Refactor to split Apply and Tablesync Workers code.

Both apply and tablesync workers were using ApplyWorkerMain() as entry
point. As the name implies, ApplyWorkerMain() should be considered as
the main function for apply workers. Tablesync worker's path was hidden
and does not have enough in common to share the same main function with
apply worker.

Also, most of the code shared by both worker types is already combined
in LogicalRepApplyLoop(). There is no need to combine the rest in
ApplyWorkerMain() anymore.

This patch introduces TablesyncWorkerMain() as a new entry point for
tablesync workers. This aims to increase code readability and would help
with future improvements like the reuse of tablesync workers in the
initial synchronization.

Author: Melih Mutlu based on suggestions by Melanie Plageman
Reviewed-by: Peter Smith, Kuroda Hayato, Amit Kapila
Discussion: http://postgr.es/m/CAGPVpCTq=rUDd4JUdaRc1XUWf4BrH2gdSNf3rtOMUGj9rPpfzQ@mail.gmail.com

1 files changed, 173 insertions, 207 deletions

diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 832b1cf7642..a9f5fa7dfc0 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -396,8 +396,6 @@ static void stream_close_file(void);
 
 static void send_feedback(XLogRecPtr recvpos, bool force, bool requestReply);
 
-static void DisableSubscriptionAndExit(void);
-
 static void apply_handle_commit_internal(LogicalRepCommitData *commit_data);
 static void apply_handle_insert_internal(ApplyExecutionData *edata,
 										 ResultRelInfo *relinfo,
@@ -4328,6 +4326,57 @@ stream_open_and_write_change(TransactionId xid, char action, StringInfo s)
 }
 
 /*
+ * Sets streaming options including replication slot name and origin start
+ * position. Workers need these options for logical replication.
+ */
+void
+set_stream_options(WalRcvStreamOptions *options,
+				   char *slotname,
+				   XLogRecPtr *origin_startpos)
+{
+	int			server_version;
+
+	options->logical = true;
+	options->startpoint = *origin_startpos;
+	options->slotname = slotname;
+
+	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;
+
+	/*
+	 * 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);
+}
+
+/*
  * Cleanup the memory for subxacts and reset the related variables.
  */
 static inline void
@@ -4361,24 +4410,18 @@ TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
 }
 
 /*
- * Execute the initial sync with error handling. Disable the subscription,
- * if it's required.
+ * Common function to run the apply loop with error handling. Disable the
+ * subscription, if necessary.
  *
- * Allocate the slot name in long-lived context on return. Note that we don't
- * handle FATAL errors which are probably because of system resource error and
- * are not repeatable.
+ * Note that we don't handle FATAL errors which are probably because
+ * of system resource error and are not repeatable.
  */
-static void
-start_table_sync(XLogRecPtr *origin_startpos, char **myslotname)
+void
+start_apply(XLogRecPtr origin_startpos)
 {
-	char	   *syncslotname = NULL;
-
-	Assert(am_tablesync_worker());
-
 	PG_TRY();
 	{
-		/* Call initial sync. */
-		syncslotname = LogicalRepSyncTableStart(origin_startpos);
+		LogicalRepApplyLoop(origin_startpos);
 	}
 	PG_CATCH();
 	{
@@ -4387,65 +4430,132 @@ start_table_sync(XLogRecPtr *origin_startpos, char **myslotname)
 		else
 		{
 			/*
-			 * Report the worker failed during table synchronization. Abort
-			 * the current transaction so that the stats message is sent in an
+			 * Report the worker failed while applying changes. Abort the
+			 * current transaction so that the stats message is sent in an
 			 * idle state.
 			 */
 			AbortOutOfAnyTransaction();
-			pgstat_report_subscription_error(MySubscription->oid, false);
+			pgstat_report_subscription_error(MySubscription->oid, !am_tablesync_worker());
 
 			PG_RE_THROW();
 		}
 	}
 	PG_END_TRY();
-
-	/* allocate slot name in long-lived context */
-	*myslotname = MemoryContextStrdup(ApplyContext, syncslotname);
-	pfree(syncslotname);
 }
 
