The percent used of the query cache. The query cache stores the contents of a select statement with the corresponding result; these results are invalidated after an insert, update, or delete statement. The query cache size is controlled using the global variable “query_cache_size”. The size of a query that can be inserted into the query cache is controlled by the global variable “query_cache_limit”. The monitor threshold is analyzed against an average of values returned in polls to the agent where the Number of Samples parameter controls the number of samples included in the calculation of the average.
An unhealthy state indicates the percentage use of the MySQL query cache is high. The query cache might not have enough storage for recently used queries. The query cache limit for individual queries might be too high causing less queries to be stored and higher percent usage.
To address high query cache usage percent increase the query_cache_size to allow additional queries to be stored. Decreasing query_cache_limit can allow additional queries to be stored in the query cache.