Fix cache look-up failures while applying changes in logical replication.

While building a new attrmap which maps partition attribute numbers to
remoterel's, we incorrectly update the map for dropped column attributes.
Later, it caused cache look-up failure when we tried to use the map to
fetch the information about attributes.

This also fixes the partition map cache invalidation which was using the
wrong type cast to fetch the entry. We were using stale partition map
entry after invalidation which leads to the assertion or cache look-up
failure.

Reported-by: Shi Yu
Author: Hou Zhijie, Shi Yu
Reviewed-by: Amit Langote, Amit Kapila
Backpatch-through: 13, where it was introduced
Discussion: https://postgr.es/m/OSZPR01MB6310F46CD425A967E4AEF736FDA49@OSZPR01MB6310.jpnprd01.prod.outlook.com

src/backend/replication/logical/relation.c

@@ -451,7 +451,7 @@ logicalrep_rel_close(LogicalRepRelMapEntry *rel, LOCKMODE lockmode)
 static void
 logicalrep_partmap_invalidate_cb(Datum arg, Oid reloid)
 {
-	LogicalRepRelMapEntry *entry;
+	LogicalRepPartMapEntry *entry;
 
 	/* Just to be sure. */
 	if (LogicalRepPartMap == NULL)
@@ -464,11 +464,11 @@ logicalrep_partmap_invalidate_cb(Datum arg, Oid reloid)
 		hash_seq_init(&status, LogicalRepPartMap);
 
 		/* TODO, use inverse lookup hashtable? */
-		while ((entry = (LogicalRepRelMapEntry *) hash_seq_search(&status)) != NULL)
+		while ((entry = (LogicalRepPartMapEntry *) hash_seq_search(&status)) != NULL)
 		{
-			if (entry->localreloid == reloid)
+			if (entry->relmapentry.localreloid == reloid)
 			{
-				entry->localrelvalid = false;
+				entry->relmapentry.localrelvalid = false;
 				hash_seq_term(&status);
 				break;
 			}
@@ -481,8 +481,8 @@ logicalrep_partmap_invalidate_cb(Datum arg, Oid reloid)
 
 		hash_seq_init(&status, LogicalRepPartMap);
 
-		while ((entry = (LogicalRepRelMapEntry *) hash_seq_search(&status)) != NULL)
-			entry->localrelvalid = false;
+		while ((entry = (LogicalRepPartMapEntry *) hash_seq_search(&status)) != NULL)
+			entry->relmapentry.localrelvalid = false;
 	}
 }
 
@@ -534,7 +534,6 @@ logicalrep_partition_open(LogicalRepRelMapEntry *root,
 	Oid			partOid = RelationGetRelid(partrel);
 	AttrMap    *attrmap = root->attrmap;
 	bool		found;
-	int			i;
 	MemoryContext oldctx;
 
 	if (LogicalRepPartMap == NULL)
@@ -545,31 +544,40 @@ logicalrep_partition_open(LogicalRepRelMapEntry *root,
 														(void *) &partOid,
 														HASH_ENTER, &found);
 
-	if (found)
-		return &part_entry->relmapentry;
+	entry = &part_entry->relmapentry;
 
-	memset(part_entry, 0, sizeof(LogicalRepPartMapEntry));
+	if (found && entry->localrelvalid)
+		return entry;
 
 	/* Switch to longer-lived context. */
 	oldctx = MemoryContextSwitchTo(LogicalRepPartMapContext);
 
-	part_entry->partoid = partOid;
+	if (!found)
+	{
+		memset(part_entry, 0, sizeof(LogicalRepPartMapEntry));
+		part_entry->partoid = partOid;
+	}
 
-	/* Remote relation is copied as-is from the root entry. */
-	entry = &part_entry->relmapentry;
-	entry->remoterel.remoteid = remoterel->remoteid;
-	entry->remoterel.nspname = pstrdup(remoterel->nspname);
-	entry->remoterel.relname = pstrdup(remoterel->relname);
-	entry->remoterel.natts = remoterel->natts;
-	entry->remoterel.attnames = palloc(remoterel->natts * sizeof(char *));
-	entry->remoterel.atttyps = palloc(remoterel->natts * sizeof(Oid));
-	for (i = 0; i < remoterel->natts; i++)
+	if (!entry->remoterel.remoteid)
 	{
-		entry->remoterel.attnames[i] = pstrdup(remoterel->attnames[i]);
-		entry->remoterel.atttyps[i] = remoterel->atttyps[i];
+		int			i;
+
+		/* Remote relation is copied as-is from the root entry. */
+		entry = &part_entry->relmapentry;
+		entry->remoterel.remoteid = remoterel->remoteid;
+		entry->remoterel.nspname = pstrdup(remoterel->nspname);
+		entry->remoterel.relname = pstrdup(remoterel->relname);
+		entry->remoterel.natts = remoterel->natts;
+		entry->remoterel.attnames = palloc(remoterel->natts * sizeof(char *));
+		entry->remoterel.atttyps = palloc(remoterel->natts * sizeof(Oid));
+		for (i = 0; i < remoterel->natts; i++)
+		{
+			entry->remoterel.attnames[i] = pstrdup(remoterel->attnames[i]);
+			entry->remoterel.atttyps[i] = remoterel->atttyps[i];
+		}
+		entry->remoterel.replident = remoterel->replident;
+		entry->remoterel.attkeys = bms_copy(remoterel->attkeys);
 	}
-	entry->remoterel.replident = remoterel->replident;
-	entry->remoterel.attkeys = bms_copy(remoterel->attkeys);
 
