Re: MultiXact\SLRU buffers configuration

Le 13/12/2020 à 18:24, Andrey Borodin a écrit :
>
>> 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/