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I have a Java console app that's processing big xml files using DOM. Basically it creates xml files from data it takes from the DB. Now, as you guess it's using large amount of memory but, to my surprise, it's not related to bad code but to "java heap space not shrinking". I tried running my app from Eclipse using these JVM params:
-Xmx700m -XX:MinHeapFreeRatio=10 -XX:MaxHeapFreeRatio=20
i even added the
-XX:-UseSerialGC
as i found out that parallel GC ignores "MinHeap" and "MaxHeap" options. Even with all those options graph of my app's memory use looks like this:
As you can see, at one point my app takes ~400 MB of heap space, heap grows to ~650 MB, but few seconds later (when xml generation is done) my app goes down to 12MB of used heap, but "heap size" remains at ~650 MB. It takes 650 MB of my ram! It's bizzare, don't you think?
**Is there a way to force JVS to shrink availabe heap size to, like 150% of current used heap?**Like, if my app needs 15 MB of ram, heap size is ~20MB, when my app asks for 400 MB of ram, heap grows to ~600 MB and DROPS back to ~20 MB as soon as my app finish heavy-lifting operation?
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Set the Heap Size The heap must be at least large enough for all objects that are alive at the same time. Preferably the heap should be at least twice the size of the total amount of live objects, or large enough so that the JVM spends less time garbage collecting the heap than running Java code.
OutOfMemoryError: Metaspace error is thrown. To mitigate the issue, you can increase the size of the Metaspace by adding the -XX:MaxMetaspaceSize flag to startup parameters of your Java application. For example, to set the Metaspace region size to 128M, you would add the following parameter: -XX:MaxMetaspaceSize=128m .
lang. OutOfMemoryError exception. Usually, this error is thrown when there is insufficient space to allocate an object in the Java heap. In this case, The garbage collector cannot make space available to accommodate a new object, and the heap cannot be expanded further.
You should probably use Parallel collection and use -XX:-UseAdaptiveSizePolicy. Docs are for Java 1.5 but I can't find anything more recent.
The implementation of -XX:+UseAdaptiveSizePolicy used by default with the -XX:+UseParallelGC garbage collector has changed to consider three goals:
- a desired maximum GC pause goal
- a desired application throughput goal
- minimum footprint
The implementation checks (in this order):
- If the GC pause time is greater than the pause time goal then reduce the generations sizes to better attain the goal.
- If the pause time goal is being met then consider the application's throughput goal. If the application's throughput goal is not being met, then increase the sizes of the generations to better attain the goal.
- If both the pause time goal and the throughput goal are being met, then the size of the generations are decreased to reduce footprint.
EDIT
Added "-" per OP's suggestion.
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