Re: Perfomance Tuning

On Mon, Aug 11, 2003 at 06:59:30PM -0400, Bruce Momjian wrote:
> Uh, the ext2 developers say it isn't 100% reliable --- at least that is
> that was told. I don't know any personally, but I mentioned it while I
> was visiting Red Hat, and they didn't refute it.

IMHO, if we're going to say "don't use X on production PostgreSQL
systems", we need to have some better evidene than "no one has
said anything to the contrary, and I heard X is bad". If we can't
produce such evidence, we shouldn't say anything at all, and users
can decide what to use for themselves.

(Not that I'm agreeing or disagreeing about ext2 in particular...)

> > My
> > untested interpretation was that the update bookkeeping as well as data
> > update were all getting journalled, the journal space would fill, get
> > sync'd, then repeat. In effect, all blocks were being written TWICE just
> > for the journalling, never mind the overhead for PostgreSQL
> > transactions.

Journalling may or may not have been the culprit, but I doubt everything
was being written to disk twice:

(a) ext3 does metadata-only journalling by default

(b) PostgreSQL only fsyncs WAL records to disk, not the data itself

-Neil