This chapter describes a lot of things that you need to know when working on the MySQL code. The signal thread handles all signals. Every connection has its own thread. Since version 3.23.23, MySQL has support for full-text indexing and searching.
Relevance is a non- negative floating point number.
Zero relevance means no similarity. MySQL uses a very simple parser to split text into words. Every correct word in the collection and in the query is weighted, according to its significance in the query or collection. Otherwise, if the word is rare, it will receive a higher weight. Weights of the words are then combined to compute the relevance.