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

Commits 8319e5cb5 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
index 2f649ba75820f7abd4a3dba8831dbdbc3a0b610e..9819067ad9d06c3b008a6a51a7ca0a76216933fc 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -13533,6 +13533,14 @@ 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);
@@ -13549,6 +13557,20 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
        Oid         relid;
 
        relid = StatisticsGetRelation(oldId, false);
+
+       /*
+        * As above, make sure we have lock on the statistics object's table
+        * if it's not the same table.  However, we take
+        * ShareUpdateExclusiveLock here, aligning with the lock level used in
+        * CreateStatistics and RemoveStatisticsById.
+        *
+        * CAUTION: this should be done after all cases that grab
+        * AccessExclusiveLock, else we risk causing deadlock due to needing
+        * to promote our table lock.
+        */
+       if (relid != tab->relid)
+           LockRelationOid(relid, ShareUpdateExclusiveLock);
+
        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
index e1636d3f82ea4e7ee4c64438f995d0496bee8716..5b9c61914fdf16b7418399bda8458e9d8f0ae309 100644 (file)
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -4580,6 +4580,14 @@ 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 statistics atref_stat on ((b).a is not null) from atref;
+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 statistics atref_stat;
+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
index 43c3c728403055adfa65c491a175e303d6718eb7..87d6a93b1244c85cfdbf33d3e7114776a6b59f7a 100644 (file)
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -3019,6 +3019,14 @@ drop table attbl, atref;
 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 statistics atref_stat on ((b).a is not null) from atref;
+alter table attbl alter column a type numeric;  -- someday this should work
+drop statistics atref_stat;
+
+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 */