Re: [rfc] overhauling pgstat.stat

On Tue, Sep 3, 2013 at 10:09 PM, Satoshi Nagayasu <snaga@uptime.jp> wrote:
> Hi,
>
>
> (2013/09/04 13:07), Alvaro Herrera wrote:
>>
>> Satoshi Nagayasu wrote:
>>
>>> As you may know, this file could be handreds of MB in size, because
>>> pgstat.stat holds all access statistics in each database, and it needs
>>> to read/write an entire pgstat.stat frequently.
>>>
>>> As a result, pgstat.stat often generates massive I/O operation,
>>> particularly when having a large number of tables in the database.
>>
>>
>> We already changed it:
>
>>
>> commit 187492b6c2e8cafc5b39063ca3b67846e8155d24
>> Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
>> Date:   Mon Feb 18 17:56:08 2013 -0300
>>
>>      Split pgstat file in smaller pieces
>
> Thanks for the comments. I forgot to mention that.
>
> Yes, we have already split single pgstat.stat file into
> several pieces.
>
> However, we still need to read/write large amount of statistics
> data when we have a large number of tables in single database
> or multiple databases being accessed. Right?

Do you have a test case for measuring this?  I vaguely remember from
when I was testing the split patch, that I thought that after that
improvement the load that was left was so low that there was little
point in optimizing it further.

Cheers,

Jeff