diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 5d7493e1949..df5ceacc90f 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -1204,7 +1204,7 @@ brin_summarize_range_internal(PG_FUNCTION_ARGS)
 
 	/* Must be a BRIN index */
 	if (indexRel->rd_rel->relkind != RELKIND_INDEX ||
-		indexRel->rd_rel->relam != BRIN_AM_OID)
+		!IsIndexAccessMethod(indexRel->rd_rel->relam, BRIN_AM_OID))
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a BRIN index",
@@ -1290,7 +1290,7 @@ brin_desummarize_range(PG_FUNCTION_ARGS)
 
 	/* Must be a BRIN index */
 	if (indexRel->rd_rel->relkind != RELKIND_INDEX ||
-		indexRel->rd_rel->relam != BRIN_AM_OID)
+		!IsIndexAccessMethod(indexRel->rd_rel->relam, BRIN_AM_OID))
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a BRIN index",
diff --git a/src/backend/access/gin/ginfast.c b/src/backend/access/gin/ginfast.c
index 02d2d6cf4e7..88d2d9a7182 100644
--- a/src/backend/access/gin/ginfast.c
+++ b/src/backend/access/gin/ginfast.c
@@ -1042,7 +1042,7 @@ gin_clean_pending_list(PG_FUNCTION_ARGS)
 
 	/* Must be a GIN index */
 	if (indexRel->rd_rel->relkind != RELKIND_INDEX ||
-		indexRel->rd_rel->relam != GIN_AM_OID)
+		!IsIndexAccessMethod(indexRel->rd_rel->relam, GIN_AM_OID))
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a GIN index",
diff --git a/src/backend/access/index/amapi.c b/src/backend/access/index/amapi.c
index d30bc435146..028b8e9999e 100644
--- a/src/backend/access/index/amapi.c
+++ b/src/backend/access/index/amapi.c
@@ -20,7 +20,18 @@
 #include "utils/builtins.h"
 #include "utils/syscache.h"
 
+is_index_access_method_hook_type is_index_access_method_hook = NULL;
 
+bool
+IsIndexAccessMethod(Oid relam, Oid indexAccessMethod)
+{
+	if ((is_index_access_method_hook && (*is_index_access_method_hook)(relam, indexAccessMethod)) ||
+		(!is_index_access_method_hook && relam == indexAccessMethod))
+	{
+		return true;
+	}
+	return false;
+}
 /*
  * GetIndexAmRoutine - call the specified access method handler routine to get
  * its IndexAmRoutine struct, which will be palloc'd in the caller's context.
diff --git a/src/backend/access/index/indexam.c b/src/backend/access/index/indexam.c
index 095d4f84e63..ebacc2bfcb5 100644
--- a/src/backend/access/index/indexam.c
+++ b/src/backend/access/index/indexam.c
@@ -988,3 +988,54 @@ index_opclass_options(Relation indrel, AttrNumber attnum, Datum attoptions,
 
 	return build_local_reloptions(&relopts, attoptions, validate);
 }
+
+/* check_hook: validate new default_index_access_method */
+bool
+check_default_index_access_method(char **newval, void **extra, GucSource source)
+{
+	if (**newval == '\0')
+	{
+		GUC_check_errdetail("%s cannot be empty.",
+		                    "check_default_index_access_method");
+		return false;
+	}
+
+	if (strlen(*newval) >= NAMEDATALEN)
+	{
+		GUC_check_errdetail("%s is too long (maximum %d characters).",
+		                    "check_default_index_access_method", NAMEDATALEN - 1);
+		return false;
+	}
+
+	/*
+	 * If we aren't inside a transaction, or not connected to a database, we
+	 * cannot do the catalog access necessary to verify the method.  Must
+	 * accept the value on faith.
+	 */
+	if (IsTransactionState() && MyDatabaseId != InvalidOid)
+	{
+		if (!OidIsValid(get_index_am_oid(*newval, true)))
+		{
+			/*
+			 * When source == PGC_S_TEST, don't throw a hard error for a
+			 * nonexistent index access method, only a NOTICE. See comments in
+			 * guc.h.
+			 */
+			if (source == PGC_S_TEST)
+			{
+				ereport(NOTICE,
+				        (errcode(ERRCODE_UNDEFINED_OBJECT),
+					        errmsg("index access method \"%s\" does not exist",
+					               *newval)));
+			}
+			else
+			{
+				GUC_check_errdetail("index access method \"%s\" does not exist.",
+				                    *newval);
+				return false;
+			}
+		}
+	}
+
+	return true;
+}
diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
index 5e3a2b7aa47..7c3563024db 100644
--- a/src/backend/access/nbtree/nbtree.c
+++ b/src/backend/access/nbtree/nbtree.c
@@ -41,7 +41,6 @@
 #include "catalog/indexing.h"
 #include "catalog/pg_namespace.h"
 
