Re: Question on vacuuming

Chris Hoover <revoohc(at)gmail(dot)com> writes:
> there is 1 exception. Everytime there is work to do, it seems to spike our
> load from < 1 to a load of 3+ for a short time. This tends to cause
> significant slowdowns for our customer if they happen to do anything that is
> causing the database to access the drives. It does not seem to matter how
> much work there is to do. Cleaning up 1 page/tuple or 15000 page/tuples
> tends to cause this spike.

No surprise, because vacuum has to read every page of the table to see
if there is anything there to clean up.

> We are running 7.3.4 on Dell 2650 connected to a Dell powervault running
> raid5.

If you were running something a little newer (8.0) you could use the
vacuum_cost_delay knobs to reduce vacuum's impact on I/O load.

regards, tom lane