I have two machines are identical with one exception that I believed was identical when I first wrote this article: In all other aspects they are identical: Some say less is more, but it is a real surprise to see that the machine with 40 GB RAM seems to be roughly twice as fast as the machine with 64 GB RAM. The behavior is consistent, and as illustrated by this little benchmark (which is CPU intensive, but requires little memory): 
 
use warnings;
use strict;

use JSON::XS;
use Benchmark qw(cmpthese);

my $coder = JSON::XS->new->ascii->pretty->allow_nonref;

my $hashref = { one => 1, two => 2, three => 3, four => { nested => 'b
+ird' } };
my $arrayref = [ 'one', 'two', 'three', 'four', 'five', 'six' ];


# cmpthese can be used both ways as well
cmpthese(
  -1,
  {
    'enc+dec hashref ' =>
      sub { $coder->decode( $coder->encode( $hashref ) ) },
    'enc+dec arrayref ' =>
      sub { $coder->decode( $coder->encode( $arrayref ) ) },
  }
);
__END__

[download]
[me@first ~]$ ./perl-json-test.pl
                      Rate  enc+dec hashref  enc+dec arrayref
enc+dec hashref   344063/s                --              -22%
enc+dec arrayref  438597/s               27%                --

[me@second ~]$ ./perl-json-test.pl
                      Rate  enc+dec hashref  enc+dec arrayref
enc+dec hashref   153121/s                --              -24%
enc+dec arrayref  200972/s               31%                --

[download]
A collegues commented that Red Hat Linux has a terrible track record in High Performance Computing and that the memory management is not well suited for two digit gigabytes of RAM. He suggests to use another Linux distribution (such as SuSE), but client policy prevents that.

Do any of the honorable monks have made similar observations or even reasonable explanation to why the machine with the most memory is the slower one?

Update 1: Actually, I have 4 machines of which 2 are pairwise identical. Each machine behaves identically as its twin.

Update 2 : Thanks for helpful replies. As I have remote access only to the machines in question, I can't experiment as broadly as I otherwise would have, but I'll surely update this thread once I get some results. I have asked the services provider to reduce physical memory down to 16 Gb.

Update 3 : It turns the machines were not identical after all (see top), and that reducing the memory down to 16 Gb did not significantly change the benchmarks. Whether or not the PCI bus type can account for the huge difference in overall performance is unknown.

--
No matter how great and destructive your problems may seem now, remember, you've probably only seen the tip of them. [1]

In reply to Less is more? 40G memory twice as fast as 64G by andreas1234567

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