From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Ants Aasma <ants(at)cybertec(dot)at> |
Cc: | Greg Smith <greg(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Patch: add timing of buffer I/O requests |
Date: | 2012-03-28 00:30:12 |
Message-ID: | CA+Tgmoa=pt-E_F0FvJs4=FyLhFq3r0GTFNp1oj6R6zMLcrhA-A@mail.gmail.com |
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On Tue, Mar 27, 2012 at 3:22 PM, Ants Aasma <ants(at)cybertec(dot)at> wrote:
> On Tue, Mar 27, 2012 at 9:58 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> I've committed the core of this. I left out the stats collector
>> stuff, because it's still per-table and I think perhaps we should back
>> off to just per-database. I changed it so that it does not conflate
>> wait time with I/O time. Maybe there should be a separate method of
>> measuring wait time, but I don't think it's a good idea for the
>> per-backend stats to measure a different thing than what gets reported
>> up to the stats collector - we should have ONE definition of each
>> counter. I also tweaked the EXPLAIN output format a bit, and the
>> docs.
>
> Thank you for working on this.
>
> Taking a fresh look at it, I agree with you that conflating waiting
> for backend local IO, and IO performed by some other backend might
> paint us into a corner. For most workloads the wait for IO performed
> by others should be the minority anyway.
>
> I won't really miss the per table stats. But if the pg_stat_statements
> normalisation patch gets commited, it would be really neat to also
> have IO waits there. It would be much easier to quickly diagnose "what
> is causing all this IO" issues.
So, the pg_stat_statements part of this is committed now. Do you want
to prepare a revised patch to add per-database counters to the
statistics collector? I think that might be a good idea...
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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