-
 /*
  * BTPARALLEL_NOT_INITIALIZED indicates that the scan has not started.
  *
diff --git a/src/backend/access/spgist/spgutils.c b/src/backend/access/spgist/spgutils.c
index 4484805192c..e3e663a006e 100644
--- a/src/backend/access/spgist/spgutils.c
+++ b/src/backend/access/spgist/spgutils.c
@@ -35,7 +35,6 @@
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
 
-
 /*
  * SP-GiST handler function: return IndexAmRoutine with access method parameters
  * and callbacks.
diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 917a541c6c0..4438ca40e33 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -99,6 +99,8 @@
 #include "cdb/cdboidsync.h"
 #include "utils/faultinjector.h"
 
+/* GUC variables */
+char       *default_index_access_method = DEFAULT_INDEX_TYPE;
 /* Potentially set by pg_upgrade_support functions */
 Oid			binary_upgrade_next_index_pg_class_oid = InvalidOid;
 
@@ -2808,7 +2810,7 @@ BuildSpeculativeIndexInfo(Relation index, IndexInfo *ii)
 	 */
 	Assert(ii->ii_Unique);
 
-	if (index->rd_rel->relam != BTREE_AM_OID)
+	if (!IsIndexAccessMethod(index->rd_rel->relam, BTREE_AM_OID))
 		elog(ERROR, "unexpected non-btree speculative unique index");
 
 	ii->ii_UniqueOps = (Oid *) palloc(sizeof(Oid) * indnkeyatts);
@@ -3129,7 +3131,7 @@ index_build(Relation heapRelation,
 	 * to introduce parallelism to singlenode mode.
 	 */
 	if (parallel && !IS_SINGLENODE() && IsNormalProcessingMode() &&
-		indexRelation->rd_rel->relam == BTREE_AM_OID)
+		IsIndexAccessMethod(indexRelation->rd_rel->relam, BTREE_AM_OID))
 		indexInfo->ii_ParallelWorkers =
 			plan_create_index_workers(RelationGetRelid(heapRelation),
 									  RelationGetRelid(indexRelation));
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 12ad9fa2af0..ed0762fd42b 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -962,7 +962,7 @@ copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, bool verbose,
 	 * tells us it's cheaper.  Otherwise, always indexscan if an index is
 	 * provided, else plain seqscan.
 	 */
-	if (OldIndex != NULL && OldIndex->rd_rel->relam == BTREE_AM_OID)
+	if (OldIndex != NULL && IsIndexAccessMethod(OldIndex->rd_rel->relam, BTREE_AM_OID))
 		use_sort = plan_cluster_use_sort(OIDOldHeap, OIDOldIndex);
 	else
 		use_sort = false;
diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index 51e30960223..cfbbebdf2be 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -1021,6 +1021,10 @@ DefineIndex(Oid relationId,
 	 * look up the access method, verify it can handle the requested features
 	 */
 	accessMethodName = stmt->accessMethod;
+	if (accessMethodName == NULL)
+	{
+		accessMethodName = default_index_access_method;
+	}
 	tuple = SearchSysCache1(AMNAME, PointerGetDatum(accessMethodName));
 	if (!HeapTupleIsValid(tuple))
 	{
@@ -1268,7 +1272,7 @@ DefineIndex(Oid relationId,
 			 * btree opclasses; if there are ever any other index types that
 			 * support unique indexes, this logic will need extension.
 			 */
-			if (accessMethodId == BTREE_AM_OID)
+			if (IsIndexAccessMethod(accessMethodId, BTREE_AM_OID))
 				eq_strategy = BTEqualStrategyNumber;
 			else
 				ereport(ERROR,
diff --git a/src/backend/commands/matview.c b/src/backend/commands/matview.c
index b1f6306f681..124f764c15f 100644
--- a/src/backend/commands/matview.c
+++ b/src/backend/commands/matview.c
@@ -15,6 +15,7 @@
  */
 #include "postgres.h"
 
