Does java 6 consume more memory than you expect for largish applications? i have an application i have been developing for years, which has, until now taken about 30 40 mb in my particular test configuration now with java 6u10 and 11 it is taking several hundred while active. It bounces around a lot, anywhere between 50m and 200m, and when it idles, it does gc and drop the memory right down. So, i ran it up under my profiler jprofiler and using jvisualvm, and both of them indicate the usual moderate heap and perm gen usages of around 30m combined, even when fully active doing my load test cycle. So i am mystified! and it not just requesting more memory from the windows virtual memory pool this is showing up as 200m mem usage. Clarification: i want to be perfectly clear on this observed over an 18 hour period with java visualvm the class heap and perm gen heap have been perfectly stable. The allocated volatile heap eden and tenured sits unmoved at 16mb which it reaches in the first few minutes , and the use of this memory fluctuates in a perfect pattern of growing evenly from 8mb to 16mb, at which point gc kicks in an drops it back to 8mb.

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Over this 18 hour period, the system was under constant maximum load since i was running a stress test. This behavior is perfectly and consistently reproducible, seen over numerous runs. The only anomaly is that while this is going on the memory taken from windows, observed via task manager, fluctuates all over the place from 64mb up to 900+mb. Update 2008 12 18: i have run the program with xms16m xmx16m without any apparent adverse affect performance is fine, total run time is about the same. Update 2009 01 21: it seems the answer may be in the number of threads see my answer below. java definition continued: 133 can also be used to build a small application module or applet for use as part of a web page.

Ask your java questions at itknowledgeexchange.comthe major characteristics of java are:the programs you create are portable in a network. Your source program is compiled into what java calls bytecode, which can be run anywhere in a network on a server or client that has a java virtual machine. The java virtual machine interprets the bytecode into code that will run on the real computer hardware. These optimizations rely on the property that not only are most monitors uncontended, they are locked by at most one thread during their lifetime. An object is biased toward the thread which first acquires its monitor via a monitorenter bytecode or synchronized method invocation subsequent monitor related operations can be performed by that thread without using atomic operations resulting in much better performance, particularly on multiprocessor machines.

Locking attempts by threads other that the one toward which the object is biased will cause a relatively expensive operation whereby the bias is revoked. The benefit of the elimination of atomic operations must exceed the penalty of revocation for this optimization to be profitable. Applications with substantial amounts of uncontended synchronization may attain significant speedups while others with certain patterns of locking may see slowdowns.

2.1.2 lock coarsening

there are some patterns of locking where a lock is released and then reacquired within a piece of code where no observable operations occur in between. The lock coarsening optimization technique implemented in hotspot eliminates the unlock and relock operations in those situations when a lock is released and then reacquired with no meaningful work done in between those operations. It basically reduces the amount of synchronization work by enlarging an existing synchronized region. Doing this around a loop could cause a lock to be held for long periods of times, so the technique is only used on non looping control flow.

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To disable it, please add the following option to the command line: xx: eliminatelocks q: what sort of memory leaks are possible in java and how do i prevent them? a: in the case of incomplete deallocation, there are two subcases: coding bugs and design bugs. In the case of c, this would involve free ing less than was malloc ed, while in c++ this might involve using delete in lieu of delete . Design bugs, on the other hand, do not depend on the language instead, they involve simple programmer negligence. In languages like c/c++, all memory management is handled by the programmer, so all of these problems can arise, even after the programmer has expended much effort to ensure the code is free of such defects. In fact, in c/c++ the more you try to avoid memory leaks, the more likely you are to create corrupted pointers, and vice versa.

And, by nature the risk of such bugs increases with code size and complexity, so it's difficult to protect large c/c++ applications from these types of bugs. In java, on the other hand, the java language and runtime together entirely eliminate the problems of corrupted pointers and code level memory leaks. There is no explicit allocation of memory, there is only the creation of new objects.

The java runtime employs a garbage collector that reclaims the memory occupied by an object once it determines that object is no longer accessible. This automatic process makes it safe to throw away unneeded object references because the garbage collector does not collect the object if it is still needed elsewhere. Therefore, in java the act of letting go of unneeded references never runs the risk of deallocating memory prematurely. In java, it's easy to let go of an entire tree of objects by setting the reference to the tree's root to null the garbage collector will then reclaim all the objects unless some of the objects are needed elsewhere.

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This is a lot easier than coding each of the objects' destructors to let go of its own dependencies which is a coding level problem with c++. So what about memory leaks caused by poor program design? in such designs, unnecessary object references originating in long lived parts of the system prevent the garbage collector from reclaiming objects that are in fact no longer needed. Such errors typically involve a failure in the large to properly encapsulate object references among various parts of the code.

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Another design flaw occurs in the small, at the level of a faulty algorithm the use of collections objects in such cases will typically magnify the error. As the technology improves, a suitably implemented jvm could help reduce the effects of such designed in memory leaks by using the garbage collector to track object usage over time. The garbage collector could then rearrange objects in memory according to a freshness factor based on when they were last referenced, for example. Stale objects would become eligible for physical ram swap out even though, for safety, they would still exist. Ideally of course, programmers would design applications with objects' lifecycles in mind, rather than rely on clever features of state of the art jvm implementations. In conclusion: design problems can be mitigated by letting go of object references in one's own classes as soon as one can knowing that in java there is no risk of damaging another part of the code. tip: the kl group's jprobe tool can help identify possible sources of memory leaks by showing which objects are holding on to graphs of references to other objects.