如何找到哪个类导致JVM的OutOfMemory？

Question

Oflate our Weblogic server is frequently crashing with OutOfMemory error. Is there any way I can monitor the JVM to find out which Classes are are hogging the memory and have the maximum number of objects?

Answer 1

yes. The way I did it was to configure the jvm to create a heap dump on OOM, then I pulled the heap down and ran it thru jvisualvm. You can compute the retained sizes (took a long time) but it will be very clear what the offender is.

You can also attach jvisualvm to a running instance, but you need to configure the jvm to accept the connection. That way you can watch the heap grow in real time. See this; its for jboss but should be very similar: https://wiki.projectbamboo.org/display/BTECH/VisualVM+Profiler

I think it is easier to get to the answer after you have a heap dump though, as when you watch it in real time things get garbage collected and whatnot.

EDIT -- here are my startup configs.

-XX:+PrintGCDetails -XX:+PrintGCTimeStamps  
-Xloggc:/path/to/memlogs/memlog.txt -XX:+PrintTenuringDistribution   
-Xms1024m -Xmx2048m -XX:MaxPermSize=128m   
-server -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=xxxx   
-Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false   
-Djava.rmi.server.hostname=<ip-address> -XX:+HeapDumpOnOutOfMemoryError   
-XX:HeapDumpPath=/path/to/heapdumps/ -XX:+CMSClassUnloadingEnabled   
-XX:+CMSPermGenSweepingEnabled -XX:+UseConcMarkSweepGC  

because I configured it to drop memory logs, I can tail the memlog.txt file in real time to see what happened. I can connect to the jvm if I want, but like I said I will just analyze the heap after a crash to see what the issue is, because after the fact its really clear....

Answer 2

从JDK 1.5开始有JConsole （或5.0，如果你进入那个）。

Answer 3

There are a number of tools out there but I use Eclipse's Memory Analysis Toolkit. You can download it as a standalone tool and it will let you do heap analysis and even connect to a JVM and analyze there.

Answer 4

除了JConsole，jRat是一款优秀的免费啤酒分析器，YourKit是另一款出色的商业产品。

Answer 5

From some other Questions I came to know about jhat and jmap. These are already available in JDK packages. Also the below link provides a good list on which tool to use in which scenarios:-

http://java.sun.com/developer/technicalArticles/J2SE/monitoring/