Fix updating of pg_subscription_rel from workers

petere · petere · commit 644ea35fc135 · 2017-06-07T13:49:14.000-04:00
A logical replication worker should not insert new rows into
pg_subscription_rel, only update existing rows, so that there are no
races if a concurrent refresh removes rows.  Adjust the API to be able
to choose that behavior.

Author: Masahiko Sawada &lt;sawada.mshk@gmail.com&gt;
Reported-by: tushar &lt;tushar.ahuja@enterprisedb.com&gt;
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
@@ -227,17 +227,22 @@ textarray_to_stringlist(ArrayType *textarray)
 /*
  * Set the state of a subscription table.
  *
+ * If update_only is true and the record for given table doesn't exist, do
+ * nothing.  This can be used to avoid inserting a new record that was deleted
+ * by someone else.  Generally, subscription DDL commands should use false,
+ * workers should use true.
+ *
  * The insert-or-update logic in this function is not concurrency safe so it
  * might raise an error in rare circumstances.  But if we took a stronger lock
  * such as ShareRowExclusiveLock, we would risk more deadlocks.
  */
 Oid
 SetSubscriptionRelState(Oid subid, Oid relid, char state,
-						XLogRecPtr sublsn)
+						XLogRecPtr sublsn, bool update_only)
 {
 	Relation	rel;
 	HeapTuple	tup;
-	Oid			subrelid;
+	Oid			subrelid = InvalidOid;
 	bool		nulls[Natts_pg_subscription_rel];
 	Datum		values[Natts_pg_subscription_rel];
 
@@ -252,7 +257,7 @@ SetSubscriptionRelState(Oid subid, Oid relid, char state,
 	 * If the record for given table does not exist yet create new record,
 	 * otherwise update the existing one.
 	 */
-	if (!HeapTupleIsValid(tup))
+	if (!HeapTupleIsValid(tup) && !update_only)
 	{
 		/* Form the tuple. */
 		memset(values, 0, sizeof(values));
@@ -272,7 +277,7 @@ SetSubscriptionRelState(Oid subid, Oid relid, char state,
 
 		heap_freetuple(tup);
 	}
-	else
+	else if (HeapTupleIsValid(tup))
 	{
 		bool		replaces[Natts_pg_subscription_rel];
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
@@ -451,7 +451,7 @@ CreateSubscription(CreateSubscriptionStmt *stmt, bool isTopLevel)
 										 rv->schemaname, rv->relname);
 
 				SetSubscriptionRelState(subid, relid, table_state,
-										InvalidXLogRecPtr);
+										InvalidXLogRecPtr, false);
 			}
 
 			ereport(NOTICE,
@@ -574,7 +574,7 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data)
 		{
 			SetSubscriptionRelState(sub->oid, relid,
 						  copy_data ? SUBREL_STATE_INIT : SUBREL_STATE_READY,
-									InvalidXLogRecPtr);
+									InvalidXLogRecPtr, false);
 			ereport(NOTICE,
 					(errmsg("added subscription for table %s.%s",
 							quote_identifier(rv->schemaname),
diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
@@ -287,7 +287,8 @@ process_syncing_tables_for_sync(XLogRecPtr current_lsn)
 		SetSubscriptionRelState(MyLogicalRepWorker->subid,
 								MyLogicalRepWorker->relid,
 								MyLogicalRepWorker->relstate,
-								MyLogicalRepWorker->relstate_lsn);
+								MyLogicalRepWorker->relstate_lsn,
+								true);
 
 		walrcv_endstreaming(wrconn, &tli);
 		finish_sync_worker();
@@ -414,7 +415,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 				}
 				SetSubscriptionRelState(MyLogicalRepWorker->subid,
 										rstate->relid, rstate->state,
-										rstate->lsn);
+										rstate->lsn, true);
 			}
 		}
 		else
@@ -845,7 +846,8 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
 				SetSubscriptionRelState(MyLogicalRepWorker->subid,
 										MyLogicalRepWorker->relid,
 										MyLogicalRepWorker->relstate,
-										MyLogicalRepWorker->relstate_lsn);
+										MyLogicalRepWorker->relstate_lsn,
+										true);
 				CommitTransactionCommand();
 				pgstat_report_stat(false);
 
@@ -932,7 +934,8 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
 					SetSubscriptionRelState(MyLogicalRepWorker->subid,
 											MyLogicalRepWorker->relid,
 											SUBREL_STATE_SYNCDONE,
-											*origin_startpos);
+											*origin_startpos,
+											true);
 					finish_sync_worker();
 				}
 				break;
diff --git a/src/include/catalog/pg_subscription_rel.h b/src/include/catalog/pg_subscription_rel.h
@@ -71,7 +71,7 @@ typedef struct SubscriptionRelState
 } SubscriptionRelState;
 
 extern Oid SetSubscriptionRelState(Oid subid, Oid relid, char state,
-						XLogRecPtr sublsn);
+						XLogRecPtr sublsn, bool update_only);
 extern char GetSubscriptionRelState(Oid subid, Oid relid,
 						XLogRecPtr *sublsn, bool missing_ok);
 extern void RemoveSubscriptionRel(Oid subid, Oid relid);
