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> 31 авг. 2021 г., в 11:43, Pengchengliu <pengchengliu@tju.edu.cn> написал(а):
>
> Hi Andrey,
> Thanks a lot for your replay and reference information.
>
> The default NUM_SUBTRANS_BUFFERS is 32. My implementation is local_cache_subtrans_pages can be adjusted dynamically.
> If we configure local_cache_subtrans_pages as 64, every backend use only extra 64*8192=512KB memory.
> So the local cache is similar to the first level cache. And subtrans SLRU is the second level cache.
> And I think extra memory is very well worth it. It really resolve massive subtrans stuck issue which I mentioned in
previousemail.
>
> I have view the patch of [0] before. For SLRU buffers adding GUC configuration parameters are very nice.
> I think for subtrans, its optimize is not enough. For SubTransGetTopmostTransaction, we should get the
SubtransSLRULockfirst, then call SubTransGetParent in loop.
> Prevent acquire/release SubtransSLRULock in SubTransGetTopmostTransaction-> SubTransGetParent in loop.
> After I apply this patch which I optimize SubTransGetTopmostTransaction, with my test case, I still get stuck
result.
SubTransGetParent() acquires only Shared lock on SubtransSLRULock. The problem may arise only when someone reads page
fromdisk. But if you have big enough cache - this will never happen. And this cache will be much less than
512KB*max_connections.
I think if we really want to fix exclusive SubtransSLRULock I think best option would be to split SLRU control lock
intoarray of locks - one for each bank (in v17-0002-Divide-SLRU-buffers-into-n-associative-banks.patch). With this
approachwe will have to rename s/bank/partition/g for consistency with locks and buffers partitions. I really liked
havingmy own banks, but consistency worth it anyway.
Thanks!
Best regards, Andrey Borodin.