Re: Longer and longer updates

On Mon, 5 Feb 2001, Alfred Perlstein wrote:

> > ...
> > 3) executed this statement tons of times:
> >
> >    update test set data=1234 where key=1
> >
> > Here are the results -- it's pretty discouraging, I hope I'm making some
> > simple mistake, or maybe this is expected behavior for some reason?
> >
> > After this many updates        ...it took this long for 1000 more updates
> > -----------------------        ------------------------------------------
> >         0                                   10880 ms
> >       5,000                                 10549 ms
> >      10,000                                 17380 ms
> >      15,000                                 20040 ms
> >      20,000                                 20060 ms
> >      25,000                                 20589 ms
> >      30,000                                 30749 ms
> >      35,000                                 30350 ms
> >      40,000                                 30910 ms
> >      45,000                                 37570 ms
> >      50,000                                 40379 ms
> >
> > This seems to be independent of starting and stopping my client and the
> > postmaster, running vacuum, praying, etc.  I'm on RedHat6.2
> > running with the 7.1beta4 rpms.
> >
> > Anyone know what's going on here?
>
> You're not vacuuming.

VACUUMing shows some improvement -- it takes me back to the 20000ms level
or so, but I can never seem to get back to the 10000ms. Is this what you'd
expect?

Also, any thoughts on how often to run VACUUM?  The manual recommends
"nightly" for an operational database, but mine was slowing down
significantly after only a couple of hours of use.  Are there any rules
of thumb people use?  Also, VACUUM can take a few seconds to run -- is
that something people just live with and let the waiting transactions pile
up?  Or do you do something like VACUUM a single table at a time and
rotate which table gets done?  Is that a reasonable thing to do?


Thanks very much for the help-

Steve Wilmarth