optimize tables for search using LIKE clause in MySQL

Question

I am building a search feature for the messages part of my site, and have a messages database with a little over 9,000,000 rows, and and index on the sender,

Answer 1

You should either use full-text indexes (you said you can't), design a full-text search by yourself or offload the search from MySQL and use Sphinx/Lucene. For Lucene you can use Zend_Search_Lucene implementation from Zend Framework or use Solr.

Normal indexes in MySQL are B+Trees, and they can't be used if the starting of the string is not known (and this is the case when you have wildcard in the beginning)

Another option is to implement search on your own, using reference table. Split text in words and create table that contains word, record_id. Then in the search you split the query in words and search for each of the words in the reference table. In this way you are not limitting yourself to the beginning of the whole text, but only to the beginning of the given word (and you'll match the rest of the words anyway)