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From André Warnier ...@ice-sa.com>
Subject Re: mod_jk question about lingering close_waits
Date Wed, 13 Jul 2011 21:16:34 GMT
Hi.

I am not the one who can really answer your question, but

1) this is the right list for Apache/Tomcat connectors (mod_jk among them)

2) a question : do these CLOSE_WAIT sockets bother you for some specific reason ?
In a totally different context, I have had problems with Linux systems when hundreds of 
such sockets accumulated over time (entire TCP stack becoming unresponsive at some point),

but they do not seem to have an impact when the number remains "reasonable" (below one 
hundred or so).
In this case, as I understand things, there will be a maximum of N such sockets, where N 
is the maximum number of threads which Tomcat may have, at some point, running 
simultaneously from this AJP Connector. (And it is also the number of connections which 
mod_jk will automatically configure in its pool).
On many of the sites which I take care of, I regularly see 25-50 such mod_jk sockets in 
CLOSE_WAIT state for extended periods of time, and they do not seem to have any negative 
consequences on the system.  They just clutter the netstat displays, but you can always 
"grep -v" them out.


Edward Quick wrote:
> Hi,
> 
> Apologies in advance if this is the wrong mailing list. I was unable to find one specific
to mod_jk and this looked the most relevant.
> 
> I have the following apache tomcat server configuration set up: Apache  2.2.3 , mod_jk
1.2.32 , and tomcat 6.0.32 running HelloWorld.war
> If I send a request to http://remotehost/HelloWorld/index.jsp, I observe the following
behaviour:
> 
> 
> 1 ) My tomcat AJP connector is listening on port 8010
> 
> TEST [root@remotehost]$ netstat -an | grep 8010
> tcp        0      0 0.0.0.0:8010                0.0.0.0:*                   LISTEN
> 
> 
> 2) I make a request to http://remotehost/HelloWorld/index.jsp and see the apache establish
a connection to tomcat. The response comes back straightaway.
> 
> TEST [root@remotehost]$ netstat -an | grep 8010
> tcp        0      0 0.0.0.0:8010                0.0.0.0:*                   LISTEN
> tcp        0      0 10.34.2.140:8010            10.34.2.140:46792           ESTABLISHED
> tcp        0      0 10.34.2.140:46792           10.34.2.140:8010            ESTABLISHED
> 
> 3) After reaching KeepAliveTimeout on the Tomcat AJP connector, the connections change
state:
> 
> TEST [root@ remotehost]$ netstat -an | grep 8010
> tcp        0      0 0.0.0.0:8010                0.0.0.0:*                   LISTEN
> tcp        0      0 10.34.2.140:8010            10.34.2.140:46792           FIN_WAIT2
> tcp        1      0 10.34.2.140:46792           10.34.2.140:8010            CLOSE_WAIT
> 
> 4) After about another minute, the FIN_WAIT2 is cleared, but the CLOSE_WAIT remains (on
the apache) until reaching net.ipv4.tcp_keepalive_time (which is set to 7200 seconds)
> 
> TEST [root@ remotehost]$ netstat -an | grep 8010
> tcp        0      0 0.0.0.0:8010                0.0.0.0:*                   LISTEN
> tcp        1      0 10.34.2.140:46792           10.34.2.140:8010            CLOSE_WAIT
> 
> 
> Everything there looks fine except for the CLOSE_WAIT which lingers around for 2 hours
until it hits tcp_keepalive_time.
> Adding JkOptions +DisableReuse will prevent the CLOSE_WAITs staying, but that is also
said to have a performance impact.
> 
> My question is if this is the expected tcpip state after the thread has finished, because
in JDBC I see the connections permanently ESTABLISHED or in TIME_WAIT.
> 
> Thanks for any help.
> 
> Ed.
> 
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