+#include "access/amapi.h"
 #include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
@@ -908,7 +909,7 @@ refresh_by_match_merge(Oid matviewOid, Oid tempOid, Oid relowner,
 				if (!HeapTupleIsValid(cla_ht))
 					elog(ERROR, "cache lookup failed for opclass %u", opclass);
 				cla_tup = (Form_pg_opclass) GETSTRUCT(cla_ht);
-				Assert(cla_tup->opcmethod == BTREE_AM_OID);
+				Assert(IsIndexAccessMethod(cla_tup->opcmethod, BTREE_AM_OID));
 				opfamily = cla_tup->opcfamily;
 				opcintype = cla_tup->opcintype;
 				ReleaseSysCache(cla_ht);
@@ -1068,7 +1069,7 @@ is_usable_unique_index(Relation indexRel)
 	 */
 	if (indexStruct->indisunique &&
 		indexStruct->indimmediate &&
-		indexRel->rd_rel->relam == BTREE_AM_OID &&
+        IsIndexAccessMethod(indexRel->rd_rel->relam, BTREE_AM_OID) &&
 		indexStruct->indisvalid &&
 		RelationGetIndexPredicate(indexRel) == NIL &&
 		indexStruct->indnatts > 0)
diff --git a/src/backend/commands/opclasscmds.c b/src/backend/commands/opclasscmds.c
index ab9008ca9cd..4bd2716baea 100644
--- a/src/backend/commands/opclasscmds.c
+++ b/src/backend/commands/opclasscmds.c
@@ -595,7 +595,7 @@ DefineOpClass(CreateOpClassStmt *stmt)
 	if (OidIsValid(storageoid))
 	{
 		/* Just drop the spec if same as column datatype */
-		if (storageoid == typeoid)
+		if (storageoid == typeoid && !amstorage)
 			storageoid = InvalidOid;
 		else if (!amstorage)
 			ereport(ERROR,
@@ -1289,7 +1289,7 @@ assignProcTypes(OpFamilyMember *member, Oid amoid, Oid typeoid,
 	 * returning int4, while proc 2 must be a 2-arg proc returning int8.
 	 * Otherwise we don't know.
 	 */
-	else if (amoid == BTREE_AM_OID)
+	else if (IsIndexAccessMethod(amoid, BTREE_AM_OID))
 	{
 		if (member->number == BTORDER_PROC)
 		{
@@ -1372,7 +1372,7 @@ assignProcTypes(OpFamilyMember *member, Oid amoid, Oid typeoid,
 						 errmsg("btree equal image functions must not be cross-type")));
 		}
 	}
-	else if (amoid == HASH_AM_OID)
+	else if (IsIndexAccessMethod(amoid, HASH_AM_OID))
 	{
 		if (member->number == HASHSTANDARD_PROC)
 		{
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 63e1ee76d87..77adf685ddf 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -10751,7 +10751,7 @@ ATAddForeignKeyConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 		 * strategy number is equality.  (Is it reasonable to insist that
 		 * every such index AM use btree's number for equality?)
 		 */
-		if (amid != BTREE_AM_OID)
+		if (!IsIndexAccessMethod(amid, BTREE_AM_OID))
 			elog(ERROR, "only b-tree indexes are supported for foreign keys");
 		eqstrategy = BTEqualStrategyNumber;
 
diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index a083e13d6b2..4c5d3b587e0 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -1378,7 +1378,7 @@ ExecIndexBuildScanKeys(PlanState *planstate, Relation index,
 				 * We have to look up the operator's associated btree support
 				 * function
 				 */
-				if (index->rd_rel->relam != BTREE_AM_OID ||
+				if (!IsIndexAccessMethod(index->rd_rel->relam, BTREE_AM_OID) ||
 					varattno < 1 || varattno > indnkeyatts)
 					elog(ERROR, "bogus RowCompare index qualification");
 				opfamily = index->rd_opfamily[varattno - 1];
diff --git a/src/backend/mock.mk b/src/backend/mock.mk
index 11b02242aab..c72c2dca2b0 100644
--- a/src/backend/mock.mk
+++ b/src/backend/mock.mk
@@ -37,9 +37,6 @@ EXCL_OBJS=\
 # of the test programs. Feel free to link them back (i.e. remove them from
 # this exclusion list) as needed.
 EXCL_OBJS+=\
-	src/backend/access/hash/hash.o \
-	src/backend/access/hash/hashsearch.o \
-	\
 	src/backend/utils/adt/cash.o \
 	src/backend/utils/adt/char.o \
 	src/backend/utils/adt/complex_type.o \
diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 421ff7bb9ba..d1c7c631a13 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -2830,7 +2830,7 @@ match_rowcompare_to_indexcol(PlannerInfo *root,
 	Oid			expr_coll;
 
