Don't lose partitioned table reltuples=0 after relhassubclass=f.

ANALYZE sets relhassubclass=f when a partitioned table no longer has
partitions.  An ANALYZE doing that proceeded to apply the inplace update
of pg_class.reltuples to the old pg_class tuple instead of the new
tuple, losing that reltuples=0 change if the ANALYZE committed.
Non-partitioning inheritance trees were unaffected.  Back-patch to v14,
where commit 375aed3 introduced
maintenance of partitioned table pg_class.reltuples.

Reported by Alexander Lakhin.

Discussion: https://postgr.es/m/a295b499-dcab-6a99-c06e-01cf60593344@gmail.com

Author: nmisch

src/backend/commands/analyze.c

@@ -629,7 +629,11 @@ do_analyze_rel(Relation onerel, VacuumParams *params,
 		else
 			relallvisible = 0;
 
-		/* Update pg_class for table relation */
+		/*
+		 * Update pg_class for table relation.  CCI first, in case acquirefunc
+		 * updated pg_class.
+		 */
+		CommandCounterIncrement();
 		vac_update_relstats(onerel,
 							relpages,
 							totalrows,
@@ -664,6 +668,7 @@ do_analyze_rel(Relation onerel, VacuumParams *params,
 		 * Partitioned tables don't have storage, so we don't set any fields
 		 * in their pg_class entries except for reltuples and relhasindex.
 		 */
+		CommandCounterIncrement();
 		vac_update_relstats(onerel, -1, totalrows,
 							0, hasindex, InvalidTransactionId,
 							InvalidMultiXactId,

src/test/regress/expected/vacuum.out

@@ -82,6 +82,53 @@ BEGIN;
 INSERT INTO vactst SELECT generate_series(301, 400);
 DELETE FROM vactst WHERE i % 5 <> 0; -- delete a few rows inside
 ANALYZE vactst;
+COMMIT;
+-- Test ANALYZE setting relhassubclass=f for non-partitioning inheritance
+BEGIN;
+CREATE TABLE past_inh_parent ();
+CREATE TABLE past_inh_child () INHERITS (past_inh_parent);
+INSERT INTO past_inh_child DEFAULT VALUES;
+INSERT INTO past_inh_child DEFAULT VALUES;
+ANALYZE past_inh_parent;
+SELECT reltuples, relhassubclass
+  FROM pg_class WHERE oid = 'past_inh_parent'::regclass;
+ reltuples | relhassubclass 
+-----------+----------------
+         0 | t
+(1 row)
+
+DROP TABLE past_inh_child;
+ANALYZE past_inh_parent;
+SELECT reltuples, relhassubclass
+  FROM pg_class WHERE oid = 'past_inh_parent'::regclass;
+ reltuples | relhassubclass 
+-----------+----------------
+         0 | f
+(1 row)
+
+COMMIT;
+-- Test ANALYZE setting relhassubclass=f for partitioning
+BEGIN;
+CREATE TABLE past_parted (i int) PARTITION BY LIST(i);
+CREATE TABLE past_part PARTITION OF past_parted FOR VALUES IN (1);
+INSERT INTO past_parted VALUES (1),(1);
+ANALYZE past_parted;
+DROP TABLE past_part;
+SELECT reltuples, relhassubclass
+  FROM pg_class WHERE oid = 'past_parted'::regclass;
+ reltuples | relhassubclass 
+-----------+----------------
+         2 | t
+(1 row)
+
+ANALYZE past_parted;
+SELECT reltuples, relhassubclass
+  FROM pg_class WHERE oid = 'past_parted'::regclass;
+ reltuples | relhassubclass 
+-----------+----------------
+         0 | f
+(1 row)
+
 COMMIT;
 VACUUM FULL pg_am;
 VACUUM FULL pg_class;

src/test/regress/sql/vacuum.sql

@@ -67,6 +67,35 @@ DELETE FROM vactst WHERE i % 5 <> 0; -- delete a few rows inside
 ANALYZE vactst;
 COMMIT;
 
+-- Test ANALYZE setting relhassubclass=f for non-partitioning inheritance
+BEGIN;
+CREATE TABLE past_inh_parent ();
+CREATE TABLE past_inh_child () INHERITS (past_inh_parent);
+INSERT INTO past_inh_child DEFAULT VALUES;
+INSERT INTO past_inh_child DEFAULT VALUES;
+ANALYZE past_inh_parent;
+SELECT reltuples, relhassubclass
+  FROM pg_class WHERE oid = 'past_inh_parent'::regclass;
+DROP TABLE past_inh_child;
+ANALYZE past_inh_parent;
+SELECT reltuples, relhassubclass
+  FROM pg_class WHERE oid = 'past_inh_parent'::regclass;
+COMMIT;
+
+-- Test ANALYZE setting relhassubclass=f for partitioning
+BEGIN;
+CREATE TABLE past_parted (i int) PARTITION BY LIST(i);
+CREATE TABLE past_part PARTITION OF past_parted FOR VALUES IN (1);
+INSERT INTO past_parted VALUES (1),(1);
+ANALYZE past_parted;
+DROP TABLE past_part;
+SELECT reltuples, relhassubclass
+  FROM pg_class WHERE oid = 'past_parted'::regclass;
+ANALYZE past_parted;
+SELECT reltuples, relhassubclass
+  FROM pg_class WHERE oid = 'past_parted'::regclass;
+COMMIT;
+
 VACUUM FULL pg_am;
 VACUUM FULL pg_class;
 VACUUM FULL pg_database;