Thanks for your reply.
I learnt something again!
On Fri, 22 Dec 2006, Alvaro Herrera wrote:
> Date: Fri, 22 Dec 2006 17:25:43 -0300
> From: Alvaro Herrera <alvherre@commandprompt.com>
> To: ohp@pyrenet.fr
> Cc: Tom Lane <tgl@sss.pgh.pa.us>,
> Kevin Grittner <Kevin.Grittner@wicourts.gov>,
> Jeremy Haile <jhaile@fastmail.fm>, pgsql-performance@postgresql.org
> Subject: Re: [PERFORM] URGENT: Out of disk space pg_xlog
>
> ohp@pyrenet.fr wrote:
> > On Fri, 22 Dec 2006, Tom Lane wrote:
> >
> > > Date: Fri, 22 Dec 2006 13:14:18 -0500
> > > From: Tom Lane <tgl@sss.pgh.pa.us>
> > > To: Kevin Grittner <Kevin.Grittner@wicourts.gov>
> > > Cc: Jeremy Haile <jhaile@fastmail.fm>, pgsql-performance@postgresql.org
> > > Subject: Re: [PERFORM] URGENT: Out of disk space pg_xlog
> > >
> > > "Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> > > > As I understand it, the log space accumulates for the oldest transaction
> > > > which is still running, and all transactions which started after it.
> > >
> > > No, pg_xlog can be truncated as soon as a checkpoint occurs.
> >
> > Even for currently running transactions ?
> >
> > My understanding was that checkpoint was syncing data files for commited
> > transactions.
>
> No, it syncs data files for all transactions, even those currently
> running.
>
> > What happens to pg_xlogs when a transaction updates M of rows/tables and
> > runs for hours?
>
> They get recycled as the update goes.
>
>
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