use strict;
use warnings;

use List::Util qw( shuffle );

my $j = 90;

sub extract_id {
   my ($line) = @_;
   ...
   return ...;
}

my @m;
my $id;
my $last_id;

for (;;) {
   my $line = <DATA>;

   $id = extract_id($line)
      if defined($line);

   if (@m) {
      if (!defined($line) || $id ne $last_id) {
         my $j = $j < @m ? $j : @m;
         print $m[$_] foreach (shuffle(0..$#m))[0..$j-1];
         @m = ();
      }
   }

   last if !defined($line);

   push(@m, $line);
   $last_id = $id;
}