 	/* Forget it if we're not dealing with a btree index */
-	if (index->relam != BTREE_AM_OID)
+	if (!IsIndexAccessMethod(index->relam, BTREE_AM_OID))
 		return NULL;
 
 	index_relid = index->rel->relid;
@@ -3529,7 +3529,7 @@ ec_member_matches_indexcol(PlannerInfo *root, RelOptInfo *rel,
 	 * generate_implied_equalities_for_column; see
 	 * match_eclass_clauses_to_index.
 	 */
-	if (index->relam == BTREE_AM_OID &&
+	if (IsIndexAccessMethod(index->relam, BTREE_AM_OID) &&
 		!list_member_oid(ec->ec_opfamilies, curFamily))
 		return false;
 
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index 918c554579e..2371df4eacc 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -19,6 +19,7 @@
 
 #include <math.h>
 
+#include "access/amapi.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/extensible.h"
@@ -1124,7 +1125,7 @@ create_index_path(PlannerInfo *root,
 														  required_outer);
 	pathnode->path.parallel_aware = false;
 	/* GPDB_12_MERGE_FEATURE_NOT_SUPPORTED: the parallel StreamBitmap scan is not implemented */
-	pathnode->path.parallel_safe = rel->consider_parallel && (index->relam != BITMAP_AM_OID);
+	pathnode->path.parallel_safe = rel->consider_parallel && !IsIndexAccessMethod(index->relam, BITMAP_AM_OID);
 	pathnode->path.parallel_workers = 0;
 	pathnode->path.pathkeys = pathkeys;
 
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 2281294422c..832635cb981 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -311,7 +311,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 			/*
 			 * Fetch the ordering information for the index, if any.
 			 */
-			if (info->relam == BTREE_AM_OID)
+			if (IsIndexAccessMethod(info->relam, BTREE_AM_OID))
 			{
 				/*
 				 * If it's a btree index, we can use its opfamily OIDs
@@ -436,7 +436,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 				info->tuples > rel->tuples)
 				info->tuples = rel->tuples;
 
-			if (info->relam == BTREE_AM_OID)
+			if (IsIndexAccessMethod(info->relam, BTREE_AM_OID))
 			{
 				/* For btrees, get tree height while we have the index open */
 				info->tree_height = _bt_getrootheight(indexRelation);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index c9a49579eef..300f7da3505 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -10165,7 +10165,7 @@ opt_index_name:
 
 access_method_clause:
 			USING name								{ $$ = $2; }
-			| /*EMPTY*/								{ $$ = DEFAULT_INDEX_TYPE; }
+			| /*EMPTY*/								{ $$ = NULL; }
 		;
 
 index_params:	index_elem							{ $$ = list_make1($1); }
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index dd07b4075be..e0c8423d45c 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -3289,7 +3289,7 @@ transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 		index->idxname = NULL;	/* DefineIndex will choose name */
 
 	index->relation = cxt->relation;
-	index->accessMethod = constraint->access_method ? constraint->access_method : DEFAULT_INDEX_TYPE;
+	index->accessMethod = constraint->access_method ? constraint->access_method : default_index_access_method;
 	index->options = constraint->options;
 	index->tableSpace = constraint->indexspace;
 	index->whereClause = constraint->where_clause;
@@ -3413,7 +3413,7 @@ transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 		 * else dump and reload will produce a different index (breaking
 		 * pg_upgrade in particular).
 		 */
-		if (index_rel->rd_rel->relam != get_index_am_oid(DEFAULT_INDEX_TYPE, false))
+		if (!IsIndexAccessMethod(index_rel->rd_rel->relam, BTREE_AM_OID))
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 					 errmsg("index \"%s\" is not a btree", index_name),
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 221099b03f4..086d627d4d2 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -6229,7 +6229,7 @@ get_actual_variable_range(PlannerInfo *root, VariableStatData *vardata,
 		ScanDirection indexscandir;
 
 		/* Ignore non-btree indexes */
-		if (index->relam != BTREE_AM_OID)
+		if (!IsIndexAccessMethod(index->relam, BTREE_AM_OID))
 			continue;
 
 		/*
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index fe6b8c56a56..e57e41b10ec 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -866,8 +866,8 @@ equality_ops_are_compatible(Oid opno1, Oid opno2)
 		Form_pg_amop op_form = (Form_pg_amop) GETSTRUCT(op_tuple);
 
