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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Connection count explosion due to thread http-nio-80-ClientPoller-x death
Date Thu, 26 Jun 2014 23:01:42 GMT
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André,

On 6/26/14, 11:09 AM, André Warnier wrote:
> Lars Engholm Johansen wrote:
>> Thanks for all the replies guys.
>> 
>> Have you observed a performance increase by setting
>>> acceptorThreadCount to 4 instead of a lower number? I'm just
>>> curious.
>> 
>> 
>> No, but this was the consensus after elongated discussions in my
>> team. We have 12 cpu cores - better save than sorry. I know that
>> the official docs reads "although you would never really need
>> more than 2" :-)
>> 
>> The GC that Andre suggested was to get rid of some of CLOSE_WAIT
>>> connections in netstat output, in case if those are owned by
>>> some abandoned and non properly closed I/O classes that are
>>> still present in JVM memory.
>> 
>> 
>> Please check out the "open connections" graph at
>> http://imgur.com/s4fOUte As far as I interpret, we only have a
>> slight connection count growth during the days until the poller
>> thread die. These may or may not disappear by forcing a GC, but
>> the amount is not problematic until we hit the 
>> http-nio-80-ClientPoller-x thread death.
> 
> Just to make sure : what kind of connections does this graph
> actually show ? in which TCP state ? does it count only the
> "established", or also the "FIN_WAIT", "CLOSE_WAIT", "LISTEN" etc..
> ?

I think the state of the connections is a red herring: Tomcat will
hold those connections forever because the poller thread has died.
Nothing else matters.

Even if the CLOSE_WAIT connections were somehow cleared, Tomcat would
never respond properly to another request, ever. A Tomcat restart is
required if the poller thread dies.

One could argue that the poller threads should maybe "try harder" not
to die, but sometimes you can't stop thread death.

- -chris
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