use warnings;
use strict;
use Data::Dump;
use DBI;

my $titlesperpage = 10;

# set up a dummy database
my $dbh = DBI->connect("dbi:SQLite::memory:", undef, undef,
	{ RaiseError=>1 });
$dbh->do(<<'END');
CREATE TABLE messages (
	msgID INTEGER,
	threadID INTEGER
)
END
my $sth_i = $dbh->prepare(
	'INSERT INTO messages (msgID, threadID) VALUES (?,?)');
$sth_i->execute($_,$_>>4) for 0..127;

for my $currentpage (1..5) { # simulate requests for different pages
	
	my $startcount = ($currentpage - 1) * $titlesperpage + 1;
	my $stopcount = $currentpage * $titlesperpage;
	dd $startcount, $stopcount;
	
	my $sth_s = $dbh->prepare('SELECT msgID, threadID FROM messages');
	$sth_s->execute;
	my %threadIDs;
	my $rowcnt = 1;
	while ( my $row = $sth_s->fetchrow_hashref ) {
		$threadIDs{ $row->{threadID} }++;
		if ( $rowcnt >= $startcount && $rowcnt <= $stopcount ) {
			dd $row->{msgID};
		}
	} continue { $rowcnt++ }
	dd \%threadIDs;
	
}