Presumably you want to be able to generate unique part numbers across many runs of the program and thus need to keep a tally of those already issued. (Issuing part numbers at random is a bit weird, why not just allocate the next one in order? But c'est la vie.)

This will generate N unique part numbers each run without duplicates quite efficiently. It uses a singlefile, just over a megabyte in size, for the db:

#! perl -slw
use strict;
use constant TALLY => 'tally.bin';

our $N //= 50;
my $tally = chr(0) x (10e6 / 8 );

if( -e TALLY ) {
    open I, '<:raw', TALLY or die $!;
    my $tally = do{ local $/; <I> };
    close I;
}

sub genPartNo {{
    my $partNo = int( 1e6 + rand( 9e6 ) );
    redo if vec( $tally, $partNo, 1 );
    vec( $tally, $partNo, 1 ) = 1;
    return $partNo;
}}

print genPartNo for 1 .. $N;

open O, '>:raw', TALLY or die $!;
printf O "%s", $tally;
close O;
[download]