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, 90 insertions, 1 deletions

diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
index 6d461654ab4..651a7750653 100644
--- a/src/backend/replication/logical/tablesync.c
+++ b/src/backend/replication/logical/tablesync.c
@@ -106,6 +106,7 @@
 #include "pgstat.h"
 #include "replication/logicallauncher.h"
 #include "replication/logicalrelation.h"
+#include "replication/logicalworker.h"
 #include "replication/walreceiver.h"
 #include "replication/worker_internal.h"
 #include "replication/slot.h"
@@ -1241,7 +1242,7 @@ ReplicationSlotNameForTablesync(Oid suboid, Oid relid,
  *
  * The returned slot name is palloc'ed in current memory context.
  */
-char *
+static char *
 LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
 {
 	char	   *slotname;
@@ -1585,6 +1586,94 @@ FetchTableStates(bool *started_tx)
 }
 
 /*
+ * Execute the initial sync with error handling. Disable the subscription,
+ * if it's required.
+ *
+ * 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.
+ */
+static void
+start_table_sync(XLogRecPtr *origin_startpos, char **slotname)
+{
+	char	   *sync_slotname = NULL;
+
+	Assert(am_tablesync_worker());
+
+	PG_TRY();
+	{
+		/* Call initial sync. */
+		sync_slotname = LogicalRepSyncTableStart(origin_startpos);
+	}
+	PG_CATCH();
+	{
+		if (MySubscription->disableonerr)
+			DisableSubscriptionAndExit();
+		else
+		{
+			/*
+			 * Report the worker failed during table synchronization. Abort
+			 * the current transaction so that the stats message is sent in an
+			 * idle state.
+			 */
+			AbortOutOfAnyTransaction();
+			pgstat_report_subscription_error(MySubscription->oid, false);
+
+			PG_RE_THROW();
+		}
+	}
+	PG_END_TRY();
+
+	/* allocate slot name in long-lived context */
+	*slotname = MemoryContextStrdup(ApplyContext, sync_slotname);
+	pfree(sync_slotname);
+}
+
+/*
+ * Runs the tablesync worker.
+ *
+ * It starts syncing tables. After a successful sync, sets streaming options
+ * and starts streaming to catchup with apply worker.
+ */
+static void
+run_tablesync_worker()
+{
+	char		originname[NAMEDATALEN];
+	XLogRecPtr	origin_startpos = InvalidXLogRecPtr;
+	char	   *slotname = NULL;
+	WalRcvStreamOptions options;
+
+	start_table_sync(&origin_startpos, &slotname);
+
+	ReplicationOriginNameForLogicalRep(MySubscription->oid,
+									   MyLogicalRepWorker->relid,
+									   originname,
+									   sizeof(originname));
+
+	set_apply_error_context_origin(originname);
+
+	set_stream_options(&options, slotname, &origin_startpos);
+
+	walrcv_startstreaming(LogRepWorkerWalRcvConn, &options);
+
+	/* Apply the changes till we catchup with the apply worker. */
+	start_apply(origin_startpos);
+}
+
+/* Logical Replication Tablesync worker entry point */
+void
+TablesyncWorkerMain(Datum main_arg)
+{
+	int			worker_slot = DatumGetInt32(main_arg);
+
+	SetupApplyOrSyncWorker(worker_slot);
+
+	run_tablesync_worker();
+
+	finish_sync_worker();
+}
+
+/*
  * If the subscription has no tables then return false.
  *
  * Otherwise, are all tablesyncs READY?