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Accepted
James
Asked: 2012-06-03 18:06:16 +0800 CST

What is causing the unusual high load average?

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I noticed on Tuesday night of last week, the load average went up sharply and it seemed abnormal since the traffic is small. Usually, the numbers usually average around .40 or lower and my server stuff (mysql, php and apache) are optimized. I noticed that the IOWait is unusually high even though the processes is barely using any CPU.

top - 01:44:39 up 1 day, 21:13,  1 user,  load average: 1.41, 1.09, 0.86
Tasks:  60 total,   1 running,  59 sleeping,   0 stopped,   0 zombie
Cpu0  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu1  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu2  :  0.0%us,  0.3%sy,  0.0%ni, 99.7%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu3  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu4  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu5  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu6  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu7  :  0.0%us,  0.0%sy,  0.0%ni, 91.5%id,  8.5%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   1048576k total,   331944k used,   716632k free,        0k buffers
Swap:        0k total,        0k used,        0k free,        0k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
    1 root      15   0  2468 1376 1140 S    0  0.1   0:00.92 init               
 1656 root      15   0 13652 5212  664 S    0  0.5   0:00.00 apache2            
 9323 root      18   0 13652 5212  664 S    0  0.5   0:00.00 apache2            
10079 root      18   0  3972 1248  972 S    0  0.1   0:00.00 su                 
10080 root      15   0  4612 1956 1448 S    0  0.2   0:00.01 bash               
11298 root      15   0 13652 5212  664 S    0  0.5   0:00.00 apache2            
11778 chikorit  15   0  2344 1092  884 S    0  0.1   0:00.05 top                
15384 root      18   0 17544  13m 1568 S    0  1.3   0:02.28 miniserv.pl        
15585 root      15   0  8280 2736 2168 S    0  0.3   0:00.02 sshd               
15608 chikorit  15   0  8280 1436  860 S    0  0.1   0:00.02 sshd

Here is the VMStat

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 1  0      0 768644      0      0    0    0    14    23    0   10  1  0 99  0

IOStat - Nothing unusal

Total DISK READ: 67.13 K/s | Total DISK WRITE: 0.00 B/s
  TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND          
19496 be/4 chikorit   11.85 K/s    0.00 B/s  0.00 %  0.00 % apache2 -k start
19501 be/4 mysql       3.95 K/s    0.00 B/s  0.00 %  0.00 % mysqld
19568 be/4 chikorit   11.85 K/s    0.00 B/s  0.00 %  0.00 % apache2 -k start
19569 be/4 chikorit   11.85 K/s    0.00 B/s  0.00 %  0.00 % apache2 -k start
19570 be/4 chikorit   11.85 K/s    0.00 B/s  0.00 %  0.00 % apache2 -k start
19571 be/4 chikorit    7.90 K/s    0.00 B/s  0.00 %  0.00 % apache2 -k start
19573 be/4 chikorit    7.90 K/s    0.00 B/s  0.00 %  0.00 % apache2 -k start
    1 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % init
11778 be/4 chikorit    0.00 B/s    0.00 B/s  0.00 %  0.00 % top
19470 be/4 mysql       0.00 B/s    0.00 B/s  0.00 %  0.00 % mysqld

Load Average Chart - http://i.stack.imgur.com/kYsD0.png

I want to be sure if this is not a MySQL problem before making sure. Also, this is a Ubuntu 10.04 LTS Server on OpenVZ.

