Re: Hash table performance

From:

markspace <nospam@nowhere.com>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 23 Nov 2009 12:34:40 -0800

Message-ID:

<heerl3$gd9$1@news.eternal-september.org>

Jon Harrop wrote:

markspace wrote:

Marcin Rze??nicki wrote:

That could well be hidden in GC/heap resizing costs if he did not
allocate Java heap properly. I prevented these effects mostly from
occurring by running this example with -Xms512m -Xmx512m.

I ran my test (18 seconds for Jon's code on a 32 bit laptop)

This is a 2x quadcore 2.0GHz Intel Xeon E5405. What is you CPU?

Intel Core Duo T2600 (2.16 GHz).

2 Gigs of main memory installed. 667MHz - 2 DIMM Slots (2 x 1GB).

$ time java Hashtbl

This obviously includes the start-up time of the JVM. That's not the
runtime of your algorithm.

Try this:

class HashM
{

    public static void main( String... args )
    {
       long start = System.nanoTime();
       HashMap<Double,Double> hashM = new HashMap<Double, Double>();
       for( int i = 1; i <= 10000000; ++i ) {
          double x = i;
          hashM.put( x, 1.0 / x );
       }
       long end = System.nanoTime();
       out.println( "HashMap time: "+ (end-start)/1000000 );
       out.println( "hashmap(100.0) = " +
               hashM.get( 100.0 ) );
    }
}

I'm also curious: what runs the F# runtime under Unix? Which version of
Unix are you using? Are you dual booting or running Cygwin?

I'm still suspecting that it's differences in the environment (drivers
under Unix/Cygwin vs. Microsoft) that make the most difference in your
observed times.