3) Can someone point me at some good doc for learning about memory
profiling of Java app's. Specifically over a long period of time. Even
to figure out how much ram each session is taking and when that is
being garbage collected as per Tom's example below.
I've used OptimizeIt
(http://www.borland.com/us/products/optimizeit/index.html), although
not in its most recent incarnation, of which there have been several. I
have also heard that JProbe (http://www.quest.com/jprobe) has seen
plenty of use with WebObjects, although that might be a few
incarnations ago as well. I am aware of JProfiler
(http://www.ej-technologies.com/products/jprofiler/overview.html)
although I haven't heard of it being used with WebObjects.
The first two work by connecting to the VM's JVMPI (Java Virtual
Machine Profiler Interface) ports. This slows the VM down a good deal.
You wouldn't want to hook up to this in production and leave the
profiler running for days until trouble appeared.
Some ideas:
- Check that sessions are indeed terminating.
- I have no idea how much traffic you are seeing or what percentage of
overall memory is leaking. However, you might determine how much memory
per session is leaking -- that in itself might give you a clue as to
the problem, especially if it's a lot.
- Set up the app in development with a profiler attached. Set the
session timeout to be short. Watch what happens, even with a nominal
amount of activity on the session, especially as the session
terminates. Also visit any suspicious areas of the application. Be
aware that the garbage collector collects in its own sweet time, as I
mentioned earlier. The problem is difficult in principal but,
especially if the leak is large, it may be pretty easy to spot.
I'd also give some consideration to periodically restarting instances.
Not as a solution to a real memory problem but as insurance against
your mission-critical application failing early Sunday AM.
Tom
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