Re: [rfc] overhauling pgstat.stat

Hi,

(2013/09/04 12:52), Atri Sharma wrote:
> On Wed, Sep 4, 2013 at 6:40 AM, Satoshi Nagayasu <snaga(at)uptime(dot)jp> wrote:
>> Hi,
>>
>> I'm considering overhauling pgstat.stat, and would like to know how many
>> people are interested in this topic.
>>
>> 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.
>>
>> To support multi-tenancy or just a large number of tables (up to 10k
>> tables in single database), I think pgstat.stat needs to be overhauled.
>>
>> I think using heap and btree in pgstat.stat would be preferred to reduce
>> read/write and to allow updating access statistics for specific tables
>> in pgstat.stat file.
>>
>> Is this good for us?
>
> Hi,
>
> Nice thought. I/O reduction in pgstat can be really helpful.
>
> I am trying to think of our aim here. Would we be looking to split
> pgstat per table, so that the I/O write happens for only a portion of
> pgstat? Or reduce the I/O in general?

I prefer the latter.

Under the current implementation, DBA need to split single database
into many smaller databases with considering access locality of the
tables. It's difficult and could be change in future.

And splitting the statistics data into many files (per table,
for example) would cause another performance issue when
collecting/showing statistics at once. Just my guess though.

So, I'm looking for a new way to reduce I/O for the statistics data
in general.

Regards,

>
> If the later, how would using BTree help us? I would rather go for a
> range tree or something. But again, I may be completely wrong.
>
> Please elaborate a bit more on the solution we are trying to
> achieve.It seems really interesting.
>
> Regards,
>
> Atri
>
>

--
Satoshi Nagayasu <snaga(at)uptime(dot)jp>
Uptime Technologies, LLC. http://www.uptime.jp