Reset inherited flags on chunks attached to a hypertable

Attaching an existing table as a chunk uses ALTER TABLE ... INHERIT,
which raises the inheritance count of the child columns and constraints
but leaves them marked as locally defined. A chunk is meant to be a pure
inheritance child, so a later DROP COLUMN or DROP CONSTRAINT on the
hypertable did not reach such a chunk and left an orphaned column or
constraint behind instead.

Clear the local flag on the inherited columns and constraints when a
chunk is attached so schema changes on the hypertable propagate to it.
Also add a migration that fixes chunks already left in this state by an
earlier detach and attach round-trip.

Author: svenklemm

.unreleased/fix_attach_chunk_attislocal

@@ -0,0 +1 @@
+Fixes: #10352 Reset inherited column and constraint flags on chunks during attach_chunk

sql/updates/latest-dev.sql

@@ -0,0 +1,20 @@
+-- Reset the attislocal/conislocal flags on chunk columns and constraints left
+-- marked local by a detach_chunk/attach_chunk round-trip so a later hypertable
+-- DROP COLUMN or DROP CONSTRAINT propagates to them. Restricted to chunk
+-- relations via the catalog join; locally-defined objects (inhcount = 0), such
+-- as the chunk's dimension constraints, are left untouched.
+UPDATE pg_catalog.pg_attribute a
+SET attislocal = false
+FROM _timescaledb_catalog.chunk c
+WHERE a.attrelid = c.relid
+  AND a.attnum > 0
+  AND NOT a.attisdropped
+  AND a.attislocal
+  AND a.attinhcount > 0;
+
+UPDATE pg_catalog.pg_constraint con
+SET conislocal = false
+FROM _timescaledb_catalog.chunk c
+WHERE con.conrelid = c.relid
+  AND con.conislocal
+  AND con.coninhcount > 0;

src/chunk.c

@@ -4,6 +4,7 @@
  * LICENSE-APACHE for a copy of the license.
  */
 #include <postgres.h>
+#include <access/genam.h>
 #include <access/htup.h>
 #include <access/htup_details.h>
 #include <access/reloptions.h>
@@ -13,6 +14,7 @@
 #include <access/xact.h>
 #include <catalog/indexing.h>
 #include <catalog/namespace.h>
+#include <catalog/pg_attribute.h>
 #include <catalog/pg_class.h>
 #include <catalog/pg_constraint.h>
 #include <catalog/pg_inherits.h>
@@ -46,6 +48,7 @@
 #include <utils/builtins.h>
 #include <utils/datum.h>
 #include <utils/elog.h>
+#include <utils/fmgroids.h>
 #include <utils/hsearch.h>
 #include <utils/inval.h>
 #include <utils/lsyscache.h>
@@ -1116,6 +1119,80 @@ chunk_create_from_hypercube_after_lock(const Hypertable *ht, Hypercube *cube,
 	return chunk;
 }
 
