Re: There is a statistic table?

On Wed, Oct 21, 2009 at 11:17 AM, Scott Carey <scott@richrelevance.com> wrote:
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> On 10/15/09 11:27 PM, "Albe Laurenz" <laurenz.albe@wien.gv.at> wrote:
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>> 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.

I think he meant pg's shared_buffers not the OS kernel cache.