Re: MultiXact\SLRU buffers configuration - Mailing list pgsql-hackers

13 дек. 2020 г., в 14:17, Gilles Darold <gilles@darold.net> написал(а):

I've done more review on these patches.

Thanks, Gilles! I'll incorporate all your fixes to patchset.
Can you also benchmark conditional variable sleep? The patch "Add conditional variable to wait for next MultXact offset in corner case"?
The problem manifests on Standby when Primary is heavily loaded with MultiXactOffsetControlLock.

Thanks!

Best regards, Andrey Borodin.

Hi Andrey,

Sorry for the response delay, we have run several others tests trying to figure out the performances gain per patch but unfortunately we have very heratic results. With the same parameters and patches the test doesn't returns the same results following the day or the hour of the day. This is very frustrating and I suppose that this is related to the Azure architecture. The only thing that I am sure is that we had the best performances results with all patches and

multixact_offsets_slru_buffers = 256
multixact_members_slru_buffers = 512
multixact_local_cache_entries = 4096

but I can not say if all or part of the patches are improving the performances. My feeling is that performances gain related to patches 1 (shared lock) and 3 (conditional variable) do not have much to do with the performances gain compared to just tuning the multixact buffers. This is when the multixact contention is observed but perhaps they are delaying the contention. It's all the more frustrating that we had a test case to reproduce the contention but not the architecture apparently.

Can't do much more at this point.

Best regards,

-- 
Gilles Darold
LzLabs GmbH
http://www.lzlabs.com/