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Commitf30c76c

Browse files
author
Neil Conway
committed
Adjust CREATE TRIGGER and ALTER TABLE ... ADD FOREIGN KEY to acquire
ExclusiveLock rather than AccessExclusiveLock. This will allow concurrentSELECT queries to proceed on the table. Per discussion with Andrew atSuperNews.
1 parentac32304 commitf30c76c

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3 files changed

+21
-13
lines changed

3 files changed

+21
-13
lines changed

‎doc/src/sgml/mvcc.sgml

Lines changed: 5 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.47 2005/02/26 18:37:17 tgl Exp $
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$PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.48 2005/03/23 07:44:56 neilc Exp $
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-->
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<chapter id="mvcc">
@@ -677,9 +677,10 @@ SELECT SUM(value) FROM mytab WHERE class = 2;
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</para>
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<para>
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This lock mode is not automatically acquired on user tables by any
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<productname>PostgreSQL</productname> command. However it is
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acquired on certain system catalogs in some operations.
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Acquired by <command>CREATE TRIGGER</command> and
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<command>ALTER TABLE ADD FOREIGN KEY</command>. This lock
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mode can also be acquired on certain system catalogs in some
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operations.
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</para>
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</listitem>
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</varlistentry>

‎src/backend/commands/tablecmds.c

Lines changed: 7 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.148 2005/03/20 22:00:52 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.149 2005/03/23 07:44:57 neilc Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -3829,13 +3829,13 @@ ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
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OidconstrOid;
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38313831
/*
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* Graban exclusivelock on the pk table, so that someone doesn't
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*deleterows out from under us.(Although a lesser lock would do for
3834-
*that purpose,we'll needexclusive lock anywaytoadd triggers to
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*the pk table; trying to start with a lesser lock will just create a
3836-
*risk ofdeadlock.)
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* Grabalock on the pk table, so that someone doesn't delete
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* rows out from under us.We will eventually need to add triggers
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*to the table, at which pointwe'll need toan ExclusiveLock --
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*therefore we grab an ExclusiveLock now to prevent possible
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* deadlock.
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*/
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pkrel=heap_openrv(fkconstraint->pktable,AccessExclusiveLock);
3838+
pkrel=heap_openrv(fkconstraint->pktable,ExclusiveLock);
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/*
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* Validity and permissions checks

‎src/backend/commands/trigger.c

Lines changed: 9 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.178 2005/03/20 23:40:24 neilc Exp $
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* $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.179 2005/03/23 07:44:57 neilc Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -87,7 +87,14 @@ CreateTrigger(CreateTrigStmt *stmt, bool forConstraint)
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ObjectAddressmyself,
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referenced;
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rel=heap_openrv(stmt->relation,AccessExclusiveLock);
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/*
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* We need to prevent concurrent CREATE TRIGGER commands, as well
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* as concurrent table modifications (INSERT, DELETE, UPDATE), so
93+
* acquire an ExclusiveLock -- it should be fine to allow SELECTs
94+
* to proceed. We could perhaps acquire ShareRowExclusiveLock, but
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* there seems little gain in allowing SELECT FOR UPDATE.
96+
*/
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rel=heap_openrv(stmt->relation,ExclusiveLock);
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if (stmt->constrrel!=NULL)
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constrrelid=RangeVarGetRelid(stmt->constrrel, false);

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