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25.19 The INFORMATION_SCHEMA PROCESSLIST Table

Inhoudsopgave

The PROCESSLIST table provides information about which threads are running.

The PROCESSLIST table has these columns:

  • ID

    The connection identifier. This is the same type of value displayed in the Id column of the SHOW PROCESSLIST statement, 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.

Notes

  • The PROCESSLIST table is a nonstandard INFORMATION_SCHEMA table.

  • Like the output from the SHOW PROCESSLIST statement, the PROCESSLIST table shows information only about your own threads, unless you have the PROCESS privilege, in which case you will see information about other threads, too. As an anonymous user, you cannot see any rows at all.

  • If an SQL statement refers to the PROCESSLIST table, MySQL populates the entire table once, when statement execution begins, so there is read consistency during the statement. There is no read consistency for a multi-statement transaction.

Process information is also available from the mysqladmin processlist command, the SHOW PROCESSLIST statement, and the Performance Schema threads table (see Section 4.5.2, “mysqladmin — Client for Administering a MySQL Server”, Section 13.7.6.29, “SHOW PROCESSLIST Syntax”, 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.

The following statements are equivalent:

  1. SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST
  2.  
  3. SHOW FULL PROCESSLIST

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Document heeft de 26/06/2006 gemaakt, de laatste keer de 26/10/2018 gewijzigd
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  1. Bekijk - html-document Taal van het document:en Manuel MySQL : https://dev.mysql.com/

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Inhoudsopgave Haut