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Re: Memory usage

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On 8/2/2016 4:48 PM, Cecil Westerhof wrote:
> I have a Java application which I start with the parameters:
>     -Xms4M -Xmx8M
>
> So the initial heap size will be 4 MB and the maximum will be 8 MB.
> But some strange things happen.

Given how small these values are then I am not surprised that you see
funky results.

Newer Java SE's has not been designed to run with so little heap.

> Almost immediately the GC is running:
>     2016-07-09T10:14:34.537+0200: 0.257: [GC (Allocation Failure)  512K->488K(3584K), 0.0029586 secs]
>     2016-07-09T10:14:34.771+0200: 0.491: [GC (Allocation Failure)  1000K->496K(3584K), 0.0012720 secs]
>     2016-07-09T10:14:34.815+0200: 0.535: [GC (Allocation Failure)  1008K->552K(3584K), 0.0014619 secs]
>     2016-07-09T10:14:35.496+0200: 1.216: [GC (Allocation Failure)  1064K->656K(4096K), 0.0017656 secs]
>     2016-07-09T10:14:36.035+0200: 1.755: [GC (Allocation Failure)  1680K->1048K(4096K), 0.0023148 secs]
>
> But why? Minimum size is 4 MB, so why does it run when there is only
> half an MB allocated?

Maybe because there is only 3.5M free??

I don't know, but for realistic Xmx values then 3.5M would mean that you 
are close to running out.

> At the moment I see:
>     2016-08-02T07:18:14.364+0200: 2062960.388: [GC (Allocation Failure)  4576K->3192K(5632K), 0.1543506 secs]
>     2016-08-02T09:23:04.833+0200: 2070450.857: [GC (Allocation Failure)  4728K->3168K(5632K), 0.0010015 secs]
>     2016-08-02T16:18:20.051+0200: 2095366.075: [GC (Allocation Failure)  4704K->3112K(5632K), 0.0017111 secs]
>     2016-08-02T19:37:35.176+0200: 2107321.200: [GC (Allocation Failure)  4648K->3056K(5632K), 0.0014402 secs]
>
> So the heap is still around 4 MB.

Same.

> But when I look at memory used and swap used (it is on an openSUSE
> 13.2 system) then I see that used memory is 37 MB and used swap is
> 57 MB. How is it possible that these are so high?

A Java program use more memory than the Java heap.

The JVM itself. Various native libraries. Stacks. For
older versions permgen. Etc.etc..

Arne

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Thread

Memory usage Cecil Westerhof <Cecil@decebal.nl> - 2016-08-02 22:48 +0200
  Re: Memory usage Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-08-02 17:28 -0400
  Re: Memory usage Arne Vajhøj <arne@vajhoej.dk> - 2016-08-02 17:49 -0400
    Re: Memory usage Arne Vajhøj <arne@vajhoej.dk> - 2016-08-02 17:52 -0400
  Re: Memory usage Roedy Green <inquiry@mindprod.com> - 2016-08-02 17:51 -0700
  Re: Memory usage Nigel Wade <nmw@local.domain> - 2016-08-03 13:11 +0100

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