What is the importance of ft_query_expansion_limit?

What is the importance of ft_query_expansion_limit and what exactly it’s doing?

from http://dev.mysql.com/doc/refman/5.0/en/server-system-variabl es.html

The number of top matches to use for full-text searches performed using WITH QUERY EXPANSION.
I don't unerstand what they mean by that.

Basically, query expansion performs a full text search and then uses the first few results (configured by ft_query_expansion_limit) to search again and compose your result set. The explanation in the docs is probably better than mine:

http://dev.mysql.com/doc/refman/5.1/en/fulltext-query-expans ion.html

Does increasing this value improves performance?

Unless you are specifically using WITH QUERY EXPANSION in your fulltext queries, this will have no affect on performance.

Thanks. I’ll remember that.