To: Jan Bernhardt <jb@baltic-online.de>
Cc: pgsql-sql@postgresql.org
Subject: Re: Non-Blocking Locks (i.e. Oracle NOWAIT) 
In-reply-to: <20030715144438.27550a7e.jb@baltic-online.de> 
References: <20030715144438.27550a7e.jb@baltic-online.de>
Comments: In-reply-to Jan Bernhardt <jb@baltic-online.de>
	message dated "Tue, 15 Jul 2003 14:44:38 +0200"
Date: Tue, 15 Jul 2003 11:17:35 -0400
Message-ID: <22695.1058282255@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Jan Bernhardt <jb@baltic-online.de> writes:
> 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.

You might be able to use the contrib/userlock module for this.

			regards, tom lane