Allow specifying an access method for partitioned tables

It's now possible to specify a table access method via
CREATE TABLE ... USING for a partitioned table, as well change it with
ALTER TABLE ... SET ACCESS METHOD.  Specifying an AM for a partitioned
table lets the value be used for all future partitions created under it,
closely mirroring the behavior of the TABLESPACE option for partitioned
tables.  Existing partitions are not modified.

For a partitioned table with no AM specified, any new partitions are
created with the default_table_access_method.

Also add ALTER TABLE ... SET ACCESS METHOD DEFAULT, which reverts to the
original state of using the default for new partitions.

The relcache of partitioned tables is not changed: rd_tableam is not
set, even if a partitioned table has a relam set.

Author: Justin Pryzby <pryzby@telsasoft.com>
Author: Soumyadeep Chakraborty <soumyadeep2007@gmail.com>
Author: Michaël Paquier <michael@paquier.xyz>
Reviewed-by: The authors themselves
Discussion: https://postgr.es/m/CAE-ML+9zM4wJCGCBGv01k96qQ3gFv4WFcFy=zqPHKeaEFwwv6A@mail.gmail.com
Discussion: https://postgr.es/m/20210308010707.GA29832%40telsasoft.com

2 files changed, 239 insertions, 10 deletions

diff --git a/src/test/regress/expected/create_am.out b/src/test/regress/expected/create_am.out
index 8d73e213563..a27805a8f5e 100644
--- a/src/test/regress/expected/create_am.out
+++ b/src/test/regress/expected/create_am.out
@@ -176,9 +176,16 @@ SELECT f1 FROM tableam_tblmv_heap2 ORDER BY f1;
   1
 (1 row)
 
