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 5252c971eec14391420b937e39ca1ea56eaa7bdf..016ae0a65f933ca6deae4526a856a4f0fa943c1c 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -13561,6 +13561,14 @@ 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);
@@ -13577,6 +13585,20 @@ 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 de757a94dab922ceabb20cb67d565f2d3d4bc6bf..29b7c305789a9e497ffe6e8a3baa02930cc93a45 100644 (file)
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -4588,6 +4588,14 @@ 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 b4380ca4b9cb28efcf42af410c49708c33e40e0e..c45f9af17d0852613364079502b76f45670f0244 100644 (file)
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -3025,6 +3025,14 @@ 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 */