
+		case TRANS_LEADER_SERIALIZE:
+			stream_stop_internal(stream_xid);
+			break;
+
+		case TRANS_LEADER_SEND_TO_PARALLEL:
+			Assert(winfo);
+
+			/*
+			 * Lock before sending the STREAM_STOP message so that the leader
+			 * can hold the lock first and the parallel apply worker will wait
+			 * for leader to release the lock. See Locking Considerations atop
+			 * applyparallelworker.c.
+			 */
+			pa_lock_stream(winfo->shared->xid, AccessExclusiveLock);
+
+			if (pa_send_data(winfo, s->len, s->data))
+			{
+				pa_set_stream_apply_worker(NULL);
+				break;
+			}
+
+			/*
+			 * It is possible that while sending this change to parallel apply
+			 * worker we need to switch to serialize mode.
+			 */
+			pa_switch_to_partial_serialize(winfo, true);
+
+			/* fall through */
+		case TRANS_LEADER_PARTIAL_SERIALIZE:
+			stream_write_change(LOGICAL_REP_MSG_STREAM_STOP, s);
+			stream_stop_internal(stream_xid);
+			pa_set_stream_apply_worker(NULL);
+			break;
+
+		case TRANS_PARALLEL_APPLY:
+			elog(DEBUG1, "applied %u changes in the streaming chunk",
+				 parallel_stream_nchanges);
 
-	logicalrep_read_stream_abort(s, &xid, &subxid);
+			/*
+			 * By the time parallel apply worker is processing the changes in
+			 * the current streaming block, the leader apply worker may have
+			 * sent multiple streaming blocks. This can lead to parallel apply
+			 * worker start waiting even when there are more chunk of streams
+			 * in the queue. So, try to lock only if there is no message left
+			 * in the queue. See Locking Considerations atop
+			 * applyparallelworker.c.
+			 *
+			 * Note that here we have a race condition where we can start
+			 * waiting even when there are pending streaming chunks. This can
+			 * happen if the leader sends another streaming block and acquires
+			 * the stream lock again after the parallel apply worker checks
+			 * that there is no pending streaming block and before it actually
+			 * starts waiting on a lock. We can handle this case by not
+			 * allowing the leader to increment the stream block count during
+			 * the time parallel apply worker acquires the lock but it is not
+			 * clear whether that is worth the complexity.
+			 *
+			 * Now, if this missed chunk contains rollback to savepoint, then
+			 * there is a risk of deadlock which probably shouldn't happen
+			 * after restart.
+			 */
+			pa_decr_and_wait_stream_block();
+			break;
+
+		default:
+			Assert(false);
+			break;
+	}
+
+	in_streamed_transaction = false;
+
+	/*
+	 * The parallel apply worker could be in a transaction in which case we
+	 * need to report the state as STATE_IDLEINTRANSACTION.
+	 */
+	if (IsTransactionOrTransactionBlock())
+		pgstat_report_activity(STATE_IDLEINTRANSACTION, NULL);
+	else
+		pgstat_report_activity(STATE_IDLE, NULL);
+
+	reset_apply_error_context_info();
+}
 
+/*
+ * Handle STREAM ABORT message when the transaction was serialized to file.
+ */
+static void
+stream_abort_internal(TransactionId xid, TransactionId subxid)
+{
 	/*
 	 * If the two XIDs are the same, it's in fact abort of toplevel xact, so
 	 * just delete the files with serialized info.
 	 */
 	if (xid == subxid)
-	{
-		set_apply_error_context_xact(xid, InvalidXLogRecPtr);
 		stream_cleanup_files(MyLogicalRepWorker->subid, xid);
-	}
 	else
 	{
 		/*
@@ -1318,8 +1748,6 @@ apply_handle_stream_abort(StringInfo s)
 		bool		found = false;
 		char		path[MAXPGPATH];
 
-		set_apply_error_context_xact(subxid, InvalidXLogRecPtr);
-
 		subidx = -1;
 		begin_replication_step();
 		subxact_info_read(MyLogicalRepWorker->subid, xid);
@@ -1344,47 +1772,224 @@ apply_handle_stream_abort(StringInfo s)
 			cleanup_subxact_info();
 			end_replication_step();
 			CommitTransactionCommand();
-			reset_apply_error_context_info();
 			return;
 		}
 
-		/* open the changes file */
-		changes_filename(path, MyLogicalRepWorker->subid, xid);
-		fd = BufFileOpenFileSet(MyLogicalRepWorker->stream_fileset, path,
-								O_RDWR, false);
+		/* open the changes file */
+		changes_filename(path, MyLogicalRepWorker->subid, xid);
+		fd = BufFileOpenFileSet(MyLogicalRepWorker->stream_fileset, path,
+								O_RDWR, false);
+
+		/* OK, truncate the file at the right offset */
+		BufFileTruncateFileSet(fd, subxact_data.subxacts[subidx].fileno,
+							   subxact_data.subxacts[subidx].offset);
+		BufFileClose(fd);
+
+		/* discard the subxacts added later */
+		subxact_data.nsubxacts = subidx;
+
+		/* write the updated subxact list */
+		subxact_info_write(MyLogicalRepWorker->subid, xid);
+
+		end_replication_step();
+		CommitTransactionCommand();
+	}
+}
+
+/*
+ * Handle STREAM ABORT message.
+ */
+static void
+apply_handle_stream_abort(StringInfo s)
+{
+	TransactionId xid;
+	TransactionId subxid;
+	LogicalRepStreamAbortData abort_data;
+	ParallelApplyWorkerInfo *winfo;
+	TransApplyAction apply_action;
+
+	/* Save the message before it is consumed. */
+	StringInfoData original_msg = *s;
+	bool		toplevel_xact;
+
+	if (in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("STREAM ABORT message without STREAM STOP")));
+
+	/* We receive abort information only when we can apply in parallel. */
+	logicalrep_read_stream_abort(s, &abort_data,
+								 MyLogicalRepWorker->parallel_apply);
+
+	xid = abort_data.xid;
+	subxid = abort_data.subxid;
+	toplevel_xact = (xid == subxid);
+
+	set_apply_error_context_xact(subxid, abort_data.abort_lsn);
+
+	apply_action = get_transaction_apply_action(xid, &winfo);
+
+	switch (apply_action)
+	{
+		case TRANS_LEADER_SERIALIZE:
+
+			/*
+			 * We are in the leader apply worker and the transaction has been
+			 * serialized to file.
+			 */
+			stream_abort_internal(xid, subxid);
+			break;
+
+		case TRANS_LEADER_SEND_TO_PARALLEL:
+			Assert(winfo);
+
+			/*
+			 * For the case of aborting the subtransaction, we increment the
+			 * number of streaming blocks and take the lock again before
+			 * sending the STREAM_ABORT to ensure that the parallel apply
+			 * worker will wait on the lock for the next set of changes after
+			 * processing the STREAM_ABORT message if it is not already
+			 * waiting for STREAM_STOP message.
+			 *
+			 * It is important to perform this locking before sending the
+			 * STREAM_ABORT message so that the leader can hold the lock first
+			 * and the parallel apply worker will wait for the leader to
+			 * release the lock. This is the same as what we do in
+			 * apply_handle_stream_stop. See Locking Considerations atop
+			 * applyparallelworker.c.
+			 */
+			if (!toplevel_xact)
+			{
+				pa_unlock_stream(xid, AccessExclusiveLock);
+				pg_atomic_add_fetch_u32(&winfo->shared->pending_stream_count, 1);
+				pa_lock_stream(xid, AccessExclusiveLock);
+			}
+
+			/*
+			 * Unlike STREAM_COMMIT and STREAM_PREPARE, we don't wait for the
+			 * parallel apply worker to finish as that is not required to
+			 * maintain the commit order and won't have the risk of failures
+			 * due to transaction dependencies and deadlocks.
+			 */
+			if (pa_send_data(winfo, s->len, s->data))
+			{
+				if (toplevel_xact)
+				{
+					pa_unlock_stream(xid, AccessExclusiveLock);
+					(void) pa_free_worker(winfo);
+				}
+				break;
+			}
+
+			/*
+			 * It is possible that while sending this change to parallel apply
+			 * worker we need to switch to serialize mode.
+			 */
+			pa_switch_to_partial_serialize(winfo, true);
+
+			/* fall through */
+		case TRANS_LEADER_PARTIAL_SERIALIZE:
+			Assert(winfo);
+
+			/*
+			 * Parallel apply worker might have applied some changes, so write
+			 * the STREAM_ABORT message so that it can rollback the
+			 * subtransaction if needed.
+			 */
+			stream_open_and_write_change(xid, LOGICAL_REP_MSG_STREAM_ABORT,
+										 &original_msg);
+
+			if (toplevel_xact)
+			{
+				pa_set_fileset_state(winfo->shared, FS_SERIALIZE_DONE);
+				pa_unlock_stream(xid, AccessExclusiveLock);
+				(void) pa_free_worker(winfo);
+			}
+			break;
+
+		case TRANS_PARALLEL_APPLY:
+
+			/*
+			 * If the parallel apply worker is applying spooled messages then
+			 * close the file before aborting.
+			 */
+			if (toplevel_xact && stream_fd)
+				stream_close_file();
+
+			pa_stream_abort(&abort_data);
+
+			/*
+			 * We need to wait after processing rollback to savepoint for the
+			 * next set of changes.
+			 *
+			 * We have a race condition here due to which we can start waiting
+			 * here when there are more chunk of streams in the queue. See
+			 * apply_handle_stream_stop.
+			 */
+			if (!toplevel_xact)
+				pa_decr_and_wait_stream_block();
+
+			elog(DEBUG1, "finished processing the STREAM ABORT command");
+			break;
+
+		default:
+			Assert(false);
+			break;
+	}
+
+	reset_apply_error_context_info();
+}
+
+/*
+ * Ensure that the passed location is fileset's end.
+ */
+static void
+ensure_last_message(FileSet *stream_fileset, TransactionId xid, int fileno,
+					off_t offset)
+{
+	char		path[MAXPGPATH];
+	BufFile    *fd;
+	int			last_fileno;
+	off_t		last_offset;
 
-		/* OK, truncate the file at the right offset */
-		BufFileTruncateFileSet(fd, subxact_data.subxacts[subidx].fileno,
-							   subxact_data.subxacts[subidx].offset);
-		BufFileClose(fd);
+	Assert(!IsTransactionState());
 
