Re: Major pgbench synthetic SELECT workload regression, Ubuntu 23.04+PG15

On Thu, Jun 8, 2023 at 3:09 PM Gregory Smith <gregsmithpgsql@gmail.com> wrote:
> Pushing SELECT statements at socket speeds with prepared statements is a synthetic benchmark that normally demos big
pgbenchnumbers.  My benchmark farm moved to Ubuntu 23.04/kernel 6.2.0-20 last month, and that test is badly broken on
thesystem PG15 at larger core counts, with as much as an 85% drop from expectations. 
> Attached are full scaling graphs for all 4 combinations on this AMD 32 thread 5950X, and an Intel i5-13600K with 20
threadsand similar impact.  The regular, unprepared sockets peak speeds took a solid hit in PG15 from this issue too.
Icould use some confirmation of where this happens from other tester's hardware and Linux kernels. 

Since it doesn't look like you included results on pre-23x Ubuntu, I
thought I would reply with my own results using your example. I also
have a 32 thread AMD 5950X but am on Ubuntu 22.10 (kernel 5.19). I did
not see the regression you mention.

HEAD
  pgbench -S -T 10 -c 32 -j 32 -M prepared -p 5432 pgbench
  tps = 837819.220854 (without initial connection time)

  pgbench -S -T 10 -c 32 -j 32 -M simple -p 5432 pgbench
  tps = 576845.930845 (without initial connection time)

REL_15_STABLE
  pgbench -S -T 10 -c 32 -j 32 -M prepared -p 5432 pgbench
  tps = 794380.991666 (without initial connection time)

  pgbench -S -T 10 -c 32 -j 32 -M simple -p 5432 pgbench
  tps = 534358.379838 (without initial connection time)

- Melanie