Re: cost-based vacuum

On Wed, 2005-07-13 at 11:55, Simon Riggs wrote:
> On Tue, 2005-07-12 at 13:50 -0400, Ian Westmacott wrote:
> > It appears not to matter whether it is one of the tables
> > being written to that is ANALYZEd.  I can ANALYZE an old,
> > quiescent table, or a system table and see this effect.
>
> Can you confirm that this effect is still seen even when the ANALYZE
> doesn't touch *any* of the tables being accessed?

Yes.

> > - this is a dual Xeon.
>
> Is that Xeon MP then?

Yes.

> > - Looking at oprofile reports for 10-minute runs of a
> >   database-wide VACUUM with vacuum_cost_delay=0 and 1000,
> >   shows the latter spending a lot of time in LWLockAcquire
> >   and LWLockRelease (20% each vs. 2%).
>
> Is this associated with high context switching also?

Yes, it appears that context switches increase up to 4-5x
during cost-based ANALYZE.

    --Ian