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From G VM <drums_...@hotmail.com>
Subject [users@httpd] IO load due to apache? Normal httpd behavior or script related?
Date Mon, 14 May 2012 15:41:09 GMT

Hi all,

Recently I found out one server generating alot of load on our storage.

I did a few steps to narrow down what is the cause and what might be a solution.

As first I used iostat to get what device is using most IO:

Linux 2.6.18-274.7.1.el5 (hostname)     05/14/2012

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          11.99    0.00    8.53    2.85    0.00   76.63

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda             952.75         5.54     14090.70   42708891 108632689706
sda1              0.00         0.00         0.00       6988       1802
sda2              0.51         0.17         8.29    1322786   63885168
sda3            952.24         5.37     14082.42   41378693 108568802736
sdb               8.29         1.01       739.31    7791930 5699710024
dm-0              2.14         1.48        17.03   11382146  131278120
dm-1              0.76         0.78         5.47    6030578   42202752
dm-2              8.69         3.08        68.72   23737626  529796056
dm-3           1748.90         0.03     13991.19     226754 107865527240
dm-4              0.00         0.00         0.00       1192        216
dm-5             92.49         1.01       739.31    7790146 5699710024

Using ls -lh /dev/mapper I found out that dm-3 corresponds with the mountpoint for /tmp (note
that the system is using LVM).
One thing that seems strange to me is that there is a huge load of blocks written however
almost none get red.

Then I used lsof | grep tmp:

httpd     25142    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
httpd     25386    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
httpd     25429    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
httpd     25431    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
httpd     25454    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
httpd     25622    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
httpd     25792    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
httpd     25794    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
httpd     25846    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
httpd     25849    apache  DEL       REG              253,3                   13 /tmp/apc.Fm8SAS
...

The only other is for sshd and another for vmware tools.

If I try to do ls -lh /tmp/apc.Fm8SAS I get no such file or directory. Using the access time
I would see if this file is accessed over and over again. 
Am I missing something here? Is this apache doing a fstat() call for example?
Or is this file created and deleted over and over again at a very fast pace that I can't access
it (this seems less likely to me).

Has anyone seen such behaviour in httpd? Or does someone knows a little more of the inner
workings of httpd?

The name does me think that APC (sort of php module iirc) is having something to do with this:
apc.ini:apc.mmap_file_mask=/tmp/apc.XXXXXX

The config file seems to confirm this.

Anyone has an idea how to fix this or to go further investigate?

Thanks alot in advance!
 		 	   		  
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