The setup_actors table contains information for determining whether monitoring should be enabled for new client connection threads.

The default size is 100 rows, which can be changed by modifying the performance_schema_setup_actors_size system variable at server startup.

If a row in the table matches a new foreground thread's client and host, the matching INSTRUMENTED column in the threads table is set to either YES or NO, which allows selective application of instrumenting by host, by user, or combination thereof.

Initially, any user and host is matched:

SELECT * FROM performance_schema.setup_actors;
+------+------+------+
| HOST | USER | ROLE |
+------+------+------+
| %    | %    | %    |
+------+------+------+