--- CREATE TABLE ..  PARTITION BY doesn't not support USING
+-- CREATE TABLE ..  PARTITION BY supports USING.
 CREATE TABLE tableam_parted_heap2 (a text, b int) PARTITION BY list (a) USING heap2;
-ERROR:  specifying a table access method is not supported on a partitioned table
+SELECT a.amname FROM pg_class c, pg_am a
+  WHERE c.relname = 'tableam_parted_heap2' AND a.oid = c.relam;
+ amname 
+--------
+ heap2
+(1 row)
+
+DROP TABLE tableam_parted_heap2;
 CREATE TABLE tableam_parted_heap2 (a text, b int) PARTITION BY list (a);
 -- new partitions will inherit from the current default, rather the partition root
 SET default_table_access_method = 'heap';
@@ -336,12 +343,151 @@ ALTER MATERIALIZED VIEW heapmv SET ACCESS METHOD heap, SET ACCESS METHOD heap2;
 ERROR:  cannot have multiple SET ACCESS METHOD subcommands
 DROP MATERIALIZED VIEW heapmv;
 DROP TABLE heaptable;
--- No support for partitioned tables.
-CREATE TABLE am_partitioned(x INT, y INT)
-  PARTITION BY hash (x);
+-- Partition hierarchies with access methods
+BEGIN;
+SET LOCAL default_table_access_method = 'heap';
+CREATE TABLE am_partitioned(x INT, y INT) PARTITION BY hash (x);
+-- pg_class.relam is 0, no dependency recorded between the AM and the
+-- partitioned table.
+SELECT relam FROM pg_class WHERE relname = 'am_partitioned';
+ relam 
+-------
+     0
+(1 row)
+
+SELECT pg_describe_object(classid, objid, objsubid) AS obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as refobj
+  FROM pg_depend, pg_am
+  WHERE pg_depend.refclassid = 'pg_am'::regclass
+    AND pg_am.oid = pg_depend.refobjid
+    AND pg_depend.objid = 'am_partitioned'::regclass;
+ obj | refobj 
+-----+--------
+(0 rows)
+
+-- New default is set, with dependency added.
+ALTER TABLE am_partitioned SET ACCESS METHOD heap2;
+SELECT a.amname FROM pg_class c, pg_am a
+  WHERE c.relname = 'am_partitioned' AND a.oid = c.relam;
+ amname 
+--------
+ heap2
+(1 row)
+
+SELECT pg_describe_object(classid, objid, objsubid) AS obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as refobj
+  FROM pg_depend, pg_am
+  WHERE pg_depend.refclassid = 'pg_am'::regclass
+    AND pg_am.oid = pg_depend.refobjid
+    AND pg_depend.objid = 'am_partitioned'::regclass;
+         obj          |       refobj        
+----------------------+---------------------
+ table am_partitioned | access method heap2
+(1 row)
+
+-- Default is set, with dependency updated.
+SET LOCAL default_table_access_method = 'heap2';
+ALTER TABLE am_partitioned SET ACCESS METHOD heap;
+SELECT a.amname FROM pg_class c, pg_am a
+  WHERE c.relname = 'am_partitioned' AND a.oid = c.relam;
+ amname 
+--------
+ heap
+(1 row)
+
+-- Dependency pinned, hence removed.
+SELECT pg_describe_object(classid, objid, objsubid) AS obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as refobj
+  FROM pg_depend, pg_am
+  WHERE pg_depend.refclassid = 'pg_am'::regclass
+    AND pg_am.oid = pg_depend.refobjid
+    AND pg_depend.objid = 'am_partitioned'::regclass;
+ obj | refobj 
+-----+--------
+(0 rows)
+
+-- Default and AM set in the clause are the same, relam should be set.
+SET LOCAL default_table_access_method = 'heap2';
+ALTER TABLE am_partitioned SET ACCESS METHOD heap2;
+SELECT a.amname FROM pg_class c, pg_am a
