Re: System Area

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.

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Jonah H. Harris, Software Architect | phone: 732.331.1324
EnterpriseDB Corporation | fax: 732.331.1301
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