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From "Breno Jacinto" <>
Subject Re: Hundreds of Instances
Date Tue, 04 Dec 2007 15:29:05 GMT
Hi Christopher,

> >     Not really. I dont have the exact numbers, but I think we'd get at
> > most 50 users every 10 minutes = 5 users / min. I believe that´s
> > pretty low.
> Is that estimated, or measured?

    It's just estimation. BTW, is there any tool that could help me
with effectively measuring this, get some statistics etc?

> > I assume the garbage collector cleans them all.
> As long as you are putting those search results only into request
> attributes or something like that for temporary storage, you should be
> okay. Don't forget that a single *huge* result set can still cause an
> OOME if you don't have enough memory allocated.

> Gotcha. How much memory do you have configured for the JVM, and how much
> memory is actually free? IF you're swapping a lot, maybe you need to a)
> buy more memory or b) lower the memory allocation to your app. Of
> course, lowering your memory allocation could lead to OOME, but both
> problems are effectively the same.

      This is how my JAVA_OPTS goes:

JAVA_OPTS="-server -Xms128m -Xmx384m

     I had changed the default configuration after reading a High
Performance paper on Tomcat, which is on the site.

     I'll post more details (the server status) in the reply to chuck,
please take a look.

> The memory profiler is your best bet. Look at, say, 24 hours worth of GC
> activity (if your server stays up that long). You should have a GC curve
> that looks like this: /\/\/\/\/\/\/\/\/\/. If if goes up and up and up,
> you obviously have a memory leak. If it only goes up at intervals (say,
> once an hour), then maybe you have a rare event or timed event that
> leaks, rather than something that happens all the time (say, with every
> request).
> That will give you some idea of what you are looking for.

    OK. The only problem is that this site is on production, but I
believe it'll possible to run Tomcat under the profiler and get some
significant results. An alternative is to replicate the system and try
simulating some load and common operations (which I found out JMeter
is the tool for this).

> Oh, and don't freak out when you find out how much memory is consumed by
> char[] objects ;)

    :)). I had this experience once - it's hard to believe char[] are
so evil! :).
> - -chris

best regards,

:: Breno Jacinto ::
:: breno - at - ::
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