MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6

25.12.13 Performance Schema System Variable Tables

Note

The value of the show_compatibility_56 system variable affects the information available from the tables described here. For details, see the description of that variable in Section 5.1.7, “Server System Variables”.

The MySQL server maintains many system variables that indicate how it is configured (see Section 5.1.7, “Server System Variables”). System variable information is available in these Performance Schema tables:

The session variable tables (session_variables, variables_by_thread) contain information only for active sessions, not terminated sessions.

TRUNCATE TABLE is not supported for Performance Schema system variable tables.

The global_variables and session_variables tables have these columns:

The variables_by_thread table has these columns:

The variables_by_thread table contains system variable information only about foreground threads. If not all threads are instrumented by the Performance Schema, this table will miss some rows. In this case, the Performance_schema_thread_instances_lost status variable will be greater than zero.