This tab provides information about memory caches that affect the performance of the MySQL server. For each cache, there is a display that shows the current hitrate or usage of the cache, and a display that shows the hitrate or usage for the last minutes. The size of the latter display depends on the size of the working area of the main window.
Query Cache Hitrate: When in use, the query cache of the MySQL server stores the text of a SELECT query together with the corresponding result that was sent to the client. If an identical query is later received, the server will retrieve the results from the query cache rather than parsing and executing the same query again. The hitrate indicates the ratio of queries that were cached and queries that were not cached. The higher the hitrate, the better the performance of the server regarding SELECT queries. See the MySQL Query Cache section for details.
Key Efficiency: Information about the key buffer.