 /*
- * Run the apply loop with error handling. Disable the subscription,
- * if necessary.
+ * Runs the leader apply worker.
  *
- * Note that we don't handle FATAL errors which are probably because
- * of system resource error and are not repeatable.
+ * It sets up replication origin, streaming options and then starts streaming.
  */
 static void
-start_apply(XLogRecPtr origin_startpos)
+run_apply_worker()
 {
-	PG_TRY();
+	char		originname[NAMEDATALEN];
+	XLogRecPtr	origin_startpos = InvalidXLogRecPtr;
+	char	   *slotname = NULL;
+	WalRcvStreamOptions options;
+	RepOriginId originid;
+	TimeLineID	startpointTLI;
+	char	   *err;
+	bool		must_use_password;
+
+	slotname = MySubscription->slotname;
+
+	/*
+	 * This shouldn't happen if the subscription is enabled, but guard against
+	 * DDL bugs or manual catalog changes.  (libpqwalreceiver will crash if
+	 * slot is NULL.)
+	 */
+	if (!slotname)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("subscription has no replication slot set")));
+
+	/* Setup replication origin tracking. */
+	ReplicationOriginNameForLogicalRep(MySubscription->oid, InvalidOid,
+									   originname, sizeof(originname));
+	StartTransactionCommand();
+	originid = replorigin_by_name(originname, true);
+	if (!OidIsValid(originid))
+		originid = replorigin_create(originname);
+	replorigin_session_setup(originid, 0);
+	replorigin_session_origin = originid;
+	origin_startpos = replorigin_session_get_progress(false);
+
+	/* Is the use of a password mandatory? */
+	must_use_password = MySubscription->passwordrequired &&
+		!superuser_arg(MySubscription->owner);
+
+	/* Note that the superuser_arg call can access the DB */
+	CommitTransactionCommand();
+
+	LogRepWorkerWalRcvConn = walrcv_connect(MySubscription->conninfo, true,
+											must_use_password,
+											MySubscription->name, &err);
+
+	if (LogRepWorkerWalRcvConn == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_FAILURE),
+				 errmsg("could not connect to the publisher: %s", err)));
+
+	/*
+	 * We don't really use the output identify_system for anything but it does
+	 * some initializations on the upstream so let's still call it.
+	 */
+	(void) walrcv_identify_system(LogRepWorkerWalRcvConn, &startpointTLI);
+
+	set_apply_error_context_origin(originname);
+
+	set_stream_options(&options, slotname, &origin_startpos);
+
+	/*
+	 * Even when the two_phase mode is requested by the user, it remains as
+	 * the tri-state PENDING until all tablesyncs have reached READY state.
+	 * Only then, can it become ENABLED.
+	 *
+	 * Note: If the subscription has no tables then leave the state as
+	 * PENDING, which allows ALTER SUBSCRIPTION ... REFRESH PUBLICATION to
+	 * work.
+	 */
+	if (MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_PENDING &&
+		AllTablesyncsReady())
 	{
-		LogicalRepApplyLoop(origin_startpos);
+		/* Start streaming with two_phase enabled */
+		options.proto.logical.twophase = true;
+		walrcv_startstreaming(LogRepWorkerWalRcvConn, &options);
+
+		StartTransactionCommand();
+		UpdateTwoPhaseState(MySubscription->oid, LOGICALREP_TWOPHASE_STATE_ENABLED);
+		MySubscription->twophasestate = LOGICALREP_TWOPHASE_STATE_ENABLED;
+		CommitTransactionCommand();
 	}
-	PG_CATCH();
+	else
 	{
-		if (MySubscription->disableonerr)
-			DisableSubscriptionAndExit();
-		else
-		{
-			/*
-			 * Report the worker failed while applying changes. Abort the
-			 * current transaction so that the stats message is sent in an
-			 * idle state.
-			 */
-			AbortOutOfAnyTransaction();
-			pgstat_report_subscription_error(MySubscription->oid, !am_tablesync_worker());
-
-			PG_RE_THROW();
-		}
+		walrcv_startstreaming(LogRepWorkerWalRcvConn, &options);
 	}
-	PG_END_TRY();
+
+	ereport(DEBUG1,
+			(errmsg_internal("logical replication apply worker for subscription \"%s\" two_phase is %s",
+							 MySubscription->name,
+							 MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_DISABLED ? "DISABLED" :
+							 MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_PENDING ? "PENDING" :
+							 MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED ? "ENABLED" :
+							 "?")));
+
+	/* Run the main loop. */
+	start_apply(origin_startpos);
 }
 
