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copied!<p>I suggest an on-disk key/value database. Due to Perl's <a href="http://perldoc.perl.org/functions/tie.html" rel="noreferrer">tie function</a>, they can be used identically to normal, in-memory hashes. They'll be faster than Perl's hashes for reading/writing if your hash is very large, and they support saving/loading to disk automatically.</p> <p><a href="http://search.cpan.org/perldoc?BerkeleyDB" rel="noreferrer">BerkeleyDB</a> is an old favourite:</p> <pre><code>use BerkeleyDB; # Make %db an on-disk database stored in database.dbm. Create file if needed tie my %db, 'BerkeleyDB::Hash', -Filename => "database.dbm", -Flags => DB_CREATE or die "Couldn't tie database: $BerkeleyDB::Error"; $db{foo} = 1; # get value print $db{foo}, "\n"; # set value for my $key (keys %db) { print "$key -> $db{$key}\n"; # iterate values } %db = (); # wipe </code></pre> <p>Changes to the database are automatically saved to disk and will persist through multiple invocations of your script.</p> <p>Check the perldoc for options, but the most important are:</p> <pre><code># Increase memory allocation for database (increases performance), e.g. 640 MB tie my %db, 'BerkeleyDB::Hash', -Filename => $filename, -CacheSize => 640*1024*1024; # Open database in readonly mode tie my %db, 'BerkeleyDB::Hash', -Filename => $filename, -Flags => DB_RDONLY; </code></pre> <p>A more complex but much faster database library would be <a href="http://fallabs.com/tokyocabinet/" rel="noreferrer">Tokyo Cabinet</a>, and there are of course many other options (this is Perl after all...)</p>

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