On Tue, Aug 26, 2014 at 1:02 AM, Fabien COELHO <coe...@cri.ensmp.fr> wrote:
> > Hello again, > > > I have not found any mean to force bgwriter to send writes when it can. >>> (Well, I have: create a process which sends "CHECKPOINT" every 0.2 >>> seconds... it works more or less, but this is not my point:-) >>> >> >> 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. Not that I think this will improve the situation. Afterall, my theory is that it does not matter who *writes* the pages, it only matters how they get fsynced. > > buffers_checkpoint = 26065 > buffers_clean = 5263 > buffers_backend = 367 > > Or I may have a problem interpreting pg_stat_bgwriter. > For this experiment, what was checkpoint_timeout set to? Cheers, Jeff
