On Mon, 30 Aug 2021 at 11:25, Andrey Borodin <x4...@yandex-team.ru> wrote: > > Hi Pengcheng! > > You are solving important problem, thank you! > > > 30 авг. 2021 г., в 13:43, Pengchengliu <pengcheng...@tju.edu.cn> написал(а): > > > > To resolve this performance problem, we think about a solution which cache > > SubtransSLRU to local cache. > > First we can query parent transaction id from SubtransSLRU, and copy the > > SLRU page to local cache page. > > After that if we need query parent transaction id again, we can query it > > from local cache directly. > > A copy of SLRU in each backend's cache can consume a lot of memory.
Yes, copying the whole SLRU into local cache seems overkill. > Why create a copy if we can optimise shared representation of SLRU? transam.c uses a single item cache to prevent thrashing from repeated lookups, which reduces problems with shared access to SLRUs. multitrans.c also has similar. I notice that subtrans. doesn't have this, but could easily do so. Patch attached, which seems separate to other attempts at tuning. On review, I think it is also possible that we update subtrans ONLY if someone uses >PGPROC_MAX_CACHED_SUBXIDS. This would make subtrans much smaller and avoid one-entry-per-page which is a major source of cacheing. This would means some light changes in GetSnapshotData(). Let me know if that seems interesting also? -- Simon Riggs http://www.EnterpriseDB.com/
subtrans_single_item_cache.v1.patch
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