Fix possible crash in ALTER TABLE ... REPLICA IDENTITY USING INDEX.

Careless coding added by commit 07cacba9 could result in a crash
or a bizarre error message if someone tried to select an index on the
OID column as the replica identity index for a table.  Back-patch to 9.4
where the feature was introduced.

Discussion: CAKJS1f8TQYgTRDyF1_u9PVCKWRWz+DkieH=U7954HeHVPJKaKg@mail.gmail.com

David Rowley

src/backend/commands/tablecmds.c

@@ -11052,10 +11052,20 @@ ATExecReplicaIdentity(Relation rel, ReplicaIdentityStmt *stmt, LOCKMODE lockmode
 		int16		attno = indexRel->rd_index->indkey.values[key];
 		Form_pg_attribute attr;
 
-		/* Of the system columns, only oid is indexable. */
-		if (attno <= 0 && attno != ObjectIdAttributeNumber)
-			elog(ERROR, "internal column %u in unique index \"%s\"",
-				 attno, RelationGetRelationName(indexRel));
+		/* Allow OID column to be indexed; it's certainly not nullable */
+		if (attno == ObjectIdAttributeNumber)
+			continue;
+
+		/*
+		 * Reject any other system columns.  (Going forward, we'll disallow
+		 * indexes containing such columns in the first place, but they might
+		 * exist in older branches.)
+		 */
+		if (attno <= 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
+					 errmsg("index \"%s\" cannot be used as replica identity because column %d is a system column",
+							RelationGetRelationName(indexRel), attno)));
 
 		attr = rel->rd_att->attrs[attno - 1];
 		if (!attr->attnotnull)

src/test/regress/expected/replica_identity.out

@@ -5,10 +5,11 @@ CREATE TABLE test_replica_identity (
        nonkey text,
        CONSTRAINT test_replica_identity_unique_defer UNIQUE (keya, keyb) DEFERRABLE,
        CONSTRAINT test_replica_identity_unique_nondefer UNIQUE (keya, keyb)
-);
+) WITH OIDS;
 CREATE TABLE test_replica_identity_othertable (id serial primary key);
 CREATE INDEX test_replica_identity_keyab ON test_replica_identity (keya, keyb);
 CREATE UNIQUE INDEX test_replica_identity_keyab_key ON test_replica_identity (keya, keyb);
+CREATE UNIQUE INDEX test_replica_identity_oid_idx ON test_replica_identity (oid);
 CREATE UNIQUE INDEX test_replica_identity_nonkey ON test_replica_identity (keya, nonkey);
 CREATE INDEX test_replica_identity_hash ON test_replica_identity USING hash (nonkey);
 WARNING:  hash indexes are not WAL-logged and their use is discouraged
@@ -88,12 +89,15 @@ Indexes:
     "test_replica_identity_expr" UNIQUE, btree (keya, keyb, (3))
     "test_replica_identity_keyab_key" UNIQUE, btree (keya, keyb)
     "test_replica_identity_nonkey" UNIQUE, btree (keya, nonkey)
+    "test_replica_identity_oid_idx" UNIQUE, btree (oid)
     "test_replica_identity_partial" UNIQUE, btree (keya, keyb) WHERE keyb <> '3'::text
     "test_replica_identity_unique_defer" UNIQUE CONSTRAINT, btree (keya, keyb) DEFERRABLE
     "test_replica_identity_unique_nondefer" UNIQUE CONSTRAINT, btree (keya, keyb)
     "test_replica_identity_hash" hash (nonkey)
     "test_replica_identity_keyab" btree (keya, keyb)
 
+-- succeed, oid unique index
+ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_identity_oid_idx;
 -- succeed, nondeferrable unique constraint over nonullable cols
 ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_identity_unique_nondefer;
 -- succeed unique index over nonnullable cols
@@ -118,6 +122,7 @@ Indexes:
     "test_replica_identity_expr" UNIQUE, btree (keya, keyb, (3))
     "test_replica_identity_keyab_key" UNIQUE, btree (keya, keyb) REPLICA IDENTITY
     "test_replica_identity_nonkey" UNIQUE, btree (keya, nonkey)
+    "test_replica_identity_oid_idx" UNIQUE, btree (oid)
     "test_replica_identity_partial" UNIQUE, btree (keya, keyb) WHERE keyb <> '3'::text
     "test_replica_identity_unique_defer" UNIQUE CONSTRAINT, btree (keya, keyb) DEFERRABLE
     "test_replica_identity_unique_nondefer" UNIQUE CONSTRAINT, btree (keya, keyb)
@@ -166,12 +171,14 @@ Indexes:
     "test_replica_identity_expr" UNIQUE, btree (keya, keyb, (3))
     "test_replica_identity_keyab_key" UNIQUE, btree (keya, keyb)
     "test_replica_identity_nonkey" UNIQUE, btree (keya, nonkey)
+    "test_replica_identity_oid_idx" UNIQUE, btree (oid)
     "test_replica_identity_partial" UNIQUE, btree (keya, keyb) WHERE keyb <> '3'::text
     "test_replica_identity_unique_defer" UNIQUE CONSTRAINT, btree (keya, keyb) DEFERRABLE
     "test_replica_identity_unique_nondefer" UNIQUE CONSTRAINT, btree (keya, keyb)
     "test_replica_identity_hash" hash (nonkey)
     "test_replica_identity_keyab" btree (keya, keyb)
 Replica Identity: FULL
+Has OIDs: yes
 
 ALTER TABLE test_replica_identity REPLICA IDENTITY NOTHING;
 SELECT relreplident FROM pg_class WHERE oid = 'test_replica_identity'::regclass;

src/test/regress/sql/replica_identity.sql

@@ -5,12 +5,13 @@ CREATE TABLE test_replica_identity (
        nonkey text,
        CONSTRAINT test_replica_identity_unique_defer UNIQUE (keya, keyb) DEFERRABLE,
        CONSTRAINT test_replica_identity_unique_nondefer UNIQUE (keya, keyb)
-);
+) WITH OIDS;
 
 CREATE TABLE test_replica_identity_othertable (id serial primary key);
 
 CREATE INDEX test_replica_identity_keyab ON test_replica_identity (keya, keyb);
 CREATE UNIQUE INDEX test_replica_identity_keyab_key ON test_replica_identity (keya, keyb);
+CREATE UNIQUE INDEX test_replica_identity_oid_idx ON test_replica_identity (oid);
 CREATE UNIQUE INDEX test_replica_identity_nonkey ON test_replica_identity (keya, nonkey);
 CREATE INDEX test_replica_identity_hash ON test_replica_identity USING hash (nonkey);
 CREATE UNIQUE INDEX test_replica_identity_expr ON test_replica_identity (keya, keyb, (3));
@@ -52,6 +53,9 @@ ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_iden
 SELECT relreplident FROM pg_class WHERE oid = 'test_replica_identity'::regclass;
 \d test_replica_identity
 
+-- succeed, oid unique index
+ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_identity_oid_idx;
+
 -- succeed, nondeferrable unique constraint over nonullable cols
 ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_identity_unique_nondefer;