Re: 9.4 -> 9.5 regression with queries through pgbouncer on RHEL 6

Hi,

On 2016-05-27 19:57:34 +0300, Vladimir Borodin wrote:
> -performance
> > Here is how the results look like for 9.4, 9.5 and 9.6. All are built from latest commits on yesterday in
> > * REL9_4_STABLE (a0cc89a28141595d888d8aba43163d58a1578bfb),
> > * REL9_5_STABLE (e504d915bbf352ecfc4ed335af934e799bf01053),
> > * master (6ee7fb8244560b7a3f224784b8ad2351107fa55d).
> >
> > All of them are build on the host where testing is done (with stock gcc versions). Sysctls, pgbouncer config and everything we found are the same, postgres configs are default, PGDATA is in tmpfs. All numbers are reproducible, they are stable between runs.
> >
> > Shortly:
> >
> > OS PostgreSQL version TPS Avg. latency
> > RHEL 6 9.4 44898 1.425 ms
> > RHEL 6 9.5 26199 2.443 ms
> > RHEL 6 9.5 43027 1.487 ms
> > Ubuntu 14.04 9.4 67458 0.949 ms
> > Ubuntu 14.04 9.5 64065 0.999 ms
> > Ubuntu 14.04 9.6 64350 0.995 ms
>
> The results above are not really fair, pgbouncer.ini was a bit different on Ubuntu host (application_name_add_host was disabled). Here are the right results with exactly the same configuration:
>
> OS PostgreSQL version TPS Avg. latency
> RHEL 6 9.4 44898 1.425 ms
> RHEL 6 9.5 26199 2.443 ms
> RHEL 6 9.5 43027 1.487 ms
> Ubuntu 14.04 9.4 45971 1.392 ms
> Ubuntu 14.04 9.5 40282 1.589 ms
> Ubuntu 14.04 9.6 45410 1.409 ms

Hm. I'm a bit confused. You show one result for 9.5 with bad and one
with good performance. I suspect the second one is supposed to be a 9.6?

Am I understanding correctly that the performance near entirely
recovered with 9.6? If so, I suspect we might be dealing with a memory
alignment issue. Do the 9.5 results change if you increase
max_connections by one or two (without changing anything else)?

What's the actual hardware?

Greetings,

Andres Freund