On 22.12.2017 21:02, Eric Robinson wrote:
With the exact same Xms and Xmx settings, I get vastly different
resident and virtual image sizes from the Linux ps command.
tomcatA: jdk1.8.0_152, res: 694312, virt: 5045084
tomcatB: jdk1.6.0_21, res: 332840, virt: 3922656
-Xmx is not all that's determining how much memory the JVM actually
allocates.
https://jguru.fi/why-is-my-java-process-taking-more-memory-than-i-gave-it.html
gives some more hints on factors that have to be taken into account.
32 vs 64 bit architectures might do something to the sizes. And, now
that you gave your JVM options in another answer, you're not specifying
the GC algorithm and parameters, other than just logging. This means
that most likely you're using another algorithm with different
parameters, e.g. it might kick in later.
Coming back to the linked article: Tomcat might have different default
thread pool sizes - I don't know if you explicitly configure them. And
I've lost track if the default connectors are different ones between
Tomcat 6 and 8, or if you have ex- or implicitly configured them
differently (e.g. through using your Linux distribution's implementation
and they might have changed it).
Unrelated: I like to configure my production servers with identical -Xms
and -Xmx, so that they either start or don't start when I'm around (or
when the server boots) and not fail to allocate more memory from the OS
sunday night at 3am.
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