 	entry->localrel = partrel;
 	entry->localreloid = partOid;
@@ -594,7 +602,11 @@ logicalrep_partition_open(LogicalRepRelMapEntry *root,
 		{
 			AttrNumber	root_attno = map->attnums[attno];
 
-			entry->attrmap->attnums[attno] = attrmap->attnums[root_attno - 1];
+			/* 0 means it's a dropped attribute.  See comments atop AttrMap. */
+			if (root_attno == 0)
+				entry->attrmap->attnums[attno] = -1;
+			else
+				entry->attrmap->attnums[attno] = attrmap->attnums[root_attno - 1];
 		}
 	}
 	else

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

@@ -800,9 +800,57 @@ ok( $logfile =~
 	  qr/logical replication did not find row to be deleted in replication target relation "tab2_1"/,
 	'delete target row is missing in tab2_1');
 
-# No need for this until more tests are added.
-# $node_subscriber1->append_conf('postgresql.conf',
-# 	"log_min_messages = warning");
-# $node_subscriber1->reload;
+$node_subscriber1->append_conf('postgresql.conf',
+	"log_min_messages = warning");
+$node_subscriber1->reload;
+
+# Test that replication continues to work correctly after altering the
+# partition of a partitioned target table.
+
+$node_publisher->safe_psql(
+	'postgres', q{
+	CREATE TABLE tab5 (a int NOT NULL, b int);
+	CREATE UNIQUE INDEX tab5_a_idx ON tab5 (a);
+	ALTER TABLE tab5 REPLICA IDENTITY USING INDEX tab5_a_idx;});
+
+$node_subscriber2->safe_psql(
+	'postgres', q{
+	CREATE TABLE tab5 (a int NOT NULL, b int, c int) PARTITION BY LIST (a);
+	CREATE TABLE tab5_1 PARTITION OF tab5 DEFAULT;
+	CREATE UNIQUE INDEX tab5_a_idx ON tab5 (a);
+	ALTER TABLE tab5 REPLICA IDENTITY USING INDEX tab5_a_idx;
+	ALTER TABLE tab5_1 REPLICA IDENTITY USING INDEX tab5_1_a_idx;});
+
+$node_subscriber2->safe_psql('postgres',
+	"ALTER SUBSCRIPTION sub2 REFRESH PUBLICATION");
+
+$node_subscriber2->poll_query_until('postgres', $synced_query)
+  or die "Timed out while waiting for subscriber to synchronize data";
+
+# Make partition map cache
+$node_publisher->safe_psql('postgres', "INSERT INTO tab5 VALUES (1, 1)");
+$node_publisher->safe_psql('postgres', "UPDATE tab5 SET a = 2 WHERE a = 1");
+
+$node_publisher->wait_for_catchup('sub2');
+
+$result = $node_subscriber2->safe_psql('postgres',
+	"SELECT a, b FROM tab5 ORDER BY 1");
+is($result, qq(2|1), 'updates of tab5 replicated correctly');
+
+# Change the column order of partition on subscriber
+$node_subscriber2->safe_psql(
+	'postgres', q{
+	ALTER TABLE tab5 DETACH PARTITION tab5_1;
+	ALTER TABLE tab5_1 DROP COLUMN b;
+	ALTER TABLE tab5_1 ADD COLUMN b int;
+	ALTER TABLE tab5 ATTACH PARTITION tab5_1 DEFAULT});
+
+$node_publisher->safe_psql('postgres', "UPDATE tab5 SET a = 3 WHERE a = 2");
+
+$node_publisher->wait_for_catchup('sub2');
+
+$result = $node_subscriber2->safe_psql('postgres',
+	"SELECT a, b, c FROM tab5 ORDER BY 1");
+is($result, qq(3|1|), 'updates of tab5 replicated correctly after altering table on subscriber');
 
 done_testing();