Sometimes I don't like MySQL for the way it documents its software. And I don't like people who would try to define something and get the definition from the MySQL documentation. Let me give an example, MySQL defines Handler_read_key server status variable as the number of requests to read a row based on a fixed position. This value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that don't use keys properly.
If you search around the web, people will also use this definition. But what does this actually? No one would try to go deeper because they actually don't know. Don't get me wrong, I also don't know what this actually means.
Let me dissect the way this definition is written, what does number of requests means? Is it the number of queries? What does a "fixed position" mean? And how is this related to being high when a lot of sorting is done? And finally how is this related to table scan?