Support for GiST in get_equal_strategy_number()

A WITHOUT OVERLAPS primary key or unique constraint is accepted as a
REPLICA IDENTITY, since it guarantees uniqueness.  But subscribers
applying logical decoding messages would fail because there was not
support for looking up the equals operator for a gist index.  This
fixes that: For GiST indexes we can use the stratnum GiST support
function.

Reviewed-by: Paul Jungwirth <pj@illuminatedcomputing.com>
Reviewed-by: vignesh C <vignesh21@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CA+renyUApHgSZF9-nd-a0+OPGharLQLO=mDHcY4_qQ0+noCUVg@mail.gmail.com

Author: petere

src/backend/executor/execReplication.c

@@ -15,6 +15,7 @@
 #include "postgres.h"
 
 #include "access/genam.h"
+#include "access/gist.h"
 #include "access/relscan.h"
 #include "access/tableam.h"
 #include "access/transam.h"
@@ -40,11 +41,6 @@ static bool tuples_equal(TupleTableSlot *slot1, TupleTableSlot *slot2,
 /*
  * Returns the fixed strategy number, if any, of the equality operator for the
  * given operator class, otherwise, InvalidStrategy.
- *
- * Currently, only Btree and Hash indexes are supported. The other index access
- * methods don't have a fixed strategy for equality operation - instead, the
- * support routines of each operator class interpret the strategy numbers
- * according to the operator class's definition.
  */
 StrategyNumber
 get_equal_strategy_number(Oid opclass)
@@ -60,8 +56,10 @@ get_equal_strategy_number(Oid opclass)
 		case HASH_AM_OID:
 			ret = HTEqualStrategyNumber;
 			break;
+		case GIST_AM_OID:
+			ret = GistTranslateStratnum(opclass, RTEqualStrategyNumber);
+			break;
 		default:
-			/* XXX: Only Btree and Hash indexes are supported */
 			ret = InvalidStrategy;
 			break;
 	}