Re: autovacuum launcher eating too much CPU

Alvaro Herrera wrote:

> Darcy Buskermolen noticed that when one has many databases, the autovac
> launcher starts eating too much CPU.
>
> I tried it here with 200 databases and indeed it does seem to eat its
> share. Even with the default naptime, which I wouldn't have thought
> that was too high (it does make the launcher wake up about three times a
> second though).

This patch does not solve the whole problem but it alleviates it a bit
by throttling pgstat reads. One problem with it is that the interval
for this increases:

/*
* Check whether pgstat data still says we need to vacuum this table.
* It could have changed if something else processed the table while we
* weren't looking.
*
* FIXME we ignore the possibility that the table was finished being
* vacuumed in the last 500ms (PGSTAT_STAT_INTERVAL). This is a bug.
*/
MemoryContextSwitchTo(AutovacMemCxt);
tab = table_recheck_autovac(relid);

which could be a problem in itself, by causing unnecessary vacuums.

Opinions?

--
Alvaro Herrera http://www.amazon.com/gp/registry/DXLWNGRJD34J
"In Europe they call me Niklaus Wirth; in the US they call me Nickel's worth.
That's because in Europe they call me by name, and in the US by value!"