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Thinking in Java
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Tracking memory consumption

Here is the kind of data a profiler can show for memory usage:

  • Number of object allocations for a specific type.
  • Places where the object allocations are taking place.
  • Methods involved in allocation of instances of this class.
  • Loitering objects: objects that are allocated, not used, and not garbage collected. These keep increasing the size of the JVM heap and represent memory leaks, which can cause an out-of-memory error or excessive overhead on the garbage collector.
  • Excessive allocation of temporary objects that increase the work of the garbage collector and thus reduce the performance of the application.
  • Failure to release instances added to a collection and not removed (this is a special case of loitering objects). Tracking CPU usage

    Profilers also keep track of how much time the CPU spends in various parts of your code. They can tell you:

    • The number of times a method was invoked.
    • The percentage of CPU time utilized by each method. If this method calls other methods, the profiler can tell you the amount of time spent in these other methods.
    • Total absolute time spent by each method, including the time it waits for I/O, locks, etc. This time depends on the available resources of the system.

    This way you can decide which sections of your code need optimizing.
    Thinking in Java
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire