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From "Shapira, Yoav" <Yoav.Shap...@mpi.com>
Subject RE: Huge tomcat memory footprint
Date Thu, 04 Nov 2004 17:38:24 GMT

Hi,

>80MB
>and heap used was 57MB (reported by optimizeit). But the memory sizes
>reported by solairs pmap command is
>
>Size          RSS            Shared          Private
>1173.45 MB    608.125 MB     15.125 MB       593 MB

There's a mismatch here.  There's no way the OS-level overhead is
hundreds of MBs for an 80-MB heap.  Are you sure the pmap command
doesn't multiply by the number of threads or something like that
(similar to what the Linux top command does)?

>
>of few hours. Ofcourse, optimizeit itself has overheads and adds to the

A profiler typically adds an order of magnitude overhead.  So for an
80MB heap on the app normally, an 800MB heap with a profiler is within
the bounds of reason.  But that'd be within the heap and the JVM.

>process on solaris is 4GB. What will happen when the JVM process size
>reaches 4GB?

Changes are it'll crash.

>2. I see that GC is running, reclaiming memory periodically. But I
noticed
>that after a while GC is running more frequently and each run takes a
>substantial amount of time (in one instance GC took about 14 secs).
This
>may
>affect the throughput, but will it have any impact on the memory?

If GC can't free up memory, then not only will your throughput suffer
but it'll be for naught.  This is a classic memory leak scenario.

>3. I read somewhere that if you use reflection,  the reflective data
>structures (whatever that means) also contribute to the memory
footprint.
>It
>sounded as though these are not part of the heap. So if we are creating
>instances of Method, Constructor, etc, are they not allocated in the
heap?
>We are using reflection heavily.

Where's "somewhere" ? ;)  That's mostly old information.  The JVM is
very efficient at handling reflection and properly storing Method
references.

As you said, you need to look at the profiler more carefully.

Yoav



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