MySQL 9.5 Reference Manual Including MySQL NDB Cluster 9.5

10.15.1 Typical Usage

To perform optimizer tracing entails the following steps:

  1. Enable tracing by executing SET optimizer_trace="enabled=ON".

  2. Execute the statement to be traced. See Section 10.15.3, “Traceable Statements”, for a listing of statements which can be traced.

  3. Examine the contents of the INFORMATION_SCHEMA.OPTIMIZER_TRACE table.

  4. To examine traces for multiple queries, repeat the previous two steps as needed.

  5. To disable tracing after you have finished, execute SET optimizer_trace="enabled=OFF".

You can trace only statements which are executed within the current session; you cannot see traces from other sessions.

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