From: | "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com> |
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To: | "Achilleas Mantzios" <achill(at)matrix(dot)gatewaynet(dot)com> |
Cc: | pgsql-admin(at)postgresql(dot)org |
Subject: | Re: System Area |
Date: | 2007-02-01 13:54:12 |
Message-ID: | 36e682920702010554ld995211jba31cf3023592626@mail.gmail.com |
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Lists: | pgsql-admin |
On 2/1/07, Achilleas Mantzios <achill(at)matrix(dot)gatewaynet(dot)com> wrote:
> > I would like to know if Postgres has shared memory like Library Cache
> > (avoid to do parse the same sql), Dictionary Cache (metadata
> > information), Sort Area and so on?
>
> Yes, PostgreSQL makes use of SYSV IPC shared mem and semaphores.
That's not the question that was asked though. The correct answer is
no, PostgreSQL does not have a global statement caching subsystem like
Oracle's Library Cache. The majority of PostgreSQL caches are
backend-local... which means that each backend maintains its own
cache. PostgreSQL has no algorithms similar to a hard, soft, or
soft-soft parse; it's all hard parsing in PostgreSQL unless you
explicitly prepare a statement.
Keep in mind that, once your session is terminated, so is all of your
cache data (including prepared statements). This isn't too much of an
issue on a connection-pooled system, but if you have lots of
client/server activity, you'll want to make sure you use prepared
statements.
> > Oracle has this structures. And Postgres?
> > I couldn't find anything about memory on Postgres.
PostgreSQL uses shared memory, but it's primarily for the buffer cache
and some shared variables.
--
Jonah H. Harris, Software Architect | phone: 732.331.1324
EnterpriseDB Corporation | fax: 732.331.1301
33 Wood Ave S, 3rd Floor | jharris(at)enterprisedb(dot)com
Iselin, New Jersey 08830 | http://www.enterprisedb.com/
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