Are you really wanting to skip over records as per your example above?

Memory mapping can be a better choice, if I/O has been identified as a bottleneck and you want 'semi-random' access to you data. I.e. if you can be a bit selective, skipping records, based on the headers and thus skipping significant blocks of data.

For example, the following uses Sys::Mmap: 

#!/usr/bin/perl
use common::sense;

use Sys::Mmap;

my $path = '/tmp/stuff';

my $file_size = -s $path;
die "empty or missing file: $path"
    unless $file_size;

open (my $fh, '+<', $path)
    or die "unable to open $path for read: $!";

mmap(my $data, 0, PROT_READ, MAP_SHARED, $fh)
    or die "mmap: $!";

my $pos = 0;

while ($pos < $file_size) {

    my ($size, $code, $ftype)
      = unpack ("nCC", substr($data, $pos, 4));

    $pos += 4;        # advance past header

    $size = $size - 4;

    if ($size > 0) {
       $pos += $size; # advance past record
   }
}

[download]
If you've identified I/O as a bottleneck, it's worthwhile benchmarking this against your above solution anyway, even if you are reading sequentially. It'll help to determine if read really is imposing a performance penalty!

In reply to Re: Perl's poor disk IO performance by snoopy
in thread Perl's poor disk IO performance by TROGDOR

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.