Performance Schema General Table Characteristics
The name of the performance_schema database is lowercase, as are the names of tables within it.
Queries should specify the names in lowercase.
Most tables in the performance_schema database are read only and cannot be modified. Some
of the setup tables have columns that can be modified to affect Performance Schema operation;
some also permit rows to be inserted or deleted. Truncation is permitted to clear collected events, so
TRUNCATE TABLE can be used on tables containing those kinds of information, such as tables named
with a prefix of events_waits_.
TRUNCATE TABLE can also be used with summary tables, but except for
events_statements_summary_by_digest, the effect is to reset the summary columns to 0 or
NULL, not to remove rows.
Privileges are as for other databases and tables:
• To retrieve from performance_schema tables, you must have the SELECT  privilege.
• To change those columns that can be modified, you must have the UPDATE  privilege.
• To truncate tables that can be truncated, you must have the DROP  privilege.
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