Jeffrey Janner wrote:
-----Original Message-----
From: André Warnier [mailto:a...@ice-sa.com]
Sent: Thursday, April 04, 2013 12:34 PM
To: Tomcat Users List
Subject: Re: Tomcat and Window nonpaged pool
Jeffrey Janner wrote:
-----Original Message-----
From: Harris, Jeffrey E. [mailto:jeffrey.har...@mantech.com]
Sent: Thursday, April 04, 2013 10:45 AM
To: Tomcat Users List
Subject: RE: Tomcat and Window nonpaged pool
-----Original Message-----
From: Jeffrey Janner [mailto:jeffrey.jan...@polydyne.com]
Sent: Thursday, April 04, 2013 11:04 AM
To: 'Tomcat Users List'
Subject: Tomcat and Window nonpaged pool
Tomcat 6.0.x (unsure but 33+) with Java 1.6 and Windows 2008
Server.
I've got a customer who is monitoring his system using the Windows
Performance Monitor and is concerned about Tomcat usage of the
nonpaged pool. When monitoring just the Tomcat service, it shows
the line for the pool to slowly rise over time, with hardly ever a
drop that cannot be attributed to a restart of the service (I
think).
I know that the nonpaged pool contains structures that should not
be
paged out by Windows per this quote:
"Nonpaged pool is therefore always kept present in physical
memory
and nonpaged pool virtual memory is assigned physical memory.
Common
system data structures stored in nonpaged pool include the kernel
and objects that represent processes and threads, synchronization
objects like mutexes, semaphores and events, references to files,
which are represented as file objects, and I/O request packets
(IRPs), which represent I/O operations."
I am struggling with how this relates to internal workings of
Tomcat
&
Java. Obviously, as more processing threads, in this case
connectors not executors, are opened, I would expect to see a rise
in this pool to support all the items it uses. I would expect to
see a drop as usage dropped and connectors were returned (or are
they permanent at
6).
Also, I assume processing threads for the Oracle connection pool
will cause this to increase as well, and should drop as the pool
size drop back to normal. Any app-based threads would also cause a
rise, but should drop if the thread is properly terminated.
I guess that this shows a potential memory leak somewhere, I'm just
wondering if there are other things I should look at that could
determine if this is normal behavior or indicative of a real issue.
I do most of my Tomcat app monitoring using jconsole, jvisualvm,
and
the Oracle OEM for looking for connection pool leaks there (not an
easy task).
Any help is appreciated.
Jeff
You might try the procedure in this URL to further isolate the
issue:
https://www.simple-talk.com/sysadmin/general/troubleshooting-
nonpaged
-
and-paged-pool-errors-in-windows/
If you have the ability, you might also try disconnecting your
Webapps and Oracle and see if simply running Tomcat by itself still
displays the same behavior; if so, then the issue is probably
Tomcat,
rather than a Webapp or Oracle.
If you are not using the latest version of Tomcat 6.0, you might
also
want to try upgrading and see if the behavior changes, as it is
possible there are memory leaks in earlier versions of Tomcat (some
of the Tomcat developers can speak to that).
Jeffrey Harris
Oh, I fully expect any problems to be with our webapp and not Tomcat.
The end user should be on a version of Tomcat6 very near the latest
release, at least if they are following our usage recommendations.
Unfortunately, it's at a customer site and I have not access to it.
I'm totally dependent on their willingness to research the issue on
their end and any information about how they are using the app vs. our
other customers. I think they are using a specific feature that is
little used by 90% of our customer base causing the issue.
I ran the same monitor against two of my hosted Tomcat instances,
with several virtual hosts each, meaning a diverse user base. It does
not appear to show the pattern. However, I may need to do a longer run
to see if I replicate their results. My results were over a 15 minute
period. Theirs was several days. Mine remained flat, or nearly so.
In fact, I saw a nice little random rise and fall in the graph right
around a central value for both Tomcats. One actually ended lower than
it started.
So, I'm pretty sure it's our app and how it's being used. Just
trying to understand what objects might be getting tossed into this
pool, so I know what to go after.
Does you app connect to anything by itself ?
If so, does it close these connections properly ?
"netstat -pan" might show something.
Yes, it connects to an Oracle DB, and I strongly suspect they may be seeing a
connection pool leak in a little-used bit of code. But I'm also trying to
figure this out without access to the machines themselves, so was hoping to get
guidance on other questions to ask them.
Essentially, as I understand it, the non-paged pool primarily stores data
structures needed to manage threads and semaphores, which in tomcat terms is
connectors, executors, and any DB pool connections, etc. I would assume that
the heap and classes get put into the paged pool. I was hoping someone here
knew exactly if there was something other I should suspect.
Reviewing older posts, thanks Christopher, it does appear that there could be
some release-level issues in Java/Tomcat/native as well as it could be Windows
OS issues itself. (Didn't realize I'd seen this on a local machine 2 years ago
until I checked the archive.) So I do have some questions to ask the customer
admin.
I am totally out of my depth regarding the type of things which are stored in this
non-paged memory (to tell the truth, I did not even know that there existed such a thing..)
But since you mentioned that the kind of things stored there included structures allocated
for the access to files e.g. (I suppose that each opened file must have some kind of "file
descriptor" structure along with low-level I/O buffers and the like), this would probably
also apply to any kind of network connection that is not being properly closed, or
"returned to the OS" at the end of it's usage. That is why I suggested a "netstat", to
display such and get an idea if there are things lingering there longer than they should.
If there are, then I suppose that over time this could amount to a leak of memory.
It could also be a bit "sneaky", in the sense that from the Tomcat/java point of view,
these things are no longer connected to the process, but from the OS point of view, they
are not really released, so they stick around.
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