Re: autovacuum suggestions for 500,000,000+ row tables?

Alex,

> Hi, i'm trying to optimise our autovacuum configuration so that it
> vacuums / analyzes some of our larger tables better. It has been set
> to the default settings for quite some time. We never delete
> anything (well not often, and not much) from the tables, so I am not
> so worried about the VACUUM status, but I am wary of XID wraparound
> nuking us at some point if we don't sort vacuuming out so we VACUUM
> at least once every year ;)

I personally don't use autovaccuum on very large databases. For DW,
vacuuming is far better tied to ETL operations or a clock schedule of
downtime.

XID wraparound may be further away than you think. Try checking
pg_controldata, which will give you the current XID, and you can calculate
how long you are away from wraparound. I just tested a 200G data warehouse
and figured out that we are 800 months away from wraparound, despite hourly
ETL.

> However not running ANALYZE for such huge
> periods of time is probably impacting the statistics accuracy
> somewhat, and I have seen some unusually slow queries at times.
> Anyway, does anyone think we might benefit from a more aggressive
> autovacuum configuration?

Hmmm, good point, you could use autovacuum for ANALYZE only. Just set the
VACUUM settings preposterously high (like 10x) so it never runs. Then it'll
run ANALYZE only. I generally threshold 200, multiple 0.1x for analyze;
that is, re-analyze after 200+10% of rows have changed.

--
Josh Berkus
Aglio Database Solutions
San Francisco