Java GC 上的低内存停止和崩溃程序

Question

I am using parallel GC in my java program. But when jvm have less then ~400mb of free memory GC starts to consume all of CPU. And after some time jvm crash with java.lang.OutOfMemoryError: GC overhead limit exceeded . But i am printing the amount of free memory with Runtime.getRuntime().freeMemory() , and i am sure that jvm have ~400mb of free space. I tried to set -XX:MinHeapFreeRatio to 1 or 5 but it made everything worst.

How to config GC or which one should i choose to prevent it from consumimg all of CPU and crashing jvm? My jvm flags is -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -Xmx3800m -server -Djava.library.path="native_libs"

Answer 1

The Error

The error java.lang.OutOfMemoryError: GC overhead limit exceeded occurs when the JVM spends most of it's time garbage collecting without being able to free much memory at the end of a garbage collection cycle. A good detailed description can be found here . Note this does not necessarily mean that you are out of memory! You may have a lot of memory left, but the garbage collector may just not be able to free anything and is giving up early.

The Cause

Since you are saying that you only need 50 mb memory at the time this exception happens, you are likely leaking memory. Using only 50 mb of memory would not cause the garbage collector to fail like this. Leaking memory happens when you still have references to objects that you no longer need. When too many objects are still accessible garbage takes a long time, and the garbage collector is not able free any Objects because they are still accessible to the program.

The Solution

You need to find the source of the memory leak. Common causes are keeping objects in data structures like Lists, Maps, and Sets without removing them. You can take a heap dump, which essentially saves all the Objects in your java program's memory to a file, which you can then inspect. You can configure java to do a heap dump when an OutOfMemoryException happens by adding the -XX:+HeapDumpOnOutOfMemoryError flag to your java command. More details about where the heap dump is stored can be found on this question Using HeapDumpOnOutOfMemoryError parameter for heap dump for JBoss . Then the next time things crash you can use a tool like Eclipse MAT to inspect the heap dump and see what objects are consuming memory. This will point you in the direction of your memory leak so that you can fix it.

Answer 2

My app have a lot stuff in old gen, so how i understood GC was trying to free enough memory for young gen and have been making full gc very often. So by reducing Young gen size i extend size of old gen, which was heavily used by me.

To reduce Young gen size you can use -XX:MaxNewSize , -XX:NewRatio , -XX:NewSize . I used -XX:MaxNewSize . You can read about it here https://docs.oracle.com/cd/E19900-01/819-4742/abeik/index.html

Answer 3

java.lang.OutOfMemoryError exception is one common indication of a memory leak.

Usually, this error is thrown when there is insufficient space to allocate an object in the Java heap . In this case, The garbage collector cannot make space available to accommodate a new object, and the heap cannot be expanded further.

Also, this error may be thrown when there is insufficient native memory to support the loading of a Java class .

In a rare instance, a java.lang.OutOfMemoryError may be thrown when an excessive amount of time is being spent doing garbage collection and little memory is being freed .

Details here