Develop Reference

Find the memory allocated by the JVM

I am looking for an easy way to find out how much memory the JVM on my computer has allocated to a specific process, i have tried using VisualVM, but it cannot find the process.
I should mention that this it's running a Windows Service, not a regular process.
Any suggestions ?
Thank in advance.

there is a command that comes with the JRE called jps which you can use to see all the running java processes. using jps with -v gives you the launch parameters of each process.
You can see here the launch parameters which will tell you the memory usage of each process.
This command should run also on Windows, just replace the terminal with a command prompt.

I use in android (if you want to know a programatic way):
// get the total memory for my app
long total = Runtime.getRuntime().totalMemory();
// get the free memory available
long free = Runtime.getRuntime().freeMemory();
// some simple arithmetic to see how much i use
long used = total - free;
System.out.println("Used memory in bytes: " + used);
Works for the PC too(just tested)!

JVisualVM should work for you. There are specific cases where the process is not shown in visualVM.
See some known issues
Local Applications Cannot Be Monitored (Error Dialog On Startup) Description: An error dialog saying that local applications cannot be monitored is shown immediately after VisualVM startup. Locally running Java applications are displayed as (pid ###). Resolution: This can happen on Windows systems if the username contains capitalized letters. In this case, username is UserName but the jvmstat directory created by JDK is %TMP%\hsperfdata_username. To workaround the problem, exit all Java applications, delete the %TMP%\hsperfdata_username directory and create new%TMP%\hsperfdata_UserName directory.

How to define host of some strange java-process?

Good day everybody!
I'm developing java GWT web application. Yesterday it was working fine - task manager was showing netbeans process and ONE java process - definetely it was tomcat. But today I'm observing netbeans process, java process of tomcat and some unknown java process which causes java heap space error. This strange process eats a lot of memory and it's memory consumption grows dramatically in time.
Probably useful information: the only thing I changed in my app is dropping database and creating it again from some backup. I suspect java JDBC driver can't connect to DB because of probable incorrect user privileges - it is not a problem, queries are performing successfully but strange java process is exists.
Question: How to define host of this unknown java-process? What application, netbeans or tomcat or something else creates it?

On a Unix platform, ps has several options that show more than just the process name ("java") - e.g. on Linux try ps ax | grep java and you'll see the whole command line that was used to start the java process. It's easy to determine from there what process is running and what they're supposed to do.
On Windows you'll have to find an equivalent - if you're lucky the user executing the process will help you as well - e.g. if it's you or SYSTEM (for services), but the full commandline definitely beats it.

OK, I found the reason - I select a lot of data from my DB. It seems JDBC driver was loading incoming data continuously until memory was enough.

Slow Oracle connection on Fedora virtual machine

We have a Java application running on Solaris which makes a connection to Oracle and checks the database for work to perform, and it runs just fine. We tried running the same code on a standalone Fedora system, its performance is good too. However, when we move it to its home on a Fedora VMWare virtual machine, it can take upwards of five minutes for the application to make the connection to the database. It ultimately DOES make the connection - it's just snail-slow. We suspect it's a configuration issue somewhere but can't find it. So far as we can tell, the two Fedora boxes have nearly identical configurations. Has anyone run into this problem before? If so, how did you get around it?
Thanks in advance for your help.
Mike Preston

Found it! When we are running under Solaris, we are running a 32-bit JVM with 32-bit extensions. We are executing through a Korn shell script and had an added -d64 flag to coerce 64-bit processing. On the Linux boxes we removed the -d64 flag from the shell script and everybody's happy. Thanks Alex for your thoughts and assistance.

Here is the solution which settled the issue...our headless development server was only occasionally getting any keyboard activity to fill the entropy pool (please read the article - I won't try to explain it here) and I assume it was blocking until there was enough "noise" to generate the requisite random numbers.Since there is only one other developer working on the system, it might take a couple of minutes to fill the buffer. Once the buffer was full it went ahead and executed the connection as expected. That also explains why we sometimes would see crisp performance followed by slow. In a nutshell, we added the string "-Djava.security.egd=file:///dev/urandom" to the Korn shell script between the call to java and the jar file name and now it works like a champ. Here's the full command string:
/usr/bin/java -Xms64m -Xmx1024m -Djava.security.egd=file:///dev/urandom -jar $1 $2 $PID
If you DO read the article, be sure to read the comments below. One of them is really funny!

