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List:       openjdk-serviceability-dev
Subject:    jconsole question -- probably the wrong mailing list but here goes...
From:       Luis-Miguel.Alventosa () Sun ! COM (Luis-Miguel Alventosa)
Date:       2008-04-09 14:11:27
Message-ID: 47FCCE8F.2040707 () Sun ! COM
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It looks like someone is adding lots of entries to a HashMap,
probably with Strings as keys so try to find out in your code
where this could happen.

Regards,
Luis

 > On 4/9/2008 3:57 PM, Stephen Ryan wrote:
 >
 > Hi Luis.
 >
 > I just discovered visualvm this morning in my quest. Its has some nice
 > features and all the same stuff that jconsole delivers as well.
 >
 > Heres the top chunk of what jmap -histo delivers. Also the classes
 > loaded count is still increasing. Im starting to lean towards a bug in
 > the code of my webserver.
 >
 > Size    Count   Class description
 > -------------------------------------------------------
 > 70483456        210902  char[]
 > 22539768        939157  java.lang.String
 > 10608936        442039  java.util.HashMap$Entry
 > 3876512 18922   java.util.HashMap$Entry[]
 > 3823192 22119   * ConstMethodKlass
 > 3046768 4349    byte[]
 > 2724968 47155   java.lang.Object[] ...
 >
 > Luis-Miguel Alventosa wrote:
 >
 >> Hi Stephen,
 >>
 >> Could you try to use jmap -dump and/or jmap -histo to see the names
 >> of the instances being created?
 >>
 >> You could also have a look at VisualVM in order to profile the
 >> application.
 >>
 >> https://visualvm.dev.java.net
 >>
 >> Regards,
 >> Luis
 >>
 >> > On 4/9/2008 3:24 PM, Stephen Ryan wrote:
 >> >
 >> > Hi Alan,
 >> > Thanks for that but Im not sure its that at all. I've other servers
 >> > being monitored and Ive never seen jConsole have this effect. I did a
 >> > jmap on the server and saw some huge numbers. Im begining to think that
 >> > theres bad code thats causing classes to be loaded too many times. The
 >> > 'Classes' view in jConsole is showing me a constant rise in class
 >> > numbers. I would have  expected this to be more or less stable,
 >> > considering that the server is serving about 4 requests per second. The
 >> > CPU is pretty busy too.Busy  garbage collecting the eden space I guess.
 >> >
 >> > I was considering increasing the eden space to see if that alleavates
 >> > the problem, but if its a code problem, it wont help at all.
 >> >
 >> > Thanks!
 >> > Stephen.
 >> >
 >> > Alan Bateman wrote:
 >> >
 >> >> Stephen Ryan wrote:
 >> >>
 >> >>> Hi,
 >> >>>
 >> >>> I was wondering if its possible to get the size of the classes loaded
 >> >>> from jConsole. Im seeing a lot of GC's in the Eden Space in a server
 >> >>> thats basically doing nothing. Im thinking that the jvm is trying to
 >> >>> load classes in there that are just too close to the size of that
 >> space.
 >> >>>
 >> >>> Any help appreciated!
 >> >>>
 >> >>> Stephen.
 >> >>
 >> >> Classes are essentially allocated from the perm generation so I don't
 >> >> think this is what you are observing. Instead it is likely that you
 >> >> are observing the effect of the JMX agent in the target VM due to the
 >> >> polling by jconsole. Each time jconsole updates the display it must
 >> >> interact with agent in the agent VM so this means some objects are
 >> >> allocated which can lead to periodic scavenging that you observe. You
 >> >> can reduce the polling interval via jconsole's -interval=value option
 >> >> (interval is specified in seconds). The management interface for class
 >> >> loading doesn't include the size of the classes but if you try jstat
 >> >> then you can get this information (jstat -class <vmid>  for example).
 >> >>
 >> >> -Alan.


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