I'm currently using MYSQL,
and it becomes the bottle neck of the whole system
I'm currently using MYSQL,
and it becomes the bottle neck of the whole system
Try Lucene indexing: lucene.apache.org. There is also a very good implementation in PHP as a part of Zend Framework.
Consider Solr (not to be confused with the Solar Framework for PHP). It is based on Lucene and designed to scale, if that is one of your concerns.
Other Solr-related links you might find helpful: