Message-ID: <3F1415B7.9001551F@rodos.fzk.de>
Date: Tue, 15 Jul 2003 16:54:48 +0200
From: Christoph Haller <ch@rodos.fzk.de>
MIME-Version: 1.0
To: pgsql-sql@postgresql.org, jb@baltic-online.de
Subject: Re: Non-Blocking Locks (i.e. Oracle NOWAIT)
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>
> though this question has been asked several times before (but never
really
> answered), I have to give it another try.
>
> I have a multi-user application which synchronizes access to certain
datasets
> via the database itself. If a user has a project in that application
open no
> other user should be able to work on it too. When developing the
application I
> considered the database to be a place to handle the synchronization
since
> transactions are (normally) an integral part of a database system.
When a user
> opens a project the application firstly locks a corresponding row. But
since I
> don't want the application to block if that row is already locked I
use the
> Oracle "NOWAIT" feature (SELECT ... FOR UPDATE NOWAIT) which tries to
receive
> the lock on the specified row and if that row is already locked it
returns
> with an error without blocking and I can tell the user that the
project is
> already in use.
>
> Now that the application is to be ported to PG I need a similar
functionality.
> Is there that an animal? If not, what would you recommend?
>
PostgreSQL 7.3.2
T1: begin; select * from foo for update;
T2: set STATEMENT_TIMEOUT = 1000; -- milliseconds
T2: select * from foo for update;
T2: ERROR:  Query was cancelled.

HTH, Christoph