We have Apache running with the worker MPM and have MaxClients set to 6, yet when I open up top I can see more than 6 Apache processes running. 13 visible in the screen dump below. Can someone explain this? There's also a screen dump from /server-status/, taken around the same time. Under our normal load there seems to be 2-6 requests processing at a time, so I would expect to see that many apache2 processes running in top. The only way I can reconcile this is to assume at max load, there's 3 servers running (ServerLimit 3, 3 apache2 processes) each with 2 threads (3x2 = 6 apache2 processes), but even this would result in 9 apache processes running at most.

Apache is essentially running away and never releasing memory. We serve about 5-6 requests per second, monitored using /server-status/ so I figured setting MaxRequestsPerChild to 1000 (we've had it as low as 500) would cause the processes to recycle and release memory, but this doesn't appear to happen. We're monitoring apache process memory via New Relic. When we restart Apache it consumes about 550M of memory with our configuration below. Each process will eventually swell to VIRT: 300m RES: 80m and we seemingly can't control the number of processes running, so the apache goes from 550M - 5G within 12-14 hours and wipes us out.

I've checked the /conf.d/ directory to make sure that we're not overriding any settings in our apache config. Does anyone have any advice for getting apache under control? I know we have a fat python application running mod_wsgi that probably has memory leaks and certainly could be optimized, but I'm simply looking to control the number of apache processes that are spawned.

Apache Config:

### Section 1: Global Environment
# The directives in this section affect the overall operation of Apache,
# such as the number of concurrent requests it can handle or where it
# can find its configuration files.

ServerRoot "/etc/apache2"
ServerName localhost
LockFile ${APACHE_LOCK_DIR}/accept.lock
Timeout 120
KeepAlive Off
ExtendedStatus On

# worker MPM
# StartServers: initial number of server processes to start
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadLimit: ThreadsPerChild can be changed to this maximum value during a
#              graceful restart. ThreadLimit can only be changed by stopping
#              and starting Apache.
# ThreadsPerChild: constant number of worker threads in each server process
# MaxClients: maximum number of simultaneous client connections
# MaxRequestsPerChild: maximum number of requests a server process serves
<IfModule mpm_worker_module>
    StartServers             1
    ThreadsPerChild          2
    MinSpareThreads          1
    MaxSpareThreads          2
    MaxClients               6
    ServerLimit              3
    MaxRequestsPerChild   1000

# These need to be set in /etc/apache2/envvars

AccessFileName .htaccess

<Files ~ "^\.ht">
    Order allow,deny
    Deny from all
    Satisfy all

DefaultType None
HostnameLookups Off
ErrorLog ${APACHE_LOG_DIR}/error.log
LogLevel warn

LogFormat "%v:%p %a %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" vhost_combined
LogFormat "%a %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" combined
LogFormat "%a %l %u %t \"%r\" %>s %O" common
LogFormat "%{Referer}i -> %U" referer
LogFormat "%{User-agent}i" agent

# Include module configuration:
Include mods-enabled/*.load
Include mods-enabled/*.conf

# Include ports listing
Include ports.conf

# Include generic snippets of statements
Include conf.d/


  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                   
24775 www-data  20   0  282m  68m 5160 S  104  0.8   3:04.67 apache2                                                                                                                                    
24782 www-data  20   0  283m  66m 5376 S   57  0.8   3:24.31 apache2                                                                                                                                    
24780 www-data  20   0  280m  65m 4976 S   55  0.8   3:20.74 apache2                                                                                                                                    
24778 www-data  20   0  289m  72m 5540 S   29  0.9   3:09.55 apache2                                                                                                                                    
24773 www-data  20   0  278m  64m 5116 S   26  0.8   2:55.66 apache2                                                                                                                                    
24777 www-data  20   0  282m  65m 4664 S   20  0.8   3:08.39 apache2                                                                                                                                    
13433 memcache  20   0  642m 597m  876 S   16  7.4  11:46.62 memcached                                                                                                                                  
24774 www-data  20   0  288m  71m 4672 S   15  0.9   3:12.58 apache2                                                                                                                                    
24781 www-data  20   0  283m  66m 5160 S   11  0.8   3:16.01 apache2                                                                                                                                    
24779 www-data  20   0  281m  64m 4676 S    8  0.8   3:11.44 apache2                                                                                                                                    
24776 www-data  20   0  284m  74m 4660 S    8  0.9   2:56.38 apache2                                                                                                                                    
27105 www-data  20   0 49520 6180 2636 S    2  0.1   0:00.05 apache2                                                                                                                                    
27100 www-data  20   0 49432 6084 2628 S    1  0.1   0:00.06 apache2                                                                                                                                    
    9 root      20   0     0    0    0 S    1  0.0  62:05.25 rcu_sched                                                                                                                                  
27007 www-data  20   0 49568 6292 2684 S    1  0.1   0:00.60 apache2                                                                                                                                                                                                                                                                      
    1 root      20   0  3496  872  428 S    0  0.0   0:04.61 init                                                                                                                                       
    2 root      20   0     0    0    0 S    0  0.0   0:00.00 kthreadd                                                                                                                                   
    3 root      20   0     0    0    0 S    0  0.0   0


