Re: Another garbage collection question

Lew <>
Fri, 01 Feb 2008 21:15:11 -0500
Arne VajhQj wrote:

Donkey Hot wrote:

KevinHanna <> wrote in

No, you can't control Java's garbage collection. You can only adjust
the heap and stack sizes to effect how often Java runs GC, the
ultimate decision is always left to the JVM. If garbage collection is
noticeably effecting the performance (and I'd be surprised if it is).
Then you'd be better served to make sure you're instantiating as few
objects as possible. Google the singleton design pattern.

You indeed can start the garbage collection whenever you want, it's
just an API call on Runtime or such (I can't remember). You can start
gc when your app is idle and hope it helps.


If you read the docs for the System/Runtime gc call you will see
"Calling this method suggests that the Java virtual machine ..." - the
keyword being "suggest".

It is very unlikely that calling gc explicit will improve
performance - it will likely make performance worse.

If memory is tight when you call System.gc(), it's very likely the VM has just
invoked GC or was just about to, making it superfluous. If memory isn't
tight, either the VM will ignore your request, making it superfluous, or will
honor it with a full GC, not a young-generation collection, thus causing the
very overhead you seek to avoid.


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