From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Neil Conway <nconway(at)klamath(dot)dyndns(dot)org> |
Cc: | tgl(at)sss(dot)pgh(dot)pa(dot)us, zakkr(at)zf(dot)jcu(dot)cz, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: 7.3 schedule |
Date: | 2002-04-12 21:25:31 |
Message-ID: | 200204122125.g3CLPVa14231@candle.pha.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Neil Conway wrote:
> On Fri, 12 Apr 2002 12:21:04 -0400 (EDT)
> "Bruce Momjian" <pgman(at)candle(dot)pha(dot)pa(dot)us> wrote:
> > Tom Lane wrote:
> > > A per-backend cache kept in local memory avoids all of these problems,
> > > and I have seen no numbers to make me think that a shared plan cache
> > > would achieve significantly more performance benefit than a local one.
> >
> > Certainly a shared cache would be good for apps that connect to issue a
> > single query frequently. In such cases, there would be no local cache
> > to use.
>
> One problem with this kind of scenario is: what to do if the plan no
> longer exists for some reason? (e.g. the code that was supposed to be
> PREPARE-ing your statements failed to execute properly, or the cached
> plan has been evicted from shared memory, or the database was restarted,
> etc.) -- EXECUTE in and of itself won't have enough information to do
> anything useful. We could perhaps provide a means for an application
> to test for the existence of a cached plan (in which case the
> application developer will need to add logic to their application
> to re-prepare the query if necessary, which could get complicated).
Oh, are you thinking that one backend would do the PREPARE and another
one the EXECUTE? I can't see that working at all. I thought there
would some way to quickly test if the submitted query was in the cache,
but maybe that is too much of a performance penalty to be worth it.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
From | Date | Subject | |
---|---|---|---|
Next Message | Bruce Momjian | 2002-04-12 21:30:58 | Re: numeric/decimal docs bug? |
Previous Message | Neil Conway | 2002-04-12 20:24:48 | Re: 7.3 schedule |