Hello,
I'm currently analysing issues with a quite old Tomcat 5.5.17, mod_jk
1.2.15 and Apache 2.0.55 loadbalanced setup with 4 Apaches (worker.c)
and 4 Tomcats.
Questions are:
* Can anyone explain why Apache SYN requests to Tomcat don't get
answered (probably this happens only if maxClients exceeds Tomcat AJP
pool sizes).
* Shouldn't the AJP thread pool shrink to maxSpareThreads, if idle, or
will threads stay open if Apache ever requested them?
Currently there are 4 Apaches, 2 with
StartServers 2
MaxClients 300
MinSpareThreads 25
MaxSpareThreads 75
ThreadsPerChild 25
MaxRequestsPerChild 0
and 2 more with
StartServers 2
MaxClients 200
MinSpareThreads 25
MaxSpareThreads 75
ThreadsPerChild 25
MaxRequestsPerChild 0
that have problems with hung SYN requests when getting near the 4
Tomcat's default AJP thread pool size of 200.
Current guess was that it's simply a bad idea to have 2*300+2*200=1000
maxClients on Apache side and just 4*200=800 AJP threads (if evenly
balanced) on Tomcat side.
So firstly increased Tomcat threads to maxThreads=500 to find some peak.
All other AJP connector settings are default, resp. not defined.
Meanwhile we log the JMX currentThreadCount for the AJP-Pools and the
thread count only increases. However even after peak hours the
currentThreadCount does not decrease. However would expect to get back
to the maxSpareThreads default of 50 during night time.
Can anyone explain why the AJP thread count stays high? I saw that one
could configure mod_jk connection_pool_timeout which is not done yet.
Could that be the reason for the thread pool never reducing the thread
count even though the AJP thread pool has a maxSpareThread setting (i.e.
doesn't this have an effect without pool timeout?)?
What could be the reason for SYN requests of the Apache that never get
answered by Tomcat?
Thanks,
Michael Echerer
--
TNG Technology Consulting GmbH, Betastr. 13a, D-85774 Unterföhring
Geschäftsführer: Henrik Klagges, Gerhard Müller, Christoph Stock
Amtsgericht München, HRB 135082
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