On Fri, 12 Apr 2002 12:21:04 -0400 (EDT)
"Bruce Momjian" <pgman@candle.pha.pa.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).
Cheers,
Neil
--
Neil Conway <neilconway@rogers.com>
PGP Key ID: DB3C29FC