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    <p>Two micro optimizations: map inner hash instead of constant dereferencing and buffer instead of constant print. It's possible to get rid of sorting using alternative storage formats, tested two variants. Results:</p> <pre><code> Rate original try3 alternative alternative2 original 46.1/s -- -12% -21% -32% try3 52.6/s 14% -- -10% -22% alternative 58.6/s 27% 11% -- -13% alternative2 67.5/s 46% 28% 15% -- </code></pre> <p>Conclusion:</p> <p>It's better to use presorted storage format, but without C win would probably be within 100% (on my test dataset). Provided information about data suggests that keys in outer hash are almost sequential numbers, so this cries for array.</p> <p>Script:</p> <pre><code>#!/usr/bin/env perl use strict; use warnings; use Benchmark qw/timethese cmpthese/; my %signal_db = map { $_ =&gt; {} } 1..1000; %$_ = map { $_ =&gt; $_ } 'a'..'z' foreach values %signal_db; my @signal_db = map { { cycle =&gt; $_ } } 1..1000; $_-&gt;{'samples'} = { map { $_ =&gt; $_ } 'a'..'z' } foreach @signal_db; my @signal_db1 = map { $_ =&gt; [] } 1..1000; @$_ = map { $_ =&gt; $_ } 'a'..'z' foreach grep ref $_, @signal_db1; use Sort::Key qw(nsort); sub numerically { $a &lt;=&gt; $b } my $result = cmpthese( -2, { 'original' =&gt; sub { open my $out, '&gt;', 'tmp.out'; foreach my $cycle (sort numerically keys %signal_db) { foreach my $key (sort keys %{$signal_db{$cycle}}) { print $out $signal_db{$cycle}{$key}.$key."\n"; } } }, 'try3' =&gt; sub { open my $out, '&gt;', 'tmp.out'; foreach my $cycle (map $signal_db{$_}, sort numerically keys %signal_db) { my $tmp = ''; foreach my $key (sort keys %$cycle) { $tmp .= $cycle-&gt;{$key}.$key."\n"; } print $out $tmp; } }, 'alternative' =&gt; sub { open my $out, '&gt;', 'tmp.out'; foreach my $cycle (map $_-&gt;{'samples'}, @signal_db) { my $tmp = ''; foreach my $key (sort keys %$cycle) { $tmp .= $cycle-&gt;{$key}.$key."\n"; } print $out $tmp; } }, 'alternative2' =&gt; sub { open my $out, '&gt;', 'tmp.out'; foreach my $cycle (grep ref $_, @signal_db1) { my $tmp = ''; foreach (my $i = 0; $i &lt; @$cycle; $i+=2) { $tmp .= $cycle-&gt;[$i+1].$cycle-&gt;[$i]."\n"; } print $out $tmp; } }, } ); </code></pre>
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