Re: configure option for XLOG_BLCKSZ

On Mon, 5 May 2008 11:09:32 -0400 Alvaro Herrera wrote:

> Andreas 'ads' Scherbaum wrote:
> > On Sat, 03 May 2008 13:14:35 -0400 Tom Lane wrote:
> >
> > > Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> > >
> > > > Not seen any gains from varying the WAL file size since then...
> > >
> > > I think the use-case for varying the WAL segment size is unrelated to
> > > performance of the master server, but would instead be concerned with
> > > adjusting the granularity of WAL log shipping.
> >
> > *nod* I heard this argument several times. Simon: there was a discussion
> > about this topic in Prato last year. Since WAL logfiles are usually
> > binary stuff, the files can't be compressed much so a smaller logfile
> > size on a not-so-much-used system would save a noticeable amount of
> > bandwith (and cpu cycles for compression).
>
> Seems the stuff to zero out the unused segment tail would be more useful
> here.

Yeah, that was the original question, if i remember correctly.
If the WAL logfile is zeroed out just before start using it and PG only
needs a small part of this logfile, the remaining zeroes are easily
compressable. Useful for PITR and good for backups/rsync/scp.

Kind regards

--
Andreas 'ads' Scherbaum
German PostgreSQL User Group