-		/* discard the subxacts added later */
-		subxact_data.nsubxacts = subidx;
+	begin_replication_step();
 
-		/* write the updated subxact list */
-		subxact_info_write(MyLogicalRepWorker->subid, xid);
+	changes_filename(path, MyLogicalRepWorker->subid, xid);
 
-		end_replication_step();
-		CommitTransactionCommand();
-	}
+	fd = BufFileOpenFileSet(stream_fileset, path, O_RDONLY, false);
 
-	reset_apply_error_context_info();
+	BufFileSeek(fd, 0, 0, SEEK_END);
+	BufFileTell(fd, &last_fileno, &last_offset);
+
+	BufFileClose(fd);
+
+	end_replication_step();
+
+	if (last_fileno != fileno || last_offset != offset)
+		elog(ERROR, "unexpected message left in streaming transaction's changes file \"%s\"",
+			 path);
 }
 
 /*
  * Common spoolfile processing.
  */
-static void
-apply_spooled_messages(TransactionId xid, XLogRecPtr lsn)
+void
+apply_spooled_messages(FileSet *stream_fileset, TransactionId xid,
+					   XLogRecPtr lsn)
 {
 	StringInfoData s2;
 	int			nchanges;
 	char		path[MAXPGPATH];
 	char	   *buffer = NULL;
 	MemoryContext oldcxt;
-	BufFile    *fd;
+	ResourceOwner oldowner;
+	int			fileno;
+	off_t		offset;
 
-	maybe_start_skipping_changes(lsn);
+	if (!am_parallel_apply_worker())
+		maybe_start_skipping_changes(lsn);
 
 	/* Make sure we have an open transaction */
 	begin_replication_step();
@@ -1400,8 +2005,16 @@ apply_spooled_messages(TransactionId xid, XLogRecPtr lsn)
 	changes_filename(path, MyLogicalRepWorker->subid, xid);
 	elog(DEBUG1, "replaying changes from file \"%s\"", path);
 
-	fd = BufFileOpenFileSet(MyLogicalRepWorker->stream_fileset, path, O_RDONLY,
-							false);
+	/*
+	 * Make sure the file is owned by the toplevel transaction so that the
+	 * file will not be accidentally closed when aborting a subtransaction.
+	 */
+	oldowner = CurrentResourceOwner;
+	CurrentResourceOwner = TopTransactionResourceOwner;
+
+	stream_fd = BufFileOpenFileSet(stream_fileset, path, O_RDONLY, false);
+
+	CurrentResourceOwner = oldowner;
 
 	buffer = palloc(BLCKSZ);
 	initStringInfo(&s2);
@@ -1432,7 +2045,7 @@ apply_spooled_messages(TransactionId xid, XLogRecPtr lsn)
 		CHECK_FOR_INTERRUPTS();
 
 		/* read length of the on-disk record */
-		nbytes = BufFileRead(fd, &len, sizeof(len));
+		nbytes = BufFileRead(stream_fd, &len, sizeof(len));
 
 		/* have we reached end of the file? */
 		if (nbytes == 0)
@@ -1453,12 +2066,14 @@ apply_spooled_messages(TransactionId xid, XLogRecPtr lsn)
 		buffer = repalloc(buffer, len);
 
 		/* and finally read the data into the buffer */
-		if (BufFileRead(fd, buffer, len) != len)
+		if (BufFileRead(stream_fd, buffer, len) != len)
 			ereport(ERROR,
 					(errcode_for_file_access(),
 					 errmsg("could not read from streaming transaction's changes file \"%s\": %m",
 							path)));
 
+		BufFileTell(stream_fd, &fileno, &offset);
+
 		/* copy the buffer to the stringinfo and call apply_dispatch */
 		resetStringInfo(&s2);
 		appendBinaryStringInfo(&s2, buffer, len);
@@ -1474,15 +2089,24 @@ apply_spooled_messages(TransactionId xid, XLogRecPtr lsn)
 
 		nchanges++;
 
+		/*
+		 * It is possible the file has been closed because we have processed
+		 * the transaction end message like stream_commit in which case that
+		 * must be the last message.
+		 */
+		if (!stream_fd)
+		{
+			ensure_last_message(stream_fileset, xid, fileno, offset);
+			break;
+		}
+
 		if (nchanges % 1000 == 0)
 			elog(DEBUG1, "replayed %d changes from file \"%s\"",
 				 nchanges, path);
 	}
 
-	BufFileClose(fd);
-
-	pfree(buffer);
-	pfree(s2.data);
+	if (stream_fd)
+		stream_close_file();
 
 	elog(DEBUG1, "replayed %d (all) changes from file \"%s\"",
 		 nchanges, path);
@@ -1498,6 +2122,11 @@ apply_handle_stream_commit(StringInfo s)
 {
 	TransactionId xid;
 	LogicalRepCommitData commit_data;
+	ParallelApplyWorkerInfo *winfo;
+	TransApplyAction apply_action;
+
+	/* Save the message before it is consumed. */
+	StringInfoData original_msg = *s;
 
 	if (in_streamed_transaction)
 		ereport(ERROR,
@@ -1507,14 +2136,79 @@ apply_handle_stream_commit(StringInfo s)
 	xid = logicalrep_read_stream_commit(s, &commit_data);
 	set_apply_error_context_xact(xid, commit_data.commit_lsn);
 
-	elog(DEBUG1, "received commit for streamed transaction %u", xid);
+	apply_action = get_transaction_apply_action(xid, &winfo);
 
-	apply_spooled_messages(xid, commit_data.commit_lsn);
+	switch (apply_action)
+	{
+		case TRANS_LEADER_SERIALIZE:
 
-	apply_handle_commit_internal(&commit_data);
+			/*
+			 * The transaction has been serialized to file, so replay all the
+			 * spooled operations.
+			 */
+			apply_spooled_messages(MyLogicalRepWorker->stream_fileset, xid,
+								   commit_data.commit_lsn);
+
+			apply_handle_commit_internal(&commit_data);
+
+			/* Unlink the files with serialized changes and subxact info. */
+			stream_cleanup_files(MyLogicalRepWorker->subid, xid);
+			break;
+
+		case TRANS_LEADER_SEND_TO_PARALLEL:
+			Assert(winfo);
+
+			if (pa_send_data(winfo, s->len, s->data))
+			{
+				/* Finish processing the streaming transaction. */
+				pa_xact_finish(winfo, commit_data.end_lsn);
+				break;
+			}
+
+			/*
+			 * It is possible that while sending this change to parallel apply
+			 * worker we need to switch to serialize mode.
+			 */
+			pa_switch_to_partial_serialize(winfo, true);
+
+			/* fall through */
+		case TRANS_LEADER_PARTIAL_SERIALIZE:
+			Assert(winfo);
 
-	/* unlink the files with serialized changes and subxact info */
-	stream_cleanup_files(MyLogicalRepWorker->subid, xid);
+			stream_open_and_write_change(xid, LOGICAL_REP_MSG_STREAM_COMMIT,
+										 &original_msg);
+
+			pa_set_fileset_state(winfo->shared, FS_SERIALIZE_DONE);
+
+			/* Finish processing the streaming transaction. */
+			pa_xact_finish(winfo, commit_data.end_lsn);
+			break;
+
+		case TRANS_PARALLEL_APPLY:
+
+			/*
+			 * If the parallel apply worker is applying spooled messages then
+			 * close the file before committing.
+			 */
+			if (stream_fd)
+				stream_close_file();
+
+			apply_handle_commit_internal(&commit_data);
+
+			MyParallelShared->last_commit_end = XactLastCommitEnd;
+
+			pa_set_xact_state(MyParallelShared, PARALLEL_TRANS_FINISHED);
+			pa_unlock_transaction(xid, AccessExclusiveLock);
+
+			pa_reset_subtrans();
+
+			elog(DEBUG1, "finished processing the STREAM COMMIT command");
+			break;
+
+		default:
+			Assert(false);
+			break;
+	}
 
 	/* Process any tables that are being synchronized in parallel. */
 	process_syncing_tables(commit_data.end_lsn);
@@ -1558,9 +2252,16 @@ apply_handle_commit_internal(LogicalRepCommitData *commit_data)
 		replorigin_session_origin_timestamp = commit_data->committime;
 
 		CommitTransactionCommand();
+
+		if (IsTransactionBlock())
+		{
+			EndTransactionBlock(false);
+			CommitTransactionCommand();
+		}
+
 		pgstat_report_stat(false);
 
-		store_flush_position(commit_data->end_lsn);
+		store_flush_position(commit_data->end_lsn, XactLastCommitEnd);
 	}
 	else
 	{
@@ -2511,7 +3212,7 @@ apply_handle_truncate(StringInfo s)
 /*
  * Logical replication protocol message dispatcher.
  */
-static void
+void
 apply_dispatch(StringInfo s)
 {
 	LogicalRepMsgType action = pq_getmsgbyte(s);
@@ -2675,17 +3376,24 @@ get_flush_position(XLogRecPtr *write, XLogRecPtr *flush,
 /*
  * Store current remote/local lsn pair in the tracking list.
  */
-static void
-store_flush_position(XLogRecPtr remote_lsn)
+void
+store_flush_position(XLogRecPtr remote_lsn, XLogRecPtr local_lsn)
 {
 	FlushPosition *flushpos;
 
+	/*
+	 * Skip for parallel apply workers, because the lsn_mapping is maintained
+	 * by the leader apply worker.
+	 */
+	if (am_parallel_apply_worker())
+		return;
+
 	/* Need to do this in permanent context */
 	MemoryContextSwitchTo(ApplyContext);
 
 	/* Track commit lsn  */
 	flushpos = (FlushPosition *) palloc(sizeof(FlushPosition));
-	flushpos->local_end = XactLastCommitEnd;
+	flushpos->local_end = local_lsn;
 	flushpos->remote_end = remote_lsn;
 
 	dlist_push_tail(&lsn_mapping, &flushpos->node);
@@ -2744,6 +3452,7 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
 	errcallback.callback = apply_error_callback;
 	errcallback.previous = error_context_stack;
 	error_context_stack = &errcallback;
+	apply_error_context_stack = error_context_stack;
 