Apache Server Status for www.mysite.com

Server Version: Apache/2.2.22 (Ubuntu) mod_ssl/2.2.22 OpenSSL/1.0.1 mod_wsgi/3.3 Python/2.7.3
Server Built: Feb 13 2012 01:37:45
Current Time: Tuesday, 18-Feb-2014 10:53:01 EST
Restart Time: Tuesday, 18-Feb-2014 10:25:32 EST
Parent Server Generation: 0
Server uptime: 27 minutes 28 seconds
Total accesses: 8248 - Total Traffic: 126.6 MB
CPU Usage: u.36 s.15 cu0 cs0 - .0309% CPU load
5 requests/sec - 78.7 kB/second - 15.7 kB/request
2 requests currently being processed, 0 idle workers
Scoreboard Key:
"_" Waiting for Connection, "S" Starting up, "R" Reading Request,
"W" Sending Reply, "K" Keepalive (read), "D" DNS Lookup,
"C" Closing connection, "L" Logging, "G" Gracefully finishing,
"I" Idle cleanup of worker, "." Open slot with no current process

Srv PID Acc M   CPU SS  Req Conn    Child   Slot    Client  VHost   Request
0-0 -   0/0/1569    .   0.02    0   37  0.0 0.00    25.22  www.mysite.com  GET /imgname.jpg HTTP/1.0
0-0 -   0/0/1502    .   0.03    0   786 0.0 0.00    22.47    www.mysite.com  GET / HTTP/1.0
1-0 -   0/0/1629    .   0.04    13  260 0.0 0.00    24.85   www.mysite.com  GET /article/s
1-0 -   0/0/1416    .   0.04    13  469 0.0 0.00    21.42   www.mysite.com  GET / HTTP/1.0
2-0 27863   0/54/1021   W   0.44    0   0   0.0 0.69    15.95 www.mysite.com  GET /storm-h
2-0 27863   0/50/1111   W   0.44    0   0   0.0 0.61    16.73    www.mysite.com  GET /server-status/ HTTP/1.0


There was a multiple step solution to this problem.

1) Identify that mod_wsgi processes were being reported by top as apache2. To correct this add the display-name=my-mod-wsgi-app parameter to your WSGIDaemonProcess config.

2) We discovered that there is some horrible part of our python/Django application that causes a mod_wsgi process to bloat to 600M. Running 5 of these would consume 3G of memory on our VPS and make it very sad.

3) We added inactivity-timeout=300 and maximum-requests=200 to our WSGIDaemonProcess config and mod_wsgi nicely restarts itself when a process is not in use or it gets over 500 requests, which keeps our overweight, sloppy Django application running smoothly.

Thanks to Graham for getting me started in this direction. You can read as I talk my way through this problem over on the mod_wsgi Google group. https://groups.google.com/forum/#!topic/modwsgi/wYScZlqgjgA


The breakdown of processes is:

  • One Apache parent process. If Apache is being started from system init.d scripts, then this process will be running as 'root'. It will be the parent process ID of all other processes.
  • A variable number of Apache child worker processes. The exact number is dependent on the Apache MPM settings and the amount of traffic your site is receiving. It varies because Apache will dynamically control the number of child worker processes based on what is required.
  • A fixed number of mod_wsgi daemon mode processes. This is determined by how many processes you specified to the WSGIDaemonProcess directive.

If you use the display-name option to WSGIDaemonProcess, then some tools such as BSD derived 'ps' command and 'htop' will show the name you specify rather than 'apache2'. This way you can distinguish which are actually the mod_wsgi daemon processes running you web application.

To infer more you would need to show what the mod_wsgi configuration you are using is. Right now though it looks like you have a poor configuration even with the MPM settings as running with such a low number of threads and favouring processes when using Apache worker MPM doesn't make a great deal of sense.

Either way, StackOverflow is not a forum and as a result is a really bad place to try and carry out a long discussion to help sort out your configuration. You would be better off using the mod_wsgi mailing list.

I would also suggest you watch/read:

  • This was right on. We had bloated numbers in WSGIDaemonProcess processes=10 threads=20 that were being reported in top as 'apache2'. Going to start out turning that down to processes=2 threads=5 and use the NR Capacity report to fine tune. Thanks, Graham. – scoopseven Feb 19 '14 at 3:42
  • Of course, I'll be upping my Apache client #'s too, because we know that processes*threads > MaxClients is useless :) – scoopseven Feb 19 '14 at 3:44
  • For capacity analysis, have a read of blog.newrelic.com/2012/09/11/… – Graham Dumpleton Feb 19 '14 at 4:58

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