MySQL 9.0 Reference Manual Including MySQL NDB Cluster 9.0

29.12.22.8 The threads Table

The threads table contains a row for each server thread. Each row contains information about a thread and indicates whether monitoring and historical event logging are enabled for it: 

mysql> SELECT * FROM performance_schema.threads\G
*************************** 1. row ***************************
            THREAD_ID: 1
                 NAME: thread/sql/main
                 TYPE: BACKGROUND
       PROCESSLIST_ID: NULL
     PROCESSLIST_USER: NULL
     PROCESSLIST_HOST: NULL
       PROCESSLIST_DB: mysql
  PROCESSLIST_COMMAND: NULL
     PROCESSLIST_TIME: 418094
    PROCESSLIST_STATE: NULL
     PROCESSLIST_INFO: NULL
     PARENT_THREAD_ID: NULL
                 ROLE: NULL
         INSTRUMENTED: YES
              HISTORY: YES
      CONNECTION_TYPE: NULL
         THREAD_OS_ID: 5856
       RESOURCE_GROUP: SYS_default
     EXECUTION_ENGINE: PRIMARY
    CONTROLLED_MEMORY: 1456
MAX_CONTROLLED_MEMORY: 67480
         TOTAL_MEMORY: 1270430
     MAX_TOTAL_MEMORY: 1307317
     TELEMETRY_ACTIVE: NO
...

When the Performance Schema initializes, it populates the threads table based on the threads in existence then. Thereafter, a new row is added each time the server creates a thread.

The INSTRUMENTED and HISTORY column values for new threads are determined by the contents of the setup_actors table. For information about how to use the setup_actors table to control these columns, see Section 29.4.6, “Pre-Filtering by Thread”.

Removal of rows from the threads table occurs when threads end. For a thread associated with a client session, removal occurs when the session ends. If a client has auto-reconnect enabled and the session reconnects after a disconnect, the session becomes associated with a new row in the threads table that has a different PROCESSLIST_ID value. The initial INSTRUMENTED and HISTORY values for the new thread may be different from those of the original thread: The setup_actors table may have changed in the meantime, and if the INSTRUMENTED or HISTORY value for the original thread was changed after the row was initialized, the change does not carry over to the new thread.

You can enable or disable thread monitoring (that is, whether events executed by the thread are instrumented) and historical event logging. To control the initial INSTRUMENTED and HISTORY values for new foreground threads, use the setup_actors table. To control these aspects of existing threads, set the INSTRUMENTED and HISTORY columns of threads table rows. (For more information about the conditions under which thread monitoring and historical event logging occur, see the descriptions of the INSTRUMENTED and HISTORY columns.)

For a comparison of the threads table columns with names having a prefix of PROCESSLIST_ to other process information sources, see Sources of Process Information.

Important

For thread information sources other than the threads table, information about threads for other users is shown only if the current user has the PROCESS privilege. That is not true of the threads table; all rows are shown to any user who has the SELECT privilege for the table. Users who should not be able to see threads for other users by accessing the threads table should not be given the SELECT privilege for it.

The threads table has these columns:

The threads table has these indexes:

TRUNCATE TABLE is not permitted for the threads table.

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