Out of Memory on Tomcat Shutdown

Short description of my problem: I start up Tomcat with my deployed Wicket application. When I want to shut down tomcat I get this error message:
Error occurred during initialization of VM
java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Thread.java:640)
at java.lang.ref.Reference.<clinit>(Reference.java:145)
I am running the following setup:
Ubuntu Linux: 10.04 (lucid) with a 2.6.18-028stab094.3 kernel
Java Version: "1.6.0_26" Java HotSpot(TM) 64-Bit Server VM
Tomcat Version: 7.0.23
jvm_args: -Xms512m -Xmx512m -XX:MaxPermSize=205m (these are added via CATALINA_OPTS, nothing else)
Wicket 1.5.1
Tomcat is configured with two virtual hosts on subdomains with ModProxy
My application is deployed as ROOT.war in the appbase directory (it makes no difference if I deploy one or both applications)
'''No application deployed does not result in OOM on shutdown''', unless I mess around with the jvm args
The size of the war is about 500k, all libraries are deployed in tomcat/common/lib (directory which I added to common.loader in conf/catalina.properties)
ulimit -u -> unlimited
When I check the Tomcat manager app it says the following about the JVM memory:
Free memory: 470.70 MB Total memory: 490.68 MB Max memory: 490.68 MB
(http connector) Max threads: 200 Current thread count: 6 Current thread busy: 1
'top' or 'free -m' is similar:
Mem: 2097152k total, 1326772k used, 770380k free, 0k buffers
20029 myuser 18 0 805m 240m 11m S 0 11.7 0:19.24 java
I tried to start jmap to get a dump of the heap, it also fails with an OutOfMemoryError. Actually as long as one or both of my applications are deployed any other java process fails with the same OOM Error (see top).
The problem occurs while the application is deployed. So something is seriously wrong with it. However the application is actually running smoothly for quite a while. But I have seen OOMs in the application as well, so I don't trust the calm.
My application is using a custom filter class? Could that be it?
For completeness (hopefully), here's the list of libraries in my common/lib:
activation-1.1.jar
antlr-2.7.6.jar
antlr-runtime-3.3.jar
asm-3.1.jar
asm-commons-3.1.jar
asm-tree-3.1.jar
c3p0-0.9.1.1.jar
commons-collections-3.1.jar
commons-email-1.2.jar
dependencies-provided.tgz
dom4j-1.6.1.jar
ejb3-persistence-1.0.2.GA.jar
geronimo-annotation_1.0_spec-1.1.1.jar
geronimo-jaspic_1.0_spec-1.0.jar
geronimo-jta_1.1_spec-1.1.1.jar
hibernate-annotations-3.4.0.GA.jar
hibernate-commons-annotations-3.1.0.GA.jar
hibernate-core-3.3.0.SP1.jar
hibernate-entitymanager-3.4.0.GA.jar
hibernate-search-3.1.0.GA.jar
javassist-3.4.GA.jar
joda-time-1.6.2.jar
jta-1.1.jar
log4j-1.2.16.jar
lombok-0.9.3.jar
lucene-core-2.4.0.jar
mail-1.4.1.jar
mysql-connector-java-5.1.14.jar
persistence-api-1.0.jar
quartz-2.1.1.jar
servlet-api-2.5.jar
slf4j-api-1.6.1.jar
slf4j-log4j12-1.6.1.jar
stringtemplate-4.0.2.jar
wicket-auth-roles-1.5.1.jar
wicket-core-1.5.1.jar
wicket-datetime-1.5.1.jar
wicket-extensions-1.5.1.jar
wicket-request-1.5.1.jar
wicket-util-1.5.1.jar
xml-apis-1.0.b2.jar
I appreciate any hint or even speculation that gives me additional ideas what to try.
Update: I tested some more and found that this behaviour only occurs while one or both of my applications are deployed. The behaviour does not occur on "empty" tomcat (that was a mistake on my part messing with jvm args)
Update2: I am currently experimenting trying to reproduce this behaviour in a virtual box, I want to debug this with a profiler. I am still not convinved that it should be impossible to run my setup on 2GB RAM.
Update3 (10/01/12): I am trying to run jenkins instead of my own application. Same behaviour, so it is definitely server configuration issues. Jenkins jobs fail when maven is called, so I need not even try the shutdown hack suggested below because I need a second java process while running Jenkins. It was suggested to me that because this is a Virtual Server ulimits may be imposed from outside and I would not be able to see them. I think I'll ask a new question regarding this. Thx all.
Update4 (02/05/12): see below for the answer that contains the hint. I'll clarify some more up here: I am now 95% sure that the errors occur because I am reaching my thread limit. However because this is a virtual server the method described below would not work to check this value because it is not visible with ulimit, that was what was confusing me and only today I found out that this is the "numproc" value that I can see in the Parallels Power Panel that I can log into for my virtual server. There were Resource Alerts for numproc but I did not see those either until just now. The value has a hard limit of 96 which I cannot change of course. The current value of numproc corresponds to the number of processes I see with "top" after toggling "H" to see threads. I had a very hard time finding this because this numproc value is hidden deep inside the panel. Sadly 96 is a rather low number if you want to run a tomcat with apache and mysql. I am also very sad that I cannot even find this value in the small print of my hosting contract and it is rather relevant to my application I dare say. So I guess I'll need a server upgrade.
Thanks all for your helpful answers in the end everyone helped me a bit to find out what the problem was.

