Re: Memory utilization

According to http://java.sun.com/javase/technologies/hotspot/vmoptions.jsp
, default value is -XX:MaxHeapFreeRatio=70 , I think that mean 70%
memory allocated from OS to JVM is leave as free, not sure if that is
the reason of your finding.

By the way, is that default value really good??
http://forum.java.sun.com/thread.jspa?threadID=5250587

On Jan 31, 2008 12:40 AM, Peter Booth <[email protected]> wrote:
> Avinash,
>
> A very crude experiment (say +/- 20%):
>
> I ran your test program on my MacBook Pro after changing the upper
> bound to Integer.MAX_VALUE / 512;
>
> It took 7.5 secs to complete and had a heap size of 572MB just prior
> to exiting.
>
> 7.500: [GC 7.500: [DefNew: 72576K->8064K(72576K), 0.4641337 secs]
> 584898K->572609K(1040512K), 0.4642092 secs]
>
> 1. Changing the code to avoid the unnecessary Integer creation reduced
> execution time to 4.34 sec (42%) and heap size to 313 MB (45%)
>
>         int COUNT = Integer.MAX_VALUE / 512;
>            Map<String, String> map = new HashMap<String, String>();
>            for( int i = 0; i < COUNT; ++i )
>            {
>                 String s = Integer.toString(i);
>                 map.put(s,s);
>            }
>
> 4.340: [GC 4.341: [DefNew: 72576K->8063K(72576K), 0.5675008 secs]
> 313491K->313491K(1040512K), 0.5675750 secs]
>
> 2. Changing the code to create the HashMap presized, reduced execution
> time to 4.3 sec(5%) and increased heap size to 319 MB(2%)
>
>     Map<String, String> map = new HashMap<String, String>(COUNT);
>
> 4.089: [GC 4.089: [DefNew: 72576K->8064K(72576K), 0.5929834 secs]
> 318993K->318993K(1040512K), 0.5930458 secs]
>
> There is always more you can do, so long as you know more about your
> data's characteristics than the programmer of the general purpose
> collection code you are using.
>
> Peter
>
>
> > I was trying to profile the following piece of code using NetBeans:
> >
> > public static void main(String[] args)
> > {
> >    Map<String, String> map = new HashMap<String, String>();
> >    for( int i = 0; i < Integer.MAX_VALUE; ++i )
> >    {
> >        map.put(Integer.valueOf(i).toString(),
> > Integer.valueOf(i).toString());
> >    }
> > }
> >
> >
> > I set my max and min heap size to be 1GB. I find that the program
> > dies after having created 4M entries (at which point the heap used
> > is at 1GB) although the memory used by the objects as indicated by
> > the Netbeans memory profiler is the following:
> >
> > String -- 48MB
> > char[] -- 48 MB
> > HeapCharBuffer -- 45MB
> > Integer -- 19MB
> > HashMap$Entry -- 19MB
> >
> >
> > This totals to less than 200 MB and the rest of the objects are at
> > 0% of the total used memory. How come the heap usage is at 1GB at
> > this point of time? I am extremely confused. Could someone please
> > explain what might be going on?
> >
> > Thanks
> > A
> >
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