Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commit00d00b5

Browse files
committed
Fix ALTER COLUMN TYPE to not open a relation without any lock.
If the column being modified is referenced by a foreign key constraintof another table, ALTER TABLE would open the other table (to re-parsethe constraint's definition) without having first obtained a lock on it.This was evidently intentional, but that doesn't mean it's really safe.It's especially not safe in 9.3, which pre-dates use of MVCC scans forcatalog reads, but even in current releases it doesn't seem like a goodidea.We know we'll need AccessExclusiveLock shortly to drop the obsoletedconstraint, so just get that a little sooner to close the hole.Per testing with a patch that complains if we open a relation withoutholding any lock on it. I don't plan to back-patch that patch, but weshould close the holes it identifies in all supported branches.Discussion:https://postgr.es/m/2038.1538335244@sss.pgh.pa.us
1 parent08aad3c commit00d00b5

File tree

1 file changed

+12
-2
lines changed

1 file changed

+12
-2
lines changed

‎src/backend/commands/tablecmds.c

Lines changed: 12 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7949,8 +7949,7 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
79497949
* appropriate work queue entries. We do this before dropping because in
79507950
* the case of a FOREIGN KEY constraint, we might not yet have exclusive
79517951
* lock on the table the constraint is attached to, and we need to get
7952-
* that before dropping. It's safe because the parser won't actually look
7953-
* at the catalogs to detect the existing entry.
7952+
* that before reparsing/dropping.
79547953
*
79557954
* We can't rely on the output of deparsing to tell us which relation
79567955
* to operate on, because concurrent activity might have made the name
@@ -7966,6 +7965,7 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
79667965
Form_pg_constraintcon;
79677966
Oidrelid;
79687967
Oidconfrelid;
7968+
charcontype;
79697969
boolconislocal;
79707970

79717971
tup=SearchSysCache1(CONSTROID,ObjectIdGetDatum(oldId));
@@ -7974,6 +7974,7 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
79747974
con= (Form_pg_constraint)GETSTRUCT(tup);
79757975
relid=con->conrelid;
79767976
confrelid=con->confrelid;
7977+
contype=con->contype;
79777978
conislocal=con->conislocal;
79787979
ReleaseSysCache(tup);
79797980

@@ -7986,6 +7987,15 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
79867987
if (!conislocal)
79877988
continue;
79887989

7990+
/*
7991+
* When rebuilding an FK constraint that references the table we're
7992+
* modifying, we might not yet have any lock on the FK's table, so get
7993+
* one now. We'll need AccessExclusiveLock for the DROP CONSTRAINT
7994+
* step, so there's no value in asking for anything weaker.
7995+
*/
7996+
if (relid!=tab->relid&&contype==CONSTRAINT_FOREIGN)
7997+
LockRelationOid(relid,AccessExclusiveLock);
7998+
79897999
ATPostAlterTypeParse(oldId,relid,confrelid,
79908000
(char*)lfirst(def_item),
79918001
wqueue,lockmode,tab->rewrite);

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp