Re: Some silly questions

On Wed, Oct 30, 2002 at 01:36:28AM +0100, Michiel Lange wrote:
> I was just wondering about a few options that I would think might be pretty
> useful. They might exist, but then, I don't know how to get it done...
>
> Here's my list:
> - multi-volume database. Is it possible to split the complete database so it
> will use several disks? One reason might be load-balancing of the disks,
> another might be a very full disk... there may be even more...
> - If multi-voluming exists, is it possible to make certain specific tables
> can get in a special 'area', so you'd know on which disk it would be?

There have been several suggestions to implement this functionality,
but it's been a relatively low priority, it seems.  You can sort of
mimic this with symlinks, but it's a pain to do.  My suggestion is to
throw money at a RAID configuration, instead.  We've had very good
luck with RAID 1+0.

> - Every database system has a ROLLBACK function, also known as
> 'before-imaging'. Postgres no doubt has this technique as well? How (which
> file(s)) is this done in Postges, and how can you manage the size of these
> before images?

ROLLBACK is a feature of the transaction model in Postgres.  You
already have it; you need to initiate a transaction to get to it.

Postgres does this with the WAL.  You _do_ want to put the WAL files
(which are in pg_xlog in your data directory) on another disk.  You
may do this with a symlink; SHUT DOWN YOUR DATABASE before you do it!
Check out the WAL section of the manual for more details on how to
use and configure the facility.

> - In a situation of a crash, a rollback is a MUST. A rollforward is
> desirable... does postgres offer this functionality as well? (I guess it
> does) and the same question as the before-image arises as with this
> so-called after-imaging.

There is automatic recovery in the event of a crash, but you can't
get point-in-time recovery yet.  It's in the hopper for 7.4,
apparently.

> Oh... and does anyone know something about the relation Postgres and
> Progress? the names seem so similar...

Not as far as I know.  There is an historical relationship between
PostgreSQL, Postgres (which is actually different from PostgreSQL,
and had a commercial variant in Illustra), and Ingres.  See the
history section of the manual for details.

> and... do my questions sound stupid? ;-)

No, but you might want to have a look at the manuals: there's a lot
of info there.

A

--
----
Andrew Sullivan                         204-4141 Yonge Street
Liberty RMS                           Toronto, Ontario Canada
<andrew@libertyrms.info>                              M2P 2A8
                                         +1 416 646 3304 x110