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What is the overhead of generating a lot of temporary objects (i.e. for interim results) that "die young" (never promoted to the next generation during a garbage collection interval)? I'm assuming that the "new" operation is very cheap, as it is really just a pointer increment. However, what are the hidden costs of dealing with this temporary "litter"?
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The Java heap is roughly broken up into 3 parts, permanent, old (long lived) generation, and young (short lived) generation. Young gen is further broken up into S1, S2 and eden.
Short lived objects will collect first and frequently. Gen 0 collection is cheap, but depending on the scale of the number of objects you're creating, it could be quite costly.
When the garbage collector performs a collection, it releases the memory for objects that are no longer being used by the application. It determines which objects are no longer being used by examining the application's roots.
Short of avoiding garbage collection altogether, there is only one way to make garbage collection faster: ensure that as few objects as possible are reachable during the garbage collection. The fewer objects that are alive, the less there is to be marked.
Not a lot - the garbage collector is very fast for gen0. It also tunes itself, adjusting the size of gen0 depending on how much it manages to collect each time it goes. (If it's managed to collect a lot, it will reduce the size of gen0 to collect earlier next time, and vice versa.)
The ultimate test is how your application performs though. Perfmon is very handy here, showing how much time has been spent in GC, how many collections there have been of each generation etc.
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