10.7.1 The events_transactions_current Table

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

mysql> SELECT *
       FROM performance_schema.events_transactions_current LIMIT 1\G
*************************** 1. row ***************************
                      THREAD_ID: 26
                       EVENT_ID: 7
                   END_EVENT_ID: NULL
                     EVENT_NAME: transaction
                          STATE: ACTIVE
                         TRX_ID: NULL
                           GTID: 3E11FA47-71CA-11E1-9E33-C80AA9429562:56
                            XID: NULL
                       XA_STATE: NULL
                         SOURCE: transaction.cc:150
                    TIMER_START: 420833537900000
                      TIMER_END: NULL
                     TIMER_WAIT: NULL
                    ACCESS_MODE: READ WRITE
                ISOLATION_LEVEL: REPEATABLE READ
                     AUTOCOMMIT: NO
           NUMBER_OF_SAVEPOINTS: 0
NUMBER_OF_ROLLBACK_TO_SAVEPOINT: 0
    NUMBER_OF_RELEASE_SAVEPOINT: 0
          OBJECT_INSTANCE_BEGIN: NULL
               NESTING_EVENT_ID: 6
             NESTING_EVENT_TYPE: STATEMENT

Of the tables that contain transaction event rows, events_transactions_current is the most fundamental. Other tables that contain transaction event rows are logically derived from the current events. For example, the events_transactions_history and events_transactions_history_long tables are collections of the most recent transaction 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 transaction event tables, see Performance Schema Tables for Current and Historical Events.

For information about configuring whether to collect transaction events, see Section 10.7, “Performance Schema Transaction Tables”.

The events_transactions_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 from which the event was collected. 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.

• STATE

  The current transaction state. The value is ACTIVE (after START TRANSACTION or BEGIN), COMMITTED (after COMMIT), or ROLLED BACK (after ROLLBACK).

• TRX_ID

  Unused.

• GTID

  The GTID column contains the value of gtid_next, which can be one of ANONYMOUS, AUTOMATIC, or a GTID using the format UUID:NUMBER. For transactions that use gtid_next=AUTOMATIC, which is all normal client transactions, the GTID column changes when the transaction commits and the actual GTID is assigned. If gtid_mode is either ON or ON_PERMISSIVE, the GTID column changes to the transaction's GTID. If gtid_mode is either OFF or OFF_PERMISSIVE, the GTID column changes to ANONYMOUS.

• XID_FORMAT_ID, XID_GTRID, and XID_BQUAL

  The elements of the XA transaction identifier. They have the format described in XA Transaction SQL Statements.

• XA_STATE

  The state of the XA transaction. The value is ACTIVE (after XA START), IDLE (after XA END), PREPARED (after XA PREPARE), ROLLED BACK (after XA ROLLBACK), or COMMITTED (after XA COMMIT).

  On a replica, the same XA transaction can appear in the events_transactions_current table with different states on different threads. This is because immediately after the XA transaction is prepared, it is detached from the replication applier thread, and can be committed or rolled back by any thread on the replica. The events_transactions_current table displays the current status of the most recent monitored transaction event on the thread, and does not update this status when the thread is idle. So the XA transaction can still be displayed in the PREPARED state for the original applier thread, after it has been processed by another thread. To positively identify XA transactions that are still in the PREPARED state and need to be recovered, use the XA RECOVER statement rather than the Performance Schema transaction tables.

• 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”.

• ACCESS_MODE

  The transaction access mode. The value is READ WRITE or READ ONLY.

• ISOLATION_LEVEL

  The transaction isolation level. The value is REPEATABLE READ, READ COMMITTED, READ UNCOMMITTED, or SERIALIZABLE.

• AUTOCOMMIT

  Whether autcommit mode was enabled when the transaction started.

• NUMBER_OF_SAVEPOINTS, NUMBER_OF_ROLLBACK_TO_SAVEPOINT, NUMBER_OF_RELEASE_SAVEPOINT

  The number of SAVEPOINT, ROLLBACK TO SAVEPOINT, and RELEASE SAVEPOINT statements issued during the transaction.

• OBJECT_INSTANCE_BEGIN

  Unused.

• NESTING_EVENT_ID

  The EVENT_ID value of the event within which this event is nested.

• NESTING_EVENT_TYPE

  The nesting event type. The value is TRANSACTION, STATEMENT, STAGE, or WAIT. (TRANSACTION does not appear because transactions cannot be nested.)

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