Hm. I'm not sure that doing 4 lookups of the same value from the same process and then discarding the first one is much of a demonstration.

It is effectively the same thing as doing this:

c:\test> perl -MDigest::MD5=md5_hex -E"printf qq[%s %07d\n], md5_hex($
+_),$_ for 1..1e6" >hstore

c:\test > type hstore.pl
#! perl -slw
use strict;
use Time::HiRes qw[ time ];
use Digest::MD5 qw[ md5_hex ];

my $table = do{ local( @ARGV, $/ ) = 'hstore'; <> };
my %cache;

my $v = '9509342c6a6b283d07a3ce406b06eb1e';
my $val = ( $cache{ $v } ) //= $table =~ m[$v (\d+)$];

for ( 1 .. 3 ) {
    my $start = time;
    my $val = ( $cache{ $v } ) //= $table =~ m[$v (\d+)$];
    printf "Time: %.9f\n", time() - $start;
}

c:\test> hstore
Time: 0.000007868
Time: 0.000009060
Time: 0.000001907
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