PERFORMANCE_SCHEMA Storage Engine
If you run SHOW ENGINES, you'll see the following storage engine listed.
SHOW ENGINES\G ... Engine: PERFORMANCE_SCHEMA Support: YES Comment: Performance Schema Transactions: NO XA: NO Savepoints: NO ...
The PERFORMANCE_SCHEMA is not a regular storage engine for storing data, it's a mechanism for implementing the Performance Schema feature.
The SHOW ENGINE PERFORMANCE_SCHEMA STATUS statement is also available, which shows how much memory is used by the tables and internal buffers.
See Performance Schema for more details.