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Been following this tutorial https://stackoverflow.com/questions/3927690/howto-clean-a-mysql-innodb-storage-engine/4056261#comment14041132_4056261

in the process I deleted performance_schema along with the other dbs.

I dont see it reappear after reimporting dbs. Is it ok if I dont have performance schema?

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The MySQL Performance Schema is a feature for monitoring MySQL Server execution at a low level. The Performance Schema is available as of MySQL 5.5.3.

From MySQL Manual there are some of the features of the performance_schema database.

The Performance Schema provides a way to inspect internal execution of the server at runtime. It is implemented using the PERFORMANCE_SCHEMA storage engine and the performance_schema database. The Performance Schema focuses primarily on performance data. This differs from INFORMATION_SCHEMA, which serves for inspection of metadata.

The Performance Schema monitors server events. An “event” is anything the server does that takes time and has been instrumented so that timing information can be collected. In general, an event could be a function call, a wait for the operating system, a stage of an SQL statement execution such as parsing or sorting, or an entire statement or group of statements. Currently, event collection provides access to information about synchronization calls (such as for mutexes) file and table I/O, table locks, and so forth for the server and for several storage engines

Performance Schema events are distinct from events written to the server's binary log (which describe data modifications) and Event Scheduler events (which are a type of stored program).

For detailed information look this Link Performance Schema.

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