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

On Thu, Jun 8, 2023 at 3:09 PM Gregory Smith <gregsmithpgsql(at)gmail(dot)com> wrote:
> Pushing SELECT statements at socket speeds with prepared statements is a synthetic benchmark that normally demos big pgbench numbers. My benchmark farm moved to Ubuntu 23.04/kernel 6.2.0-20 last month, and that test is badly broken on the system 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 threads and similar impact. The regular, unprepared sockets peak speeds took a solid hit in PG15 from this issue too. I could 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