Am 03.01.2013 15:31, schrieb kharp...@oreillyauto.com:
Hello All,
Yesterday we had a Tomcat6 server reach maxThreads and stay that way until
we restarted it. After researching a thread dump and some log files, we
found one of the applications is creating NullPointerExceptions and
subsequently leaving a TP-ProcessorX in WAITING state indefinitely for a DB
closePreparedStatement return. As more requests come in for this
application threads are being established and put into BLOCKED state,
waiting on TP-ProcessorX. Eventually, the server hits maxThreads and stops
serving requests almost entirely.
Obviously the application causing this needs to (and is being) fixed. But
I'm curious if there is a higher level of protection that could be
implemented to help protect the other applications (contexts) on this
server? For example, is there a way to specify that a context can only use
X number of request threads? Or perhaps X number of threads from an
executor? Et cetera.
On tomcat 6 - at least the most recent one - there is a Valve which can
limit the concurrent access to a context. Sadly it seems not to be
mentioned in the docs. So you would have to look at the code to see the
possible params (concurrency [=10], fairness [=false], blocking [=true],
interruptible [=false]) and the name
(org.apache.catalina.valves.SemaphoreValve) to be able to add the
(hopefully) right entry to your context:
<Valve class="org.apache.catalina.valves.SemaphoreValve"
concurrency="25"
blocking="false"
/>
I haven't tested it, but it should limit the concurrent threads used by
that context to 25 at most and give an error to any request while those
threads stay busy.
Regards
Felix
I haven't seen anything in the docs that would do this, but it never hurts
to ask. Here's our server info in case it's helpful:
OS: Ubuntu 12.04 64-bit
Front-end Server: Apache 2.2.22 (mod_ajp to back-end via Balancer setup)
Back-end App Server: Tomcat 6.0.24 (AJP & HTTP connectors, no executor)
Java -version output:
java version "1.6.0_20"
OpenJDK Runtime Environment (IcedTea6 1.9.13)
(6b20-1.9.13-0ubuntu1~10.04.1)
OpenJDK 64-Bit Server VM (build 19.0-b09, mixed mode)
Thanks,
Kyle Harper
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