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From Victor Granic <victorgra...@yahoo.com>
Subject Re: number of established connections keep growing
Date Fri, 24 Feb 2006 19:17:30 GMT
--- Mladen Turk <mladen.turk@jboss.com> wrote:

> Victor Granic wrote:
> > Hello!
> > 
> > I'm running Tomcat 5.0.28 on a Windows 2000 server.  Tomcat is
> wrapped
> > using the Java Service Wrapper.  All connections to the Tomcat
> service
> > come from a proxy running apache+mod_jk on linux.
> > 
> > Problem:  The number of ESTABLISHED connections continue to grow on
> the
> > Windows server until users are unable to access the web site.
> 
> 
> This is because mod_jk uses constant connection pool, and once
> when the connection is established it stays open for the
> server lifetime.
> The reason why connections are growing is because the Apache will
> create up to MaxClient connections.

That's true.  Most of the time the proxy has around 20 established
connections to Tomcat.  The number of connections is probably growing
during times of high traffic and they close when they become unused. 
But, why aren't the sockets closing on the Tomcat server?


> Also if you have a firewall between mod_jk and Tomcat that tends
> to cut the inactive connections, the Tomcat connection will be
> half-closed. Apache will reconnect and your connection count will
> rise.
> 

I do have a firewall between mod_jk and Tomcat but it has been
configured with very high inactivity timeouts so I don't think it is
interfering with the persistent connections from the proxy.  On the
proxy server I see fully established connections to Tomcat and on the
Tomcat server I see those same fully established connections and an
additional 150 or more stale established connections.  They could very
well be in a half open state.  But why?  Why didn't they close when the
FIN was received/sent?  A 18 hour tcpdump on either side of the
firewall shows that FIN/ACKs are being sent and received by both the
proxy and Tomcat server.


> The solution is to set the connectionTimeout in server.xml
> that will close the inactive connections. This number should be
> large, like 10 ... 30 minutes, so that performance doesn't suffer.
> 

It looks like this parameter is not set for the active connector. 
Tomcat documentation states that the default is 60 seconds.  I'm
wondering if it's possible that in reality, if it's not set then a
timeout will never be reached which could be the cause of my problem.  

I'm a little confused by you're recommendation since it is a far
greater timeout than the default and the main issue is that these
half-closed connections are lingering and multiplying, effectively
rendering the service unavailable after a few days.  Would a lower
timeout be a better cure?

> Regards,
> Mladen.
> 

Thanks for the helpful response Mladen!

Victor


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