Thread: database caches

database caches

From
Ruslan A Dautkhanov
Date:
Hi,

    I have problem in PG performance - all database caches is allocated
    to one table, which is much greater than all other tables together, but
    requests to this huge table much rarely, than requests with other tables.
    How can I adjust which tables should be cached more (cache rate), and
    which less, if this possible?? Or which tables not to cache completely.
    Thanks a lot in advice.


    ---
       best regards,
    Ruslan A Dautkhanov   rusland@scn.ru

Re: database caches

From
Neil Conway
Date:
Ruslan A Dautkhanov <rusland@scn.ru> writes:
>     I have problem in PG performance - all database caches is allocated
>     to one table, which is much greater than all other tables together, but
>     requests to this huge table much rarely, than requests with
>     other tables.

What makes you think that all the cache is allocated for this one
specific table?

Also, caching is done on a page-by-page basis, not per-relation.

>     How can I adjust which tables should be cached more (cache rate), and
>     which less, if this possible?? Or which tables not to cache
>     completely.

The buffer manager decides what to cache by itself; there are a few
knobs you can tweak (shared_buffers, for example), but for the most
part the buffer manager is expected to do its job.

In your specific example, it doesn't sound like there's a need to
manually tweak the buffer manager: the large but infrequently accessed
table will likely not have very many buffers kept in memory.

Cheers,

Neil

--
Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC