Apache httpd & "W" Sending Reply

[Oleksandr Samoylyk]

Dear Subscribers,

I've some problems with Apache under high load (usually more than > 512
clients).

When httpd runs for several days some of the slots hung while 'Sending
Reply'.

When I enter server-status I see the following (BTW, it's not a "rush
hour"):

Current Time: Friday, 15-Dec-2006 08:50:44 EET
Restart Time: Tuesday, 12-Dec-2006 09:10:53 EET
Parent Server Generation: 0
Server uptime: 2 days 23 hours 39 minutes 50 seconds
Total accesses: 6442835 - Total Traffic: 86.3 GB
CPU Usage: u3302.37 s375.414 cu.265625 cs0 - 1.43% CPU load
25 requests/sec - 350.6 kB/second - 14.0 kB/request
62 requests currently being processed, 58 idle workers

WWWWWWWWWW......................................................
................................................................
________K_......................................................
WWWWWWWWWW......................................................
................................................................
_K____K___......................................................
_________K......................................................
K___K_____......................................................
W___K_K___......................................................
WWWWWWWWW.......................................................
WWWWWWWWWW......................................................
WWWWWWWWWW......................................................
WWWWWWWWWW......................................................
................................................................

I use:

# uname -a
FreeBSD webhosting.xxxxx.net 6.1-RELEASE FreeBSD 6.1-RELEASE #0: Fri Jun
 9 08:45:16 EEST 2006

# httpd -V
Server version: Apache/2.2.3
Server built:   Nov 30 2006 00:43:16
Server's Module Magic Number: 20051115:3
Server loaded:  APR 1.2.7, APR-Util 1.2.7
Compiled using: APR 1.2.7, APR-Util 1.2.7
Architecture:   64-bit
Server MPM:     Worker
  threaded:     yes (fixed thread count)
    forked:     yes (variable process count)
Server compiled with....
 -D APACHE_MPM_DIR="server/mpm/worker"
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
 -D APR_USE_FLOCK_SERIALIZE
 -D APR_USE_PTHREAD_SERIALIZE
 -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D DYNAMIC_MODULE_LIMIT=128
 -D HTTPD_ROOT="/usr/local"
 -D SUEXEC_BIN="/usr/local/bin/suexec"
 -D DEFAULT_SCOREBOARD="/var/run/apache_runtime_status"
 -D DEFAULT_ERRORLOG="/var/log/httpd-error.log"
 -D AP_TYPES_CONFIG_FILE="etc/apache22/mime.types"
 -D SERVER_CONFIG_FILE="etc/apache22/httpd.conf"

# php -v
PHP 4.4.4 with Suhosin-Patch 0.9.5 (cli) (built: Nov 30 2006 00:52:20)
Copyright (c) 1997-2004 The PHP Group
Zend Engine v1.3.0, Copyright (c) 1998-2004 Zend Technologies
    with eAccelerator v0.9.5, Copyright (c) 2004-2006 eAccelerator, by
eAccelerator

# mysql -V
mysql  Ver 14.7 Distrib 4.1.22, for portbld-freebsd6.1 (amd64) using  5.0

Some settings from httpd.conf:

Timeout 30
KeepAlive On
MaxKeepAliveRequests 150
KeepAliveTimeout 2
<IfModule mpm_worker_module>
    StartServers 2
    ServerLimit 80
    MaxClients 800
    MinSpareThreads 25
    MaxSpareThreads 75
    ThreadsPerChild 10
    MaxRequestsPerChild 0
</IfModule>

Why does it happen? How can I prevent it?

Thank you!

-- 
 Oleksandr Samoylyk
 OVS-RIPE