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From Joe Baldwin <jfbald...@earthlink.net>
Subject Re: Memory Usage Problem with Tomcat
Date Tue, 13 Mar 2012 19:41:31 GMT
Mike,

thanks for your ideas.  I am still a bit mystified by the rules concerning garbage collection
I worked on a a project some time back on this and became very adept at managing memory. 
However, when I have advanced software like Tomcat & Cayenne in between my software and
the JVM, then I get a tad confused with what is going on.

What I have been reading today tells me that the "rule of thumb" is to simply increase memory.
 However, I have two conflicting thoughts about this: 
	1. if I do, in fact, have an error in my code then increasing memory will simply hide the
error for a while.
	2. if you look at it like an operating system, if you try to run OSX on a computer with 128MB
of ram, then you are insane - and no amount of correct programming will allow your app to
run without running out of memory.

As to your questions: the stack trace was not terribly helpful since it indicated an out of
memory error when a query was launched (on a table that had all of 7 items in it).

Your idea of trying to set up a similar config on my dev server may be a good idea.  I probably
need to take a look at the general health of the memory management.  Of course, I could just
be running with way too-little memory.

I wonder what a good base memory setting should be: 64, 128, 512, 1Gig?  The comments on the
web seem to indicate all of them.

Thanks
Joe



On Mar 13, 2012, at 3:19 PM, Mike Kienenberger wrote:

> If you have almost no activity, why not set up a duplicate environment
> running the same version of Tomcat and hit your application  using
> JMeter or some other testing tool?
> 
> Or perhaps you can get sent the application http access.log file and
> duplicate the exact series of requests that generated the problem in
> your dev environment.
> 
> That said, Tomcat did often seem to have intrinsic memory issues,
> which is another reason I stopped using a few years back.
> 
> Also, you might want to ask what the exact stacktrace is.   We've had
> situations where it was a Tomcat permgen memory issue.   See this
> article for details -- there are more details in the comments by
> others:
> 
> http://www.mkyong.com/tomcat/tomcat-javalangoutofmemoryerror-permgen-space/
> 
> Again, a disclaimer as I haven't used Tomcat personally in a while,
> although some of my colleagues continue to do so for development.  And
> we don't run app servers using it.
> 
> 
> On Tue, Mar 13, 2012 at 2:59 PM, Joe Baldwin <jfbaldwin@earthlink.net> wrote:
>> OK, I think that I may have run into this before.  The ultimate "solution" was to
increase memory - however, I am concerned that may have been a quick-fix and not a long-term
fix.
>> 
>> The problem is out of memory errors associated with tomcat heap.
>> 
>> I have a webapp (powered primarily by cayenne).  The database has *very* little in
it.  I am essentially serving data (via cayenne & tomcat) and images (via tomcat).
>> 
>> I have a private tomcat instance running on a webhost in a "shared" environment.
 What this means is that I *absolutely* cannot attach a profiler.
>> 
>> I am being told by the webhost IT people (who are not always accurate in their objectivity)
that my app is leaking memory (badly), and that is what caused tomcat to crash.
>> 
>> My intuition tells me that with almost no activity on the website (because it is
not live yet) and Cayenne memory management that I should be able to manage memory well, but
it is not the case.
>> 
>> So, if my goal is to determine what the problem is, and if I simply increase heap
size, won't I just be masking a potential problem?  i.e. if the app runs fine for a while,
then mysteriously causes tomcat to run out of heap space, then couldn't there be a memory
leak?
>> 
>> If there is a memory leak, and I don't see it on my development server, and I *can't*
use a profiler on my webhost, then how do I get visibility into the memory usage?
>> 
>> Thanks
>> Joe
>> 


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