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13.7.6.29 SHOW PROCESSLIST Syntax

Inhoudsopgave
  1. SHOW [FULL] PROCESSLIST

SHOW PROCESSLIST shows which threads are running. If you have the PROCESS privilege, you can see all threads. Otherwise, you can see only your own threads (that is, threads associated with the MySQL account that you are using). If you do not use the FULL keyword, only the first 100 characters of each statement are shown in the Info field.

The SHOW PROCESSLIST statement is very useful if you get the “too many connections” error message and want to find out what is going on. MySQL reserves one extra connection to be used by accounts that have the CONNECTION_ADMIN or SUPER privilege, to ensure that administrators should always be able to connect and check the system (assuming that you are not giving this privilege to all your users).

Threads can be killed with the KILL statement. See Section 13.7.7.4, “KILL Syntax”.

Example of SHOW PROCESSLIST output:

  1. mysql> SHOW FULL PROCESSLIST\G
  2. *************************** 1. row ***************************
  3. Id: 1
  4. User: system user
  5. Host:
  6. db: NULL
  7. Command: Connect
  8. Time: 1030455
  9. State: Waiting for master to send event
  10. Info: NULL
  11. *************************** 2. row ***************************
  12. Id: 2
  13. User: system user
  14. Host:
  15. db: NULL
  16. Command: Connect
  17. Time: 1004
  18. State: Has read all relay log; waiting for the slave
  19.        I/O thread to update it
  20. Info: NULL
  21. *************************** 3. row ***************************
  22. Id: 3112
  23. User: replikator
  24. Host: artemis:2204
  25. db: NULL
  26. Command: Binlog Dump
  27. Time: 2144
  28. State: Has sent all binlog to slave; waiting for binlog to be updated
  29. Info: NULL
  30. *************************** 4. row ***************************
  31. Id: 3113
  32. User: replikator
  33. Host: iconnect2:45781
  34. db: NULL
  35. Command: Binlog Dump
  36. Time: 2086
  37. State: Has sent all binlog to slave; waiting for binlog to be updated
  38. Info: NULL
  39. *************************** 5. row ***************************
  40. Id: 3123
  41. User: stefan
  42. Host: localhost
  43. db: apollon
  44. Command: Query
  45. Time: 0
  46. State: NULL
  47. Info: SHOW FULL PROCESSLIST
  48. 5 rows in set (0.00 sec)

SHOW PROCESSLIST output has these columns:

  • Id

    The connection identifier. This is the same type of value displayed in the ID column of the INFORMATION_SCHEMA PROCESSLIST table, the PROCESSLIST_ID column of the Performance Schema threads table, and returned by the CONNECTION_ID() function.

  • User

    The MySQL user who issued the statement. A value of system user refers to a nonclient thread spawned by the server to handle tasks internally. This could be the I/O or SQL thread used on replication slaves or a delayed-row handler. For system user, there is no host specified in the Host column. unauthenticated user refers to a thread that has become associated with a client connection but for which authentication of the client user has not yet been done. event_scheduler refers to the thread that monitors scheduled events (see Section 24.4, “Using the Event Scheduler”).

    Note

    A User value of system user is distinct from the SYSTEM_USER privilege. The former designates internal threads. The latter distinguishes the system user and regular user account categories (see Section 6.2.11, “Account Categories”).

  • Host

    The host name of the client issuing the statement (except for system user, for which there is no host). The host name for TCP/IP connections is reported in host_name:client_port format to make it easier to determine which client is doing what.

  • db

    The default database, if one is selected; otherwise NULL.

  • Command

    The type of command the thread is executing. For descriptions for thread commands, see Section 8.14, “Examining Thread Information”. The value of this column corresponds to the COM_xxx commands of the client/server protocol and Com_xxx status variables. See Section 5.1.10, “Server Status Variables”.

  • Time

    The time in seconds that the thread has been in its current state. For a slave SQL thread, the value is the number of seconds between the timestamp of the last replicated event and the real time of the slave machine. See Section 17.2.2, “Replication Implementation Details”.

  • State

    An action, event, or state that indicates what the thread is doing. Descriptions for State values can be found at Section 8.14, “Examining Thread Information”.

    Most states correspond to very quick operations. If a thread stays in a given state for many seconds, there might be a problem that needs to be investigated.

    For the SHOW PROCESSLIST statement, the value of State is NULL.

  • Info

    The statement the thread is executing, or NULL if it is not executing any statement. The statement might be the one sent to the server, or an innermost statement if the statement executes other statements. For example, if a CALL statement executes a stored procedure that is executing a SELECT statement, the Info value shows the SELECT statement.

Process information is also available from the mysqladmin processlist command, the INFORMATION_SCHEMA PROCESSLIST table, and the Performance Schema threads table (see Section 4.5.2, “mysqladmin — Client for Administering a MySQL Server”, Section 25.19, “The INFORMATION_SCHEMA PROCESSLIST Table”, and Section 26.12.18.5, “The threads Table”). In contrast to the INFORMATION_SCHEMA PROCESSLIST table and SHOW PROCESSLIST statement, which have negative performance consequences because they require a mutex, access to threads does not require a mutex and has minimal impact on server performance. The threads table also shows information about background threads, which the PROCESSLIST table and SHOW PROCESSLIST do not. This means that threads can be used to monitor activity the other thread information sources cannot.


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