On Sat, Feb 25, 2006 at 08:15:15AM +0000, Robin Iddon wrote:
> From README.pg_autovacuum (and I think 22.1.4 of the 8.1.x document
> says the same thing):
>
> - If the number of (deletes + updates) > VacuumThreshold, then a
> vacuum analyze is performed.
>
> VacuumThreshold is equal to:
> vacuum_base_value + (vacuum_scaling_factor * "number of tuples in
> the table")
By "number of tuples in the table", I'm pretty sure they mean visible
tuples; ie: the row count. In any case, I've seen pg_autovacuum work
with my own eyes, so as long as it stays running long enough there's no
reason it shouldn't end up vacuuming pg_statistics.
> In general deletes is 0 for the pg_statistic table so for the default
> values we're looking at
>
> n_tup_upd >= 1000 + (2.0 * reltuples)
>
> to trigger a vacuum.
>
> We know for each increment of n_tup_upd, reltuples will receive the same
> increment. Thus if the above expression isn't true for any non-zero
> starting values of n_tup_upd and reltuples, it won't ever be true:
>
> If:
> n_tup_upd < 1000 + (2.0 * reltuples)
> Then:
> n_tup_upd+X < 1000 + (2.0 * (reltuples+X))
>
> I see that in 8.1.x this has been resolved by defaulting the scale to
> 0.4. Rightly or wrongly I have set my scale to 0.3.
You should probably drop the threshold to something closer to 200, too.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
