Fix ALTER TABLE / REPLICA IDENTITY for temporal tables

REPLICA IDENTITY USING INDEX did not accept a GiST index.  This should
be allowed when used as a temporal primary key.

Author: Paul Jungwirth <pj@illuminatedcomputing.com>
Discussion: https://www.postgresql.org/message-id/04579cbf-b134-45e1-8f2d-8c54c849c1ee@illuminatedcomputing.com

src/backend/commands/tablecmds.c

@@ -17296,9 +17296,14 @@ ATExecReplicaIdentity(Relation rel, ReplicaIdentityStmt *stmt, LOCKMODE lockmode
 				 errmsg("\"%s\" is not an index for table \"%s\"",
 						RelationGetRelationName(indexRel),
 						RelationGetRelationName(rel))));
-	/* The AM must support uniqueness, and the index must in fact be unique. */
-	if (!indexRel->rd_indam->amcanunique ||
-		!indexRel->rd_index->indisunique)
+	/*
+	 * The AM must support uniqueness, and the index must in fact be unique.
+	 * If we have a WITHOUT OVERLAPS constraint (identified by uniqueness +
+	 * exclusion), we can use that too.
+	 */
+	if ((!indexRel->rd_indam->amcanunique ||
+		 !indexRel->rd_index->indisunique) &&
+		!(indexRel->rd_index->indisunique && indexRel->rd_index->indisexclusion))
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("cannot use non-unique index \"%s\" as replica identity",

src/test/regress/expected/without_overlaps.out

@@ -978,9 +978,25 @@ SELECT * FROM tp2 ORDER BY id, valid_at;
 
 DROP TABLE temporal_partitioned;
 -- ALTER TABLE REPLICA IDENTITY
--- (should fail)
+\d temporal_rng
+              Table "public.temporal_rng"
+  Column  |   Type    | Collation | Nullable | Default 
+----------+-----------+-----------+----------+---------
+ id       | int4range |           | not null | 
+ valid_at | daterange |           | not null | 
+Indexes:
+    "temporal_rng_pk" PRIMARY KEY (id, valid_at WITHOUT OVERLAPS)
+
 ALTER TABLE temporal_rng REPLICA IDENTITY USING INDEX temporal_rng_pk;
-ERROR:  cannot use non-unique index "temporal_rng_pk" as replica identity
+\d temporal_rng
+              Table "public.temporal_rng"
+  Column  |   Type    | Collation | Nullable | Default 
+----------+-----------+-----------+----------+---------
+ id       | int4range |           | not null | 
+ valid_at | daterange |           | not null | 
+Indexes:
+    "temporal_rng_pk" PRIMARY KEY (id, valid_at WITHOUT OVERLAPS) REPLICA IDENTITY
+
 --
 -- ON CONFLICT: ranges
 --

src/test/regress/sql/without_overlaps.sql

@@ -691,8 +691,9 @@ SELECT * FROM tp2 ORDER BY id, valid_at;
 DROP TABLE temporal_partitioned;
 
 -- ALTER TABLE REPLICA IDENTITY
--- (should fail)
+\d temporal_rng
 ALTER TABLE temporal_rng REPLICA IDENTITY USING INDEX temporal_rng_pk;
+\d temporal_rng
 
 --
 -- ON CONFLICT: ranges