 		/* must be btree or hash */
-		if (op_form->amopmethod == BTREE_AM_OID ||
-			op_form->amopmethod == HASH_AM_OID)
+		if (IsIndexAccessMethod(op_form->amopmethod, BTREE_AM_OID) ||
+			IsIndexAccessMethod(op_form->amopmethod, HASH_AM_OID))
 		{
 			if (op_in_opfamily(opno2, op_form->amopfamily))
 			{
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 5cc58b4f5d6..d4df12d2ebd 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -48,6 +48,7 @@
 #include "catalog/pg_authid.h"
 #include "catalog/pg_profile.h"
 #include "catalog/storage.h"
+#include "catalog/index.h"
 #include "commands/async.h"
 #include "commands/prepare.h"
 #include "commands/trigger.h"
diff --git a/src/backend/utils/misc/guc_gp.c b/src/backend/utils/misc/guc_gp.c
index e19ebd0e951..a25db7f796a 100644
--- a/src/backend/utils/misc/guc_gp.c
+++ b/src/backend/utils/misc/guc_gp.c
@@ -58,6 +58,7 @@
 #include "utils/resource_manager.h"
 #include "utils/varlena.h"
 #include "utils/vmem_tracker.h"
+#include "catalog/index.h"
 
 /*
  * These constants are copied from guc.c. They should not bitrot when we
@@ -4572,6 +4573,17 @@ struct config_string ConfigureNamesString_gp[] =
 		GP_VERSION,
 		NULL, NULL, NULL
 	},
+
+	{
+		{"default_index_access_method", PGC_USERSET, CLIENT_CONN_STATEMENT,
+		 gettext_noop("Sets the default index access method."),
+		 NULL,
+		 GUC_IS_NAME
+		},
+		&default_index_access_method,
+		DEFAULT_INDEX_TYPE,
+		check_default_index_access_method, NULL, NULL
+	},
 #ifndef USE_INTERNAL_FTS
 	{
 		{"gp_etcd_account_id", PGC_BACKEND, CUSTOM_OPTIONS,
diff --git a/src/backend/utils/sort/sortsupport.c b/src/backend/utils/sort/sortsupport.c
index 6a889ec189f..97d8c580d64 100644
--- a/src/backend/utils/sort/sortsupport.c
+++ b/src/backend/utils/sort/sortsupport.c
@@ -167,7 +167,7 @@ PrepareSortSupportFromIndexRel(Relation indexRel, int16 strategy,
 
 	Assert(ssup->comparator == NULL);
 
-	if (indexRel->rd_rel->relam != BTREE_AM_OID)
+	if (!IsIndexAccessMethod(indexRel->rd_rel->relam, BTREE_AM_OID))
 		elog(ERROR, "unexpected non-btree AM: %u", indexRel->rd_rel->relam);
 	if (strategy != BTGreaterStrategyNumber &&
 		strategy != BTLessStrategyNumber)
@@ -194,7 +194,7 @@ PrepareSortSupportFromGistIndexRel(Relation indexRel, SortSupport ssup)
 
 	Assert(ssup->comparator == NULL);
 
-	if (indexRel->rd_rel->relam != GIST_AM_OID)
+	if (!IsIndexAccessMethod(indexRel->rd_rel->relam, GIST_AM_OID))
 		elog(ERROR, "unexpected non-gist AM: %u", indexRel->rd_rel->relam);
 	ssup->ssup_reverse = false;
 
diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c
index 8d2bdc3df94..0b9c16f9417 100644
--- a/src/backend/utils/sort/tuplesort.c
+++ b/src/backend/utils/sort/tuplesort.c
@@ -985,7 +985,7 @@ tuplesort_begin_cluster(TupleDesc tupDesc,
 	MemoryContext oldcontext;
 	int			i;
 
-	Assert(indexRel->rd_rel->relam == BTREE_AM_OID);
+	Assert(IsIndexAccessMethod(indexRel->rd_rel->relam, BTREE_AM_OID));
 
 	oldcontext = MemoryContextSwitchTo(state->maincontext);
 
diff --git a/src/include/access/amapi.h b/src/include/access/amapi.h
index 02be79c3663..a30f4bb6a63 100644
--- a/src/include/access/amapi.h
+++ b/src/include/access/amapi.h
@@ -14,6 +14,7 @@
 #define AMAPI_H
 
 #include "access/genam.h"
+#include "catalog/pg_index.h"
 
