The percent of the key cache that is currently being utilized. The MyISAM Key cache is a data structure that contains the most-used index blocks. The key cache size is controlled using the global variable ‘key_buffer_size’. 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 of the key cache in use is high. The key cache does not have enough space to store recently used key blocks and will continue to drop the least recently used key block.
To address high percent use of the key cache increase key_buffer_size the configuration file. This can be done by adding the following line along with size under the instance group options: “key_buffer_size=size”. Alternatively the server can be started with the following option: “--key_buffer_size=size”