pgoutput: Fix memory leak due to RelationSyncEntry.map.

Release memory allocated when creating the tuple-conversion map and its
component TupleDescs when its owning sync entry is invalidated.
TupleDescs must also be freed when no map is deemed necessary, to begin
with.

Reported-by: Andres Freund
Author: Amit Langote
Reviewed-by: Takamichi Osumi, Amit Kapila
Backpatch-through: 13, where it was introduced
Discussion: https://postgr.es/m/MEYP282MB166933B1AB02B4FE56E82453B64D9@MEYP282MB1669.AUSP282.PROD.OUTLOOK.COM

Author: Amit Kapila

src/backend/replication/pgoutput/pgoutput.c

@@ -57,17 +57,17 @@ static void send_relation_and_attrs(Relation relation, LogicalDecodingContext *c
 /*
  * Entry in the map used to remember which relation schemas we sent.
  *
+ * The schema_sent flag determines if the current schema record for the
+ * relation (and for its ancestor if publish_as_relid is set) was already sent
+ * to the subscriber (in which case we don't need to send it again).
+ *
  * For partitions, 'pubactions' considers not only the table's own
  * publications, but also those of all of its ancestors.
  */
 typedef struct RelationSyncEntry
 {
 	Oid			relid;			/* relation oid */
 
-	/*
-	 * Did we send the schema?  If ancestor relid is set, its schema must also
-	 * have been sent for this to be true.
-	 */
 	bool		schema_sent;
 
 	bool		replicate_valid;
@@ -292,10 +292,17 @@ static void
 maybe_send_schema(LogicalDecodingContext *ctx,
 				  Relation relation, RelationSyncEntry *relentry)
 {
+	/* Nothing to do if we already sent the schema. */
 	if (relentry->schema_sent)
 		return;
 
-	/* If needed, send the ancestor's schema first. */
+	/*
+	 * Nope, so send the schema.  If the changes will be published using an
+	 * ancestor's schema, not the relation's own, send that ancestor's schema
+	 * before sending relation's own (XXX - maybe sending only the former
+	 * suffices?).  This is also a good place to set the map that will be used
+	 * to convert the relation's tuples into the ancestor's format, if needed.
+	 */
 	if (relentry->publish_as_relid != RelationGetRelid(relation))
 	{
 		Relation	ancestor = RelationIdGetRelation(relentry->publish_as_relid);
@@ -305,8 +312,21 @@ maybe_send_schema(LogicalDecodingContext *ctx,
 
 		/* Map must live as long as the session does. */
 		oldctx = MemoryContextSwitchTo(CacheMemoryContext);
-		relentry->map = convert_tuples_by_name(CreateTupleDescCopy(indesc),
-											   CreateTupleDescCopy(outdesc));
+
+		/*
+		 * Make copies of the TupleDescs that will live as long as the map
+		 * does before putting into the map.
+		 */
+		indesc = CreateTupleDescCopy(indesc);
+		outdesc = CreateTupleDescCopy(outdesc);
+		relentry->map = convert_tuples_by_name(indesc, outdesc);
+		if (relentry->map == NULL)
+		{
+			/* Map not necessary, so free the TupleDescs too. */
+			FreeTupleDesc(indesc);
+			FreeTupleDesc(outdesc);
+		}
+
 		MemoryContextSwitchTo(oldctx);
 		send_relation_and_attrs(ancestor, ctx);
 		RelationClose(ancestor);
@@ -759,6 +779,7 @@ get_rel_sync_entry(PGOutputData *data, Oid relid)
 		list_free(pubids);
 
 		entry->publish_as_relid = publish_as_relid;
+		entry->map = NULL;	/* will be set by maybe_send_schema() if needed */
 		entry->replicate_valid = true;
 	}
 
@@ -801,9 +822,23 @@ rel_sync_cache_relation_cb(Datum arg, Oid relid)
 
 	/*
 	 * Reset schema sent status as the relation definition may have changed.
+	 * Also, free any objects that depended on the earlier definition.
 	 */
 	if (entry != NULL)
+	{
 		entry->schema_sent = false;
+		if (entry->map)
+		{
+			/*
+			 * Must free the TupleDescs contained in the map explicitly,
+			 * because free_conversion_map() doesn't.
+			 */
+			FreeTupleDesc(entry->map->indesc);
+			FreeTupleDesc(entry->map->outdesc);
+			free_conversion_map(entry->map);
+		}
+		entry->map = NULL;
+	}
 }
 
 /*

src/test/subscription/t/013_partition.pl

@@ -3,7 +3,7 @@
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 54;
+use Test::More tests => 56;
 
 # setup
 
@@ -621,3 +621,29 @@ BEGIN
 
 $result = $node_subscriber2->safe_psql('postgres', "SELECT a FROM tab3_1");
 is($result, qq(), 'truncate of tab3_1 replicated');
+
+# check that the map to convert tuples from leaf partition to the root
+# table is correctly rebuilt when a new column is added
+$node_publisher->safe_psql('postgres',
+	"ALTER TABLE tab2 DROP b, ADD COLUMN c text DEFAULT 'pub_tab2', ADD b text");
+$node_publisher->safe_psql('postgres',
+	"INSERT INTO tab2 (a, b) VALUES (1, 'xxx'), (3, 'yyy'), (5, 'zzz')");
+$node_publisher->safe_psql('postgres',
+	"INSERT INTO tab2 (a, b, c) VALUES (6, 'aaa', 'xxx_c')");
+
+$node_publisher->wait_for_catchup('sub_viaroot');
+$node_publisher->wait_for_catchup('sub2');
+
+$result = $node_subscriber1->safe_psql('postgres',
+	"SELECT c, a, b FROM tab2 ORDER BY 1, 2");
+is( $result, qq(pub_tab2|1|xxx
+pub_tab2|3|yyy
+pub_tab2|5|zzz
+xxx_c|6|aaa), 'inserts into tab2 replicated');
+
+$result = $node_subscriber2->safe_psql('postgres',
+	"SELECT c, a, b FROM tab2 ORDER BY 1, 2");
+is( $result, qq(pub_tab2|1|xxx
+pub_tab2|3|yyy
+pub_tab2|5|zzz
+xxx_c|6|aaa), 'inserts into tab2 replicated');