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From "Tauzell, Dave" <Dave.Tauz...@surescripts.com>
Subject RE: Tomcat caching
Date Mon, 16 Nov 2015 15:20:37 GMT
If you can reproduce this problem in your development environment and you cannot track down
the reason then try out the free version of App Dynamics: http://www.appdynamics.com/lite/.

-Dave

-----Original Message-----
From: David E. Filip [mailto:dfilip@colornet.com]
Sent: Monday, November 16, 2015 9:09 AM
To: Tomcat Users List
Subject: Re: Tomcat caching

None of those numbers alarming, unless you see Eden regularly increase beyond 90% and stay
there, especially when you are seeing slowness, as then you might want to consider increasing
your heap.  In my view - and others may disagree! - understanding tuning JVM heap is more
of an art than a science.

>From the 30K foot view, objects get created in Eden (previously called NewGen I believe),
then get moved to OldGen by the GC when they are still referenced after a certain period of
time, and finally get moved to Survivor when if they are still referenced even later.

However, when you say 'developing', if the problem is only when you are editing JSP pages
- which Jasper then needs to recompile - or when performing new webapp deployments, I would
also keep an eye on PermGen, which gets used when instantiating new static objects (as I understand
it).  I have seen "weird" things happen when PermGen fills up, including seeing the server
stop responding to certain requests, JSP pages not compiling, or "class not found" errors
on the compiled JSP classes (org.apache.jsp.*).

Of course, when either the heap or PermGen runs out, then you will start seeing a stack trace.
 However, in my experience, there is this grey area between when you are almost out of memory
but not quite yet.

The caveat to all of this, however, is that everything gets cleared out when you restart the
server.  And that is one of the ways to tell if that is indeed the problem, is when everything
starlings running correctly right after a server restart.  However, if you are not seeing
everything clear up after a clean restart of Tomcat, then I'm afraid this is not your problem.

On Nov 16, 2015, at 9:48 AM, Daniel Küppers <daniel@tetralog.com> wrote:

>
>
> Am 16.11.2015 um 14:56 schrieb David E. Filip:
>> In my experience, the most common explanation (but certainly not the only!) for an
active webapp to be occasionally and sporadically running extremely slow, but run fine at
other times, is running low on heap space.
>>
>> If you have not already, I would suggest checking the Tomcat Server Status app (http://localhost:8080/manager/status)
and determine if any of the heaps are filling up while you are experiencing this slowness.
 If they are, your app could be spending too much time waiting for the garbage collector,
and you will need to increase the heap size in your startup file.
>>
>> On Nov 16, 2015, at 6:45 AM, Konstantin Kolinko <knst.kolinko@gmail.com> wrote:
>>
>>> 2015-11-16 12:22 GMT+03:00 Daniel Küppers <daniel@tetralog.com>:
>>>> Hi,
>>>> i have a recurring issue, that tomcat caches my jsf webapp pages in
>>>> a strange manner.
>>>> Sometimes for multiple days/hours, one or two explict pages or the
>>>> whole webapp is loading very slowly.
>>>> My setup is a locally used tomcat 8.0.28 for debugging in Eclipse
>>>> and a local database.
>>>> The behaviour persists also after browser cache clearing and with
>>>> different browsers.
>>>> Does anyone else have seen this behaviour before?
>>>> Do i miss a specific parameter?
>>>
>>> Your problem is "one or two explict pages or the whole webapp is
>>> loading very slowly".  Why are you blaming caching?
>>>
>>> Stack trace when application behaves slowly =? Is it know what it
>>> actually does at that time?
>>>
>>> Is the clock on your server set correctly?
>>> Is autoDeploy tuned off on a Host, or it wastes time checking for
>>> changes of a war file?
>>> Is Jasper (JspServlet) configured with development=false, or it
>>> wastes time checking and recompiling the pages?
>>>
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>>
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>>
> Thanks for the replies. I will monitor the free heapspace from now on. If i see something
that concludes to this problem, i'll let you know.
> For which exact Memory Pool i should have a watchout? Here are my current used loads:
> - PS Eden Space: 89%
> - PS Old Gen: 4%
> - PS Survivor Space: 33%
> I dont get a stacktrace when the app runs slowly. I also only get this issues when the
configuration is in developing mode. It persists even restarts.
> Clock is set correctly, AutoDeploy is On, running in development mode (myFaces). I cant
determine how Jasper should be configured.
>
> Daniel
>
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