To generate execution plans, the optimizer uses a cost model that is based on estimates of the cost of various operations that occur during query execution. The optimizer has a set of compiled-in default cost constants available to it, to make decisions regarding execution plans. You can adjust them by updating or inserting the mysql.engine_cost table and executing the FLUSH OPTIMIZER_COSTS command:
mysql> SELECT * FROM mysql.engine_cost\G*************************** 1. row *************************** engine_name: InnoDB device_type: 0 cost_name: io_block_read_cost cost_value: 1 last_update: 2017-11-20 16:24:56 comment: NULLdefault_value: 1*************************** 2. row *************************** engine_name: ...
