From b753be38a4a239b7cd4d2c289d8737c955c46f6f Mon Sep 17 00:00:00 2001 From: =?utf8?q?=C3=81lvaro=20Herrera?= Date: Sat, 11 Oct 2025 20:30:12 +0200 Subject: [PATCH] Stop creating constraints during DETACH CONCURRENTLY Commit 71f4c8c6f74b (which implemented DETACH CONCURRENTLY) added code to create a separate table constraint when a table is detached concurrently, identical to the partition constraint, on the theory that such a constraint was needed in case the optimizer had constructed any query plans that depended on the constraint being there. However, that theory was apparently bogus because any such plans would be invalidated. For hash partitioning, those constraints are problematic, because their expressions reference the OID of the parent partitioned table, to which the detached table is no longer related; this causes all sorts of problems (such as inability of restoring a pg_dump of that table, and the table no longer working properly if the partitioned table is later dropped). We'd like to get rid of all those constraints. In fact, for branch master, do that -- no longer create any substitute constraints. However, out of fear that some users might somehow depend on these constraints for other partitioning strategies, for stable branches (back to 14, which added DETACH CONCURRENTLY), only do it for hash partitioning. (If you repeatedly DETACH CONCURRENTLY and then ATTACH a partition, then with this constraint addition you don't need to scan the table in the ATTACH step, which presumably is good. But if users really valued this feature, they would have requested that it worked for non-concurrent DETACH also.) Author: Haiyang Li Reported-by: Fei Changhong Reported-by: Haiyang Li Backpatch-through: 14 Discussion: https://postgr.es/m/18371-7fef49f63de13f02@postgresql.org Discussion: https://postgr.es/m/19070-781326347ade7c57@postgresql.org --- src/backend/commands/tablecmds.c | 14 +++++++++----- src/test/regress/expected/alter_table.out | 8 ++++++++ src/test/regress/sql/alter_table.sql | 9 +++++++++ 3 files changed, 26 insertions(+), 5 deletions(-) diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c index 015e11af67b..09f8569d4e8 100644 --- a/src/backend/commands/tablecmds.c +++ b/src/backend/commands/tablecmds.c @@ -18096,13 +18096,14 @@ ATExecDetachPartition(List **wqueue, AlteredTableInfo *tab, Relation rel, Relation partRel; ObjectAddress address; Oid defaultPartOid; + PartitionDesc partdesc; /* * We must lock the default partition, because detaching this partition * will change its partition constraint. */ - defaultPartOid = - get_default_oid_from_partdesc(RelationGetPartitionDesc(rel, true)); + partdesc = RelationGetPartitionDesc(rel, true); + defaultPartOid = get_default_oid_from_partdesc(partdesc); if (OidIsValid(defaultPartOid)) { /* @@ -18169,10 +18170,13 @@ ATExecDetachPartition(List **wqueue, AlteredTableInfo *tab, Relation rel, char *partrelname; /* - * Add a new constraint to the partition being detached, which - * supplants the partition constraint (unless there is one already). + * For strategies other than hash, add a constraint to the partition + * being detached which supplants the partition constraint. For hash + * we cannot do that, because the constraint would reference the + * partitioned table OID, possibly causing problems later. */ - DetachAddConstraintIfNeeded(wqueue, partRel); + if (partdesc->boundinfo->strategy != PARTITION_STRATEGY_HASH) + DetachAddConstraintIfNeeded(wqueue, partRel); /* * We're almost done now; the only traces that remain are the diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out index fcae98a7aff..5cdf64e829b 100644 --- a/src/test/regress/expected/alter_table.out +++ b/src/test/regress/expected/alter_table.out @@ -4345,6 +4345,14 @@ Check constraints: "part_rp100_a_check" CHECK (a >= 123 AND a < 133 AND a IS NOT NULL) DROP TABLE range_parted2; +-- Test that hash partitions continue to work after they're concurrently +-- detached (bugs #18371, #19070) +CREATE TABLE hash_parted2 (a int) PARTITION BY HASH(a); +CREATE TABLE part_hp PARTITION OF hash_parted2 FOR VALUES WITH (MODULUS 2, REMAINDER 0); +ALTER TABLE hash_parted2 DETACH PARTITION part_hp CONCURRENTLY; +DROP TABLE hash_parted2; +INSERT INTO part_hp VALUES (1); +DROP TABLE part_hp; -- Check ALTER TABLE commands for partitioned tables and partitions -- cannot add/drop column to/from *only* the parent ALTER TABLE ONLY list_parted2 ADD COLUMN c int; diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql index fe59ff42546..a4c7dfadece 100644 --- a/src/test/regress/sql/alter_table.sql +++ b/src/test/regress/sql/alter_table.sql @@ -2794,6 +2794,15 @@ ALTER TABLE range_parted2 DETACH PARTITION part_rp100 CONCURRENTLY; \d part_rp100 DROP TABLE range_parted2; +-- Test that hash partitions continue to work after they're concurrently +-- detached (bugs #18371, #19070) +CREATE TABLE hash_parted2 (a int) PARTITION BY HASH(a); +CREATE TABLE part_hp PARTITION OF hash_parted2 FOR VALUES WITH (MODULUS 2, REMAINDER 0); +ALTER TABLE hash_parted2 DETACH PARTITION part_hp CONCURRENTLY; +DROP TABLE hash_parted2; +INSERT INTO part_hp VALUES (1); +DROP TABLE part_hp; + -- Check ALTER TABLE commands for partitioned tables and partitions -- cannot add/drop column to/from *only* the parent -- 2.47.3