The tomcat shutdown procedure consits of sending an command/word via a tcp port to the running tomcat VM. This port is configured in the server.xml (if I remember corretly, writting on my phone right now). So far so good.
Unfortunately, the shutdown script does this by starting a 2. VM using the same java options used for the tomcat. Your system simply has not enough memory for this.
As a sollution you could write your own stop script using telnet or something.
I could help with later if needed.
Hope that helps.
Viele grüsse Bert

Seems you have too many threads open.
Use this command :
ulimit -u
What is the result ?
Should be something like :
max user processes (-u) 100
If this is correct, you can edit this file :
/etc/security/limits.conf
and the the following modifications :
#<domain> <type> <item> <value>
user soft nproc 10000
user hard nproc 10000

You can probably survive for a while like this. All you need to do is kill the tomcat process whenever you need to restart it. It is not a nice approach, but the main concern is that your application runs correctly.
It seems to me though, that on the long run, you might need to order a hosting plan with more RAM available.

I was having a similar problem with a tomcat installation just last week. I managed to fix it by giving tomcat a smaller heap. Something like this:
export CATALINA_OPTS=”-Xms256m -Xmx512m”
Before starting Tomcat may help. In the meantime you'll have to kill it the old fashioned way, with a kill -9 ;)
EDIT: you could also take look here, it appears tomcat automatically creates a bunch of "spare" threads, but you can limit those as well as your max thread count in the config. Hope it helps.

Jstack and Not enough storage is available to process this command

I'm trying to run jstack command on my java application. Application is rather big, running inside jboss AS occupying about 4gb of memory. OS is Windows Server 2003 Standard edition. Every time i get an error "Not enough storage is available to process this command". There is enough ram, 16gb, and disk space. So, any ideas?

I ran into this recently on Win2008r2 and thought I'd share my solution since it took a while to figure out. Rob's comment about psexec -s is what did it for me.
It appears that on Vista and later jstack doesn't work against services because of the user context. It has nothing to do with memory. I suspect this is the same reason people have seen this problem on 2003 via remote desktop, unless you use the /admin or /console switch on mstsc. As of Vista the tightened security is probably what broke it.
Starting my app from a cmd window worked fine, but that doesn't help me debug our standard install. Enabling the java debug port (for VisualVM, Eclipse or most any Java debugger) requires an app restart, so you lose the state you're probably trying to capture if you don't already have debugging enabled. Starting the service under my user credentials did not work - I was a little surprised at that. But psexec -s runs jstack from the system context, which worked like a charm. Oh, and you'll need to run psexec from an elevated cmd prompt, if UAC is on.

In the past I have seen this when the JVM is running as a Windows Service on Windows 2003.
First, check to see if this is an issue with the TMP directory.
Second, jstack (or the other utilities like jconsole) will not connect to the local process unless it is running in the same session. If the service is running as a specific user, you may be able to connect by logging into the same session. If you are using Remote Desktop, you can connect using "mstsc /admin" (used to be /console) and try to run jstack again. Definitely check to make sure the TMP directory is set properly if this doesn't fix the problem.
If the service is running as LocalSystem, the above procedure probably will not help much. I don't know if there is a way to log into the same session as LocalSystem.
Some other alternatives may be to set the process up for remote monitoring and use jvisualvm (from the server itself or another machine) to connect over a port and do a thread dump.

We had problems running JStack on a Windows machine with even a modest application (1GB). We ended up doing our stack and heap analysis using Netbeans. This seemed to cope with the parsing of dump files a lot better. YMMV.
Give Netbeans a try for profiling - its very good. Note that VisualVM is a cutdown NB profiler and comes with 6u7.

psexec -s jstack PID >> c:\jstack.log perfectly works on the same machine. For the first time it took some time but again I executed with the redirect to file option, it completed with in few seconds.

This is an error message from the underlying O/S. There's not much you can do in your code to deal with this other than catch the exception which is thrown. Boo to Windows for being so limited.
http://technet.microsoft.com/en-us/library/cc978735.aspx