Re: BDR, wal sender, high system cpu, mutex_lock_common

additional info, strace output :

% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
98.30 1.030072 5 213063 201463 read
1.69 0.017686 0 201464 201464 recvfrom
0.01 0.000110 0 806 lseek
0.00 0.000043 0 474 468 rt_sigreturn
0.00 0.000000 0 6 open
0.00 0.000000 0 6 close
------ ----------- ----------- --------- --------- ----------------
100.00 1.047911 415819 403395 total

On Sat, Sep 30, 2017 at 6:07 AM, milist ujang <ujang(dot)milist(at)gmail(dot)com>
wrote:

> Hi all,
>
>
> I've an environment 9.4 + bdr:
> PostgreSQL 9.4.4 on x86_64-unknown-linux-gnu, compiled by gcc (Debian
> 4.7.2-5) 4.7.2, 64-bit
>
> kernel version:
> 3.2.0-4-amd64 #1 SMP Debian 3.2.65-1 x86_64 GNU/Linux
>
> This is consolidation databases, in this machine there are around 250+ wal
> sender processes.
>
> top output revealed high system cpu:
> %Cpu(s): 1.4 us, 49.7 sy, 0.0 ni, 48.8 id, 0.0 wa, 0.0 hi, 0.0 si,
> 0.0 st
>
> profiling cpu with perf:
>
> perf top -e cpu-clock
>
> Events: 142K cpu-clock
> 82.37% [kernel] [k] __mutex_lock_common.isra.5
> 4.49% [kernel] [k] do_raw_spin_lock
> 2.23% [kernel] [k] mutex_lock
> 2.16% [kernel] [k] mutex_unlock
> 2.12% [kernel] [k] arch_local_irq_restore
> 1.73% postgres [.] ValidXLogRecord
> 0.87% [kernel] [k] __mutex_unlock_slowpath
> 0.78% [kernel] [k] arch_local_irq_enable
> 0.63% [kernel] [k] sys_recvfrom
>
>
> finally get which processes (wal senders) that are using mutexes:
>
> perf top -e task-clock -p 55382
>
> Events: 697 task-clock
> 88.08% [kernel] [k] __mutex_lock_common.isra.5
> 3.27% [kernel] [k] do_raw_spin_lock
> 2.34% [kernel] [k] arch_local_irq_restore
> 2.10% postgres [.] ValidXLogRecord
> 1.87% [kernel] [k] mutex_unlock
> 1.87% [kernel] [k] mutex_lock
> 0.47% [kernel] [k] sys_recvfrom
>
> I think bdr is only reading wal file (current state is we behind current
> wal lsn),
> so why reading wal file needs mutex?
>
> I wonder, is there kernel version has better handling mutexes?
>
>
> --
> regards
>
> ujang jaenudin | DBA Consultant (Freelancer)
> http://ora62.wordpress.com
> http://id.linkedin.com/pub/ujang-jaenudin/12/64/bab
>

--
regards

ujang jaenudin | DBA Consultant (Freelancer)
http://ora62.wordpress.com
http://id.linkedin.com/pub/ujang-jaenudin/12/64/bab