MySQL Administrator :: 10.3 Memory Health

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: The horizontal bar graph indicates how much of the allocated key buffer is in use. If a fairly large percentage of the key buffer is in use you may wish to increase the key_cache_size setting in the Startup Variables section. The line graph is an indication of the number of key_read_requests that resulted in actual key_reads. The higher the hitrate the more effective your key buffer is. A low hitrate can indicate that you need to increate the size of your keycache.