+  WHERE c.relname = 'am_partitioned' AND a.oid = c.relam;
+ amname 
+--------
+ heap2
+(1 row)
+
+-- Reset to default
+ALTER TABLE am_partitioned SET ACCESS METHOD DEFAULT;
+SELECT relam FROM pg_class WHERE relname = 'am_partitioned';
+ relam 
+-------
+     0
+(1 row)
+
+-- Upon ALTER TABLE SET ACCESS METHOD on a partitioned table, new partitions
+-- will inherit the AM set.  Existing partitioned are unchanged.
+SELECT relam FROM pg_class WHERE relname = 'am_partitioned';
+ relam 
+-------
+     0
+(1 row)
+
+SET LOCAL default_table_access_method = 'heap';
+CREATE TABLE am_partitioned_0 PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 0);
+SET LOCAL default_table_access_method = 'heap2';
+CREATE TABLE am_partitioned_1 PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 1);
+SET LOCAL default_table_access_method = 'heap';
 ALTER TABLE am_partitioned SET ACCESS METHOD heap2;
-ERROR:  cannot change access method of a partitioned table
+CREATE TABLE am_partitioned_2 PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 2);
+ALTER TABLE am_partitioned SET ACCESS METHOD DEFAULT;
+SELECT relam FROM pg_class WHERE relname = 'am_partitioned';
+ relam 
+-------
+     0
+(1 row)
+
+CREATE TABLE am_partitioned_3 PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 3);
+-- Partitioned table with relam at 0
+ALTER TABLE am_partitioned SET ACCESS METHOD DEFAULT;
+CREATE TABLE am_partitioned_5p PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 5) PARTITION BY hash(y);
+-- Partitions of this partitioned table inherit default AM at creation
+-- time.
+CREATE TABLE am_partitioned_5p1 PARTITION OF am_partitioned_5p
+  FOR VALUES WITH (MODULUS 10, REMAINDER 1);
+-- Partitioned table with relam set.
+ALTER TABLE am_partitioned SET ACCESS METHOD heap2;
+CREATE TABLE am_partitioned_6p PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 6) PARTITION BY hash(y);
+-- Partitions of this partitioned table inherit its AM.
+CREATE TABLE am_partitioned_6p1 PARTITION OF am_partitioned_6p
+  FOR VALUES WITH (MODULUS 10, REMAINDER 1);
+SELECT c.relname, a.amname FROM pg_class c, pg_am a
+  WHERE c.relam = a.oid AND
+        c.relname LIKE 'am_partitioned%'
+UNION ALL
+SELECT c.relname, 'default' FROM pg_class c
+  WHERE c.relam = 0
+        AND c.relname LIKE 'am_partitioned%' ORDER BY 1;
+      relname       | amname  
+--------------------+---------
+ am_partitioned     | heap2
+ am_partitioned_0   | heap
+ am_partitioned_1   | heap2
+ am_partitioned_2   | heap2
+ am_partitioned_3   | heap
+ am_partitioned_5p  | default
+ am_partitioned_5p1 | heap
+ am_partitioned_6p  | heap2
+ am_partitioned_6p1 | heap2
+(9 rows)
+
 DROP TABLE am_partitioned;
+COMMIT;
 -- Second, create objects in the new AM by changing the default AM
 BEGIN;
 SET LOCAL default_table_access_method = 'heap2';
diff --git a/src/test/regress/sql/create_am.sql b/src/test/regress/sql/create_am.sql
index 606ee4cb241..adff0079f98 100644
--- a/src/test/regress/sql/create_am.sql
+++ b/src/test/regress/sql/create_am.sql
@@ -124,8 +124,11 @@ CREATE SEQUENCE tableam_seq_heap2 USING heap2;
 CREATE MATERIALIZED VIEW tableam_tblmv_heap2 USING heap2 AS SELECT * FROM tableam_tbl_heap2;
 SELECT f1 FROM tableam_tblmv_heap2 ORDER BY f1;
 
