Fix initialization of RelationSyncEntry for streaming transactions.

Amit Kapila · Amit Kapila · commit 69bd60672af6 · 2020-09-16T07:45:44.000+05:30
In commit 4648243, for each RelationSyncEntry we maintained the list of xids (streamed_txns) for which we have already sent the schema. This helps us to track when to send the schema to the downstream node for replication of streaming transactions. Before this list got initialized, we were processing invalidation messages which access this list and led to an assertion failure. In passing, clean up the nearby code: * Initialize the list of xids with NIL instead of NULL which is our usual coding practice. * Remove the MemoryContext switch for creating a RelationSyncEntry in dynahash. Diagnosed-by: Amit Kapila and Tom Lane Author: Amit Kapila Reviewed-by: Tom Lane and Dilip Kumar Discussion: https://postgr.es/m/904373.1600033123@sss.pgh.pa.us
diff --git a/src/backend/replication/pgoutput/pgoutput.c b/src/backend/replication/pgoutput/pgoutput.c
@@ -945,16 +945,26 @@ get_rel_sync_entry(PGOutputData *data, Oid relid)
 
 	Assert(RelationSyncCache != NULL);
 
-	/* Find cached function info, creating if not found */
-	oldctx = MemoryContextSwitchTo(CacheMemoryContext);
+	/* Find cached relation info, creating if not found */
 	entry = (RelationSyncEntry *) hash_search(RelationSyncCache,
 											  (void *) &relid,
 											  HASH_ENTER, &found);
-	MemoryContextSwitchTo(oldctx);
 	Assert(entry != NULL);
 
 	/* Not found means schema wasn't sent */
-	if (!found || !entry->replicate_valid)
+	if (!found)
+	{
+		/* immediately make a new entry valid enough to satisfy callbacks */
+		entry->schema_sent = false;
+		entry->streamed_txns = NIL;
+		entry->replicate_valid = false;
+		entry->pubactions.pubinsert = entry->pubactions.pubupdate =
+			entry->pubactions.pubdelete = entry->pubactions.pubtruncate = false;
+		entry->publish_as_relid = InvalidOid;
+	}
+
+	/* Validate the entry */
+	if (!entry->replicate_valid)
 	{
 		List	   *pubids = GetRelationPublications(relid);
 		ListCell   *lc;
@@ -977,9 +987,6 @@ get_rel_sync_entry(PGOutputData *data, Oid relid)
 		 * relcache considers all publications given relation is in, but here
 		 * we only need to consider ones that the subscriber requested.
 		 */
-		entry->pubactions.pubinsert = entry->pubactions.pubupdate =
-			entry->pubactions.pubdelete = entry->pubactions.pubtruncate = false;
-
 		foreach(lc, data->publications)
 		{
 			Publication *pub = lfirst(lc);
@@ -1054,12 +1061,6 @@ get_rel_sync_entry(PGOutputData *data, Oid relid)
 		entry->replicate_valid = true;
 	}
 
-	if (!found)
-	{
-		entry->schema_sent = false;
-		entry->streamed_txns = NULL;
-	}
-
 	return entry;
 }
 
@@ -1145,7 +1146,7 @@ rel_sync_cache_relation_cb(Datum arg, Oid relid)
 	{
 		entry->schema_sent = false;
 		list_free(entry->streamed_txns);
-		entry->streamed_txns = NULL;
+		entry->streamed_txns = NIL;
 	}
 }
 