 	/* This outer loop iterates once per wait. */
 	for (;;)
@@ -2958,6 +3667,7 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
 
 	/* Pop the error context stack */
 	error_context_stack = errcallback.previous;
+	apply_error_context_stack = error_context_stack;
 
 	/* All done */
 	walrcv_endstreaming(LogRepWorkerWalRcvConn, &tli);
@@ -3056,9 +3766,31 @@ send_feedback(XLogRecPtr recvpos, bool force, bool requestReply)
 }
 
 /*
- * Reread subscription info if needed. Most changes will be exit.
+ * Exit routine for apply workers due to subscription parameter changes.
  */
 static void
+apply_worker_exit(void)
+{
+	if (am_parallel_apply_worker())
+	{
+		/*
+		 * Don't stop the parallel apply worker as the leader will detect the
+		 * subscription parameter change and restart logical replication later
+		 * anyway. This also prevents the leader from reporting errors when
+		 * trying to communicate with a stopped parallel apply worker, which
+		 * would accidentally disable subscriptions if disable_on_error was
+		 * set.
+		 */
+		return;
+	}
+
+	proc_exit(0);
+}
+
+/*
+ * Reread subscription info if needed. Most changes will be exit.
+ */
+void
 maybe_reread_subscription(void)
 {
 	MemoryContext oldctx;
@@ -3088,9 +3820,9 @@ maybe_reread_subscription(void)
 	if (!newsub)
 	{
 		ereport(LOG,
-				(errmsg("logical replication apply worker for subscription \"%s\" will "
-						"stop because the subscription was removed",
-						MySubscription->name)));
+		/* translator: first %s is the name of logical replication worker */
+				(errmsg("%s for subscription \"%s\" will stop because the subscription was removed",
+						get_worker_name(), MySubscription->name)));
 
 		proc_exit(0);
 	}
@@ -3099,11 +3831,11 @@ maybe_reread_subscription(void)
 	if (!newsub->enabled)
 	{
 		ereport(LOG,
-				(errmsg("logical replication apply worker for subscription \"%s\" will "
-						"stop because the subscription was disabled",
-						MySubscription->name)));
+		/* translator: first %s is the name of logical replication worker */
+				(errmsg("%s for subscription \"%s\" will stop because the subscription was disabled",
+						get_worker_name(), MySubscription->name)));
 
-		proc_exit(0);
+		apply_worker_exit();
 	}
 
 	/* !slotname should never happen when enabled is true. */
@@ -3114,7 +3846,10 @@ maybe_reread_subscription(void)
 
 	/*
 	 * Exit if any parameter that affects the remote connection was changed.
-	 * The launcher will start a new worker.
+	 * The launcher will start a new worker but note that the parallel apply
+	 * worker won't restart if the streaming option's value is changed from
+	 * 'parallel' to any other value or the server decides not to stream the
+	 * in-progress transaction.
 	 */
 	if (strcmp(newsub->conninfo, MySubscription->conninfo) != 0 ||
 		strcmp(newsub->name, MySubscription->name) != 0 ||
@@ -3125,11 +3860,17 @@ maybe_reread_subscription(void)
 		newsub->owner != MySubscription->owner ||
 		!equal(newsub->publications, MySubscription->publications))
 	{
-		ereport(LOG,
-				(errmsg("logical replication apply worker for subscription \"%s\" will restart because of a parameter change",
-						MySubscription->name)));
+		if (am_parallel_apply_worker())
+			ereport(LOG,
+					(errmsg("logical replication parallel apply worker for subscription \"%s\" will stop because of a parameter change",
+							MySubscription->name)));
+		else
+			ereport(LOG,
+			/* translator: first %s is the name of logical replication worker */
+					(errmsg("%s for subscription \"%s\" will restart because of a parameter change",
+							get_worker_name(), MySubscription->name)));
 
-		proc_exit(0);
+		apply_worker_exit();
 	}
 
 	/* Check for other changes that should never happen too. */
@@ -3381,7 +4122,7 @@ changes_filename(char *path, Oid subid, TransactionId xid)
  * toplevel transaction. Each subscription has a separate set of files
  * for any toplevel transaction.
  */
-static void
+void
 stream_cleanup_files(Oid subid, TransactionId xid)
 {
 	char		path[MAXPGPATH];
@@ -3404,9 +4145,6 @@ stream_cleanup_files(Oid subid, TransactionId xid)
  * by stream_xid (global variable). If it's the first chunk of streamed
  * changes for this transaction, create the buffile, otherwise open the
  * previously created file.
- *
- * This can only be called at the beginning of a "streaming" block, i.e.
- * between stream_start/stream_stop messages from the upstream.
  */
 static void
 stream_open_file(Oid subid, TransactionId xid, bool first_segment)
@@ -3414,7 +4152,6 @@ stream_open_file(Oid subid, TransactionId xid, bool first_segment)
 	char		path[MAXPGPATH];
 	MemoryContext oldcxt;
 
-	Assert(in_streamed_transaction);
 	Assert(OidIsValid(subid));
 	Assert(TransactionIdIsValid(xid));
 	Assert(stream_fd == NULL);
@@ -3453,15 +4190,10 @@ stream_open_file(Oid subid, TransactionId xid, bool first_segment)
 /*
  * stream_close_file
  *	  Close the currently open file with streamed changes.
- *
- * This can only be called at the end of a streaming block, i.e. at stream_stop
- * message from the upstream.
  */
 static void
 stream_close_file(void)
 {
-	Assert(in_streamed_transaction);
-	Assert(TransactionIdIsValid(stream_xid));
 	Assert(stream_fd != NULL);
 
 	BufFileClose(stream_fd);
@@ -3483,8 +4215,6 @@ stream_write_change(char action, StringInfo s)
 {
 	int			len;
 
-	Assert(in_streamed_transaction);
-	Assert(TransactionIdIsValid(stream_xid));
 	Assert(stream_fd != NULL);
 
 	/* total on-disk size, including the action type character */
@@ -3502,6 +4232,26 @@ stream_write_change(char action, StringInfo s)
 	BufFileWrite(stream_fd, &s->data[s->cursor], len);
 }
 
+/*
+ * stream_open_and_write_change
+ *	  Serialize a message to a file for the given transaction.
+ *
+ * This function is similar to stream_write_change except that it will open the
+ * target file if not already before writing the message and close the file at
+ * the end.
+ */
+static void
+stream_open_and_write_change(TransactionId xid, char action, StringInfo s)
+{
+	Assert(!in_streamed_transaction);
+
+	if (!stream_fd)
+		stream_start_internal(xid, false);
+
+	stream_write_change(action, s);
+	stream_stop_internal(xid);
+}
+
 /*
  * Cleanup the memory for subxacts and reset the related variables.
  */
@@ -3613,37 +4363,16 @@ start_apply(XLogRecPtr origin_startpos)
 	PG_END_TRY();
 }
 
-/* Logical Replication Apply worker entry point */
+/*
+ * Common initialization for leader apply worker and parallel apply worker.
+ *
+ * Initialize the database connection, in-memory subscription and necessary
+ * config options.
+ */
 void
-ApplyWorkerMain(Datum main_arg)
+InitializeApplyWorker(void)
 {
-	int			worker_slot = DatumGetInt32(main_arg);
 	MemoryContext oldctx;
-	char		originname[NAMEDATALEN];
-	XLogRecPtr	origin_startpos = InvalidXLogRecPtr;
-	char	   *myslotname = NULL;
-	WalRcvStreamOptions options;
-	int			server_version;
-
-	/* Attach to slot */
-	logicalrep_worker_attach(worker_slot);
-
-	/* Setup signal handling */
-	pqsignal(SIGHUP, SignalHandlerForConfigReload);
-	pqsignal(SIGTERM, die);
-	BackgroundWorkerUnblockSignals();
-
-	/*
-	 * We don't currently need any ResourceOwner in a walreceiver process, but
-	 * if we did, we could call CreateAuxProcessResourceOwner here.
-	 */
-
-	/* Initialise stats to a sanish value */
-	MyLogicalRepWorker->last_send_time = MyLogicalRepWorker->last_recv_time =
-		MyLogicalRepWorker->reply_time = GetCurrentTimestamp();
-
-	/* Load the libpq-specific functions */
-	load_file("libpqwalreceiver", false);
 
 	/* Run as replica session replication role. */
 	SetConfigOption("session_replication_role", "replica",
@@ -3671,9 +4400,10 @@ ApplyWorkerMain(Datum main_arg)
 	if (!MySubscription)
 	{
 		ereport(LOG,
-				(errmsg("logical replication apply worker for subscription %u will not "
-						"start because the subscription was removed during startup",
-						MyLogicalRepWorker->subid)));
+		/* translator: %s is the name of logical replication worker */
+				(errmsg("%s for subscription %u will not start because the subscription was removed during startup",
+						get_worker_name(), MyLogicalRepWorker->subid)));
+
 		proc_exit(0);
 	}
 
@@ -3683,11 +4413,11 @@ ApplyWorkerMain(Datum main_arg)
 	if (!MySubscription->enabled)
 	{
 		ereport(LOG,
-				(errmsg("logical replication apply worker for subscription \"%s\" will not "
-						"start because the subscription was disabled during startup",
-						MySubscription->name)));
+		/* translator: first %s is the name of logical replication worker */
+				(errmsg("%s for subscription \"%s\" will not start because the subscription was disabled during startup",
+						get_worker_name(), MySubscription->name)));
 
-		proc_exit(0);
+		apply_worker_exit();
 	}
 
 	/* Setup synchronous commit according to the user's wishes */
@@ -3702,13 +4432,49 @@ ApplyWorkerMain(Datum main_arg)
 	if (am_tablesync_worker())
 		ereport(LOG,
 				(errmsg("logical replication table synchronization worker for subscription \"%s\", table \"%s\" has started",
-						MySubscription->name, get_rel_name(MyLogicalRepWorker->relid))));
+						MySubscription->name,
+						get_rel_name(MyLogicalRepWorker->relid))));
 	else
 		ereport(LOG,
-				(errmsg("logical replication apply worker for subscription \"%s\" has started",
-						MySubscription->name)));
+		/* translator: first %s is the name of logical replication worker */
+				(errmsg("%s for subscription \"%s\" has started",
+						get_worker_name(), MySubscription->name)));
 
