Re: recovery from xid wraparound

On Tue, Oct 24, 2006 at 04:18:09PM +0100, Shane Wright wrote:
> If I change vacuum_mem I'll need to at least 'pg_ctl reload' - will
> it apply straightaway with the next vacuum query or does it need a
> full restart?

You can control it per session I think. So you can start psql and type:

# set vacuum_mem=<huge>;
SET
# VACUUM VERBOSE;
<blah>

You don't have to change the main config, unless you want it to apply
forever. Although, 8MB is small in general so you might want to up it
anyway. But for this one-off vacuum of this large table you could give
a much larger amount of memory.

> Does vacuum_mem need shared memory? (i.e. is it subject to the OS's
> limit) - have looked in the docs and googled but can't see detail on
> this

It's just ordinary memory. If you have a few gig to spare, you can give
it all to the vacuum.

> If I have managed to vacuum all the catalog tables, and my script has
> ensured all user tables other than this one have been vacuumed,
> then... will the first pass of vacuum on this have set the xid to
> FrozenXID for all rows - i.e. is the table safe?

Pass.

Although I think the point is that it hasn't scanned to whole table yet
because it ran out of memory...

> Is it safe to say that if the catalog tables are ok and an individual
> tables has been vacuumed then its data is safe?

Yes...

Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.