what is mysql expression metric mean?

Hi,

Each mysql expression metric measure the own value. Example:
Heavy join rate - it's a percent of heavy (full join, range check and scan) operations
On-disk temporary table rate - it's a percent of temporary tables that was placed on disk instead of memory
Query cache miss rate - it's a percent of select operations which missed query cache
Innodb buffer pool usage - it's a percent of innodb pool usage