 	CommitTransactionCommand();
+}
+
+/* Logical Replication Apply worker entry point */
+void
+ApplyWorkerMain(Datum main_arg)
+{
+	int			worker_slot = DatumGetInt32(main_arg);
+	char		originname[NAMEDATALEN];
+	XLogRecPtr	origin_startpos = InvalidXLogRecPtr;
+	char	   *myslotname = NULL;
+	WalRcvStreamOptions options;
+	int			server_version;
+
+	/* Attach to slot */
+	logicalrep_worker_attach(worker_slot);
+
+	/* Setup signal handling */
+	pqsignal(SIGHUP, SignalHandlerForConfigReload);
+	pqsignal(SIGTERM, die);
+	BackgroundWorkerUnblockSignals();
+
+	/*
+	 * We don't currently need any ResourceOwner in a walreceiver process, but
+	 * if we did, we could call CreateAuxProcessResourceOwner here.
+	 */
+
+	/* Initialise stats to a sanish value */
+	MyLogicalRepWorker->last_send_time = MyLogicalRepWorker->last_recv_time =
+		MyLogicalRepWorker->reply_time = GetCurrentTimestamp();
+
+	/* Load the libpq-specific functions */
+	load_file("libpqwalreceiver", false);
+
+	InitializeApplyWorker();
 
 	/* Connect to the origin and start the replication. */
 	elog(DEBUG1, "connecting to publisher using connection string \"%s\"",
@@ -3718,20 +4484,15 @@ ApplyWorkerMain(Datum main_arg)
 	{
 		start_table_sync(&origin_startpos, &myslotname);
 
-		/*
-		 * Allocate the origin name in long-lived context for error context
-		 * message.
-		 */
 		ReplicationOriginNameForLogicalRep(MySubscription->oid,
 										   MyLogicalRepWorker->relid,
 										   originname,
 										   sizeof(originname));
-		apply_error_callback_arg.origin_name = MemoryContextStrdup(ApplyContext,
-																   originname);
+		set_apply_error_context_origin(originname);
 	}
 	else
 	{
-		/* This is main apply worker */
+		/* This is the leader apply worker */
 		RepOriginId originid;
 		TimeLineID	startpointTLI;
 		char	   *err;
@@ -3755,7 +4516,7 @@ ApplyWorkerMain(Datum main_arg)
 		originid = replorigin_by_name(originname, true);
 		if (!OidIsValid(originid))
 			originid = replorigin_create(originname);
-		replorigin_session_setup(originid);
+		replorigin_session_setup(originid, 0);
 		replorigin_session_origin = originid;
 		origin_startpos = replorigin_session_get_progress(false);
 		CommitTransactionCommand();
@@ -3773,12 +4534,7 @@ ApplyWorkerMain(Datum main_arg)
 		 */
 		(void) walrcv_identify_system(LogRepWorkerWalRcvConn, &startpointTLI);
 
-		/*
-		 * Allocate the origin name in long-lived context for error context
-		 * message.
-		 */
-		apply_error_callback_arg.origin_name = MemoryContextStrdup(ApplyContext,
-																   originname);
+		set_apply_error_context_origin(originname);
 	}
 
 	/*
@@ -3796,13 +4552,36 @@ ApplyWorkerMain(Datum main_arg)
 
 	server_version = walrcv_server_version(LogRepWorkerWalRcvConn);
 	options.proto.logical.proto_version =
+		server_version >= 160000 ? LOGICALREP_PROTO_STREAM_PARALLEL_VERSION_NUM :
 		server_version >= 150000 ? LOGICALREP_PROTO_TWOPHASE_VERSION_NUM :
 		server_version >= 140000 ? LOGICALREP_PROTO_STREAM_VERSION_NUM :
 		LOGICALREP_PROTO_VERSION_NUM;
 
 	options.proto.logical.publication_names = MySubscription->publications;
 	options.proto.logical.binary = MySubscription->binary;
-	options.proto.logical.streaming = MySubscription->stream;
+
+	/*
+	 * Assign the appropriate option value for streaming option according to
+	 * the 'streaming' mode and the publisher's ability to support that mode.
+	 */
+	if (server_version >= 160000 &&
+		MySubscription->stream == LOGICALREP_STREAM_PARALLEL)
+	{
+		options.proto.logical.streaming_str = "parallel";
+		MyLogicalRepWorker->parallel_apply = true;
+	}
+	else if (server_version >= 140000 &&
+			 MySubscription->stream != LOGICALREP_STREAM_OFF)
+	{
+		options.proto.logical.streaming_str = "on";
+		MyLogicalRepWorker->parallel_apply = false;
+	}
+	else
+	{
+		options.proto.logical.streaming_str = NULL;
+		MyLogicalRepWorker->parallel_apply = false;
+	}
+
 	options.proto.logical.twophase = false;
 	options.proto.logical.origin = pstrdup(MySubscription->origin);
 
@@ -3899,6 +4678,15 @@ IsLogicalWorker(void)
 	return MyLogicalRepWorker != NULL;
 }
 
+/*
+ * Is current process a logical replication parallel apply worker?
+ */
+bool
+IsLogicalParallelApplyWorker(void)
+{
+	return IsLogicalWorker() && am_parallel_apply_worker();
+}
+
 /*
  * Start skipping changes of the transaction if the given LSN matches the
  * LSN specified by subscription's skiplsn.
@@ -3961,7 +4749,7 @@ clear_subscription_skip_lsn(XLogRecPtr finish_lsn)
 	XLogRecPtr	myskiplsn = MySubscription->skiplsn;
 	bool		started_tx = false;
 
-	if (likely(XLogRecPtrIsInvalid(myskiplsn)))
+	if (likely(XLogRecPtrIsInvalid(myskiplsn)) || am_parallel_apply_worker())
 		return;
 
 	if (!IsTransactionState())
@@ -4033,7 +4821,7 @@ clear_subscription_skip_lsn(XLogRecPtr finish_lsn)
 }
 
 /* Error callback to give more context info about the change being applied */
-static void
+void
 apply_error_callback(void *arg)
 {
 	ApplyErrorCallbackArg *errarg = &apply_error_callback_arg;
@@ -4061,23 +4849,47 @@ apply_error_callback(void *arg)
 					   errarg->remote_xid,
 					   LSN_FORMAT_ARGS(errarg->finish_lsn));
 	}
-	else if (errarg->remote_attnum < 0)
-		errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" in transaction %u, finished at %X/%X",
-				   errarg->origin_name,
-				   logicalrep_message_type(errarg->command),
-				   errarg->rel->remoterel.nspname,
-				   errarg->rel->remoterel.relname,
-				   errarg->remote_xid,
-				   LSN_FORMAT_ARGS(errarg->finish_lsn));
 	else
-		errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" column \"%s\" in transaction %u, finished at %X/%X",
-				   errarg->origin_name,
-				   logicalrep_message_type(errarg->command),
-				   errarg->rel->remoterel.nspname,
-				   errarg->rel->remoterel.relname,
-				   errarg->rel->remoterel.attnames[errarg->remote_attnum],
-				   errarg->remote_xid,
-				   LSN_FORMAT_ARGS(errarg->finish_lsn));
+	{
+		if (errarg->remote_attnum < 0)
+		{
+			if (XLogRecPtrIsInvalid(errarg->finish_lsn))
+				errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" in transaction %u",
+						   errarg->origin_name,
+						   logicalrep_message_type(errarg->command),
+						   errarg->rel->remoterel.nspname,
+						   errarg->rel->remoterel.relname,
+						   errarg->remote_xid);
+			else
+				errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" in transaction %u, finished at %X/%X",
+						   errarg->origin_name,
+						   logicalrep_message_type(errarg->command),
+						   errarg->rel->remoterel.nspname,
+						   errarg->rel->remoterel.relname,
+						   errarg->remote_xid,
+						   LSN_FORMAT_ARGS(errarg->finish_lsn));
+		}
+		else
+		{
+			if (XLogRecPtrIsInvalid(errarg->finish_lsn))
+				errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" column \"%s\" in transaction %u",
+						   errarg->origin_name,
+						   logicalrep_message_type(errarg->command),
+						   errarg->rel->remoterel.nspname,
+						   errarg->rel->remoterel.relname,
+						   errarg->rel->remoterel.attnames[errarg->remote_attnum],
+						   errarg->remote_xid);
+			else
+				errcontext("processing remote data for replication origin \"%s\" during message type \"%s\" for replication target relation \"%s.%s\" column \"%s\" in transaction %u, finished at %X/%X",
+						   errarg->origin_name,
+						   logicalrep_message_type(errarg->command),
+						   errarg->rel->remoterel.nspname,
+						   errarg->rel->remoterel.relname,
+						   errarg->rel->remoterel.attnames[errarg->remote_attnum],
+						   errarg->remote_xid,
+						   LSN_FORMAT_ARGS(errarg->finish_lsn));
+		}
+	}
 }
 
 /* Set transaction information of apply error callback */
@@ -4097,3 +4909,52 @@ reset_apply_error_context_info(void)
 	apply_error_callback_arg.remote_attnum = -1;
 	set_apply_error_context_xact(InvalidTransactionId, InvalidXLogRecPtr);
 }
+
+/*
+ * Allocate the origin name in long-lived context for error context message.
+ */
+void
+set_apply_error_context_origin(char *originname)
+{
+	apply_error_callback_arg.origin_name = MemoryContextStrdup(ApplyContext,
+															   originname);
+}
+
+/*
+ * Return the action to be taken for the given transaction. *winfo is
+ * assigned to the destination parallel worker info when the given
+ * transaction is being processed using a parallel apply worker.
+ */
+static TransApplyAction
+get_transaction_apply_action(TransactionId xid, ParallelApplyWorkerInfo **winfo)
+{
+	*winfo = NULL;
+
+	if (am_parallel_apply_worker())
+	{
+		return TRANS_PARALLEL_APPLY;
+	}
+	else if (in_remote_transaction)
+	{
+		return TRANS_LEADER_APPLY;
+	}
+
+	/*
+	 * Check if we are processing this transaction using a parallel apply
+	 * worker.
+	 */
+	*winfo = pa_find_worker(xid);
+
+	if (!*winfo)
+	{
+		return TRANS_LEADER_SERIALIZE;
+	}
+	else if ((*winfo)->serialize_changes)
+	{
+		return TRANS_LEADER_PARTIAL_SERIALIZE;
+	}
+	else
+	{
+		return TRANS_LEADER_SEND_TO_PARALLEL;
+	}
+}
diff --git a/src/backend/replication/pgoutput/pgoutput.c b/src/backend/replication/pgoutput/pgoutput.c
index ca46fba3af..40c44bb7e9 100644
--- a/src/backend/replication/pgoutput/pgoutput.c
+++ b/src/backend/replication/pgoutput/pgoutput.c
@@ -18,6 +18,7 @@
 #include "catalog/pg_publication_rel.h"
 #include "catalog/pg_subscription.h"
 #include "commands/defrem.h"
+#include "commands/subscriptioncmds.h"
 #include "executor/executor.h"
 #include "fmgr.h"
 #include "nodes/makefuncs.h"
@@ -290,7 +291,7 @@ parse_output_parameters(List *options, PGOutputData *data)
 	bool		origin_option_given = false;
 
 	data->binary = false;
-	data->streaming = false;
+	data->streaming = LOGICALREP_STREAM_OFF;
 	data->messages = false;
 	data->two_phase = false;
 