 /*
- * Common initialization for leader apply worker and parallel apply worker.
+ * Common initialization for leader apply worker, parallel apply worker and
+ * tablesync worker.
  *
  * Initialize the database connection, in-memory subscription and necessary
  * config options.
  */
 void
-InitializeApplyWorker(void)
+InitializeLogRepWorker(void)
 {
 	MemoryContext oldctx;
 
@@ -4518,22 +4628,15 @@ InitializeApplyWorker(void)
 	CommitTransactionCommand();
 }
 
-/* Logical Replication Apply worker entry point */
+/* Common function to setup the leader apply or tablesync worker. */
 void
-ApplyWorkerMain(Datum main_arg)
+SetupApplyOrSyncWorker(int worker_slot)
 {
-	int			worker_slot = DatumGetInt32(main_arg);
-	char		originname[NAMEDATALEN];
-	XLogRecPtr	origin_startpos = InvalidXLogRecPtr;
-	char	   *myslotname = NULL;
-	WalRcvStreamOptions options;
-	int			server_version;
-
-	InitializingApplyWorker = true;
-
 	/* Attach to slot */
 	logicalrep_worker_attach(worker_slot);
 
+	Assert(am_tablesync_worker() || am_leader_apply_worker());
+
 	/* Setup signal handling */
 	pqsignal(SIGHUP, SignalHandlerForConfigReload);
 	pqsignal(SIGTERM, die);
@@ -4551,79 +4654,12 @@ ApplyWorkerMain(Datum main_arg)
 	/* Load the libpq-specific functions */
 	load_file("libpqwalreceiver", false);
 
-	InitializeApplyWorker();
-
-	InitializingApplyWorker = false;
+	InitializeLogRepWorker();
 
 	/* Connect to the origin and start the replication. */
 	elog(DEBUG1, "connecting to publisher using connection string \"%s\"",
 		 MySubscription->conninfo);
 
