Re: postgresql latency & bgwriter not doing its job

>>> There is scan_whole_pool_milliseconds, which currently forces bgwriter to
>>> circle the buffer pool at least once every 2 minutes. It is currently
>>> fixed, but it should be trivial to turn it into an experimental guc that
>>> you could use to test your hypothesis.
>>
>> I recompiled with the variable coldly set to 1000 instead of 120000. The
>> situation is slightly degraded (15% of transactions were above 200 ms
>> late). However it seems that bgwriter did not write much more pages:
>
>
> You should probably try it set to 200 rather than 1000, to put it on an
> equal footing with the checkpoint_timeout of 0.2 seconds you reported on.

As I understand it, the setting makes the bgwriter processe scan all
shared_buffers every this amount of time... but ITSM that the key point is
that bgwriter has no insentive to start writing out buffers anyway with
its current decision rules, and that should not change with the frequency
at which they are scanned (?)

> For this experiment, what was checkpoint_timeout set to?

AFAICR, the default, 5min.

--
Fabien.