Re: No control over max.num. WAL files

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 05/25/2011 02:08 PM, Andrew Sullivan wrote:
> On Wed, May 25, 2011 at 01:30:35PM +0200, Rafael Martinez wrote:

Thanks for your answer.

>>
>> According to the documentation [1] we can expect a maximum of
>> (3 * checkpoint_segments + 1 segment files) WAL files in pg_xlog.
>
> That isn't what the documentation says. It says this:
>
> If, due to a short-term peak of log output rate, there are more
> than 3 * checkpoint_segments + 1 segment files, the unneeded
> segment files will be deleted instead of recycled until the system
> gets back under this limit.
>
> Note that "unneeded". Obviously, you need more than that, probably
> because you're restoring the database in one transaction (so none of
> the files can be flushed).
>

We are not restoring the database in one transaction so it is not so
clear to me you need all these extra WAL files around.

If this is the case, I think the documentation is not clear enough and
can lead to misunderstandings.

If we cannot calculate roughly how much disk we need for WAL files, how
can we be sure we won't get into another situation that needs even more
space than the space we have allocated?

[......]
>
> Disk is cheap. 8G is hardly anything any more; I'd buy some more disk for WAL.
>

That is not the problem, we have our data in a SAN. Our problem is that
if what you are saying is true, how much diskspace is enough?

regards,
- --
Rafael Martinez Guerrero
Center for Information Technology
University of Oslo, Norway

PGP Public Key: http://folk.uio.no/rafael/
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.14 (GNU/Linux)

iEYEARECAAYFAk3c9vQACgkQBhuKQurGihQupQCeJaIsZFs/AhrMoP/jDS5R+gTj
CwIAnA36bb8/bOrezC91lNQAvXP5nmMc
=VOGM
-----END PGP SIGNATURE-----