Memory Accounting, JDKs [was: Re: [Techtalk] Java on Linux]

Kathryn Hogg kjh at
Thu Jan 10 19:45:03 EST 2002

> At 16:56 on Jan 10, Kathryn Hogg combined all the right letters to say:
> The problem is that we need to know on the fly...

Yep but you need baseline numbers as a reference.

> to be able to track down what causes rogue memory usage if it happens.
> Every time I tell someone I am using 236M of memory, they freak out and
> say "that's not right!" but we can never figure out exactly why. We want
to be able to
> see on the fly "oh, you have 30 online connections, that explains why
> it happens" (when at noon I have more memory usage) or "hey wait, you
> only had 5 online connections, why is your memory usage higher?" (at
> midnight when things go crazy).

I don't know of java does anything differently but it is quite rare for
malloc() based allocators on Unix ever return memory to the OS so your
memory utilization is actually a high water mark.  Of course java could end
up using mmap() to manage heaps instead of malloc().

We have a java tool around here that reports all kind of interesting
statistics - kind of like Quantify for java.  The name escapes me at the
moment and the person who is using it, has left for the day.


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