Menu
We have a Java webapp that we upgraded from Java 1.5.0.19 to Java 1.6.0.21
/usr/java/jdk1.6.0_21/bin/java -server -Xms2000m -Xmx3000m -XX:MaxPermSize=256m -Djava.awt.headless=true -Dwg.environment=production -Djava.io.tmpdir=/var/cache/jetty -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=31377 -Dcom.sun.management.jmxremote.authenticate=true -Dcom.sun.management.jmxremote.ssl=false -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/tmp/webapp -Dprogram.name=run.sh -Djava.endorsed.dirs=/opt/3p/jboss/lib/endorsed -classpath /opt/3p/jboss/bin/run.jar:/usr/java/jdk1.6.0_21/lib/tools.jar org.jboss.Main -c default
As you can see it should preallocate 2GB of heap and max out at 3GB (why we preallocate so much is because this app is ancient and poorly designed so has a ton of things to load up). The issue we have seen recently after upgrading to the 1.6 is that on occasion memory goes through the roof. While memory usage is likely an app issue the JVM is exceeding the 3GB max setup for heap. Using top I see:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
8449 apache 18 0 19.6g 6.9g 5648 S 4.0 84.8 80:42.27 java
So how could a JVM with 3GB heap, 256MB permgen, and even some overhead consume 6.9GB? Bug in the JVM that would be fixed by upgrading to build #35? Something missing on what in java could be using the extra memory? Just trying to see if anyone has seen this before.
250
The theoretical limit is 2^64 bytes, which is 16 exabytes (1 exabyte = 1024 petabytes, 1 petabyte = 1024 terabytes). However, most OS's can't handle that. For instance, Linux can only support 64 terabytes of data. Note: We don't recommend you exceed 2 GB of in use JVM heap.
-xmx and -xms are the parameters used to adjust the heap size. -Xms: It is used for setting the initial and minimum heap size. It is recommended to set the minimum heap size equivalent to the maximum heap size in order to minimize the garbage collection. -Xmx: It is used for setting the maximum heap size.
The Java™ virtual machine (JVM) heap size setting directly relates to how many server instances can be started within a dynamic cluster on a specific node. You might need to modify the JVM heap size setting based on your environment configuration. The default value is 256 MB.
So how could a JVM with 3GB heap, 256MB permgen, and even some overhead consume 6.9GB?
Possible explanations include:
I would be inclined to blame the application before blaming the JVM.
87
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
