At Tue, 6 Feb 2018 14:50:01 +0900, Masahiko Sawada <sawada.m...@gmail.com> wrote in <cad21aocrn6q0wgg7uwgvsqjzbocnsrazbyjomuy+-grkvh-...@mail.gmail.com> > On Mon, Dec 11, 2017 at 8:15 PM, Kyotaro HORIGUCHI > <horiguchi.kyot...@lab.ntt.co.jp> wrote: > > I considered dshash for pgstat.c and the attached is a *PoC* > > patch, which is not full-fledged and just working under a not so > > concurrent situation. > > > > - Made stats collector an auxiliary process. A crash of stats > > collector leads to a whole-server restarting. > > > > - dshash lacks capability of sequential scan so added it. > > > > - Also added snapshot function to dshash. It just copies > > unerlying DSA segments into local memory but currently it > > doesn't aquire dshash-level locks at all. I tried the same > > thing with resize but it leads to very quick exhaustion of > > LWLocks. An LWLock for the whole dshash would be required. (and > > it is also useful to resize() and sequential scan. > > > > - The current dshash doesn't shrink at all. Such a feature also > > will be required. (A server restart causes a shrink of hashes > > in the same way as before but bloat dshash requires copying > > more than necessary size of memory on takeing a snapshot.) > > > > The size of DSA is about 1MB at minimum. Copying entry-by-entry > > into (non-ds) hash might be better than copying underlying DSA as > > a whole, and DSA/DSHASH snapshot brings a kind of dirty.. > > > > > > Does anyone give me opinions or suggestions? > > > > The implementation of autovacuum work-item has been changed (by commit > 31ae1638) because dynamic shared memory is not portable enough. IIUC > this patch is going to do the similar thing. Since stats collector is > also a critical part of the server, should we consider whether we can > change it? Or the portability problem is not relevant with this patch?
Thank you for the pointer. I digged out the following thread from this and the the patch seems to be the consequence of the discussion. I'll study it and think what to do on this. https://www.postgresql.org/message-id/20170814005656.d5tvz464qkmz6...@alap3.anarazel.de regards. -- Kyotaro Horiguchi NTT Open Source Software Center
