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From André Warnier ...@ice-sa.com>
Subject Re: Too many connections in keepalive state in jk threadpool
Date Fri, 02 Mar 2012 12:01:26 GMT
Beier Michael wrote:
> Hi all,
> 
> we're running tomcat 7.0.23 on sun jdk 1.6.0_29, connected via ajp to httpd 2.2.21 using
mod_jk 1.2.32.
> 
> I observed the behavior, that tomcat keeps threads in its ajp pool in keepalive state,
regardless of which timeouts (connectionTimeout and keepAliveTimeout) are configured in tomcat.
> I tested three connector configurations and with all I see connections in tomcat server
status where the "Time" value amounts up to several million milliseconds, which is more than
configured in connectionTimeout/keepAliveTimeout.
> This results in having 60-80 percent of the thread pool being in state "keepAlive".
> 
> 1)
>     <Connector port="8309" protocol="AJP/1.3"
>                maxThreads="200" redirectPort="8343" tomcatAuthentication="false"
>                keepAliveTimeout="300000" connectionTimeout="300000" />
> 2)
>     <Connector port="8309" protocol="AJP/1.3"
>                maxThreads="200" redirectPort="8343" tomcatAuthentication="false"
>                keepAliveTimeout="300000" />
> 3)
>     <Connector port="8309" protocol="AJP/1.3"
>                maxThreads="200" redirectPort="8343" tomcatAuthentication="false" />
> 
> In mod_jk the connection_pool_timeout is set to the same value as connectionTimeout (only
in seconds, not milliseconds).
> I verified that the values are set correctly querying the parameters via JMX.
> 
> How can I avoid having so many threads in keepalive state - I don't have any idea at
the moment and can't see that there is an error in my configuration.

Before discussing this, I find it useful to review the basics, such as in :

http://en.wikipedia.org/wiki/HTTP_persistent_connection
and
http://tomcat.apache.org/connectors-doc/generic_howto/timeouts.html

In other words, at the level of your front-end webserver (which I suppose you have, since

you are talking about mod_jk and AJP), do you really need a long KeepAliveTimeout ?
(and similarly at the level of your Tomcat <Connector>'s above).

As per the documentation :

connectionTimeout	

The number of milliseconds this Connector will wait, after accepting a connection, for the

request URI line to be presented. The default value is 60000 (i.e. 60 seconds).

keepAliveTimeout	

The number of milliseconds this Connector will wait for another AJP request before closing

the connection. The default value is to use the value that has been set for the 
connectionTimeout attribute.

In other words,
- connectionTimeout defaults to 60 seconds
- if you do not specify either one of them, then they both default to 60 seconds.
- if you do specify connectionTimeout and not KeepAliveTimeout, then KeepAliveTimeout 
defaults to the same value as connectionTimeout.
- your value above for KeepAliveTimeout (300000) means 5 minutes

Do you really want one Tomcat thread to wait for 5 minutes doing nothing, just in case the

browser would decide to send another request on the same connection ?
And do you really want, when a browser creates its initial TCP connection to your 
webserver, to give it 60 seconds (or 5 mintes !) before it even starts sending its HTTP 
request on that connection ?




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