According to mysql full text search (when you index your table with according properly) and lucene, they all use same algorithm for relevancy. TF-IDF with full reverse indexing. However, comparing the speed in text search between lucene and mysql, there is tremendous differences between them in terms of Relevancy and the speed. What are the main reasons for it ?
[1] https://dev.mysql.com/doc/internals/en/full-text-search.html