@@ -369,7 +370,7 @@ parse_output_parameters(List *options, PGOutputData *data)
 						 errmsg("conflicting or redundant options")));
 			streaming_given = true;
 
-			data->streaming = defGetBoolean(defel);
+			data->streaming = defGetStreamingMode(defel);
 		}
 		else if (strcmp(defel->defname, "two_phase") == 0)
 		{
@@ -461,13 +462,20 @@ pgoutput_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
 		 * we only allow it with sufficient version of the protocol, and when
 		 * the output plugin supports it.
 		 */
-		if (!data->streaming)
+		if (data->streaming == LOGICALREP_STREAM_OFF)
 			ctx->streaming = false;
-		else if (data->protocol_version < LOGICALREP_PROTO_STREAM_VERSION_NUM)
+		else if (data->streaming == LOGICALREP_STREAM_ON &&
+				 data->protocol_version < LOGICALREP_PROTO_STREAM_VERSION_NUM)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("requested proto_version=%d does not support streaming, need %d or higher",
 							data->protocol_version, LOGICALREP_PROTO_STREAM_VERSION_NUM)));
+		else if (data->streaming == LOGICALREP_STREAM_PARALLEL &&
+				 data->protocol_version < LOGICALREP_PROTO_STREAM_PARALLEL_VERSION_NUM)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("requested proto_version=%d does not support parallel streaming, need %d or higher",
+							data->protocol_version, LOGICALREP_PROTO_STREAM_PARALLEL_VERSION_NUM)));
 		else if (!ctx->streaming)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -1841,6 +1849,8 @@ pgoutput_stream_abort(struct LogicalDecodingContext *ctx,
 					  XLogRecPtr abort_lsn)
 {
 	ReorderBufferTXN *toptxn;
+	PGOutputData *data = (PGOutputData *) ctx->output_plugin_private;
+	bool		write_abort_info = (data->streaming == LOGICALREP_STREAM_PARALLEL);
 
 	/*
 	 * The abort should happen outside streaming block, even for streamed
@@ -1854,7 +1864,9 @@ pgoutput_stream_abort(struct LogicalDecodingContext *ctx,
 	Assert(rbtxn_is_streamed(toptxn));
 
 	OutputPluginPrepareWrite(ctx, true);
-	logicalrep_write_stream_abort(ctx->out, toptxn->xid, txn->xid);
+	logicalrep_write_stream_abort(ctx->out, toptxn->xid, txn->xid, abort_lsn,
+								  txn->xact_time.abort_time, write_abort_info);
+
 	OutputPluginWrite(ctx, true);
 
 	cleanup_rel_sync_cache(toptxn->xid, false);
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 7767657f27..7c009d525a 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -22,6 +22,7 @@
 #include "commands/async.h"
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "replication/logicalworker.h"
 #include "replication/walsender.h"
 #include "storage/condition_variable.h"
 #include "storage/ipc.h"
@@ -657,6 +658,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_LOG_MEMORY_CONTEXT))
 		HandleLogMemoryContextInterrupt();
 
+	if (CheckProcSignal(PROCSIG_PARALLEL_APPLY_MESSAGE))
+		HandleParallelApplyMessageInterrupt();
+
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_DATABASE))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_DATABASE);
 
diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c
index 1043068bac..2f171f5528 100644
--- a/src/backend/storage/lmgr/lmgr.c
+++ b/src/backend/storage/lmgr/lmgr.c
@@ -1117,6 +1117,45 @@ UnlockSharedObjectForSession(Oid classid, Oid objid, uint16 objsubid,
 	LockRelease(&tag, lockmode, true);
 }
 
+/*
+ *		LockApplyTransactionForSession
+ *
+ * Obtain a session-level lock on a transaction being applied on a logical
+ * replication subscriber. See LockRelationIdForSession for notes about
+ * session-level locks.
+ */
+void
+LockApplyTransactionForSession(Oid suboid, TransactionId xid, uint16 objid,
+							   LOCKMODE lockmode)
+{
+	LOCKTAG		tag;
+
+	SET_LOCKTAG_APPLY_TRANSACTION(tag,
+								  MyDatabaseId,
+								  suboid,
+								  xid,
+								  objid);
+
+	(void) LockAcquire(&tag, lockmode, true, false);
+}
+
+/*
+ *		UnlockApplyTransactionForSession
+ */
+void
+UnlockApplyTransactionForSession(Oid suboid, TransactionId xid, uint16 objid,
+								 LOCKMODE lockmode)
+{
+	LOCKTAG		tag;
+
+	SET_LOCKTAG_APPLY_TRANSACTION(tag,
+								  MyDatabaseId,
+								  suboid,
+								  xid,
+								  objid);
+
+	LockRelease(&tag, lockmode, true);
+}
 
 /*
  * Append a description of a lockable object to buf.
@@ -1202,6 +1241,13 @@ DescribeLockTag(StringInfo buf, const LOCKTAG *tag)
 							 tag->locktag_field3,
 							 tag->locktag_field4);
 			break;
+		case LOCKTAG_APPLY_TRANSACTION:
+			appendStringInfo(buf,
+							 _("remote transaction %u of subscription %u of database %u"),
+							 tag->locktag_field3,
+							 tag->locktag_field2,
+							 tag->locktag_field1);
+			break;
 		default:
 			appendStringInfo(buf,
 							 _("unrecognized locktag type %d"),
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 01d264b5ab..d5295c45fa 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3391,6 +3391,9 @@ ProcessInterrupts(void)
 
 	if (LogMemoryContextPending)
 		ProcessLogMemoryContextInterrupt();
+
+	if (ParallelApplyMessagePending)
+		HandleParallelApplyMessages();
 }
 
 /*
diff --git a/src/backend/utils/activity/wait_event.c b/src/backend/utils/activity/wait_event.c
index b2abd75ddb..1fab45e740 100644
--- a/src/backend/utils/activity/wait_event.c
+++ b/src/backend/utils/activity/wait_event.c
@@ -230,6 +230,9 @@ pgstat_get_wait_activity(WaitEventActivity w)
 		case WAIT_EVENT_LOGICAL_LAUNCHER_MAIN:
 			event_name = "LogicalLauncherMain";
 			break;
+		case WAIT_EVENT_LOGICAL_PARALLEL_APPLY_MAIN:
+			event_name = "LogicalParallelApplyMain";
+			break;
 		case WAIT_EVENT_RECOVERY_WAL_STREAM:
 			event_name = "RecoveryWalStream";
 			break;
@@ -388,6 +391,9 @@ pgstat_get_wait_ipc(WaitEventIPC w)
 		case WAIT_EVENT_HASH_GROW_BUCKETS_REINSERT:
 			event_name = "HashGrowBucketsReinsert";
 			break;
+		case WAIT_EVENT_LOGICAL_PARALLEL_APPLY_STATE_CHANGE:
+			event_name = "LogicalParallelApplyStateChange";
+			break;
 		case WAIT_EVENT_LOGICAL_SYNC_DATA:
 			event_name = "LogicalSyncData";
 			break;
diff --git a/src/backend/utils/adt/lockfuncs.c b/src/backend/utils/adt/lockfuncs.c
index f9b324efec..3bf04831f3 100644
--- a/src/backend/utils/adt/lockfuncs.c
+++ b/src/backend/utils/adt/lockfuncs.c
@@ -37,10 +37,11 @@ const char *const LockTagTypeNames[] = {
 	"spectoken",
 	"object",
 	"userlock",
-	"advisory"
+	"advisory",
+	"applytransaction"
 };
 
-StaticAssertDecl(lengthof(LockTagTypeNames) == (LOCKTAG_ADVISORY + 1),
+StaticAssertDecl(lengthof(LockTagTypeNames) == (LOCKTAG_LAST_TYPE + 1),
 				 "array length mismatch");
 
 /* This must match enum PredicateLockTargetType (predicate_internals.h) */
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 436afe1d21..bc56c32373 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2996,6 +2996,18 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"max_parallel_apply_workers_per_subscription",
+			PGC_SIGHUP,
+			REPLICATION_SUBSCRIBERS,
+			gettext_noop("Maximum number of parallel apply workers per subscription."),
+			NULL,
+		},
+		&max_parallel_apply_workers_per_subscription,
+		2, 0, MAX_PARALLEL_WORKER_LIMIT,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"log_rotation_age", PGC_SIGHUP, LOGGING_WHERE,
 			gettext_noop("Sets the amount of time to wait before forcing "
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 5afdeb04de..c2ada92054 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -359,6 +359,7 @@
 #max_logical_replication_workers = 4	# taken from max_worker_processes
 					# (change requires restart)
 #max_sync_workers_per_subscription = 2	# taken from max_logical_replication_workers
+#max_parallel_apply_workers_per_subscription = 2	# taken from max_logical_replication_workers
 
