I have a spring batch application, it consumes ~16GB Memory & 75% of CPU(4core X2.5Ghz) and at times it throws out of memory exception.
I want to optimize the Heap allocation & Garbage collection and tried with the following JVM options so resolve the out of memory exception.
I could not understand some of these parameters as I copy pasted directly from an article
JAVA_OPTS="-server -Xmx20480m -Xms512m -XX: UseConcMarkSweepGC -XX: UseParNewGC -XX: CMSClassUnloadingEnabled -XX: CMSParallelRemarkEnabled -XX:CMSInitiatingOccupancyFraction=30 -XX: CMSIncrementalMode -XX: CMSIncrementalPacing -XX:ParallelCMSThreads=2 -XX: UseCMSCompactAtFullCollection -XX: DisableExplicitGC -XX:MaxHeapFreeRatio=70 -XX:MinHeapFreeRatio=40 -XX:MaxTenuringThreshold=0 -XX:NewSize=450m -XX:MaxNewSize=650m"
would it really optimize the Heap allocation & Garbage collection and resolve the out of memory exception.?
CodePudding user response：
This error is usually thrown when there is insufficient space to allocate an object on the Java heap or if the Java process is spending more than 98% of its time doing garbage collection and if it is recovering less than 2% of the heap and has been doing so far the last 5 garbage collection cycles.
I would first use a Java profiler to determine what methods are allocating large numbers of objects on the heap and make sure that they are no longer referenced after they are not needed. If this doesn't fix the issue and I have confirmed that I need all the objects, the other option would be to increase the max heap size of the program.
CodePudding user response：
First, you need to take a heap dump of the process when it is throwing the OOM error. You can do that by adding -XX: HeapDumpOnOutOfMemoryError JVM option. After when you have the heap dump try using any of the following tool to analyze your heap dump. Locate which object is growing in the memory and then optimize it. Heap dump analyze tools are :
CodePudding user response：
- This could also happen when you are using too many 'String' objects or updating those strings again and again.
- Strings are stored in a hashed string pool, which resides in the Heap space. When you manipulate a string, a new string is formed and stored in a different pool (hashed pools) but the original string is not deleted until the garbage collector does it.
- If we use StringBuilder or StringBuffer (both are mutable, unlike strings), the space is better utilised.
Read more about strings immutability and why stringbuilder should be preferred when you need a lot of string manipulations to be performed.
StringBuilder-StringBuffer-Strings in java Why strings are immutable in java?