Feature: add user-defined index access method

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",

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",

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.

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;
+}

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.
  *

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.

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));

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;

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,

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)

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)
 		{

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;
 

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];

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 \

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;
 

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;
 

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);

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); }

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),

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;
 
 		/*

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))
 			{

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"

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,