 
 #------------------------------------------------------------------------------
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 44d957c038..f454b31c58 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -4533,7 +4533,7 @@ getSubscriptions(Archive *fout)
 	if (fout->remoteVersion >= 140000)
 		appendPQExpBufferStr(query, " s.substream,\n");
 	else
-		appendPQExpBufferStr(query, " false AS substream,\n");
+		appendPQExpBufferStr(query, " 'f' AS substream,\n");
 
 	if (fout->remoteVersion >= 150000)
 		appendPQExpBufferStr(query,
@@ -4670,8 +4670,10 @@ dumpSubscription(Archive *fout, const SubscriptionInfo *subinfo)
 	if (strcmp(subinfo->subbinary, "t") == 0)
 		appendPQExpBufferStr(query, ", binary = true");
 
-	if (strcmp(subinfo->substream, "f") != 0)
+	if (strcmp(subinfo->substream, "t") == 0)
 		appendPQExpBufferStr(query, ", streaming = on");
+	else if (strcmp(subinfo->substream, "p") == 0)
+		appendPQExpBufferStr(query, ", streaming = parallel");
 
 	if (strcmp(subinfo->subtwophasestate, two_phase_disabled) != 0)
 		appendPQExpBufferStr(query, ", two_phase = on");
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index df166365e8..265b28d90c 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -6502,11 +6502,24 @@ describeSubscriptions(const char *pattern, bool verbose)
 	{
 		/* Binary mode and streaming are only supported in v14 and higher */
 		if (pset.sversion >= 140000)
+		{
 			appendPQExpBuffer(&buf,
-							  ", subbinary AS \"%s\"\n"
-							  ", substream AS \"%s\"\n",
-							  gettext_noop("Binary"),
-							  gettext_noop("Streaming"));
+							  ", subbinary AS \"%s\"\n",
+							  gettext_noop("Binary"));
+
+			if (pset.sversion >= 160000)
+				appendPQExpBuffer(&buf,
+								  ", (CASE substream\n"
+								  "    WHEN 'f' THEN 'off'\n"
+								  "    WHEN 't' THEN 'on'\n"
+								  "    WHEN 'p' THEN 'parallel'\n"
+								  "   END) AS \"%s\"\n",
+								  gettext_noop("Streaming"));
+			else
+				appendPQExpBuffer(&buf,
+								  ", substream AS \"%s\"\n",
+								  gettext_noop("Streaming"));
+		}
 
 		/* Two_phase and disable_on_error are only supported in v15 and higher */
 		if (pset.sversion >= 150000)
diff --git a/src/include/catalog/pg_subscription.h b/src/include/catalog/pg_subscription.h
index 7b98714f30..5b9e5a399a 100644
--- a/src/include/catalog/pg_subscription.h
+++ b/src/include/catalog/pg_subscription.h
@@ -80,7 +80,8 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 	bool		subbinary;		/* True if the subscription wants the
 								 * publisher to send data in binary */
 
-	bool		substream;		/* Stream in-progress transactions. */
+	char		substream;		/* Stream in-progress transactions. See
+								 * SUBSTREAM_xxx constants. */
 
 	char		subtwophasestate;	/* Stream two-phase transactions */
 
@@ -124,7 +125,8 @@ typedef struct Subscription
 	bool		enabled;		/* Indicates if the subscription is enabled */
 	bool		binary;			/* Indicates if the subscription wants data in
 								 * binary format */
-	bool		stream;			/* Allow streaming in-progress transactions. */
+	char		stream;			/* Allow streaming in-progress transactions.
+								 * See SUBSTREAM_xxx constants. */
 	char		twophasestate;	/* Allow streaming two-phase transactions */
 	bool		disableonerr;	/* Indicates if the subscription should be
 								 * automatically disabled if a worker error
@@ -137,6 +139,21 @@ typedef struct Subscription
 								 * specified origin */
 } Subscription;
 
+/* Disallow streaming in-progress transactions. */
+#define LOGICALREP_STREAM_OFF 'f'
+
+/*
+ * Streaming in-progress transactions are written to a temporary file and
+ * applied only after the transaction is committed on upstream.
+ */
+#define LOGICALREP_STREAM_ON 't'
+
+/*
+ * Streaming in-progress transactions are applied immediately via a parallel
+ * apply worker.
+ */
+#define LOGICALREP_STREAM_PARALLEL 'p'
+
 extern Subscription *GetSubscription(Oid subid, bool missing_ok);
 extern void FreeSubscription(Subscription *sub);
 extern void DisableSubscription(Oid subid);
diff --git a/src/include/commands/subscriptioncmds.h b/src/include/commands/subscriptioncmds.h
index 2cbe7d7b65..779474f565 100644
--- a/src/include/commands/subscriptioncmds.h
+++ b/src/include/commands/subscriptioncmds.h
@@ -26,4 +26,6 @@ extern void DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel);
 extern ObjectAddress AlterSubscriptionOwner(const char *name, Oid newOwnerId);
 extern void AlterSubscriptionOwner_oid(Oid subid, Oid newOwnerId);
 
+extern char defGetStreamingMode(DefElem *def);
+
 #endif							/* SUBSCRIPTIONCMDS_H */
diff --git a/src/include/replication/logicallauncher.h b/src/include/replication/logicallauncher.h
index f1e2821e25..d513ef533a 100644
--- a/src/include/replication/logicallauncher.h
+++ b/src/include/replication/logicallauncher.h
@@ -14,6 +14,7 @@
 
 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 void ApplyLauncherRegister(void);
 extern void ApplyLauncherMain(Datum main_arg);
diff --git a/src/include/replication/logicalproto.h b/src/include/replication/logicalproto.h
index 1eb7dda529..4fa2bd37de 100644
--- a/src/include/replication/logicalproto.h
+++ b/src/include/replication/logicalproto.h
@@ -32,12 +32,17 @@
  *
  * LOGICALREP_PROTO_TWOPHASE_VERSION_NUM is the minimum protocol version with
  * support for two-phase commit decoding (at prepare time). Introduced in PG15.
+ *
+ * LOGICALREP_PROTO_STREAM_PARALLEL_VERSION_NUM is the minimum protocol version
+ * where we support applying large streaming transactions in parallel.
+ * Introduced in PG16.
  */
 #define LOGICALREP_PROTO_MIN_VERSION_NUM 1
 #define LOGICALREP_PROTO_VERSION_NUM 1
 #define LOGICALREP_PROTO_STREAM_VERSION_NUM 2
 #define LOGICALREP_PROTO_TWOPHASE_VERSION_NUM 3
-#define LOGICALREP_PROTO_MAX_VERSION_NUM LOGICALREP_PROTO_TWOPHASE_VERSION_NUM
+#define LOGICALREP_PROTO_STREAM_PARALLEL_VERSION_NUM 4
+#define LOGICALREP_PROTO_MAX_VERSION_NUM LOGICALREP_PROTO_STREAM_PARALLEL_VERSION_NUM
 
 /*
  * Logical message types
@@ -175,6 +180,17 @@ typedef struct LogicalRepRollbackPreparedTxnData
 	char		gid[GIDSIZE];
 } LogicalRepRollbackPreparedTxnData;
 
+/*
+ * Transaction protocol information for stream abort.
+ */
+typedef struct LogicalRepStreamAbortData
+{
+	TransactionId xid;
+	TransactionId subxid;
+	XLogRecPtr	abort_lsn;
+	TimestampTz abort_time;
+} LogicalRepStreamAbortData;
+
 extern void logicalrep_write_begin(StringInfo out, ReorderBufferTXN *txn);
 extern void logicalrep_read_begin(StringInfo in,
 								  LogicalRepBeginData *begin_data);
@@ -246,9 +262,13 @@ extern void logicalrep_write_stream_commit(StringInfo out, ReorderBufferTXN *txn
 extern TransactionId logicalrep_read_stream_commit(StringInfo in,
 												   LogicalRepCommitData *commit_data);
 extern void logicalrep_write_stream_abort(StringInfo out, TransactionId xid,
-										  TransactionId subxid);
-extern void logicalrep_read_stream_abort(StringInfo in, TransactionId *xid,
-										 TransactionId *subxid);
+										  TransactionId subxid,
+										  XLogRecPtr abort_lsn,
+										  TimestampTz abort_time,
+										  bool write_abort_info);
+extern void logicalrep_read_stream_abort(StringInfo in,
+										 LogicalRepStreamAbortData *abort_data,
+										 bool read_abort_info);
 extern char *logicalrep_message_type(LogicalRepMsgType action);
 
 #endif							/* LOGICAL_PROTO_H */
diff --git a/src/include/replication/logicalworker.h b/src/include/replication/logicalworker.h
index cd1b6e8afc..dc68cd89c8 100644
--- a/src/include/replication/logicalworker.h
+++ b/src/include/replication/logicalworker.h
@@ -12,8 +12,16 @@
 #ifndef LOGICALWORKER_H
 #define LOGICALWORKER_H
 
+#include <signal.h>
+
+extern PGDLLIMPORT volatile sig_atomic_t ParallelApplyMessagePending;
+
 extern void ApplyWorkerMain(Datum main_arg);
+extern void ParallelApplyWorkerMain(Datum main_arg);
 
 extern bool IsLogicalWorker(void);
+extern bool IsLogicalParallelApplyWorker(void);
+extern void HandleParallelApplyMessageInterrupt(void);
+extern void HandleParallelApplyMessages(void);
 
 #endif							/* LOGICALWORKER_H */
diff --git a/src/include/replication/origin.h b/src/include/replication/origin.h
index 2a50d10b52..c7b1adfff5 100644
--- a/src/include/replication/origin.h
+++ b/src/include/replication/origin.h
@@ -53,7 +53,7 @@ extern XLogRecPtr replorigin_get_progress(RepOriginId node, bool flush);
 
 extern void replorigin_session_advance(XLogRecPtr remote_commit,
 									   XLogRecPtr local_commit);
-extern void replorigin_session_setup(RepOriginId node);
+extern void replorigin_session_setup(RepOriginId node, int acquired_by);
 extern void replorigin_session_reset(void);
 extern XLogRecPtr replorigin_session_get_progress(bool flush);
 
diff --git a/src/include/replication/pgoutput.h b/src/include/replication/pgoutput.h
index 02027550e2..3c30da8205 100644
--- a/src/include/replication/pgoutput.h
+++ b/src/include/replication/pgoutput.h
@@ -26,7 +26,7 @@ typedef struct PGOutputData
 	List	   *publication_names;
 	List	   *publications;
 	bool		binary;
-	bool		streaming;
+	char		streaming;
 	bool		messages;
 	bool		two_phase;
 	char	   *origin;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index c700b55b1c..f0eb6c4f74 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -308,6 +308,7 @@ typedef struct ReorderBufferTXN
 	{
 		TimestampTz commit_time;
 		TimestampTz prepare_time;
+		TimestampTz abort_time;
 	}			xact_time;
 
