Hello!
On 2020-11-14 20:07, Alexander Korotkov wrote:
Hmm... Let's see the big picture. You've recently committed a
patchset, which greatly improved the performance of GetSnapshotData().
And you're making further improvements in this direction. But you're
getting trouble in measuring the effect, because Postgres is still
stuck on ProcArrayLock. And in this thread you propose a workaround
for that implemented on the pgbench side. My very dumb idea is
following: should we finally give a chance to more fair lwlocks rather
than inventing workarounds?
As I remember, your major argument against more fair lwlocks was the
idea that we should fix lwlocks use-cases rather than lwlock mechanism
themselves. But can we expect that we fix all the lwlocks use-case in
any reasonable prospect? My guess is 'no'.
Links
1.
https://www.postgresql.org/message-id/CAPpHfdvJhO1qutziOp%3Ddy8TO8Xb4L38BxgKG4RPa1up1Lzh_UQ%40mail.gmail.com
Sorry I'm not familiar with the internal architecture of snapshots,
locks etc. in postgres, but I wanted to ask - what exact kind of patch
for fair lwlocks do you want to offer to the community? I applied the
6-th version of the patch for fair lwlocks from [1] to the old master
branch (see commit [2]), started many threads in pgbench (-M prepared -c
1000 -j 500 -T 10 -P1 -S) and I did not receive stable first progress
reports, which IIUC are one of the advantages of the discussed patch for
the pgbench (see [3])...
[1]
https://www.postgresql.org/message-id/CAPpHfduV3v3EG7K74-9htBZz_mpE993zGz-%3D2k5RNA3tqabUAA%40mail.gmail.com
[2]
https://github.com/postgres/postgres/commit/84d514887f9ca673ae688d00f8b544e70f1ab270
[3]
https://www.postgresql.org/message-id/20200227185129.hikscyenomnlrord%40alap3.anarazel.de
--
Marina Polyakova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
