pager_query() - How to fetch only 100 records with a pagination 10 items per page?
You can pass a $count_query argument to pager_query(), which you can use to control the overall count:

e.g.

$sql = 'SELECT * FROM my_table';
$count_sql = 'SELECT COUNT(id) FROM my_table LIMIT 100';

$result = pager_query($sql, 10, 0, $count_sql);