TYPO3 Core

I went through the query and tried to reproduce the speed enhancements with approx. 3000 rows of sample data.

The index seems never to be used:

mysql> EXPLAIN SELECT pid, domainName, forced FROM sys_domain WHERE redirectTo='http://foobar/' AND hidden=0 ORDER BY sorting ASC;
+----+-------------+------------+------+-------------------+------+---------+------+------+-----------------------------+
| id | select_type | table      | type | possible_keys     | key  | key_len | ref  | rows | Extra                       |
+----+-------------+------------+------+-------------------+------+---------+------+------+-----------------------------+
|  1 | SIMPLE      | sys_domain | ALL  | redirectTo_hidden | NULL | NULL    | NULL | 3032 | Using where; Using filesort |
+----+-------------+------------+------+-------------------+------+---------+------+------+-----------------------------+
1 row in set (0.00 sec)

Can you reproduce this or otherwise provide some more details about your test setup where the index is used?