Show a list of active threads

show processlist;

Review the Time field to identify the longest-running query and run the following command to kill it:

kill < thread_id >;

Kill All Queries

If a large number of bad requests are blocking valid queries, you can clear them out without having to run kill on every individual thread.
Execute the following to generate kill commands from the PROCESSLIST table:

kill all processes' FROM information_schema.processlist WHERE user<>'system user'\G