 	/*
@@ -670,7 +671,8 @@ extern void ReorderBufferAssignChild(ReorderBuffer *rb, TransactionId xid,
 extern void ReorderBufferCommitChild(ReorderBuffer *rb, TransactionId xid,
 									 TransactionId subxid, XLogRecPtr commit_lsn,
 									 XLogRecPtr end_lsn);
-extern void ReorderBufferAbort(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn);
+extern void ReorderBufferAbort(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+							   TimestampTz abort_time);
 extern void ReorderBufferAbortOld(ReorderBuffer *rb, TransactionId oldestRunningXid);
 extern void ReorderBufferForget(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn);
 extern void ReorderBufferInvalidate(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 9339f29303..0c8bbddabe 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -182,7 +182,7 @@ typedef struct
 			uint32		proto_version;	/* Logical protocol version */
 			List	   *publication_names;	/* String list of publications */
 			bool		binary; /* Ask publisher to use binary */
-			bool		streaming;	/* Streaming of large transactions */
+			char	   *streaming_str;	/* Streaming of large transactions */
 			bool		twophase;	/* Streaming of two-phase transactions at
 									 * prepare time */
 			char	   *origin; /* Only publish data originating from the
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 2b7114ff6d..0ba20a1ea7 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -17,8 +17,13 @@
 #include "access/xlogdefs.h"
 #include "catalog/pg_subscription.h"
 #include "datatype/timestamp.h"
+#include "miscadmin.h"
+#include "replication/logicalrelation.h"
+#include "storage/buffile.h"
 #include "storage/fileset.h"
 #include "storage/lock.h"
+#include "storage/shm_mq.h"
+#include "storage/shm_toc.h"
 #include "storage/spin.h"
 
 
@@ -53,13 +58,24 @@ typedef struct LogicalRepWorker
 
 	/*
 	 * Used to create the changes and subxact files for the streaming
-	 * transactions.  Upon the arrival of the first streaming transaction, the
-	 * fileset will be initialized, and it will be deleted when the worker
-	 * exits.  Under this, separate buffiles would be created for each
-	 * transaction which will be deleted after the transaction is finished.
+	 * transactions.  Upon the arrival of the first streaming transaction or
+	 * when the first-time leader apply worker times out while sending changes
+	 * to the parallel apply worker, the fileset will be initialized, and it
+	 * will be deleted when the worker exits.  Under this, separate buffiles
+	 * would be created for each transaction which will be deleted after the
+	 * transaction is finished.
 	 */
 	FileSet    *stream_fileset;
 
+	/*
+	 * PID of leader apply worker if this slot is used for a parallel apply
+	 * worker, InvalidPid otherwise.
+	 */
+	pid_t		apply_leader_pid;
+
+	/* Indicates whether apply can be performed in parallel. */
+	bool		parallel_apply;
+
 	/* Stats. */
 	XLogRecPtr	last_lsn;
 	TimestampTz last_send_time;
@@ -68,9 +84,133 @@ typedef struct LogicalRepWorker
 	TimestampTz reply_time;
 } LogicalRepWorker;
 
+/*
+ * State of the transaction in parallel apply worker.
+ *
+ * The enum values must have the same order as the transaction state
+ * transitions.
+ */
+typedef enum ParallelTransState
+{
+	PARALLEL_TRANS_UNKNOWN,
+	PARALLEL_TRANS_STARTED,
+	PARALLEL_TRANS_FINISHED
+} ParallelTransState;
+
+/*
+ * State of fileset used to communicate changes from leader to parallel
+ * apply worker.
+ *
+ * FS_EMPTY indicates an initial state where the leader doesn't need to use
+ * the file to communicate with the parallel apply worker.
+ *
+ * FS_SERIALIZE_IN_PROGRESS indicates that the leader is serializing changes
+ * to the file.
+ *
+ * FS_SERIALIZE_DONE indicates that the leader has serialized all changes to
+ * the file.
+ *
+ * FS_READY indicates that it is now ok for a parallel apply worker to
+ * read the file.
+ */
+typedef enum PartialFileSetState
+{
+	FS_EMPTY,
+	FS_SERIALIZE_IN_PROGRESS,
+	FS_SERIALIZE_DONE,
+	FS_READY
+} PartialFileSetState;
+
+/*
+ * Struct for sharing information between leader apply worker and parallel
+ * apply workers.
+ */
+typedef struct ParallelApplyWorkerShared
+{
+	slock_t		mutex;
+
+	TransactionId xid;
+
+	/*
+	 * State used to ensure commit ordering.
+	 *
+	 * The parallel apply worker will set it to PARALLEL_TRANS_FINISHED after
+	 * handling the transaction finish commands while the apply leader will
+	 * wait for it to become PARALLEL_TRANS_FINISHED before proceeding in
+	 * transaction finish commands (e.g. STREAM_COMMIT/STREAM_PREPARE).
+	 */
+	ParallelTransState xact_state;
+
+	/* Information from the corresponding LogicalRepWorker slot. */
+	uint16		logicalrep_worker_generation;
+	int			logicalrep_worker_slot_no;
+
+	/*
+	 * Indicates whether there are pending streaming blocks in the queue. The
+	 * parallel apply worker will check it before starting to wait.
+	 */
+	pg_atomic_uint32	pending_stream_count;
+
+	/*
+	 * XactLastCommitEnd from the parallel apply worker. This is required by
+	 * the leader worker so it can update the lsn_mappings.
+	 */
+	XLogRecPtr	last_commit_end;
+
+	/*
+	 * After entering PARTIAL_SERIALIZE mode, the leader apply worker will
+	 * serialize changes to the file, and share the fileset with the parallel
+	 * apply worker when processing the transaction finish command. Then the
+	 * parallel apply worker will apply all the spooled messages.
+	 *
+	 * FileSet is used here instead of SharedFileSet because we need it to
+	 * survive after releasing the shared memory so that the leader apply
+	 * worker can re-use the same fileset for the next streaming transaction.
+	 */
+	PartialFileSetState fileset_state;
+	FileSet		fileset;
+} ParallelApplyWorkerShared;
+
+/*
+ * Information which is used to manage the parallel apply worker.
+ */
+typedef struct ParallelApplyWorkerInfo
+{
+	shm_mq_handle *mq_handle;
+
+	/*
+	 * The queue used to transfer error messages from the parallel apply
+	 * worker to the leader apply worker.
+	 */
+	shm_mq_handle *error_mq_handle;
+
+	dsm_segment *dsm_seg;
+
+	/*
+	 * Indicates whether the leader apply worker needs to serialize the
+	 * remaining changes to a file due to timeout when attempting to send data
+	 * to the parallel apply worker via shared memory.
+	 */
+	bool		serialize_changes;
+
+	/*
+	 * True if the worker is being used to process a parallel apply
+	 * transaction. False indicates this worker is available for re-use.
+	 */
+	bool		in_use;
+
+	ParallelApplyWorkerShared *shared;
+} ParallelApplyWorkerInfo;
+
 /* Main memory context for apply worker. Permanent during worker lifetime. */
 extern PGDLLIMPORT MemoryContext ApplyContext;
 
+extern PGDLLIMPORT MemoryContext ApplyMessageContext;
+
+extern PGDLLIMPORT ErrorContextCallback *apply_error_context_stack;
+
+extern PGDLLIMPORT ParallelApplyWorkerShared *MyParallelShared;
+
 /* libpqreceiver connection */
 extern PGDLLIMPORT struct WalReceiverConn *LogRepWorkerWalRcvConn;
 
@@ -84,9 +224,11 @@ extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
 extern List *logicalrep_workers_find(Oid subid, bool only_running);
-extern void logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname,
-									 Oid userid, Oid relid);
+extern bool logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname,
+									 Oid userid, Oid relid,
+									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_pa_worker_stop(int slot_no, uint16 generation);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
 
@@ -103,10 +245,79 @@ extern void process_syncing_tables(XLogRecPtr current_lsn);
 extern void invalidate_syncing_table_states(Datum arg, int cacheid,
 											uint32 hashvalue);
 
+extern void stream_start_internal(TransactionId xid, bool first_segment);
+extern void stream_stop_internal(TransactionId xid);
+
+/* Common streaming function to apply all the spooled messages */
+extern void apply_spooled_messages(FileSet *stream_fileset, TransactionId xid,
+								   XLogRecPtr lsn);
+
+extern void apply_dispatch(StringInfo s);
+
+extern void maybe_reread_subscription(void);
+
+extern void stream_cleanup_files(Oid subid, TransactionId xid);
+
+extern void InitializeApplyWorker(void);
+
+extern void store_flush_position(XLogRecPtr remote_lsn, XLogRecPtr local_lsn);
+
+/* Function for apply error callback */
+extern void apply_error_callback(void *arg);
+extern void set_apply_error_context_origin(char *originname);
+
+/* Parallel apply worker setup and interactions */
+extern void pa_allocate_worker(TransactionId xid);
+extern ParallelApplyWorkerInfo *pa_find_worker(TransactionId xid);
+extern bool pa_free_worker(ParallelApplyWorkerInfo *winfo);
+extern void pa_detach_all_error_mq(void);
+
+extern bool pa_send_data(ParallelApplyWorkerInfo *winfo, Size nbytes,
+						 const void *data);
+extern void pa_switch_to_partial_serialize(ParallelApplyWorkerInfo *winfo,
+										   bool stream_locked);
+
+extern void pa_set_xact_state(ParallelApplyWorkerShared *wshared,
+							  ParallelTransState in_xact);
+extern void pa_set_stream_apply_worker(ParallelApplyWorkerInfo *winfo);
+
+extern void pa_start_subtrans(TransactionId current_xid,
+							  TransactionId top_xid);
+extern void pa_reset_subtrans(void);
+extern void pa_stream_abort(LogicalRepStreamAbortData *abort_data);
+extern void pa_set_fileset_state(ParallelApplyWorkerShared *wshared,
+								 PartialFileSetState fileset_state);
+
+extern void pa_lock_stream(TransactionId xid, LOCKMODE lockmode);
+extern void pa_unlock_stream(TransactionId xid, LOCKMODE lockmode);
+
+extern void pa_lock_transaction(TransactionId xid, LOCKMODE lockmode);
+extern void pa_unlock_transaction(TransactionId xid, LOCKMODE lockmode);
+
+extern void pa_decr_and_wait_stream_block(void);
+
+extern void pa_xact_finish(ParallelApplyWorkerInfo *winfo,
+						   XLogRecPtr remote_lsn);
+
+#define isParallelApplyWorker(worker) ((worker)->apply_leader_pid != InvalidPid)
+
 static inline bool
 am_tablesync_worker(void)
 {
 	return OidIsValid(MyLogicalRepWorker->relid);
 }
 