+/*
+ * A chunk should have all columns and constraints inherited and none marked as
+ * local, so clear the attislocal/conislocal flags that ALTER TABLE ... INHERIT
+ * leaves set when attaching a pre-existing table. Otherwise a later DROP COLUMN
+ * or DROP CONSTRAINT on the hypertable would not propagate to the chunk.
+ * Locally-defined objects (inhcount == 0), such as the chunk's dimension
+ * constraints, are left untouched.
+ */
+static void
+chunk_reset_inherited_flags(Oid chunk_relid)
+{
+	/* Columns */
+	Relation attrel = table_open(AttributeRelationId, RowExclusiveLock);
+	Relation chunkrel = table_open(chunk_relid, AccessShareLock);
+	TupleDesc tupdesc = RelationGetDescr(chunkrel);
+
+	for (int i = 0; i < tupdesc->natts; i++)
+	{
+		Form_pg_attribute att = TupleDescAttr(tupdesc, i);
+
+		if (att->attisdropped || !att->attislocal || att->attinhcount == 0)
+		{
+			continue;
+		}
+
+		HeapTuple tuple = SearchSysCacheCopyAttNum(chunk_relid, att->attnum);
+		if (!HeapTupleIsValid(tuple))
+		{
+			elog(ERROR,
+				 "cache lookup failed for attribute %d of relation %u",
+				 att->attnum,
+				 chunk_relid);
+		}
+
+		((Form_pg_attribute) GETSTRUCT(tuple))->attislocal = false;
+		CatalogTupleUpdate(attrel, &tuple->t_self, tuple);
+		heap_freetuple(tuple);
+	}
+
+	table_close(chunkrel, NoLock);
+	table_close(attrel, RowExclusiveLock);
+
+	/* Constraints (CHECK and NOT NULL) */
+	ScanKeyData skey;
+	ScanKeyInit(&skey,
+				Anum_pg_constraint_conrelid,
+				BTEqualStrategyNumber,
+				F_OIDEQ,
+				ObjectIdGetDatum(chunk_relid));
+
+	Relation conrel = table_open(ConstraintRelationId, RowExclusiveLock);
+	SysScanDesc scan =
+		systable_beginscan(conrel, ConstraintRelidTypidNameIndexId, true, NULL, 1, &skey);
+	HeapTuple contup;
+
+	while (HeapTupleIsValid(contup = systable_getnext(scan)))
+	{
+		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(contup);
+
+		if (con->coninhcount == 0 || !con->conislocal)
+		{
+			continue;
+		}
+
+		HeapTuple newtup = heap_copytuple(contup);
+		((Form_pg_constraint) GETSTRUCT(newtup))->conislocal = false;
+		CatalogTupleUpdate(conrel, &newtup->t_self, newtup);
+		heap_freetuple(newtup);
+	}
+
+	systable_endscan(scan);
+	table_close(conrel, RowExclusiveLock);
+}
+
 /*
  * Make a chunk table inherit a hypertable.
  *
@@ -1149,6 +1226,8 @@ chunk_add_inheritance(Chunk *chunk, const Hypertable *ht)
 	};
 
 	AlterTable(&alterstmt, lockmode, &atcontext);
+
+	chunk_reset_inherited_flags(atcontext.relid);
 }
 
 static Chunk *

tsl/test/expected/attach_chunk.out tsl/test/expected/attach_chunk-16.outtsl/test/expected/attach_chunk.out renamed to tsl/test/expected/attach_chunk-16.out

