8.14.1 Accessing the Process List

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The following discussion enumerates the sources of process information, the privileges required to see process information, and describes the content of process list entries.

Sources of Process Information

Process information is available from these sources:

The SHOW PROCESSLIST statement: Section 13.7.7.29, “SHOW PROCESSLIST Statement”
The mysqladmin processlist command: Section 4.5.2, “mysqladmin — A MySQL Server Administration Program”
The INFORMATION_SCHEMA PROCESSLIST table: Section 26.3.23, “The INFORMATION_SCHEMA PROCESSLIST Table”
The Performance Schema processlist table: Section 27.12.21.5, “The processlist Table”
The Performance Schema threads table columns with names having a prefix of PROCESSLIST_: Section 27.12.21.6, “The threads Table”
The sys schema processlist and session views: Section 28.4.3.22, “The processlist and x$processlist Views”, and Section 28.4.3.33, “The session and x$session Views”

The threads table compares to SHOW PROCESSLIST, INFORMATION_SCHEMA PROCESSLIST, and mysqladmin processlist as follows:

Access to the threads table does not require a mutex and has minimal impact on server performance. The other sources have negative performance consequences because they require a mutex.

Note

As of MySQL 8.0.22, an alternative implementation for SHOW PROCESSLIST is available based on the Performance Schema processlist table, which, like the threads table, does not require a mutex and has better performance characteristics. For details, see Section 27.12.21.5, “The processlist Table”.
The threads table displays background threads, which the other sources do not. It also provides additional information for each thread that the other sources do not, such as whether the thread is a foreground or background thread, and the location within the server associated with the thread. This means that the threads table can be used to monitor thread activity the other sources cannot.
You can enable or disable Performance Schema thread monitoring, as described in Section 27.12.21.6, “The threads Table”.

For these reasons, DBAs who perform server monitoring using one of the other thread information sources may wish to monitor using the threads table instead.

The sys schema processlist view presents information from the Performance Schema threads table in a more accessible format. The sys schema session view presents information about user sessions like the sys schema processlist view, but with background processes filtered out.

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Privileges Required to Access the Process List

For most sources of process information, if you have the PROCESS privilege, you can see all threads, even those belonging to other users. Otherwise (without the PROCESS privilege), nonanonymous users have access to information about their own threads but not threads for other users, and anonymous users have no access to thread information.

The Performance Schema threads table also provides thread information, but table access uses a different privilege model. See Section 27.12.21.6, “The threads Table”.

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Content of Process List Entries

Each process list entry contains several pieces of information. The following list describes them using the labels from SHOW PROCESSLIST output. Other process information sources use similar labels.

Id is the connection identifier for the client associated with the thread.
User and Host indicate the account associated with the thread.
db is the default database for the thread, or NULL if none has been selected.
Command and State indicate what the thread is doing.
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.
The following sections list the possible Command values, and State values grouped by category. The meaning for some of these values is self-evident. For others, additional description is provided.

Note

Applications that examine process list information should be aware that the commands and states are subject to change.
Time indicates how long the thread has been in its current state. The thread's notion of the current time may be altered in some cases: The thread can change the time with SET TIMESTAMP = value. For a replica SQL thread, the value is the number of seconds between the timestamp of the last replicated event and the real time of the replica host. See Section 17.2.3, “Replication Threads”.
Info indicates the statement the thread is executing, or NULL if it is executing no statement. For SHOW PROCESSLIST, this value contains only the first 100 characters of the statement. To see complete statements, use SHOW FULL PROCESSLIST (or query a diffferent process information source).

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Dokument erstellt 26/06/2006, zuletzt geändert 26/10/2018
Quelle des gedruckten Dokuments:https://www.gaudry.be/de/mysql-rf-processlist-access.html

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