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

UP. repeat tests on local vm.. reults are discouraging
OS PG TPS AVG latency
Centos 7 9.5.3 23.711023 168.421
Centos 7 9.5.3 26.609271 150.188
Centos 7 9.5.3 25.220044 158.416
Centos 7 9.5.3 25.598977 156.047
Centos 7 9.4.8 278.572191 14.077
Centos 7 9.4.8 247.237755 16.177
Centos 7 9.4.8 240.007524 16.276
Centos 7 9.4.8 237.862238 16.596

ps: latest update on centos 7 +xfs + lates database version from repo, no pgbouncer

> On 25 May 2016, at 17:33, Vladimir Borodin <root(at)simply(dot)name> wrote:
>
> Hi all.
>
> We have found that queries through PgBouncer 1.7.2 (with transaction pooling) to local PostgreSQL are almost two times slower in 9.5.3 than in 9.4.8 on RHEL 6 hosts (all packages are updated to last versions). Meanwhile the problem can’t be reproduced i.e. on Ubuntu 14.04 (also fully-updated).
>
> 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
>
> You could see that the difference between major versions on Ubuntu is not significant, but on RHEL 9.5 is 70% slower than 9.4 and 9.6.
>
> Below are more details.
>
> RHEL 6:
>
> postgres(at)pgload05g ~ $ /usr/lib/postgresql/9.4/bin/pgbench -U postgres -T 60 -j 64 -c 64 -S -n 'host=localhost port=6432 dbname=pg94'
> transaction type: SELECT only
> scaling factor: 100
> query mode: simple
> number of clients: 64
> number of threads: 64
> duration: 60 s
> number of transactions actually processed: 2693962
> latency average: 1.425 ms
> tps = 44897.461518 (including connections establishing)
> tps = 44898.763258 (excluding connections establishing)
> postgres(at)pgload05g ~ $ /usr/lib/postgresql/9.4/bin/pgbench -U postgres -T 60 -j 64 -c 64 -S -n 'host=localhost port=6432 dbname=pg95'
> transaction type: SELECT only
> scaling factor: 100
> query mode: simple
> number of clients: 64
> number of threads: 64
> duration: 60 s
> number of transactions actually processed: 1572014
> latency average: 2.443 ms
> tps = 26198.928627 (including connections establishing)
> tps = 26199.803363 (excluding connections establishing)
> postgres(at)pgload05g ~ $ /usr/lib/postgresql/9.4/bin/pgbench -U postgres -T 60 -j 64 -c 64 -S -n 'host=localhost port=6432 dbname=pg96'
> transaction type: SELECT only
> scaling factor: 100
> query mode: simple
> number of clients: 64
> number of threads: 64
> duration: 60 s
> number of transactions actually processed: 2581645
> latency average: 1.487 ms
> tps = 43025.676995 (including connections establishing)
> tps = 43027.038275 (excluding connections establishing)
> postgres(at)pgload05g ~ $
>
> Ubuntu 14.04 (the same hardware):
>
> postgres(at)pgloadpublic02:~$ /usr/lib/postgresql/9.4/bin/pgbench -U postgres -T 60 -j 64 -c 64 -S -n 'host=localhost port=6432 dbname=pg94'
> transaction type: SELECT only
> scaling factor: 100
> query mode: simple
> number of clients: 64
> number of threads: 64
> duration: 60 s
> number of transactions actually processed: 4047653
> latency average: 0.949 ms
> tps = 67458.361515 (including connections establishing)
> tps = 67459.983480 (excluding connections establishing)
> postgres(at)pgloadpublic02:~$ /usr/lib/postgresql/9.4/bin/pgbench -U postgres -T 60 -j 64 -c 64 -S -n 'host=localhost port=6432 dbname=pg95'
> transaction type: SELECT only
> scaling factor: 100
> query mode: simple
> number of clients: 64
> number of threads: 64
> duration: 60 s
> number of transactions actually processed: 3844084
> latency average: 0.999 ms
> tps = 64065.447458 (including connections establishing)
> tps = 64066.943627 (excluding connections establishing)
> postgres(at)pgloadpublic02:~$ /usr/lib/postgresql/9.4/bin/pgbench -U postgres -T 60 -j 64 -c 64 -S -n 'host=localhost port=6432 dbname=pg96'
> transaction type: SELECT only
> scaling factor: 100
> query mode: simple
> number of clients: 64
> number of threads: 64
> duration: 60 s
> number of transactions actually processed: 3861088
> latency average: 0.995 ms
> tps = 64348.573126 (including connections establishing)
> tps = 64350.195750 (excluding connections establishing)
> postgres(at)pgloadpublic02:~$
>
> In both tests (RHEL and Ubuntu) the bottleneck is performance of singe CPU core which is 100% consumed by PgBouncer. If pgbench connects to postgres directly I get the following (expected) numbers:
>
> postgres(at)pgload05g ~ $ /usr/lib/postgresql/9.4/bin/pgbench -U postgres -T 60 -j 64 -c 64 -S -n 'host=localhost port=5432'
> transaction type: SELECT only
> scaling factor: 100
> query mode: simple
> number of clients: 64
> number of threads: 64
> duration: 60 s
> number of transactions actually processed: 10010710
> latency average: 0.384 ms
> tps = 166835.937859 (including connections establishing)
> tps = 166849.730224 (excluding connections establishing)
> postgres(at)pgload05g ~ $ /usr/lib/postgresql/9.4/bin/pgbench -U postgres -T 60 -j 64 -c 64 -S -n 'host=localhost port=5433'
> transaction type: SELECT only
> scaling factor: 100
> query mode: simple
> number of clients: 64
> number of threads: 64
> duration: 60 s
> number of transactions actually processed: 13373890
> latency average: 0.287 ms
> tps = 222888.311289 (including connections establishing)
> tps = 222951.470125 (excluding connections establishing)
> postgres(at)pgload05g ~ $ /usr/lib/postgresql/9.4/bin/pgbench -U postgres -T 60 -j 64 -c 64 -S -n 'host=localhost port=5434'
> transaction type: SELECT only
> scaling factor: 100
> query mode: simple
> number of clients: 64
> number of threads: 64
> duration: 60 s
> number of transactions actually processed: 12989816
> latency average: 0.296 ms
> tps = 216487.458399 (including connections establishing)
> tps = 216548.069976 (excluding connections establishing)
> postgres(at)pgload05g ~ $
>
> Compilation options look almost the same:
> # RHEL 6
> CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -g -O2
> # Ubuntu
> CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -g -O2
>
> Attached are a simple script to deploy the testing environment (PgBouncer should be installed) and pgbouncer config. I could provide any other needed information like backtraces or perf reports or anything else.
>
> <pgbouncer.ini>
> <deploy.sh>
>
> --
> May the force be with you…
> https://simply.name <https://simply.name/>