From 40b78f838af24970bb51674de1783a1ebb9cbd17 Mon Sep 17 00:00:00 2001
From: jian he <jian.universality@gmail.com>
Date: Thu, 20 Aug 2026 15:15:00 +0800
Subject: [PATCH v6 1/1] Fix access method for new partition tables

If the partitioned table has a valid table access method, newly created
partitions for MERGE/SPLIT PARTITIONS use the parent table's access method.
Otherwise, fall back to default_table_access_method.
---
 src/backend/commands/tablecmds.c              |  5 ++++-
 src/test/regress/expected/partition_merge.out | 15 +++++++++++++++
 src/test/regress/expected/partition_split.out | 18 ++++++++++++++++++
 src/test/regress/sql/partition_merge.sql      | 11 +++++++++++
 src/test/regress/sql/partition_split.sql      | 12 ++++++++++++
 5 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 1840738f3f4..4371694ed8d 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -23334,7 +23334,10 @@ createPartitionTable(RangeVar *newPartName,
 	descriptor = BuildDescForRelation(colList);
 
 	/* Look up the access method for the new relation. */
-	relamId = (parent_relform->relam != InvalidOid) ? parent_relform->relam : HEAP_TABLE_AM_OID;
+	if (OidIsValid(parent_relform->relam))
+		relamId = parent_relform->relam;
+	else
+		relamId = get_table_am_oid(default_table_access_method, false);
 
 	/* Look up the namespace in which we are supposed to create the relation. */
 	namespaceId =
diff --git a/src/test/regress/expected/partition_merge.out b/src/test/regress/expected/partition_merge.out
index 7e1aac3b44d..d16a898e6c0 100644
--- a/src/test/regress/expected/partition_merge.out
+++ b/src/test/regress/expected/partition_merge.out
@@ -791,6 +791,21 @@ ORDER BY c.relname COLLATE "C";
  tp_0_2  | partitions_merge_heap
 (2 rows)
 
+DROP TABLE t;
+CREATE TABLE t (i int) PARTITION BY RANGE (i);
+CREATE TABLE tp_0_1 PARTITION OF t FOR VALUES FROM (0) TO (1);
+CREATE TABLE tp_1_2 PARTITION OF t FOR VALUES FROM (1) TO (2);
+BEGIN;
+SET LOCAL default_table_access_method to partitions_merge_heap;
+ALTER TABLE t MERGE PARTITIONS (tp_0_1, tp_1_2) INTO tp_0_2;
+SELECT c.relname, a.amname FROM pg_class c, pg_am a
+WHERE c.relname = 'tp_0_2' AND a.oid = c.relam;
+ relname |        amname         
+---------+-----------------------
+ tp_0_2  | partitions_merge_heap
+(1 row)
+
+COMMIT;
 DROP TABLE t;
 DROP ACCESS METHOD partitions_merge_heap;
 -- Test permission checks.  The user needs to own the parent table and all
diff --git a/src/test/regress/expected/partition_split.out b/src/test/regress/expected/partition_split.out
index 98575e00119..8780d19f90a 100644
--- a/src/test/regress/expected/partition_split.out
+++ b/src/test/regress/expected/partition_split.out
@@ -1355,6 +1355,24 @@ ORDER BY c.relname COLLATE "C";
  tp_1_2  | partition_split_heap
 (3 rows)
 
+DROP TABLE t;
+CREATE TABLE t (i int) PARTITION BY RANGE (i);
+CREATE TABLE tp_0_2 PARTITION OF t FOR VALUES FROM (0) TO (2);
+BEGIN;
+SET LOCAL default_table_access_method to partition_split_heap;
+ALTER TABLE t SPLIT PARTITION tp_0_2 INTO
+  (PARTITION tp_0_1 FOR VALUES FROM (0) TO (1),
+   PARTITION tp_1_2 FOR VALUES FROM (1) TO (2));
+SELECT c.relname, a.amname FROM pg_class c, pg_am a
+WHERE c.relname IN ('tp_0_1', 'tp_1_2')
+AND a.oid = c.relam;
+ relname |        amname        
+---------+----------------------
+ tp_0_1  | partition_split_heap
+ tp_1_2  | partition_split_heap
+(2 rows)
+
+COMMIT;
 DROP TABLE t;
 DROP ACCESS METHOD partition_split_heap;
 -- Split partition of a temporary table when one of the partitions after
diff --git a/src/test/regress/sql/partition_merge.sql b/src/test/regress/sql/partition_merge.sql
index 0fcda645147..11550a00be8 100644
--- a/src/test/regress/sql/partition_merge.sql
+++ b/src/test/regress/sql/partition_merge.sql
@@ -550,6 +550,17 @@ FROM pg_class c JOIN pg_am a ON c.relam = a.oid
 WHERE c.oid IN ('t'::regclass, 'tp_0_2'::regclass)
 ORDER BY c.relname COLLATE "C";
 DROP TABLE t;
+
+CREATE TABLE t (i int) PARTITION BY RANGE (i);
+CREATE TABLE tp_0_1 PARTITION OF t FOR VALUES FROM (0) TO (1);
+CREATE TABLE tp_1_2 PARTITION OF t FOR VALUES FROM (1) TO (2);
+BEGIN;
+SET LOCAL default_table_access_method to partitions_merge_heap;
+ALTER TABLE t MERGE PARTITIONS (tp_0_1, tp_1_2) INTO tp_0_2;
+SELECT c.relname, a.amname FROM pg_class c, pg_am a
+WHERE c.relname = 'tp_0_2' AND a.oid = c.relam;
+COMMIT;
+DROP TABLE t;
 DROP ACCESS METHOD partitions_merge_heap;
 
 -- Test permission checks.  The user needs to own the parent table and all
diff --git a/src/test/regress/sql/partition_split.sql b/src/test/regress/sql/partition_split.sql
index e97f13f749c..b734d69ba68 100644
--- a/src/test/regress/sql/partition_split.sql
+++ b/src/test/regress/sql/partition_split.sql
@@ -970,6 +970,18 @@ FROM pg_class c JOIN pg_am a ON c.relam = a.oid
 WHERE c.oid IN ('t'::regclass, 'tp_0_1'::regclass, 'tp_1_2'::regclass)
 ORDER BY c.relname COLLATE "C";
 DROP TABLE t;
+CREATE TABLE t (i int) PARTITION BY RANGE (i);
+CREATE TABLE tp_0_2 PARTITION OF t FOR VALUES FROM (0) TO (2);
+BEGIN;
+SET LOCAL default_table_access_method to partition_split_heap;
+ALTER TABLE t SPLIT PARTITION tp_0_2 INTO
+  (PARTITION tp_0_1 FOR VALUES FROM (0) TO (1),
+   PARTITION tp_1_2 FOR VALUES FROM (1) TO (2));
+SELECT c.relname, a.amname FROM pg_class c, pg_am a
+WHERE c.relname IN ('tp_0_1', 'tp_1_2')
+AND a.oid = c.relam;
+COMMIT;
+DROP TABLE t;
 DROP ACCESS METHOD partition_split_heap;
 
 -- Split partition of a temporary table when one of the partitions after
-- 
2.34.1

