I had a process with a hash that grew too big for RAM, and tied it to disk with a few simple lines: 

use DB_File; # too big for RAM now
my $db = '/path/to/some.db';
my %hash;
unlink $db;  # to start fresh
tie (%hash, "DB_File", $db, $DB_BTREE) or die("Unable to tie $db: $!")
+;
# do things as before
untie %hash;

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Performance is fine.

In reply to Re: storing a large hash in a database by hbm
in thread storing a large hash in a database by Anonymous Monk

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