Re: There is a statistic table?

On 10/15/09 11:27 PM, "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at> wrote:

> waldomiro wrote:
>> I need to know how much the postgres is going to disk to get
>> blocks and how much it is going to cache? witch is the
>> statistic table and what is the field that indicates blocks
>> reads from the disk and the memory cache?
>
> The view pg_statio_all_tables will show you the number of
> disk reads and buffer hits per table.

My understanding is that it will not show that. Since postgres can't
distinguish between a read that comes from OS cache and one that goes to
disk, you're out of luck on knowing anything exact.
The above shows what comes from shared_buffers versus the OS, however. And
if reads are all buffered, they are not coming from disk. Only those that
come from the OS _may_ have come from disk.

>
> There are other statistics views, see
> http://www.postgresql.org/docs/8.4/static/monitoring-stats.html#MONITORING-STA
> TS-VIEWS
>
>> Another question is, what is the best memory configuration to
>> keep more data in cache?
>
> That's easy - the greater shared_buffers is, the more cache you have.
>
> Another option is to choose shared_buffers not too large and let
> the filesystem cache buffer the database for you.
>
> Yours,
> Laurenz Albe
>
> --
> Sent via pgsql-performance mailing list (pgsql-performance(at)postgresql(dot)org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-performance
>