If your goal is to create unguessable unique keys and you don't care about leaking info about the order in which the key are created, you could concatenate a unique incrementing number with a random number. 
my $unique = time;
my $key_bin = pack('N', $unique)
            . pack('C*', map { int(rand()*256) } 1..6);
my $key_hex = unpack('H*', $key_bin);

[download]
That gives something like 
4818e14c1662fd0dac98
\______/\__________/
   |         |
 32-bit    48-bit
 unique    random

[download]

You can reduce the size of the unique portion (by using substr(pack('N', $unique), 1)) and change the size of the random portion (by changing the "6") at will.

In reply to Re: Question: Generate unique/random 12-digit keys for 25,000K records, howto?? by ikegami
in thread Question: Generate unique/random 12-digit keys for 25,000K records, howto?? by lihao

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.