Edit: This will probably give a good picture on the IO Wait

top - 22:12:22 up 17:41, 1 user, load average: 1.10, 1.09, 0.93
Tasks: 33 total, 1 running, 32 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.6%us, 0.2%sy, 0.0%ni, 89.0%id, 10.1%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 1048576k total, 260708k used, 787868k free, 0k buffers
Swap: 0k total, 0k used, 0k free, 0k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 
1 root 15 0 2468 1376 1140 S 0 0.1 0:00.88 init 
5849 root 15 0 12336 4028 668 S 0 0.4 0:00.00 apache2 
8063 root 15 0 12336 4028 668 S 0 0.4 0:00.00 apache2 
9732 root 16 0 8280 2728 2168 S 0 0.3 0:00.02 sshd 
9746 chikorit 18 0 8412 1444 864 S 0 0.1 0:01.10 sshd 
9747 chikorit 18 0 4576 1960 1488 S 0 0.2 0:00.24 bash 
13706 chikorit 15 0 2344 1088 884 R 0 0.1 0:00.03 top 
15745 chikorit 15 0 12968 5108 1280 S 0 0.5 0:00.00 apache2 
15751 chikorit 15 0 72184 25m 18m S 0 2.5 0:00.37 php5-fpm 
15790 chikorit 18 0 12472 4640 1192 S 0 0.4 0:00.00 apache2 
15797 chikorit 15 0 72888 23m 16m S 0 2.3 0:00.06 php5-fpm 
16038 root 15 0 67772 2848 592 D 0 0.3 0:00.00 php5-fpm 
16309 syslog 18 0 24084 1316 992 S 0 0.1 0:00.07 rsyslogd 
16316 root 15 0 5472 908 500 S 0 0.1 0:00.00 sshd 
16326 root 15 0 2304 908 712 S 0 0.1 0:00.02 cron 
17464 root 15 0 10252 7560 856 D 0 0.7 0:01.88 psad 
17466 root 18 0 1684 276 208 S 0 0.0 0:00.31 psadwatchd 
17559 root 18 0 11444 2020 732 S 0 0.2 0:00.47 sendmail-mta 
17688 root 15 0 10252 5388 1136 S 0 0.5 0:03.81 python 
17752 teamspea 19 0 44648 7308 4676 S 0 0.7 1:09.70 ts3server_linux 
18098 root 15 0 12336 6380 3032 S 0 0.6 0:00.47 apache2 
18099 chikorit 18 0 10368 2536 464 S 0 0.2 0:00.00 apache2 
18120 ntp 15 0 4336 1316 984 S 0 0.1 0:00.87 ntpd 
18379 root 15 0 12336 4028 668 S 0 0.4 0:00.00 apache2 
18387 mysql 15 0 62796 36m 5864 S 0 3.6 1:43.26 mysqld 
19584 root 15 0 12336 4028 668 S 0 0.4 0:00.02 apache2 
22498 root 16 0 12336 4028 668 S 0 0.4 0:00.00 apache2 
24260 root 15 0 67772 3612 1356 S 0 0.3 0:00.22 php5-fpm 
27712 root 15 0 12336 4028 668 S 0 0.4 0:00.00 apache2 
27730 root 15 0 12336 4028 668 S 0 0.4 0:00.00 apache2 
30343 root 15 0 12336 4028 668 S 0 0.4 0:00.00 apache2 
30366 root 15 0 12336 4028 668 S 0 0.4 0:00.00 apache2

This is the free ram as of today.

             total       used       free     shared    buffers     cached
Mem:          1024        302        721          0          0          0
-/+ buffers/cache:        302        721
Swap:            0          0          0

Update: Looking into the logs, particularly the PHP5-FPM, which is causing the CPU spike. I found that its segment faulting for some apparent reason. 

[03-Jun-2012 06:11:20] NOTICE: [pool www] child 14132 started
[03-Jun-2012 06:11:25] WARNING: [pool www] child 13664 exited on signal 11 (SIGSEGV) after 53.686322 seconds from start
[03-Jun-2012 06:11:25] NOTICE: [pool www] child 14328 started
[03-Jun-2012 06:11:25] WARNING: [pool www] child 14132 exited on signal 11 (SIGSEGV) after 4.708681 seconds from start
[03-Jun-2012 06:11:25] NOTICE: [pool www] child 14329 started
[03-Jun-2012 06:11:58] WARNING: [pool www] child 14328 exited on signal 11 (SIGSEGV) after 32.981228 seconds from start
[03-Jun-2012 06:11:58] NOTICE: [pool www] child 15745 started
[03-Jun-2012 06:12:25] WARNING: [pool www] child 15745 exited on signal 11 (SIGSEGV) after 27.442864 seconds from start
[03-Jun-2012 06:12:25] NOTICE: [pool www] child 17446 started
[03-Jun-2012 06:12:25] WARNING: [pool www] child 14329 exited on signal 11 (SIGSEGV) after 60.411278 seconds from start
[03-Jun-2012 06:12:25] NOTICE: [pool www] child 17447 started
[03-Jun-2012 06:13:02] WARNING: [pool www] child 17446 exited on signal 11 (SIGSEGV) after 36.746793 seconds from start
[03-Jun-2012 06:13:02] NOTICE: [pool www] child 18133 started
[03-Jun-2012 06:13:48] WARNING: [pool www] child 17447 exited on signal 11 (SIGSEGV) after 82.710107 seconds from start

I'm thinking that this might be causing the problem. If that is the cause, probably switching it off that to fastcgi/fcgid might resolve it... but still, I want to see if something else might be causing it to do this.

iowait load-average

4 Answers

  1. I would expect the server has memory problems. This will result in the container having to wait for data to come from disk rather than buffers. If you have access to the server, try running vmstat on it rather than running it in the container. Memory management for virtual servers is dependent on the host server. The first thing I notices was no buffers, cache, or swap in your data. These are all important to performance.

    • 1

  2. To see which process is causing high I/O, you can use dstat or iotop.

    To see why php is crashing, when starting apache make sure that you run ulimit -c unlimited. Next time when php will crash you will have a core dump. Use bt command inside gdb to have a stack trace of the crash. E.g.

    gdb /usr/bin/httpd core
(gdb) bt

    See: http://www.network-theory.co.uk/articles/gccdebug.html

    • 1
  3. Best Answer

    From the look of things, the high CPU usage was probably caused by a Wordpress plugin, Google XML Sitemap generator. After disabling that, the CPU averages mostly went down. Still, auditing the plugins to remove any that might use too much CPU.

    • 0

  4. Also check/have checked that there are no actual problems with the physical disk subsystems - a rebuilding raid, failed BBU, ailing single disk... can also cause similar symptoms

    • 0