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
strace output of wal sender process:
% 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
strace detail, majority read from pipe and recvfrom from socket (but most of them are EAGAIN):
read(15, "~\320\5\0\1\0\0\0\0@\235\1\360\16\0\0\334\26\0\0\0\0\0\0\365\27\0\0\0\0\0\0"..., 8192) = 8192 <0.000025>
read(6, 0x7fffdd837b3f, 1) = -1 EAGAIN (Resource temporarily unavailable) <0.000116>
recvfrom(10, 0x7fffdd837b17, 1, 0, 0, 0) = -1 EAGAIN (Resource temporarily unavailable) <0.000049>
ls -l /proc/62388/fd/15
lr-x------ 1 postgres postgres 64 Oct 1 08:39 /proc/62388/fd/15 -> /data/pg_xlog/0000000100000EF000000061
ls -l /proc/62388/fd/6
lr-x------ 1 postgres postgres 64 Oct 1 08:39 /proc/62388/fd/6 -> pipe:[1090892506]
ls -l /proc/62388/fd/10
lrwx------ 1 postgres postgres 64 Oct 1 08:39 /proc/62388/fd/10 -> socket:[1096584060]
I wonder, is there kernel version has better handling mutexes?
Or is it the expected behavior?
Sorry for cross-posting, I have posted the same on pgsql-performance too....
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