In MySQL 8.0, the engineers have added useful meta-data to the table
SETUP_INSTRUMENT. This table lists the classes of instrumented objects for which events can be collected.
TIMED columns, were added
Let’s have a quick look at these new columns:
PROPERTIES can have the following values
- global_statistics: only global summaries are available for this instrument. Example:
memory/performance_schema/metadata_locks thatreturn the memory used for table
- mutable: only applicable for statement instruments as they can “mutate” into a more specific one. Example:
statement/abstract/relay_logthat returns the new event just read from the relay log.
- progress: applied only to stage instruments, it reports progress data. Example:
stage/sql/copy to tmp table
- singleton: instruments having a single instance. Example:
wait/synch/mutex/sql/LOCK_error_log, like most global mutex locks this lock on error log is a singleton.
- user: instrument related to user workload. Example: the instrument on
This define the life or creation occurrence of the instrument. The possible values from low to high are:
- 0 : unknown
- 1 : permanent
- 2 : provisioning
- 3 : ddl
- 4 : cache
- 5 : session
- 6 : transaction
- 7 : query
- 8 : intra_query
wait/synch/mutex/sql/THD::LOCK_thd_query as a volatility of 5, which means this mutex is created each time a session connects and destroyed when the session disconnects.
There is no point then to enable an instrument for an object already created.
Finally, now there is a documentation column describing the purpose of the instrument. Currently there are 80 instruments documented with the help of that column.
This is an example:
NAME: memory/performance_schema/prepared_statements_instances ENABLED: YES TIMED: NULL PROPERTIES: global_statistics VOLATILITY: 1 DOCUMENTATION: Memory used for table performance_schema.prepared_statements_instances
All this is explained in details in the MySQL’s manual.
Enjoy MySQL 8.0 and I wish you a pleasant discovery of all the new features !
[…] MySQL 8.0 adds meta-data such as properties, volatility, and documentation to the performance schema table setup_instruments. This read only meta-data act as online documentation for instruments, to be looked at by users or tools. See blog post by Frédéric Descamps here. […]