Java 8 JVM挂起，但内存不足时不会崩溃/堆转储

Question

When running out of memory, Java 8 running Tomcat 8 never stops after a heap dump. Instead it just hangs as it max out memory. The server becomes very slow and non-responsive because of extensive GC as it slowly approaches max memory. The memory graph in JConsole flat lines after hitting max. 64 bit linux/ java version "1.8.0_102"/ Tomcat 8. Jconsole

I have set -XX:HeapDumpOnOutOfMemoryError and -XX:HeapDumpPath. Anyone know how to force heap dump instead of JVM getting into unresponsive/ very slow response mode?

Answer 1

Anyone know how to force heap dump instead of JVM getting into unresponsive/ very slow response mode?

You need to use -XX:+UseGCOverheadLimit . This tells the GC to throw an OOME (or dump the heap if you have configured that) when the percentage time spent garbage collecting gets too high. This should be enabled by default for a recent JVM ... but you might have disabled it.

You can adjust the "overheads" thresholds for the collector giving up using -XX:GCTimeLimit=... and -XX:GCHeapFreeLimit=... ; see https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gc-ergonomics.html

The effect of "overhead" limits is that your application gets the GC failures earlier. Hopefully, this avoids the "death spiral" effect as the GC uses a larger and larger proportion of time to collect smaller and smaller amounts of actual garbage.

The other possibility is that your JVM is taking a very long time to dump the heap. That might occur if the real problem is that your JVM is causing virtual memory thrashing because Java's memory usage is significantly greater than the amount of physical memory.

Answer 2

jmap is the utility that will create a heap dump for any running jvm. This will allow you to create a heap dump before a crash

https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/tooldescr014.html

It will be a matter of timing, though, to know when you should create it. You can take subsequent heaps and use tools to compare the heaps. I highly recommend Eclipse Memory Access Tool and it's dominator tree view to identify potential memory issues ( https://www.eclipse.org/mat/ )