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8.14 Examining Thread Information
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When you are attempting to ascertain what your MySQL server is doing, it can be helpful to examine the process list, which is the set of threads currently executing within the server. Process list information is available from these sources:
The
SHOW [FULL] PROCESSLISTstatement: Section 13.7.6.29, “SHOW PROCESSLIST Syntax”The
SHOW PROFILEstatement: Section 13.7.6.31, “SHOW PROFILES Syntax”The
INFORMATION_SCHEMAPROCESSLISTtable: Section 25.19, “The INFORMATION_SCHEMA PROCESSLIST Table”The mysqladmin processlist command: Section 4.5.2, “mysqladmin — Client for Administering a MySQL Server”
The Performance Schema
threadstable, stage tables, and lock tables: Section 26.12.18, “Performance Schema Miscellaneous Tables”, Section 26.12.5, “Performance Schema Stage Event Tables”, Section 26.12.12, “Performance Schema Lock Tables”.
Access to threads does not require a
mutex and has minimal impact on server performance.
INFORMATION_SCHEMA.PROCESSLIST and
SHOW PROCESSLIST have negative
performance consequences because they require a mutex.
threads also shows information about
background threads, which
INFORMATION_SCHEMA.PROCESSLIST and
SHOW PROCESSLIST do not. This means
that threads can be used to monitor
activity the other thread information sources cannot.
You can always view information about your own threads. To view
information about threads being executed for other accounts, you
must have the PROCESS privilege.
Each process list entry contains several pieces of information:
Idis the connection identifier for the client associated with the thread.UserandHostindicate the account associated with the thread.dbis the default database for the thread, orNULLif none is selected.CommandandStateindicate 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.
Timeindicates 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 withSET TIMESTAMP =. For a thread running on a slave that is processing events from the master, the thread time is set to the time found in the events and thus reflects current time on the master and not the slave.valueInfocontains the text of the statement being executed by the thread, orNULLif it is not executing one. By default, this value contains only the first 100 characters of the statement. To see the complete statements, useSHOW FULL PROCESSLIST.The
sysschemaprocesslistview, which presents information from the Performance Schemathreadstable in a more accessible format: Section 27.4.3.22, “The processlist and x$processlist Views”The
sysschemasessionview, which presents information about user sessions (like thesysschemaprocesslistview, but with background processes filtered out): Section 27.4.3.33, “The session and x$session Views”
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.
Document created the 26/06/2006, last modified the 26/10/2018
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