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List:       tomcat-user
Subject:    Re: mod_jk makes ajp connector run out of free connections
From:       Rainer Jung <rainer.jung () kippdata ! de>
Date:       2010-10-28 10:39:47
Message-ID: 4CC952F3.2060503 () kippdata ! de
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On 26.10.2010 20:36, Marc Wilmots wrote:
> 2010/10/26 Mladen Turk<mturk@apache.org>
>
>> On 10/26/2010 02:47 PM, Marc Wilmots wrote:
>>
>>> Hi Experts,
>>>
>>> I have the following setup:
>>>
>>>                  Apache1
>>>                  /         \
>>>    Apache2           Apache3
>>>                 \          /
>>>                 Tomcat1
>>>
>>> All Apaches are version 2.2.3 (RedHat)
>>> Apache2 and Apache3 loadbalance Tomcat1 (6.0.18) with mod_jk (2.2.28).
>>>
>>> In idle state the AJP connector of Tomcat1 only has 7 active connections.
>>> After launching a stress test of Tomcat1, it's AJP connector has reached
>>> maxThreads (200). After the stress test has finished, there are still 200
>>> active connections in the AJP connector.
>>>
>>> Because of this, apache2 and apache2 cannot receive any heartbeat message
>>> anymore from the AJP connector and mark Tomcat1 as dead. I can access
>>> perfectly through port 8080, so Tomcat1 isn't dead at all!
>>>
>>>
>> You have a usual setup problem where the number of connections
>> in httpd fronting tomcat is too high for a tomcat.
>> And you don't have any mechanism for limiting those connections.
>>
>> Sorry, I realize I had to mention I have a total of 4 Tomcats, which in
> total make up a maxThreads of 800 (200 each).
> The Apaches have a maxClients of each 600 (1200 total).
>
> 1200>  1000, thus your theory is probably right. However, I'm just
> wondering... I read that when Tomcat reaches the max number of connections,
> just rejects new connections (I'm omitting the backlog on purpose).

Yes.

But your calculation above is not right. Each Apache will connect to 
each Tomcat. So from the point of view of one Tomcat, it has 200 
threads, but 1200 posible incoming connections from the Apache Servers. 
So it is not 1200 > 800 but 1200 > 200!

Regards,

Rainer

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