+static inline bool
+am_leader_apply_worker(void)
+{
+	return (!OidIsValid(MyLogicalRepWorker->relid) &&
+			!isParallelApplyWorker(MyLogicalRepWorker));
+}
+
+static inline bool
+am_parallel_apply_worker(void)
+{
+	return isParallelApplyWorker(MyLogicalRepWorker);
+}
+
 #endif							/* WORKER_INTERNAL_H */
diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h
index be1d2c99a9..5a3bd03ba5 100644
--- a/src/include/storage/lmgr.h
+++ b/src/include/storage/lmgr.h
@@ -107,6 +107,11 @@ extern void LockSharedObjectForSession(Oid classid, Oid objid, uint16 objsubid,
 extern void UnlockSharedObjectForSession(Oid classid, Oid objid, uint16 objsubid,
 										 LOCKMODE lockmode);
 
+extern void LockApplyTransactionForSession(Oid suboid, TransactionId xid, uint16 objid,
+										   LOCKMODE lockmode);
+extern void UnlockApplyTransactionForSession(Oid suboid, TransactionId xid, uint16 objid,
+											 LOCKMODE lockmode);
+
 /* Describe a locktag for error messages */
 extern void DescribeLockTag(StringInfo buf, const LOCKTAG *tag);
 
diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h
index e4e1495b24..7766123a7b 100644
--- a/src/include/storage/lock.h
+++ b/src/include/storage/lock.h
@@ -149,10 +149,12 @@ typedef enum LockTagType
 	LOCKTAG_SPECULATIVE_TOKEN,	/* speculative insertion Xid and token */
 	LOCKTAG_OBJECT,				/* non-relation database object */
 	LOCKTAG_USERLOCK,			/* reserved for old contrib/userlock code */
-	LOCKTAG_ADVISORY			/* advisory user locks */
+	LOCKTAG_ADVISORY,			/* advisory user locks */
+	LOCKTAG_APPLY_TRANSACTION	/* transaction being applied on a logical
+								 * replication subscriber */
 } LockTagType;
 
-#define LOCKTAG_LAST_TYPE	LOCKTAG_ADVISORY
+#define LOCKTAG_LAST_TYPE	LOCKTAG_APPLY_TRANSACTION
 
 extern PGDLLIMPORT const char *const LockTagTypeNames[];
 
@@ -278,6 +280,17 @@ typedef struct LOCKTAG
 	 (locktag).locktag_type = LOCKTAG_ADVISORY, \
 	 (locktag).locktag_lockmethodid = USER_LOCKMETHOD)
 
+/*
+ * ID info for a remote transaction on a logical replication subscriber is: DB
+ * OID + SUBSCRIPTION OID + TRANSACTION ID + OBJID
+ */
+#define SET_LOCKTAG_APPLY_TRANSACTION(locktag,dboid,suboid,xid,objid) \
+	((locktag).locktag_field1 = (dboid), \
+	 (locktag).locktag_field2 = (suboid), \
+	 (locktag).locktag_field3 = (xid), \
+	 (locktag).locktag_field4 = (objid), \
+	 (locktag).locktag_type = LOCKTAG_APPLY_TRANSACTION, \
+	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)
 
 /*
  * Per-locked-object lock information:
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index ee636900f3..93a51f4254 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -35,6 +35,7 @@ typedef enum
 	PROCSIG_WALSND_INIT_STOPPING,	/* ask walsenders to prepare for shutdown  */
 	PROCSIG_BARRIER,			/* global barrier interrupt  */
 	PROCSIG_LOG_MEMORY_CONTEXT, /* ask backend to log the memory contexts */
+	PROCSIG_PARALLEL_APPLY_MESSAGE, /* Message from parallel apply workers */
 
 	/* Recovery conflict reasons */
 	PROCSIG_RECOVERY_CONFLICT_DATABASE,
diff --git a/src/include/utils/wait_event.h b/src/include/utils/wait_event.h
index 0b2100be4a..763fbeadfb 100644
--- a/src/include/utils/wait_event.h
+++ b/src/include/utils/wait_event.h
@@ -42,6 +42,7 @@ typedef enum
 	WAIT_EVENT_CHECKPOINTER_MAIN,
 	WAIT_EVENT_LOGICAL_APPLY_MAIN,
 	WAIT_EVENT_LOGICAL_LAUNCHER_MAIN,
+	WAIT_EVENT_LOGICAL_PARALLEL_APPLY_MAIN,
 	WAIT_EVENT_RECOVERY_WAL_STREAM,
 	WAIT_EVENT_SYSLOGGER_MAIN,
 	WAIT_EVENT_WAL_RECEIVER_MAIN,
@@ -105,6 +106,7 @@ typedef enum
 	WAIT_EVENT_HASH_GROW_BUCKETS_ALLOCATE,
 	WAIT_EVENT_HASH_GROW_BUCKETS_ELECT,
 	WAIT_EVENT_HASH_GROW_BUCKETS_REINSERT,
+	WAIT_EVENT_LOGICAL_PARALLEL_APPLY_STATE_CHANGE,
 	WAIT_EVENT_LOGICAL_SYNC_DATA,
 	WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE,
 	WAIT_EVENT_MQ_INTERNAL,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index c13d218dcf..1ed6f4c39c 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -117,7 +117,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
                                                                                          List of subscriptions
        Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 ------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | f         | d                | f                | none   | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
@@ -125,7 +125,7 @@ ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
                                                                                          List of subscriptions
        Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 ------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub3;
@@ -138,7 +138,7 @@ ERROR:  invalid connection string syntax: missing "=" after "foobar" in connecti
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET PUBLICATION testpub2, testpub3 WITH (refresh = false);
@@ -158,7 +158,7 @@ ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/12345');
                                                                                              List of subscriptions
       Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |           Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist2 | 0/12345
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist2 | 0/12345
 (1 row)
 
 -- ok - with lsn = NONE
@@ -170,7 +170,7 @@ ERROR:  invalid WAL location (LSN): 0/0
                                                                                              List of subscriptions
       Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |           Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist2 | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 BEGIN;
@@ -205,7 +205,7 @@ HINT:  Available values: local, remote_write, remote_apply, on, off.
                                                                                                List of subscriptions
         Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |           Conninfo           | Skip LSN 
 ---------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+--------------------+------------------------------+----------
- regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | f         | d                | f                | any    | local              | dbname=regress_doesnotexist2 | 0/0
+ regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | local              | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 -- rename back to keep the rest simple
@@ -242,7 +242,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | t      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (binary = false);
@@ -251,13 +251,13 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
--- fail - streaming must be boolean
+-- fail - streaming must be boolean or 'parallel'
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, streaming = foo);
-ERROR:  streaming requires a Boolean value
+ERROR:  streaming requires a Boolean value or "parallel"
 -- now it works
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, streaming = true);
 WARNING:  subscription was created, but is not connected
@@ -266,7 +266,15 @@ HINT:  To initiate replication, you must manually create the replication slot, e
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | t         | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+(1 row)
+
+ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
+\dRs+
+                                                                                         List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
@@ -275,7 +283,7 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication already exists
@@ -293,7 +301,7 @@ ERROR:  publication "testpub1" is already in subscription "regress_testsub"
                                                                                                  List of subscriptions
       Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication used more then once
@@ -311,7 +319,7 @@ ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (ref
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -350,7 +358,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | f         | p                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 --fail - alter of two_phase option not supported.
@@ -362,7 +370,7 @@ ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | t         | p                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -375,7 +383,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | t         | p                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -391,7 +399,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | f         | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
@@ -399,7 +407,7 @@ ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
                                                                                          List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Synchronous commit |          Conninfo           | Skip LSN 
 -----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | f         | d                | t                | any    | off                | dbname=regress_doesnotexist | 0/0
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index eaeade8cce..7991abfe8f 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -167,7 +167,7 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 
 DROP SUBSCRIPTION regress_testsub;
 
--- fail - streaming must be boolean
+-- fail - streaming must be boolean or 'parallel'
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, streaming = foo);
 
 -- now it works
@@ -175,6 +175,10 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 
 \dRs+
 
+ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
+
+\dRs+
+
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 60c71d05fe..ab3f1b2082 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1472,6 +1472,7 @@ LogicalRepRelId
 LogicalRepRelMapEntry
 LogicalRepRelation
 LogicalRepRollbackPreparedTxnData
+LogicalRepStreamAbortData
 LogicalRepTupleData
 LogicalRepTyp
 LogicalRepWorker
@@ -1875,6 +1876,9 @@ PageXLogRecPtr
 PagetableEntry
 Pairs
 ParallelAppendState
+ParallelApplyWorkerEntry
+ParallelApplyWorkerInfo
+ParallelApplyWorkerShared
 ParallelBitmapHeapState
 ParallelBlockTableScanDesc
 ParallelBlockTableScanWorker
@@ -1894,6 +1898,7 @@ ParallelSlotResultHandler
 ParallelState
 ParallelTableScanDesc
 ParallelTableScanDescData
+ParallelTransState
 ParallelVacuumState
 ParallelWorkerContext
 ParallelWorkerInfo
@@ -1923,6 +1928,7 @@ ParserState
 PartClauseInfo
 PartClauseMatchStatus
 PartClauseTarget
+PartialFileSetState
 PartitionBoundInfo
 PartitionBoundInfoData
 PartitionBoundSpec
@@ -2773,6 +2779,7 @@ TocEntry
 TokenAuxData
 TokenizedAuthLine
 TrackItem
+TransApplyAction
 TransInvalidationInfo
 TransState
 TransactionId
-- 
2.31.1

