Re: checkpointer continuous flushing
От | Fabien COELHO |
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Тема | Re: checkpointer continuous flushing |
Дата | |
Msg-id | alpine.DEB.2.10.1509091042290.3177@sto обсуждение исходный текст |
Ответ на | Re: checkpointer continuous flushing (Amit Kapila <amit.kapila16@gmail.com>) |
Ответы |
Re: checkpointer continuous flushing
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Список | pgsql-hackers |
Hello Amit, >> I think that we may conclude, on these run: >> >> (1) sorting seems not to harm performance, and may help a lot. > > I agree with first part, but about helping a lot, I am not sure I'm focussing on the "sort" dimension alone, that is I'm comparing the average tps performance with sorting with the same test without sorting, : There are 4 cases from your tests, if I'm not mistaken: - T1 flush=off 27480 -> 27482 : +0.0% - T1 flush=on 25214 -> 26819 : +6.3% - T2 flush=off 5050 -> 6194 : +22.6%- T2 flush=on 2771 -> 6110 : +120.4% The average improvement induced by sort=on is +50%, if you do not agree on "a lot", maybe we can agree on "significantly":-) > based on the tests conducted by me, among all the runs, it has shown > improvement in average TPS is one case and that too with a dip in number > of times the TPS is below 10. >> (2) Linux flushing with sync_file_range may degrade a little raw tps >> average in some case, but definitely improves performance stability >> (always 100% availability when on !). > > Agreed, I think the benefit is quite clear, but it would be better if we try > to do some more test for the cases (data fits in shared_buffers) where > we saw small regression just to make sure that regression is small. I've already reported a lot of tests (several hundred of hours on two different hosts), and I did not have such a dip, but the hardware was more "usual" or "casual", really different from your runs. If you can run more tests, great! I think that the main safeguard to handle the (small) uncertainty is to keep gucs to control these features. >> (3) posix_fadvise on Linux is a bad idea... the good news is that it >> is not needed there:-) How good or bad an idea it is on other system >> is an open question... > > I don't know what is the best way to verify that, if some body else has > access to such a m/c, please help to get that verified. Yep. There has been such calls on this thread which were not very effective, up to now. -- Fabien.
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