Obtain required table lock during cross-table updates, redux.

tglsfdc · tglsfdc · commit f9ba071cc5bd · 2025-07-03T13:46:07.000-04:00
Commits 8319e5c et al missed the fact that ATPostAlterTypeCleanup contains three calls to ATPostAlterTypeParse, and the other two also need protection against passing a relid that we don't yet have lock on. Add similar logic to those code paths, and add some test cases demonstrating the need for it. In v18 and master, the test cases demonstrate that there's a behavioral discrepancy between stored generated columns and virtual generated columns: we disallow changing the expression of a stored column if it's used in any composite-type columns, but not that of a virtual column. Since the expression isn't actually relevant to either sort of composite-type usage, this prohibition seems unnecessary; but changing it is a matter for separate discussion. For now we are just documenting the existing behavior. Reported-by: jian he <jian.universality@gmail.com> Author: jian he <jian.universality@gmail.com> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: CACJufxGKJtGNRRSXfwMW9SqVOPEMdP17BJ7DsBf=tNsv9pWU9g@mail.gmail.com Backpatch-through: 13
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
@@ -12632,6 +12632,14 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
 		Oid			relid;
 
 		relid = IndexGetRelation(oldId, false);
+
+		/*
+		 * As above, make sure we have lock on the index's table if it's not
+		 * the same table.
+		 */
+		if (relid != tab->relid)
+			LockRelationOid(relid, AccessExclusiveLock);
+
 		ATPostAlterTypeParse(oldId, relid, InvalidOid,
 							 (char *) lfirst(def_item),
 							 wqueue, lockmode, tab->rewrite);
diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
@@ -4513,6 +4513,10 @@ create table attbl(a int);
 create table atref(b attbl check ((b).a is not null));
 alter table attbl alter column a type numeric;  -- someday this should work
 ERROR:  cannot alter table "attbl" because column "atref.b" uses its row type
+alter table atref drop constraint atref_b_check;
+create index atref_idx on atref (((b).a));
+alter table attbl alter column a type numeric;  -- someday this should work
+ERROR:  cannot alter table "attbl" because column "atref.b" uses its row type
 drop table attbl, atref;
 /* End test case for bug #18970 */
 -- Test that ALTER TABLE rewrite preserves a clustered index
diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
@@ -2983,6 +2983,10 @@ update bar1 set a = a + 1;
 create table attbl(a int);
 create table atref(b attbl check ((b).a is not null));
 alter table attbl alter column a type numeric;  -- someday this should work
+alter table atref drop constraint atref_b_check;
+
+create index atref_idx on atref (((b).a));
+alter table attbl alter column a type numeric;  -- someday this should work
 drop table attbl, atref;
 
 /* End test case for bug #18970 */
