Performance Schema events_waits_history Table
The events_waits_history table by default contains the ten most recent completed wait events per thread. This number can be adjusted by setting the performance_schema_events_waits_history_size system variable when the server starts up.
The table structure is identical to the events_waits_current table structure, and contains the following columns:
| Column | Description |
|---|---|
THREAD_ID | Thread associated with the event. Together with EVENT_ID uniquely identifies the row. |
EVENT_ID | Thread's current event number at the start of the event. Together with THREAD_ID uniquely identifies the row. |
END_EVENT_ID | NULL when the event starts, set to the thread's current event number at the end of the event. |
EVENT_NAME | Event instrument name and a NAME from the setup_instruments table |
SOURCE | Name and line number of the source file containing the instrumented code that produced the event. |
TIMER_START | Value in picoseconds when the event timing started or NULL if timing is not collected. |
TIMER_END | Value in picoseconds when the event timing ended, or NULL if timing is not collected. |
TIMER_WAIT | Value in picoseconds of the event's duration or NULL if timing is not collected. |
SPINS | Number of spin rounds for a mutex, or NULL if spin rounds are not used, or spinning is not instrumented. |
OBJECT_SCHEMA | Name of the schema that contains the table for table I/O objects, otherwise NULL for file I/O and synchronization objects. |
OBJECT_NAME | File name for file I/O objects, table name for table I/O objects, the socket's IP:PORT value for a socket object or NULL for a synchronization object. |
INDEX NAME | Name of the index, PRIMARY for the primary key, or NULL for no index used. |
OBJECT_TYPE | FILE for a file object, TABLE or TEMPORARY TABLE for a table object, or NULL for a synchronization object. |
OBJECT_INSTANCE_BEGIN | Address in memory of the object. |
NESTING_EVENT_ID | EVENT_ID of event within which this event nests. |
NESTING_EVENT_TYPE | Nesting event type. Either statement, stage or wait. |
OPERATION | Operation type, for example read, write or lock |
NUMBER_OF_BYTES | Number of bytes that the operation read or wrote, or NULL for table I/O waits. |
FLAGS | Reserved for use in the future. |
It is possible to empty this table with a TRUNCATE TABLE statement.
events_waits_current and events_waits_history_long are related tables.
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