$db->sync;                       # not modified
        $hash{foo} = 'bar';              # not modified
        $db->sync;                       # MODIFIED
        @hash{qw<one two three>} = 1..3; # not modified
        $db->sync;                       # MODIFIED
        delete $hash{two};               # not modified
        $db->sync;                       # MODIFIED
        $db->sync;                       # not modified