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Tag: memory
Calculate Xmx setting and actual heap size from Java dump
I’ve got a heap dump file (java_dump.hprof) written by a Java 7 JVM. Is it somehow possible to calculate the Xmx command line option as well as the actual heap size from this dump? Answer The dump is based on the size actually used but in a different format so it could be bigger. If the dump was trigger…
Memory map for Neo4j embedded
When using Neo4j in the embedded mode (Java API), one can manually set memory map settings using the following API calls (or similar): My question is: Is the mapped memory allocated out of Java heap/extended memory or from the rest of the memory available. I know that for Neo4j server the latter is correct as…
Need an explanation for apparent heap size reduction
From the GC logs, it appears that the heap size is being reduced across young and old generations after sometime. Below are three entries from the logs. {Heap before gc invocations=5: PSYoungGen total 44800K, used 44180K [0x18220000, 0x1b420000, 0x24a20000) eden space 38400K, 100% used [0x18220000,0x1a7a0000,…
About VM arguments
Am I right in thinking that when one specifies VM arguments in an IDE (I’m using NetBeans in this instance), that these arguments are only passed when the code is run through the IDE itself? Essentially, I’d like to specify that when my program runs, the VM’s minimum/initial heap size is 2Gb…
Does Java’s new keyword necessarily denote heap allocation?
I’m trying to write something fast, and that constantly allocates and deallocates memory, making where this memory is allocated important in terms of performance. Does allocating objects always allocate them to the heap? Does JIT compilation do fancy allocation optimization of any sort? Answer Objects a…
Memory size in profiling when i try to detect memory leak
I run java program with -Xms512m -Xmx1G -Xss1G. I make profiling to verify the memory, so i Track every 10 object allocations. i observe this figure : My question is, why it display me that 117mo represent 40% while i give 1G to memory ? Answer The graph is a percentage of all allocations, not the heap size. …
Java Heap and Pass By Value
I am a little confused as to how my Java program is allocating memory. Below is a typical situation in my program. I have an object created on the Heap inside of a class which I pass to other functions inside of other classes. My question(s) are about how the memory is used. When A’s list gets passed to…
How to tell if one of the heap-generations is full?
We are experiencing some problems in our production environment, where we get an InvalidPropertyException from one of the compiled jsps (which one differs from time to time) after a bit of time. I have a suspicion that this is caused by something “disappearing” from the heap. Further, I suspect th…
where is array saved in memory in java?
If I have a function that in that function I declare: Where are arr and the whole array stored? heap? stack? Does it matter if the declaration is in some function or in main()? and let’s say I also have these command lines: where are arr[0] and arr[1] stored? Answer Memory diagram: Boxes are memory loca…