Re: 7.4RC1 planned for Monday

On Thu, 30 Oct 2003, Joshua D. Drake wrote:

> If I understood correctly, Josh was complaining about VACUUM sucking too
> 
> >much of his disk bandwidth.  autovacuum wouldn't help that --- in fact
> >would likely make it worse, since a cron-driven vacuum script can at
> >least be scheduled for low-load times of day.  autovacuum is likely to
> >kick in at the least convenient times.
> >
> >  
> >
> Exactly!

Wait a minute, I thought the problem was that vacuums were happening too 
far apart, therefore taking too long, and may have been full, no?

If the autovacuum daemon causes a lazy vacuum to run on only the busiest 
(i.e. most updated) tables, then it is likely to only take a few minutes 
to run, instead of hours, plus you can try to keep things steady state.  
I.e. no more than x% or so dead tuples in a table at any given time, and 
they all get reused by fsm / lazy vacuum.

So, have you TESTED the autovacuum daemon with your load, and set it to 
run every 5 minutes?  Keep in mind, it won't actually vacuum every table 
every 5 minutes, it'll just check the stats to see which ones have updated 
a fair bit and vacuum those, and they're lazy vacuums.  I've found it to 
be a win.  If you haven't tested it and dismissed it out of hand, then you 
should really give it a try to see if it can be configured to provide good 
performance and behavior.