-	if (am_tablesync_worker())
-	{
-		start_table_sync(&origin_startpos, &myslotname);
-
-		ReplicationOriginNameForLogicalRep(MySubscription->oid,
-										   MyLogicalRepWorker->relid,
-										   originname,
-										   sizeof(originname));
-		set_apply_error_context_origin(originname);
-	}
-	else
-	{
-		/* This is the leader apply worker */
-		RepOriginId originid;
-		TimeLineID	startpointTLI;
-		char	   *err;
-		bool		must_use_password;
-
-		myslotname = MySubscription->slotname;
-
-		/*
-		 * This shouldn't happen if the subscription is enabled, but guard
-		 * against DDL bugs or manual catalog changes.  (libpqwalreceiver will
-		 * crash if slot is NULL.)
-		 */
-		if (!myslotname)
-			ereport(ERROR,
-					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-					 errmsg("subscription has no replication slot set")));
-
-		/* Setup replication origin tracking. */
-		StartTransactionCommand();
-		ReplicationOriginNameForLogicalRep(MySubscription->oid, InvalidOid,
-										   originname, sizeof(originname));
-		originid = replorigin_by_name(originname, true);
-		if (!OidIsValid(originid))
-			originid = replorigin_create(originname);
-		replorigin_session_setup(originid, 0);
-		replorigin_session_origin = originid;
-		origin_startpos = replorigin_session_get_progress(false);
-
-		/* Is the use of a password mandatory? */
-		must_use_password = MySubscription->passwordrequired &&
-			!superuser_arg(MySubscription->owner);
-
-		/* Note that the superuser_arg call can access the DB */
-		CommitTransactionCommand();
-
-		LogRepWorkerWalRcvConn = walrcv_connect(MySubscription->conninfo, true,
-												must_use_password,
-												MySubscription->name, &err);
-		if (LogRepWorkerWalRcvConn == NULL)
-			ereport(ERROR,
-					(errcode(ERRCODE_CONNECTION_FAILURE),
-					 errmsg("could not connect to the publisher: %s", err)));
-
-		/*
-		 * We don't really use the output identify_system for anything but it
-		 * does some initializations on the upstream so let's still call it.
-		 */
-		(void) walrcv_identify_system(LogRepWorkerWalRcvConn, &startpointTLI);
-
-		set_apply_error_context_origin(originname);
-	}
-
 	/*
 	 * Setup callback for syscache so that we know when something changes in
 	 * the subscription relation state.
@@ -4631,91 +4667,21 @@ ApplyWorkerMain(Datum main_arg)
 	CacheRegisterSyscacheCallback(SUBSCRIPTIONRELMAP,
 								  invalidate_syncing_table_states,
 								  (Datum) 0);
+}
 
-	/* Build logical replication streaming options. */
-	options.logical = true;
-	options.startpoint = origin_startpos;
-	options.slotname = myslotname;
-
-	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;
-
-	/*
-	 * 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);
+/* Logical Replication Apply worker entry point */
+void
+ApplyWorkerMain(Datum main_arg)
+{
+	int			worker_slot = DatumGetInt32(main_arg);
 
-	if (!am_tablesync_worker())
-	{
-		/*
-		 * Even when the two_phase mode is requested by the user, it remains
-		 * as the tri-state PENDING until all tablesyncs have reached READY
-		 * state. Only then, can it become ENABLED.
-		 *
-		 * Note: If the subscription has no tables then leave the state as
-		 * PENDING, which allows ALTER SUBSCRIPTION ... REFRESH PUBLICATION to
-		 * work.
-		 */
-		if (MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_PENDING &&
-			AllTablesyncsReady())
-		{
-			/* Start streaming with two_phase enabled */
-			options.proto.logical.twophase = true;
-			walrcv_startstreaming(LogRepWorkerWalRcvConn, &options);
+	InitializingApplyWorker = true;
 
-			StartTransactionCommand();
-			UpdateTwoPhaseState(MySubscription->oid, LOGICALREP_TWOPHASE_STATE_ENABLED);
-			MySubscription->twophasestate = LOGICALREP_TWOPHASE_STATE_ENABLED;
-			CommitTransactionCommand();
-		}
-		else
-		{
-			walrcv_startstreaming(LogRepWorkerWalRcvConn, &options);
-		}
+	SetupApplyOrSyncWorker(worker_slot);
 
-		ereport(DEBUG1,
-				(errmsg_internal("logical replication apply worker for subscription \"%s\" two_phase is %s",
-								 MySubscription->name,
-								 MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_DISABLED ? "DISABLED" :
-								 MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_PENDING ? "PENDING" :
-								 MySubscription->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED ? "ENABLED" :
-								 "?")));
-	}
-	else
-	{
-		/* Start normal logical streaming replication. */
-		walrcv_startstreaming(LogRepWorkerWalRcvConn, &options);
-	}
+	InitializingApplyWorker = false;
 
-	/* Run the main loop. */
-	start_apply(origin_startpos);
+	run_apply_worker();
 
 	proc_exit(0);
 }
@@ -4724,7 +4690,7 @@ ApplyWorkerMain(Datum main_arg)
  * After error recovery, disable the subscription in a new transaction
  * and exit cleanly.
  */
-static void
+void
 DisableSubscriptionAndExit(void)
 {
 	/*