httpd-users mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Miha Verlic>
Subject [users@httpd] server does not send synack on occasions
Date Tue, 14 Apr 2009 08:51:11 GMT

lately I noticed that our web servers don't answer to a request from 
time to time. I created a dummy http checking script every few seconds 
to debug a problem. It seems that server does not even respond with 
SYNACK packet. Here is the excerpt from wireshark/tcpdump log:

# failed request
10629	12:56:23.642861	TCP	57400 > http [SYN] Seq=0 
Win=5840 Len=0 MSS=1460 TSV=663117245 TSER=0 WS=7
10632	12:56:26.642216	TCP	57400 > http [SYN] Seq=0 
Win=5840 Len=0 MSS=1460 TSV=663117545 TSER=0 WS=7

# OK request
10767	12:57:39.643092	TCP	57209 > http [SYN] Seq=0 
Win=5840 Len=0 MSS=1460 TSV=663124844 TSER=0 WS=7
10768	12:57:39.643109	TCP	http > 57209 [SYN, ACK] 
Seq=0 Ack=1 Win=5792 Len=0 MSS=1460 TSV=134534397 TSER=663124844 WS=7
10769	12:57:39.643280	TCP	57209 > http [ACK] Seq=1 
Ack=1 Win=5888 Len=0 TSV=663124844 TSER=134534397
10770	12:57:39.710840	HTTP	GET / HTTP/1.1
10771	12:57:39.710862	TCP	http > 57209 [ACK] Seq=1 
Ack=114 Win=5888 Len=0 TSV=134534404 TSER=663124851
10772	12:57:39.711134	HTTP	HTTP/1.1 200 OK  (text/html)
10773	12:57:39.711189	TCP	http > 57209 [FIN, ACK] 
Seq=308 Ack=114 Win=5888 Len=0 TSV=134534404 TSER=663124851
10774	12:57:39.711297	TCP	57209 > http [ACK] Seq=114 
Ack=308 Win=6912 Len=0 TSV=663124851 TSER=134534404
10775	12:57:39.721484	TCP	57209 > http [FIN, ACK] 
Seq=114 Ack=309 Win=6912 Len=0 TSV=663124852 TSER=134534404
10776	12:57:39.721495	TCP	http > 57209 [ACK] Seq=309 
Ack=115 Win=5888 Len=0 TSV=134534405 TSER=663124852

OS is 64-bit slackware derivate with glibc 2.7, kernel and 
e1000e network driver. Hardware is Intel S5000PAL board, 2x Quad-Xeon 
E5345 with 16gb RAM.
We're running Apache 2.2.11 with worker mpm.

So far I've tried tweaking the following (with no luck):
  - changing accept mutex - tried sysvsem, flock, fcntl, posixsem
  - tweaked ListenBackLog + /proc/sys/net/core/somaxconn
  - tweaked various parts of mpm settings
  - tweaking at least the following settings:
     set txqueuelen on interfaces to 2000

There is no firewall on any machine and both machines on local network, 
no routers in the middle. Servers are quite loaded though - pushing 
about ~15mbit/s on each of the two interfaces. However the check also 
fails during the night, when the volume of traffic is quite low.

Any ideas?


The official User-To-User support forum of the Apache HTTP Server Project.
See <URL:> for more info.
To unsubscribe, e-mail:
   "   from the digest:
For additional commands, e-mail:

View raw message