It's been up for a few days and runs fast/well, but twice now it has suddenly locked up with NO activity at all - all of the Innodb thread slots have tasks which seem stuck, and hundreds of other threads waiting - this goes on forever, like 1-2 hours at CPU 100% idle, no queries executing, etc. until we discovered FLUSH TABLES will fix it.
Reason: You may need to increase the value of the table_cache variable. You can check whether you need to increase the table cache by checking the Opened_tables status variable. If the value is very large or increases rapidly, even when you have not issued many FLUSH TABLES statements, you should increase the table cache size
Solution: increase table_cache