[horde] Sessions consuming CPU

[Simon Wilson]

Over the last few weeks I have noticed periods of time where the  
virtual server running Horde climbs to 100% CPU utilisation. This can  
last for hours.

Last time was 6 days ago, but then it did it again at 00:41am this  
morning, so I jumped into some troubleshooting.

Stop httpd and the CPU drops to 0. Start it again, and within a minute  
or two it hits 100% again, and stays there.

So I emptied the logs, stopped httpd, and set to monitoring it.

iPhones / iPads turned off, Imp logged out.
Started httpd.
httpd access_log for Horde remains empty, with ZERO incoming requests.
After about 15 seconds this time - httpd hits 100%. AT THE SAME TIME,  
this message hits the horde log:

2011-11-04T01:04:11+10:00 ERR: HORDE [imp] Server does not support TLS  
connections. [pid 22050 on line 340 of  
"/var/www/horde4/imp/lib/Imap.php"]

This message hits /var/log/horde up to 25 times per second, during  
which CPU usage remains at 100%.

Still no incoming requests for httpd in httpd/access_log, or errors in  
httpd/error_log.

The exact second that Horde logs that error, CPU hits 100%. Stop  
httpd, restart it, reproduce it. Did this several times over an hour,  
producing the exact same result - still ZERO http requests made of  
horde, 100% CPU at the same point the error gets logged.

So I logged in to Horde, and looked in "Sessions". About 30 sessions  
sitting in there, dating back up to a week old, across iPhone, Ipad,  
Mozilla, IE.

As soon as I deleted the session files from /var/lib/php/session  
(kicked me out of Horde as expected), CPU usage immediately dropped,  
and the IMAP TLS message stopped.

It hasn't done it this morning since, and clearing the old sessions  
has stopped both the errors in the log and brought CPU usage down to  
about 3%.

Is there any way I can stop this reoccurring (other than monitoring  
for 100% CPU load and triggering a session file delete!)

Thanks
Simon.

--
Simon Wilson
M: 0400 12 11 16