The InnoDB monitor was a precursor of PERFORMANCE_SCHEMA in InnoDB, added in MySQL 5.5.
There should be only one (good) performance monitoring mechanism. Now we have several:
- SHOW ENGINE INNODB STATUS (hopefully to be removed at some part of future)
- INFORMATION_SCHEMA.INNODB_METRICS (to be removed in this task)
We should evaluate all the INNODB_METRICS counters and construct a mapping to the PERFORMANCE_SCHEMA or GLOBAL_STATUS counters correspond to them. There may be some obscure counters that can be removed; also these must be documented. Some counters may need to be added to PERFORMANCE_SCHEMA or GLOBAL_STATUS. If updating some status is not expensive, we might as well update it all the time and expose via GLOBAL_STATUS.