Hi Shawn
Thank you the response. This is not a web application, but a standalone
java program. Hence I said it's not a tomcat question, but a generic JVM
question. I have been researching about this a lot and based on many
mails on this list, lot of people here know about internal behavior of
JVM and specs lot better than I do.
Both the boxes are spawned from same AWS image, we build the image.
There is no other difference. Both receive tasks over MQ. Tasks could
be slightly different - like for different users, number of entities
user holds etc, but they should not be too different or kind of should
average out in the long run. We have examined the data for the tasks and
nothing unusual has come out so far.
Regards,
Niranjan
On 2/18/21 10:59 AM, Shawn Heisey wrote:
Regards,
Niranjan
On 2/18/2021 11:36 AM, Niranjan Rao wrote:
First apologies for non tomcat question. I have seen that there is
enough expertise here to provide hints and hints are what I am
looking for to solve the problem and question is generic enough. I
have tried researching problem to best of my abilities.
I believe you're right to think this isn't a tomcat question. There
are a lot of things it could be. Tomcat is a *possible* source,
though I think the chance of that is low. Without a LOT of info that
I would probably be useless at interpreting or asking for, it's
impossible to say for sure.
With problems like this, it is normally the application running inside
Tomcat that has a problem, not Tomcat itself. You're likely to get a
lot more useful information if you go to the people responsible for
those applications.
We have a java program that regularly throws
"java.lang.OutOfMemoryError: Java heap space" exception. Puzzling
point is it happens only on one VM. We have a set of two VMs/boxes
spawned from same AWS image. Machine class/region is exactly same and
since they are from same image, they should be mostly identical
except stuff like host name, ip address etc.
Number of tasks performed by VMs are comparable and not a significant
difference. Yet, one VM never runs of out of memory and other one
does. Sometimes it's as soon as half an hour after restarting the
process while on the other box process is running for days and no
issues.
"Comparable" isn't "identical".
Are they running the same apps? Which apps are involved? Is the one
that's throwing OOME handling substantially similar requests when
compared to one that doesn't? Is the request rate nearly the same, or
is the problematic one handling a lot more? Another applicable
question, also off topic for this mailing list: Are the apps in both
cases configured identically?
I took memory dumps from both VMs and they look similar. Program is
started with -Xmx1g flag and we have taken regular memory dumps. In
many cases eclipse MAT reports total memory usage was less than 100MB
when program crashed with out of memory exception.
That's extremely odd, unless the application requested a REALLY big
chunk of memory such that the 100MB existing plus the new allocation
would be larger than the max heap size of 1GB.
Do you have enough free memory that you could increase the max heap to
2GB or beyond and see what happens?
Has anyone seen anything similar to this? Identical bits of code
behaving differently? What else should I be looking for?
Earlier you said "comparable" and now you're saying "identical". So I
have to ask ... which is it? Remember that differences in
configurations, types of requests, and request load can lead to very
different requirements, even if the apps running inside Tomcat are the
same.
Most of my experience in the Java world comes from Solr. Apache Solr
is a servlet application, and ships with Jetty. Tomcat is not usually
involved. I joined this mailing list because I was responsible for
Tomcat servers running apps developed in-house, and every once in a
while, I needed to ask something tomcat-specific.
Thanks,
Shawn
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