10.5.1 The events_stages_current Table

The events_stages_current table contains current stage events. The table stores one row per thread showing the current status of the thread's most recent monitored stage event, so there is no system variable for configuring the table size.

Of the tables that contain stage event rows, events_stages_current is the most fundamental. Other tables that contain stage event rows are logically derived from the current events. For example, the events_stages_history and events_stages_history_long tables are collections of the most recent stage events that have ended, up to a maximum number of rows per thread and globally across all threads, respectively.

For more information about the relationship between the three stage event tables, see Performance Schema Tables for Current and Historical Events.

For information about configuring whether to collect stage events, see Section 10.5, “Performance Schema Stage Event Tables”.

The events_stages_current table has these columns:

• THREAD_ID, EVENT_ID

  The thread associated with the event and the thread current event number when the event starts. The THREAD_ID and EVENT_ID values taken together uniquely identify the row. No two rows have the same pair of values.

• END_EVENT_ID

  This column is set to NULL when the event starts and updated to the thread current event number when the event ends.

• EVENT_NAME

  The name of the instrument that produced the event. This is a NAME value from the setup_instruments table. Instrument names may have multiple parts and form a hierarchy, as discussed in Chapter 7, Performance Schema Instrument Naming Conventions.

• SOURCE

  The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.

• TIMER_START, TIMER_END, TIMER_WAIT

  Timing information for the event. The unit for these values is picoseconds (trillionths of a second). The TIMER_START and TIMER_END values indicate when event timing started and ended. TIMER_WAIT is the event elapsed time (duration).

  If an event has not finished, TIMER_END is the current timer value and TIMER_WAIT is the time elapsed so far (TIMER_END − TIMER_START).

  If an event is produced from an instrument that has TIMED = NO, timing information is not collected, and TIMER_START, TIMER_END, and TIMER_WAIT are all NULL.

  For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 5.1, “Performance Schema Event Timing”.

• WORK_COMPLETED, WORK_ESTIMATED

  These columns provide stage progress information, for instruments that have been implemented to produce such information. WORK_COMPLETED indicates how many work units have been completed for the stage, and WORK_ESTIMATED indicates how many work units are expected for the stage. For more information, see Stage Event Progress Information.

• NESTING_EVENT_ID

  The EVENT_ID value of the event within which this event is nested. The nesting event for a stage event is usually a statement event.

• NESTING_EVENT_TYPE

  The nesting event type. The value is TRANSACTION, STATEMENT, STAGE, or WAIT.

TRUNCATE TABLE is permitted for the events_stages_current table. It removes the rows.