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I have two servers - one runs a PHP webservice, and the other is the database server. I have high load (~9.0), and I believe it is a configuration issue of some sort. The PHP processing is minimal, all the heavy lifting is done by the database server. I have approximately 6-8 requests per second.

System is CentOS/Plesk (not my choice).

top looks like this:

top - 19:54:38 up  4:38,  2 users,  load average: 9.42, 9.10, 8.86
Tasks:  48 total,  12 running,  36 sleeping,   0 stopped,   0 zombie
Cpu(s): 67.4%us, 32.5%sy,  0.0%ni,  0.2%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   2097152k total,   231120k used,  1866032k free,        0k buffers
Swap:        0k total,        0k used,        0k free,        0k cached   

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                                   
11806 apache    16   0 50416  28m 4744 R 24.6  1.4   7:27.61 httpd                                                                                                                                                      
11770 apache    16   0 49140  27m 4764 R 23.6  1.4   7:32.80 httpd                                                                                                                                                      
11783 apache    16   0 50424  28m 4736 R 23.2  1.4   7:19.99 httpd                                                                                                                                                      
30217 apache    16   0 50412  28m 4732 R 21.6  1.4   3:33.00 httpd                                                                                                                                                      
26245 apache    16   0 50412  28m 4732 R 21.2  1.4   4:14.98 httpd                                                                                                                                                      
26256 apache    16   0 48880  27m 4732 R 21.2  1.3   4:15.62 httpd                                                                                                                                                      
13659 apache    15   0 52464  30m 4764 R 19.2  1.5   5:23.12 httpd                                                                                                                                                      
26255 apache    16   0 48880  27m 4748 R 17.3  1.3   4:16.62 httpd                                                                                                                                                      
30215 apache    16   0 48796  27m 4732 R 16.3  1.3   3:45.32 httpd                                                                                                                                                      
29703 apache    16   0 52208  30m 4764 R 12.3  1.5   3:46.21 httpd    

Load on the database server is next to nothing - 0.05-0.07.

I'm not a server expert so I've been messing with this issue for a while now. I thought I fixed it a while back by running a yum update on the server - many packages updated, so I presumed it was a fixed bug in httpd or similar. The issue returned, I ran yum update again, the issue went away again. Now the issue is back and updating does not fix it - I find this whole thing quite curious.

netstat has many (~100) identical entries like this (IPs and hostnames obscured for NDA reasons):

Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State      
tcp        0      0     TIME_WAIT

In addition it has another hundred or so entries for incoming connections.

I would appreciate any ideas or ways to diagnose this issue - I'm not a server guy primarily (I'm a programmer) and have been dropped in the deep end on this one. I'm reasonably certain the PHP webservice is not to blame - the fact that at one point the issue was resolved makes me feel that it is fine and it's a system config issue.

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  • Check DNS(# ping
  • Use strace(# strace -fp $APACHE_PID), to profile(# strace -cfp $APACHE_PID)
  • If use PHP-FPM, use slowlog
  • Check iptables rulues and network connectivity with MySQL server
  • Use microtime() to log your PHP script or use Pinba. Use profile tools
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