PAX: treat PAX tables as AO-like in index path generation

src/backend/optimizer/path/indxpath.c

@@ -813,7 +813,14 @@ get_index_paths(PlannerInfo *root, RelOptInfo *rel,
 		 */
 		if (index->amhasgettuple)
 		{
-			if (!AMHandlerIsAO(rel->amhandler) ||
+			/*
+			 * PAX shares AO's planner concern: random TID fetch
+			 * re-decompresses whole stripes and bypasses the buffer pool.
+			 * Treat it as AO-like so only Bitmap paths survive add_path
+			 * here.
+			 */
+			if ((!AMHandlerIsAO(rel->amhandler) &&
+				 rel->relam != PAX_AM_OID) ||
 				index->amcostestimate == bmcostestimate)
 				add_path(rel, (Path *) ipath, root);
 			else if (gp_enable_ao_indexscan && !IsA(ipath, IndexOnlyScan))

src/backend/optimizer/util/plancat.c

@@ -158,6 +158,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
      */
     rel->cdbpolicy = RelationGetPartitioningKey(relation);
 	rel->amhandler = relation->rd_amhandler;
+	rel->relam = relation->rd_rel->relam;
 
 	/*
 	 * Estimate relation size --- unless it's an inheritance parent, in which

src/include/nodes/pathnodes.h

@@ -913,6 +913,7 @@ typedef struct RelOptInfo
 	double		tuples;
     struct GpPolicy   *cdbpolicy;      /* distribution of stored tuples */
 	Oid			amhandler;			/* from relcache entry */
+	Oid			relam;				/* pg_class.relam (table AM oid) */
 	double		allvisfrac;
 	Bitmapset  *eclass_indexes; /* Indexes in PlannerInfo's eq_classes list of
 								 * ECs that mention this rel */