Home/ Questions/Q 7399605
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-29T04:04:54+00:00

I found out that if my application has much free memory available it uses

  • 0

I found out that if my application has much free memory available it uses more memory than it needs. I heard that this behavior is common for all Java applications but it’s not acceptable for me.

So the question is how can I force Java to use less memory?

I know that I can call System.gc() manually every few seconds, but is it alright to do so and are there any other methods?

P.S. my application is updated regularly on production server and I need to monitor memory usage for some leaks and so on (generally there are no leaks but if one appears I should see it as fast as possible), and also I need to predict the time when I should upgrade my hardware. All these things are very hard to do if jvm unpredictably changes its memory hunger. So the only thing I want is to force jvm to be predictable in memory usage (if number of users doubles memory should doubles too)

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    I found out that if my application has much free memory available it uses more memory than it needs. I heard that this behavior is common for all Java applications but it’s not acceptable for me.

    It depends on what you mean “more memory than it needs”. If you mean, more than the minimum memory to represent your application’s objects, then you are correct.

    It is standard behavior that Java uses more memory than the bare minimum that it could theoretically get away with. “Worse still”, most JVMs don’t give memory back to the OS … even if that memory has been freed by the GC. Both of these properties are necessary for efficient operation of a general purpose garbage collector.

    If this is unacceptable to you, you should not be using a garbage collected language. Use C or C++. (But also be aware that it is unusual for C / C++ memory allocators to be able to give memory back to the OS either … even if the implementation allows it.)

    The positive side of this is that Java (and in fact any GC’ed language) will actually run better if you give it plenty of memory. Modern GC’s work more efficiently as the ratio of garbage to non-garbage increases, and a larger heap makes that happen. (Of course, you can go too far, especially if the application is competing with other things for real memory.)

    As other answers said, calling System.gc() does not help. It is unlikely to result in any memory being given back. Worse still, you’ll most likely run the GC when the garbage level is too low for efficient operation, so you will be increasing CPU time for no benefit.

    Concerning your “PS”:

    1. I don’t think there is a way to (reliably) detect the existence of a memory leak … apart from monitoring memory usage trends.

    2. I don’t think there is a way to (reliably) predict when you will new hardware … apart from monitory memory usage (and other) trends.

    3. I don’t think there is a way to force you application’s memory usage to be proportional to the number of users … apart from designing / coding your application so that it scales in the way you want.

    On the other hand, you could say the same thing about a C / C++ application.

    • 0