Re: Memory utilization

The 70% high water mark has nothing to do with these results

This parameter defines the high-water mark. When and if the heap grows  
to this size a full GC will occur. The heap didn't grow to this size  
in this test.



On Jan 30, 2008, at 12:14 PM, Carfield Yim wrote:

> 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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