Re: Patch: add timing of buffer I/O requests

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