You may find the thread at Strategy for randomizing large files via sysseek useful.

One thing that is not clear from your post is whether you want to actually shuffle the lines in your 4GB file, or just find a mechanism for allowing many processes to be given unique random subset of the lines from that file?

It may be that they amount to the same thing in that shuffling the large file is possibly the easiest way, but it may be possible to allow each process to select lines at random without overlaps more efficiently.

Also whether you would accept a "nearly random" distribution as opposed to statistically valid randomness , may allow a more efficient, slightly less than really random solution.

Examine what is said, not who speaks.
Silence betokens consent.
Love the truth but pardon error.

In reply to Re: Randomizing Big Files by BrowserUk
in thread Randomizing Big Files by Anonymous Monk

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.