memory being used even after jvm shutdown - how do i release it?

I'm running a java application that is supposed to process a batch of files through some decisioning module. I need to process the batch for about 50 hrs. The problem I'm facing is that the process runs fine for about an hour and then starts to idle. So, I did this - I run the JVM for one hour and then shut it down, restart the JVM after 30 mins, but still for some reason the second run is taking almost 4-5 hrs. to do what the first run does in 1 hr. Any help or insights would be greatly appreciated.

I am running this on a 64-bit windows r2 server, 2 intel quad core processors(2.53 GHz), 24 GB RAM. Java version is 1.6.0_22(64-bit), memory allotted to the application is - heap(开发者_如何学Python16 GB) and PermGen(2GB).

the external module is also running on a jvm and i am shutting that down too, but i have a feeling that it is holding on to memory even after shutdown. before i start the jvm RAM usage is 1 GB, after I end it it tends to stay at about 3 GB. Is there any way i can ask JAVA to forcibly release that memory?

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Are you sure the JVM you are trying to close is indeed closed?

Once a process ends all of the RAM it had allocated is no longer allocated. There's no way for a process to hang on to it once it closes, which also means there's no way for you to tell it to do so. This is done by the Operating System.

Frankly, this sounds like the JVM is still running, or something else is eating the RAM. Also, it sounds like you're trying to workaround a vicious bug instead of hunting it down and killing it?

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I suspect the JVM isn't exiting at all. I see this symptom regularly with a JBoss instance that grinds to a halt with OutOfMemoryExceptions. When I kill the JVM (via a SIGTERM/SIGQUIT), the JVM doesn't exit in a timely fashion since it's consuming all its resources throwing/handling OOM exceptions.

Check your logs and process table carefully to ensure the JVM quits properly. At that point the OS will clear all resources related to that process (including the consumed memory)

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i've noticed something in the process.

After I shut down the JVM, if i delete all the files that i wrote to the file system, then the RAM usage comes back to the original 1 GB.

Does this lead to anything and can i possibly do something about it.

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Out of interest: Have you tried splitting up the process so that it can run in parallel?

A 50hr job is a big job! You have a decent machine there (8 cores and 24GB Ram) and you should be able to parallelise some parts of it.