This parameter sets the amount of thread for cache purposes. If client disconnects, his thread are kept in the cache. If the requests are less than the thread_cache_size then threads that are stored in cache will serve the requests.
To find the thread cache hit rate,
Kindly access MySQL and enter the following commands.
mysql> show status like 'Threads_created';
mysql> show status like 'Connections';
Now use the following formula to calculate the thread cache hit rate percentage:
100 – ((Threads_created / Connections) * 100)
In this case it is —>>> 100 – ((26/4304) * 100 ) = 99.39
The most useful thing is that the thread_cache_size can be dynamically changed without having to restart the MySQL service.