CODEWITHSUNDEEP
javajruby
Ratatouille
Ratatouille

Reputation: 1482

How come Java can allocate more memory than the specified heap size

We are basically tuning our JVM options.

-J-Xms1536M -J-Xmx1536M -J-Xss3M -J-Djruby.memory.max=1536M -J-Djruby.thread.pool.enabled=true -J-Djruby.compile.mode=FORCE -J-XX:NewRatio=3 -J-XX:NewSize=256M -J-XX:MaxNewSize=256M -J-XX:+UseParNewGC -J-XX:+CMSParallelRemarkEnabled -J-XX:+UseConcMarkSweepGC -J-XX:CMSInitiatingOccupancyFraction=75 -J-XX:+UseCMSInitiatingOccupancyOnly -J-XX:SurvivorRatio=5 -J-server -J-Xloggc:/home/deploy/gcLog/gc.log -J-XX:+PrintGCDateStamps -J-XX:+PrintGCDetails -J-XX:+PrintGCApplicationStoppedTime -J-XX:+PrintSafepointStatistics -J-XX:PrintSafepointStatisticsCount=1

We have set the -J-Xmx1536 and -J-Xms1536M to a value of 1536M. Now If I understood this correctly -J-Xmx represent the maximum size of the heap.

The system is 4 core 15GB ram process.

But when I check the RSS(using top) of my running Java process I see it is consuming a value larger than the -JXmx1536 around ~2GB.

Now clearly, the JVM heap has increased beyond the specified value of -Jmx.

So my question are..

Upvotes: 0

Views: 550

Answers (1)

kares
kares

Reputation: 7181

Why? am I not seeing any Java out of memory exception.

because you did not run out of heap memory, start VisualVM and examine the process after setting -Xmx. you'll notice there'sa region called MetaSpace (1G max by default) besides that there are also ways in which the process might use additional memory e.g. for code-cache (JIT-ed native code)

And what is an ideal setting for -JXmx with 4 cores and 15GB RAM.(given that no other process is running in the system other than Java application)

there's no "clear" answer for that, it depends from application to application, you should monitor your memory usage under various scenarios. first thing to do might be to set heap high but if you're not using up most of it and you have a memory leak it will complicate things.

Upvotes: 0

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