 /*
  * We don't wish to include planner header files here, since most of an index
@@ -285,6 +286,7 @@ typedef struct IndexAmRoutine
 
 
 /* Functions in access/index/amapi.c */
+extern bool IsIndexAccessMethod(Oid relam, Oid indexAccessMethod);
 extern IndexAmRoutine *GetIndexAmRoutine(Oid amhandler);
 extern IndexAmRoutine *GetIndexAmRoutineByAmId(Oid amoid, bool noerror);
 
diff --git a/src/include/access/brin.h b/src/include/access/brin.h
index 4e2be13cd61..5c80a6ae611 100644
--- a/src/include/access/brin.h
+++ b/src/include/access/brin.h
@@ -38,13 +38,13 @@ typedef struct BrinStatsData
 #define BRIN_DEFAULT_PAGES_PER_RANGE	128
 #define BrinGetPagesPerRange(relation) \
 	(AssertMacro(relation->rd_rel->relkind == RELKIND_INDEX && \
-				 relation->rd_rel->relam == BRIN_AM_OID), \
+				 IsIndexAccessMethod(relation->rd_rel->relam, BRIN_AM_OID)), \
 	 (relation)->rd_options ? \
 	 ((BrinOptions *) (relation)->rd_options)->pagesPerRange : \
 	  BRIN_DEFAULT_PAGES_PER_RANGE)
 #define BrinGetAutoSummarize(relation) \
 	(AssertMacro(relation->rd_rel->relkind == RELKIND_INDEX && \
-				 relation->rd_rel->relam == BRIN_AM_OID), \
+				 IsIndexAccessMethod(relation->rd_rel->relam, BRIN_AM_OID)), \
 	 (relation)->rd_options ? \
 	 ((BrinOptions *) (relation)->rd_options)->autosummarize : \
 	  false)
diff --git a/src/include/access/gin_private.h b/src/include/access/gin_private.h
index b24112ff96a..74c9b70dc32 100644
--- a/src/include/access/gin_private.h
+++ b/src/include/access/gin_private.h
@@ -32,12 +32,12 @@ typedef struct GinOptions
 #define GIN_DEFAULT_USE_FASTUPDATE	true
 #define GinGetUseFastUpdate(relation) \
 	(AssertMacro(relation->rd_rel->relkind == RELKIND_INDEX && \
-				 relation->rd_rel->relam == GIN_AM_OID), \
+				 IsIndexAccessMethod(relation->rd_rel->relam, GIN_AM_OID)), \
 	 (relation)->rd_options ? \
 	 ((GinOptions *) (relation)->rd_options)->useFastUpdate : GIN_DEFAULT_USE_FASTUPDATE)
 #define GinGetPendingListCleanupSize(relation) \
 	(AssertMacro(relation->rd_rel->relkind == RELKIND_INDEX && \
-				 relation->rd_rel->relam == GIN_AM_OID), \
+				 IsIndexAccessMethod(relation->rd_rel->relam, GIN_AM_OID)), \
 	 (relation)->rd_options && \
 	 ((GinOptions *) (relation)->rd_options)->pendingListCleanupSize != -1 ? \
 	 ((GinOptions *) (relation)->rd_options)->pendingListCleanupSize : \
diff --git a/src/include/access/hash.h b/src/include/access/hash.h
index 6de41944a9c..f29cd3db35e 100644
--- a/src/include/access/hash.h
+++ b/src/include/access/hash.h
@@ -272,7 +272,7 @@ typedef struct HashOptions
 
 #define HashGetFillFactor(relation) \
 	(AssertMacro(relation->rd_rel->relkind == RELKIND_INDEX && \
-				 relation->rd_rel->relam == HASH_AM_OID), \
+				 IsIndexAccessMethod(relation->rd_rel->relam, HASH_AM_OID)), \
 	 (relation)->rd_options ? \
 	 ((HashOptions *) (relation)->rd_options)->fillfactor :	\
 	 HASH_DEFAULT_FILLFACTOR)
diff --git a/src/include/access/nbtree.h b/src/include/access/nbtree.h
index 28d360d058f..816a0fe761d 100644
--- a/src/include/access/nbtree.h
+++ b/src/include/access/nbtree.h
@@ -1092,7 +1092,7 @@ typedef struct BTOptions
 
