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Rahul,
On 3/24/15 11:56 AM, Rahul Kumar Singh wrote:
> Some of the observations during the GC call monitoring / heap dump
> from JMAP:
>
>
> Tomcat Version
>
> Stages
>
> Java Heap Usage
>
> Java Heap Capacity
>
> Virtual memory (by top)
>
> Resident Memory (by top)
Well, that was a fun game re-formatting that into a spreadsheet. :(
> Observation:
>
> * Top’s reported virtual memory is approximately same.
>
> * Resident memory correlates with Java heap capacity. Refer to
> next slide for details.
What, no next slide?
Anyhow, you can see how top's view is a bit skewed:
Tomcat Version Java Heap Resident Memory
Tomcat 6 17.18 MB 175 MB
18.77 MB 207 MB
45.51 MB 235 MB
Tomcat 7 57.90 MB 423 MB
97.64 MB 558 MB
142.58 MB 1000 MB
In the Tomcat 6 case, there is only 45MiB heap usage and top reports
235MiB. For Tomcat 7, it's 142/1000, so 'top' is off by more than a
factor of 5.
If the question is "what is taking up all that space", then the answer
is "hook-up a memory profiler and look".
If the question is "how do I limit the amount of memory Tomcat's JVM
process will take, then the answer is "use -Xmx to set the maximum
heap size".
If the question really is is "what has changed between Tomcat
6.0.whatever and Tomcat 7.0.whatever that could account for every byte
of difference in heap usage between the two", I would say that
Tomcat's source repository is open o the public including a complete
version history, and anyone wishing to answer that question with any
degree of certainty is welcome to dig-around in there.
- -chris
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