--- CREATE TABLE ..  PARTITION BY doesn't not support USING
+-- CREATE TABLE ..  PARTITION BY supports USING.
 CREATE TABLE tableam_parted_heap2 (a text, b int) PARTITION BY list (a) USING heap2;
+SELECT a.amname FROM pg_class c, pg_am a
+  WHERE c.relname = 'tableam_parted_heap2' AND a.oid = c.relam;
+DROP TABLE tableam_parted_heap2;
 
 CREATE TABLE tableam_parted_heap2 (a text, b int) PARTITION BY list (a);
 -- new partitions will inherit from the current default, rather the partition root
@@ -213,11 +216,91 @@ ALTER TABLE heaptable SET ACCESS METHOD DEFAULT, SET ACCESS METHOD heap2;
 ALTER MATERIALIZED VIEW heapmv SET ACCESS METHOD heap, SET ACCESS METHOD heap2;
 DROP MATERIALIZED VIEW heapmv;
 DROP TABLE heaptable;
--- No support for partitioned tables.
-CREATE TABLE am_partitioned(x INT, y INT)
-  PARTITION BY hash (x);
+
+-- Partition hierarchies with access methods
+BEGIN;
+SET LOCAL default_table_access_method = 'heap';
+CREATE TABLE am_partitioned(x INT, y INT) PARTITION BY hash (x);
+-- pg_class.relam is 0, no dependency recorded between the AM and the
+-- partitioned table.
+SELECT relam FROM pg_class WHERE relname = 'am_partitioned';
+SELECT pg_describe_object(classid, objid, objsubid) AS obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as refobj
+  FROM pg_depend, pg_am
+  WHERE pg_depend.refclassid = 'pg_am'::regclass
+    AND pg_am.oid = pg_depend.refobjid
+    AND pg_depend.objid = 'am_partitioned'::regclass;
+-- New default is set, with dependency added.
+ALTER TABLE am_partitioned SET ACCESS METHOD heap2;
+SELECT a.amname FROM pg_class c, pg_am a
+  WHERE c.relname = 'am_partitioned' AND a.oid = c.relam;
+SELECT pg_describe_object(classid, objid, objsubid) AS obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as refobj
+  FROM pg_depend, pg_am
+  WHERE pg_depend.refclassid = 'pg_am'::regclass
+    AND pg_am.oid = pg_depend.refobjid
+    AND pg_depend.objid = 'am_partitioned'::regclass;
+-- Default is set, with dependency updated.
+SET LOCAL default_table_access_method = 'heap2';
+ALTER TABLE am_partitioned SET ACCESS METHOD heap;
+SELECT a.amname FROM pg_class c, pg_am a
+  WHERE c.relname = 'am_partitioned' AND a.oid = c.relam;
+-- Dependency pinned, hence removed.
+SELECT pg_describe_object(classid, objid, objsubid) AS obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as refobj
+  FROM pg_depend, pg_am
+  WHERE pg_depend.refclassid = 'pg_am'::regclass
+    AND pg_am.oid = pg_depend.refobjid
+    AND pg_depend.objid = 'am_partitioned'::regclass;
+-- Default and AM set in the clause are the same, relam should be set.
+SET LOCAL default_table_access_method = 'heap2';
+ALTER TABLE am_partitioned SET ACCESS METHOD heap2;
+SELECT a.amname FROM pg_class c, pg_am a
+  WHERE c.relname = 'am_partitioned' AND a.oid = c.relam;
+-- Reset to default
+ALTER TABLE am_partitioned SET ACCESS METHOD DEFAULT;
+SELECT relam FROM pg_class WHERE relname = 'am_partitioned';
+-- Upon ALTER TABLE SET ACCESS METHOD on a partitioned table, new partitions
+-- will inherit the AM set.  Existing partitioned are unchanged.
+SELECT relam FROM pg_class WHERE relname = 'am_partitioned';
+SET LOCAL default_table_access_method = 'heap';
+CREATE TABLE am_partitioned_0 PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 0);
+SET LOCAL default_table_access_method = 'heap2';
+CREATE TABLE am_partitioned_1 PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 1);
+SET LOCAL default_table_access_method = 'heap';
+ALTER TABLE am_partitioned SET ACCESS METHOD heap2;
+CREATE TABLE am_partitioned_2 PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 2);
+ALTER TABLE am_partitioned SET ACCESS METHOD DEFAULT;
+SELECT relam FROM pg_class WHERE relname = 'am_partitioned';
+CREATE TABLE am_partitioned_3 PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 3);
+-- Partitioned table with relam at 0
+ALTER TABLE am_partitioned SET ACCESS METHOD DEFAULT;
+CREATE TABLE am_partitioned_5p PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 5) PARTITION BY hash(y);
+-- Partitions of this partitioned table inherit default AM at creation
+-- time.
+CREATE TABLE am_partitioned_5p1 PARTITION OF am_partitioned_5p
+  FOR VALUES WITH (MODULUS 10, REMAINDER 1);
+-- Partitioned table with relam set.
 ALTER TABLE am_partitioned SET ACCESS METHOD heap2;
+CREATE TABLE am_partitioned_6p PARTITION OF am_partitioned
+  FOR VALUES WITH (MODULUS 10, REMAINDER 6) PARTITION BY hash(y);
+-- Partitions of this partitioned table inherit its AM.
+CREATE TABLE am_partitioned_6p1 PARTITION OF am_partitioned_6p
+  FOR VALUES WITH (MODULUS 10, REMAINDER 1);
+SELECT c.relname, a.amname FROM pg_class c, pg_am a
+  WHERE c.relam = a.oid AND
+        c.relname LIKE 'am_partitioned%'
+UNION ALL
+SELECT c.relname, 'default' FROM pg_class c
+  WHERE c.relam = 0
+        AND c.relname LIKE 'am_partitioned%' ORDER BY 1;
 DROP TABLE am_partitioned;
+COMMIT;
 
 -- Second, create objects in the new AM by changing the default AM
 BEGIN;