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On 03/12/07 22:57, Tom Lane wrote:
> Alvaro Herrera <alvherre@commandprompt.com> writes:
>> Tom Lane wrote:
>>> One of the reasons you don't see that is that a large fraction of the
>>> writes are triggered in background by the "bgwriter" process, which
>>> operates at too low a level to participate in the stats collection
>>> mechanism. I'm not sure what would be involved in refactoring things
>>> sufficiently to make that workable, but it'd be nontrivial.
>
>> You mean that bgwriter cannot send stat messages?
>
> Right. The stats mechanism is attached to relcache entries, which the
> bgwriter doesn't have. And if it did collect stats, it would never send
> them because that happens in the outer postgres.c loop (it's not totally
> clear what would be a good granularity for sending them in bgwriter).
> And I think it is not a backend in the stats collector's eyes, either.
>
> Surely these things could be dealt with, but it'd take some refactoring.
It would definitely be useful for the DBA to have the data to let
him graph each tablespace's read & write activity over time.
>
> regards, tom lane
>
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