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Adjust CREATE TRIGGER and ALTER TABLE ... ADD FOREIGN KEY to acquire

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ExclusiveLock rather than AccessExclusiveLock. This will allow concurrent
SELECT queries to proceed on the table. Per discussion with Andrew at
SuperNews.
This commit is contained in:
Neil Conway 2005-03-23 07:44:57 +00:00
parent ac323044cf
commit f30c76ce8d
3 changed files with 21 additions and 13 deletions
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9
doc/src/sgml/mvcc.sgml
View File

@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.47 2005/02/26 18:37:17 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.48 2005/03/23 07:44:56 neilc Exp $
-->
<chapter id="mvcc">
@ -677,9 +677,10 @@ SELECT SUM(value) FROM mytab WHERE class = 2;
</para>
<para>
This lock mode is not automatically acquired on user tables by any
<productname>PostgreSQL</productname> command. However it is
acquired on certain system catalogs in some operations.
Acquired by <command>CREATE TRIGGER</command> and
<command>ALTER TABLE ADD FOREIGN KEY</command>. This lock
mode can also be acquired on certain system catalogs in some
operations.
</para>
</listitem>
</varlistentry>

14
src/backend/commands/tablecmds.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.148 2005/03/20 22:00:52 tgl Exp $
* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.149 2005/03/23 07:44:57 neilc Exp $
*
*-------------------------------------------------------------------------
*/
@ -3829,13 +3829,13 @@ ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
Oid constrOid;
/*
* Grab an exclusive lock on the pk table, so that someone doesn't
* delete rows out from under us. (Although a lesser lock would do for
* that purpose, we'll need exclusive lock anyway to add triggers to
* the pk table; trying to start with a lesser lock will just create a
* risk of deadlock.)
* Grab a lock on the pk table, so that someone doesn't delete
* rows out from under us. We will eventually need to add triggers
* to the table, at which point we'll need to an ExclusiveLock --
* therefore we grab an ExclusiveLock now to prevent possible
* deadlock.
*/
pkrel = heap_openrv(fkconstraint->pktable, AccessExclusiveLock);
pkrel = heap_openrv(fkconstraint->pktable, ExclusiveLock);
/*
* Validity and permissions checks

11
src/backend/commands/trigger.c
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.178 2005/03/20 23:40:24 neilc Exp $
* $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.179 2005/03/23 07:44:57 neilc Exp $
*
*-------------------------------------------------------------------------
*/
@ -87,7 +87,14 @@ CreateTrigger(CreateTrigStmt *stmt, bool forConstraint)
ObjectAddress myself,
referenced;
rel = heap_openrv(stmt->relation, AccessExclusiveLock);
/*
* We need to prevent concurrent CREATE TRIGGER commands, as well
* as concurrent table modifications (INSERT, DELETE, UPDATE), so
* acquire an ExclusiveLock -- it should be fine to allow SELECTs
* to proceed. We could perhaps acquire ShareRowExclusiveLock, but
* there seems little gain in allowing SELECT FOR UPDATE.
*/
rel = heap_openrv(stmt->relation, ExclusiveLock);
if (stmt->constrrel != NULL)
constrrelid = RangeVarGetRelid(stmt->constrrel, false);