@@ -235,3 +235,122 @@ DROP TABLE regular_table_to_attach;
 DROP TABLE attach_test_ref;
 DROP TABLE attach_test;
 DROP TABLE devices CASCADE;
+-- Test dropping columns after detach/attach
+CREATE TABLE drop_after_attach(time timestamptz NOT NULL, x int);
+SELECT create_hypertable('drop_after_attach', 'time', chunk_time_interval => interval '1 day');
+       create_hypertable        
+--------------------------------
+ (3,public,drop_after_attach,t)
+
+INSERT INTO drop_after_attach VALUES ('2026-01-01', 1), ('2026-01-05', 1);
+SELECT schema_name || '.' || table_name AS "ROUNDTRIP_CHUNK", slices AS "ROUNDTRIP_SLICES"
+FROM _timescaledb_functions.show_chunk((SELECT show_chunks('drop_after_attach', older_than => '2026-01-02') LIMIT 1)); \gset
+             ROUNDTRIP_CHUNK             |                ROUNDTRIP_SLICES                
+-----------------------------------------+------------------------------------------------
+ _timescaledb_internal._hyper_3_15_chunk | {"time": [1767225600000000, 1767312000000000]}
+
+CALL detach_chunk(:'ROUNDTRIP_CHUNK');
+CALL attach_chunk('drop_after_attach', :'ROUNDTRIP_CHUNK', :'ROUNDTRIP_SLICES');
+-- The re-attached chunk inherits without any locally-defined columns.
+SELECT attname, attislocal, attinhcount
+FROM pg_attribute
+WHERE attrelid = :'ROUNDTRIP_CHUNK'::regclass AND attnum > 0 AND NOT attisdropped
+ORDER BY attnum;
+ attname | attislocal | attinhcount 
+---------+------------+-------------
+ time    | f          |           1
+ x       | f          |           1
+
+ALTER TABLE drop_after_attach DROP COLUMN x;
+-- The column is gone from the round-tripped chunk, not left orphaned.
+SELECT attname, attislocal, attinhcount
+FROM pg_attribute
+WHERE attrelid = :'ROUNDTRIP_CHUNK'::regclass AND attname = 'x' AND NOT attisdropped;
+ attname | attislocal | attinhcount 
+---------+------------+-------------
+
+DROP TABLE drop_after_attach;
+-- Test dropping a constraint after detach/attach
+CREATE TABLE drop_con_after_attach(time timestamptz NOT NULL, x int CHECK (x > 0));
+SELECT create_hypertable('drop_con_after_attach', 'time', chunk_time_interval => interval '1 day');
+         create_hypertable          
+------------------------------------
+ (4,public,drop_con_after_attach,t)
+
+INSERT INTO drop_con_after_attach VALUES ('2026-01-01', 1);
+SELECT schema_name || '.' || table_name AS "CON_CHUNK", slices AS "CON_SLICES"
+FROM _timescaledb_functions.show_chunk((SELECT show_chunks('drop_con_after_attach') LIMIT 1)); \gset
+                CON_CHUNK                |                   CON_SLICES                   
+-----------------------------------------+------------------------------------------------
+ _timescaledb_internal._hyper_4_18_chunk | {"time": [1767225600000000, 1767312000000000]}
+
+CALL detach_chunk(:'CON_CHUNK');
+CALL attach_chunk('drop_con_after_attach', :'CON_CHUNK', :'CON_SLICES');
+-- The inherited constraint is not marked local; the dimension constraint stays local.
+SELECT conname, contype, conislocal, coninhcount
+FROM pg_constraint
+WHERE conrelid = :'CON_CHUNK'::regclass
+ORDER BY conname;
+            conname            | contype | conislocal | coninhcount 
+-------------------------------+---------+------------+-------------
+ constraint_30                 | c       | t          |           0
+ drop_con_after_attach_x_check | c       | f          |           1
+
+ALTER TABLE drop_con_after_attach DROP CONSTRAINT drop_con_after_attach_x_check;
+-- The dropped constraint is gone from the round-tripped chunk.
+SELECT count(*) AS leftover_check
+FROM pg_constraint
+WHERE conrelid = :'CON_CHUNK'::regclass AND conname = 'drop_con_after_attach_x_check';
+ leftover_check 
+----------------
+              0
+
+DROP TABLE drop_con_after_attach;
+-- Test attaching a foreign table as an OSM chunk
+-- A dummy server is enough; the foreign table is never queried by attach.
+\c :TEST_DBNAME :ROLE_SUPERUSER
+CREATE EXTENSION postgres_fdw;
+CREATE SERVER attach_chunk_fdw FOREIGN DATA WRAPPER postgres_fdw;
+CREATE TABLE osm_ht(time timestamptz NOT NULL, x int CHECK (x > 0));
+SELECT create_hypertable('osm_ht', 'time', chunk_time_interval => interval '1 day');
+  create_hypertable  
+---------------------
+ (5,public,osm_ht,t)
+
+CREATE FOREIGN TABLE osm_ft(time timestamptz NOT NULL, x int) SERVER attach_chunk_fdw;
+SELECT _timescaledb_functions.attach_osm_table_chunk('osm_ht', 'osm_ft');
+ attach_osm_table_chunk 
+------------------------
+ t
+
+-- The foreign chunk inherits its columns without any left marked local.
+SELECT attname, attislocal, attinhcount
+FROM pg_attribute
+WHERE attrelid = 'osm_ft'::regclass AND attnum > 0 AND NOT attisdropped
+ORDER BY attnum;
+ attname | attislocal | attinhcount 
+---------+------------+-------------
+ time    | f          |           1
+ x       | f          |           1
+
+-- The CHECK constraint cloned from the hypertable is inherited, not local.
+SELECT conname, contype, conislocal, coninhcount
+FROM pg_constraint
+WHERE conrelid = 'osm_ft'::regclass AND contype = 'c'
+ORDER BY conname;
+    conname     | contype | conislocal | coninhcount 
+----------------+---------+------------+-------------
+ osm_ht_x_check | c       | f          |           1
+
+ALTER TABLE osm_ht DROP COLUMN x;
+-- Dropping the column on the hypertable propagates to the foreign chunk.
+SELECT attname
+FROM pg_attribute
+WHERE attrelid = 'osm_ft'::regclass AND attname = 'x' AND NOT attisdropped;
+ attname 
+---------
+
+-- Dropping the hypertable also drops the attached foreign chunk.
+DROP TABLE osm_ht;
+DROP SERVER attach_chunk_fdw;
+DROP EXTENSION postgres_fdw;