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
}
}
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!