El problema es que crear el index lleva algo de tiempo, pero en máximo 1 semana estará disponible.
Aquí la explicación en inglés:
Citar
A search index can greatly improve the performance of searches on your forum. Especially when the number of messages on a forum grows bigger, searching without an index can take a long time and increase the pressure on your database. If your forum is bigger than 50.000 messages, you might want to consider creating a search index to assure peak performance of your forum.
Note that a search index can take up quite some space. A fulltext index is a built-in index of MySQL. It's relatively compact (approximately the same size as the message table), but a lot of words aren't indexed and it can, in some search queries, turn out to be very slow. The custom index is often bigger (depending on your configuration it can be up to 3 times the size of the messages table) but it's performance is better than fulltext and relatively stable.
Note that a search index can take up quite some space. A fulltext index is a built-in index of MySQL. It's relatively compact (approximately the same size as the message table), but a lot of words aren't indexed and it can, in some search queries, turn out to be very slow. The custom index is often bigger (depending on your configuration it can be up to 3 times the size of the messages table) but it's performance is better than fulltext and relatively stable.
Esto ya se comentó aquí:
Mejorar el buscador del foro
http://foro.elhacker.net/index.php/topic,161373.0.html
Pero finalmente por problemas de espacio no se llevo a cabo. Ahora, una vez solucionados si se llevará a cabo.
Por entonces la tabla índice ocupaba 266MB cuándo sólo estaba completada en 35%.