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From Shankar P S <>
Subject 2 instance of ParallelWebAppClassLoaders in Tomcat JVM
Date Thu, 14 Mar 2019 21:15:01 GMT
Version - Tomcat 8.5.38
OS - Centos 7.6
JVM - openjdk 1.8, 4 CPU

We recently upgraded an existing server running a Spring 3.0 web app from
Tomcat 8.5.35 to 8.5.38.

After the upgrade, I noticed OutOfMemory exceptions several times.
Increasing the heap size (-Xmx) several times upto nearly twice (from 6 GB
to 10 GB) helped bring the problem under control.

I was worried about a memory leak and so took a heap dump. Upon inspection
I noticed that there were 2 copies of 2 large HashMap objects that we use
as a cache for fast lookup. I noticed that this was because there were 2
instances of org.apache.catalina.loader.ParallelWebappClassLoader.

Downgrading to 5.3.35, reduced the heap size to half and the problem was
gone. In the new heap dump, there was only one instance of

My question is - why does Tomcat 5.3.38 create 2 instances of
ParallelWebappClassLoader, while  5.3.35 creates only one?Is there a way to
conigure the number of instances of  ParallelWebappClassLoaderwhen
upgrading to 8.5.38?

Thanks for reading.

I have also posted the same problem in Stackoverflow -

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