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From Richard_vK <richar...@gmail.com>
Subject Re: [users@httpd] Apache Processes Hung "Sending Reply"
Date Sun, 07 Mar 2010 17:18:16 GMT

I had the same problem, spent hours trying to figure out what the problem
was.

We use Munin to monitor our system status (server runs FreeBSD) and noticed
that whenever Apache processes started hanging, there was a corresponding
decrease in the number of established TCP connections to the machine.  This
led us to suspect a problem with broken connections on our PIX firewall. The
firewall was rebooted and (touch wood) we have had no more problems since
then (several days now).

Note that even while the problem was active I could still make requests to
the server, but responses were very slow, but connectivity to the website
was not entirely down. It did reach MaxClients a few times which was a
problem. The only solution during the problem was to restart Apache, which
flushed the hung connections. Connections did not time out on their own,
even after more than 20 minutes of 'hanging'.

Maybe also important to note was that my database (MySQL) was almost
entirely idle while the problem was active, clearly there were no apache
processes making any new database connections.

Hope this helps someone!


Tom Ritter-2 wrote:
> 
> I have 40 or so apache processes suspended in "Sending Reply".  My
> hypothesis
> is that MySQL had a problem, and either apache or php somehow got gummed
> up
> and isn't cleaning up for some reason.  I'm hoping the list can give me
> more
> ideas for debugging or point me in the right direction.
> 
> 
> 
> Here is the output of http://localhost/server-status:
> 
> 	Server uptime: 1 day 6 hours 57 minutes 9 seconds
> 	Total accesses: 47613 - Total Traffic: 498.2 MB
> 	CPU Usage: u1446.77 s548.53 cu6.26 cs0 - 1.8% CPU load
> 	.427 requests/sec - 4688 B/second - 10.7 kB/request
> 	41 requests currently being processed, 8 idle workers
> 	WW_WWW_WWWWW_WWWWWWWWWW_W_WWWW__WWW.WWWWWWWW_WWWWW
> 
> Examining the logs confirms that the last request on each pid was quite a
> while
> ago, and they are just hanging out doing nothing.
> 
> The server:
>  - RHEL
> 		$uname -a
> 		Linux xxx 2.6.18-164.6.1.el5 #1 SMP Tue Oct 27 11:30:06 EDT 2009
> i686 i686 i386 GNU/Linux
>  - Apache:
> 		Server version: Apache/2.2.3
> 		Server built:   Nov 10 2009 09:06:57
>  - PHP:
> 		$php -v
> 		PHP 5.1.6 (cli) (built: Feb 26 2009 07:01:10)
> 		Zend Engine v2.1.0
>  - Runs Wordpress (not my choice)
>  - Receives mostly search crawler traffic at a steady rate
>  - has a lot of "(32)Broken pipe: core_output_filter: writing data to the
>      network" and "(104)Connection reset by peer: core_output_filter:
> writing
>      data to the network" messages
>  - stopping reporting to rrdtool/cacti between 18:50 and 21:30 last night
>  - Had a child process die with the error /usr/sbin/httpd: free():
> invalid pointer: 0x0a2044a4
>      however this was about 20 minutes *after* the problem began
>  - had some "database error MySQL server has gone away for query" errors
> around
>      18:50 last night
>  - is behind an F5 device that proxies all connections - so every
> connection to
>      the server comes from the same IP address
> 
> Relevant config:
> 
> 	Timeout 40
> 	KeepAlive On
> 	MaxKeepAliveRequests 200
> 	KeepAliveTimeout 5
> 	StartServers       3
> 	MinSpareServers    2
> 	MaxSpareServers   10
> 	ServerLimit       50
> 	MaxClients        50
> 	MaxRequestsPerChild  1000
> 
> 
> I've only been able to find one person who had a similar problem, and his
> was
> caused by "dodgy sql":
> http://marc.info/?l=tomcat-user&m=106319217331935&w=2
> (His was also involving tomcat which I do not have.)
> 
> The biggest issue is that the processes should time out and clean up after
> themselves, right?  But they're not - instead they're just sitting
> consuming
> RAM.  (Not entirely sure about that - in some stacktraces I see
> <signal handler called> followed by "zend_timeout ()".)
> 
> My hypothesis is that MySQL had a problem, and either apache or php
> somehow
> got gummed up and isn't cleaning up for some reason.
> 
> I'm sure a httpd restart will clean everything up, but I wanted to debug
> this
> as best I could.  I gdb-ed a stacktrace for 8 of the hung threads, but
> it's
> not compiled in debug mode.  The stacktraces, and other relevant data, is
> here:
> http://ritter.vg/misc/apache-debug/
> 
> If anyone can suggest further things to try to debug this, or any
> additional
> info, I'd appreciate it.
> 
> -tom
> 
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> 
> 

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