 #define BTGetFillFactor(relation) \
 	(AssertMacro(relation->rd_rel->relkind == RELKIND_INDEX && \
-				 relation->rd_rel->relam == BTREE_AM_OID), \
+				 IsIndexAccessMethod(relation->rd_rel->relam, BTREE_AM_OID)), \
 	 (relation)->rd_options ? \
 	 ((BTOptions *) (relation)->rd_options)->fillfactor : \
 	 BTREE_DEFAULT_FILLFACTOR)
@@ -1100,7 +1100,7 @@ typedef struct BTOptions
 	(BLCKSZ * (100 - BTGetFillFactor(relation)) / 100)
 #define BTGetDeduplicateItems(relation) \
 	(AssertMacro(relation->rd_rel->relkind == RELKIND_INDEX && \
-				 relation->rd_rel->relam == BTREE_AM_OID), \
+				 IsIndexAccessMethod(relation->rd_rel->relam, BTREE_AM_OID)), \
 	((relation)->rd_options ? \
 	 ((BTOptions *) (relation)->rd_options)->deduplicate_items : true))
 
diff --git a/src/include/access/spgist_private.h b/src/include/access/spgist_private.h
index 40d3b71b89e..cc7f0922556 100644
--- a/src/include/access/spgist_private.h
+++ b/src/include/access/spgist_private.h
@@ -31,7 +31,7 @@ typedef struct SpGistOptions
 
 #define SpGistGetFillFactor(relation) \
 	(AssertMacro(relation->rd_rel->relkind == RELKIND_INDEX && \
-				 relation->rd_rel->relam == SPGIST_AM_OID), \
+				 IsIndexAccessMethod(relation->rd_rel->relam, SPGIST_AM_OID)), \
 	 (relation)->rd_options ? \
 	 ((SpGistOptions *) (relation)->rd_options)->fillfactor : \
 	 SPGIST_DEFAULT_FILLFACTOR)
diff --git a/src/include/catalog/index.h b/src/include/catalog/index.h
index 8e0ee2349b2..28985171776 100644
--- a/src/include/catalog/index.h
+++ b/src/include/catalog/index.h
@@ -20,10 +20,13 @@
 #include "catalog/objectaddress.h"
 #include "executor/tuptable.h"  /* TupTableSlot */
 #include "nodes/execnodes.h"
+#include "utils/guc.h"
 
 struct EState;                  /* #include "nodes/execnodes.h" */
 
 #define DEFAULT_INDEX_TYPE	"btree"
+/* GUCs */
+extern char *default_index_access_method;
 
 /* Action code for index_set_state_flags */
 typedef enum
@@ -225,6 +228,8 @@ extern void SerializeReindexState(Size maxsize, char *start_address);
 extern void RestoreReindexState(void *reindexstate);
 
 extern void IndexSetParentIndex(Relation idx, Oid parentOid);
+extern bool check_default_index_access_method(char **newval, void **extra,
+                                              GucSource source);
 
 
 /*
diff --git a/src/include/catalog/pg_index.h b/src/include/catalog/pg_index.h
index 38b5bfc42c2..15794cb50ef 100644
--- a/src/include/catalog/pg_index.h
+++ b/src/include/catalog/pg_index.h
@@ -73,6 +73,8 @@ FOREIGN_KEY(indrelid REFERENCES pg_class(oid));
  * ----------------
  */
 typedef FormData_pg_index *Form_pg_index;
+typedef bool (*is_index_access_method_hook_type)(Oid id, Oid expected_oid);
+extern PGDLLIMPORT is_index_access_method_hook_type is_index_access_method_hook;
 
 DECLARE_INDEX(pg_index_indrelid_index, 2678, on pg_index using btree(indrelid oid_ops));
 #define IndexIndrelidIndexId  2678
diff --git a/src/include/utils/sync_guc_name.h b/src/include/utils/sync_guc_name.h
index 1b4c8a040c4..aefc91e8716 100644
--- a/src/include/utils/sync_guc_name.h
+++ b/src/include/utils/sync_guc_name.h
@@ -17,6 +17,7 @@
 		"DateStyle",
 		"debug_discard_caches",
 		"default_table_access_method",
+		"default_index_access_method",
 		"default_tablespace",
 		"default_toast_compression",
 		"dml_ignore_target_partition_check",
diff --git a/src/test/regress/expected/brin.out b/src/test/regress/expected/brin.out
index 73a68af6b51..bdc3dad0569 100644
--- a/src/test/regress/expected/brin.out
+++ b/src/test/regress/expected/brin.out
@@ -560,7 +560,7 @@ EXPLAIN (COSTS OFF) SELECT * FROM brin_test WHERE b = 1;
 (4 rows)
 
