Re: Multi-Versions and Vacuum

On Thu, Jul 18, 2002 at 09:23:48PM -0700, Anthony Berglas wrote:
> (Compare with Oracle -- a certain amount of space is allocated for multi
> versions ("Rollback Segments"). Old versions are moved there, I think.
> When the space is exhausted then then old versions are dropped
> automatically. Occasionally this can cause transactions to be aborted
> because the old versions they need are no longer available.)

IMHO, that is much worse than the scheme we have now -- particularly
since some kind of auto-vacuuming system is on the horizon.

> What actually is the difference between Vaccum and Vacuum Full? I assume
> that the former must release some disk space, otherwise it would be useless?

http://developer.postgresql.org/docs/postgres/sql-vacuum.html , in
particular:

VACUUM FULL does more extensive processing, including moving of tuples
across blocks to try to compact the table to the minimum number of disk
blocks. This form is much slower and requires an exclusive lock on each
table while it is being processed.

There is more information on VACUUM FULL here:
http://developer.postgresql.org/docs/postgres/routine-vacuuming.html

> EXISTING DOCS
>
> When this thread settles I'll add a note to the interactive docs.

Might be a better idea to send a patch for the SGML to pgsql-patches. Or
if you'd rather not do that, just send any additions you'd like to me
and I'll make the necessary SGML changes and send that to -patches.

> (Thanks Neil for taking the trouble to provide doc fragments. But if you
> read them again you will note that they are not at all clear on the actual
> question that I asked. Which is why I asked them.)

On the contrary, 2 of your 3 questions were clearly answered in the
docs, as is the VACUUM FULL question you just asked. If you think the
docs are unclear or incomplete, can you be more specific?

Cheers,

Neil

--
Neil Conway <neilconway(at)rogers(dot)com>
PGP Key ID: DB3C29FC