 -- make sure data are properly de-toasted in BRIN index
-CREATE TABLE brintest_3 (a text, b text, c text, d text);
+CREATE TABLE brintest_3 (a text, b text, c text, d text, e varchar);
 -- long random strings (~2000 chars each, so ~6kB for min/max on two
 -- columns) to trigger toasting
 WITH rand_value AS (SELECT string_agg(md5(i::text),'') AS val FROM generate_series(1,60) s(i))
@@ -573,6 +573,9 @@ DELETE FROM brintest_3;
 -- is a one way to achieve that, because it does exactly such wait.
 CREATE INDEX brin_test_temp_idx ON brintest_3(a);
 DROP INDEX brin_test_temp_idx;
+-- make sure varchar to text implicitly
+CREATE INDEX brin_test_varchar_to_text_idx on brintest_3(e);
+DROP INDEX brin_test_varchar_to_text_idx;
 -- vacuum the table, to discard TOAST data
 VACUUM brintest_3;
 -- retry insert with a different random-looking (but deterministic) value
@@ -596,8 +599,8 @@ SELECT * FROM brintest_3 WHERE b < '0';
 (6 rows)
 
 SELECT * FROM brintest_3 WHERE b < '0';
- a | b | c | d 
----+---+---+---
+ a | b | c | d | e 
+---+---+---+---+---
 (0 rows)
 
 DROP TABLE brintest_3;
diff --git a/src/test/regress/expected/brin_optimizer.out b/src/test/regress/expected/brin_optimizer.out
index 3dd5ff30598..a95155d8344 100644
--- a/src/test/regress/expected/brin_optimizer.out
+++ b/src/test/regress/expected/brin_optimizer.out
@@ -584,7 +584,7 @@ EXPLAIN (COSTS OFF) SELECT * FROM brin_test WHERE b = 1;
 (6 rows)
 
 -- make sure data are properly de-toasted in BRIN index
-CREATE TABLE brintest_3 (a text, b text, c text, d text);
+CREATE TABLE brintest_3 (a text, b text, c text, d text, e varchar);
 NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'a' as the Cloudberry Database data distribution key for this table.
 HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
 -- long random strings (~2000 chars each, so ~6kB for min/max on two
@@ -601,6 +601,9 @@ HINT:  For non-partitioned tables, run analyze <table_name>(<column_list>). For
 -- is a one way to achieve that, because it does exactly such wait.
 CREATE INDEX brin_test_temp_idx ON brintest_3(a);
 DROP INDEX brin_test_temp_idx;
+-- make sure varchar to text implicitly
+CREATE INDEX brin_test_varchar_to_text_idx on brintest_3(e);
+DROP INDEX brin_test_varchar_to_text_idx;
 -- vacuum the table, to discard TOAST data
 VACUUM brintest_3;
 -- retry insert with a different random-looking (but deterministic) value
@@ -624,8 +627,8 @@ SELECT * FROM brintest_3 WHERE b < '0';
 (6 rows)
 
 SELECT * FROM brintest_3 WHERE b < '0';
- a | b | c | d 
----+---+---+---
+ a | b | c | d | e 
+---+---+---+---+---
 (0 rows)
 
 DROP TABLE brintest_3;
diff --git a/src/test/regress/sql/brin.sql b/src/test/regress/sql/brin.sql
index c8879599a5f..e9704aaa0d7 100644
--- a/src/test/regress/sql/brin.sql
+++ b/src/test/regress/sql/brin.sql
@@ -511,7 +511,7 @@ EXPLAIN (COSTS OFF) SELECT * FROM brin_test WHERE a = 1;
 EXPLAIN (COSTS OFF) SELECT * FROM brin_test WHERE b = 1;
 
 -- make sure data are properly de-toasted in BRIN index
-CREATE TABLE brintest_3 (a text, b text, c text, d text);
+CREATE TABLE brintest_3 (a text, b text, c text, d text, e varchar);
 
 -- long random strings (~2000 chars each, so ~6kB for min/max on two
 -- columns) to trigger toasting
@@ -528,6 +528,10 @@ DELETE FROM brintest_3;
 CREATE INDEX brin_test_temp_idx ON brintest_3(a);
 DROP INDEX brin_test_temp_idx;
 
+-- make sure varchar to text implicitly
+CREATE INDEX brin_test_varchar_to_text_idx on brintest_3(e);
+DROP INDEX brin_test_varchar_to_text_idx;
+
 -- vacuum the table, to discard TOAST data
 VACUUM brintest_3;