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:
SHOW [FULL] PROCESSLIST statement: Section
SHOW PROCESSLIST Syntax"
PROCESSLIST table: Section
INFORMATION_SCHEMA PROCESSLIST Table"
threads does not require a mutex and has minimal impact on server performance.
SHOW PROCESSLIST have negative performance consequences because they require a
threads also shows information about background threads, which
SHOW PROCESSLIST do not. This means that
threads can be used to monitor activity the other thread information sources
You can always view information about your own threads. To view information about threads being executed for
other accounts, you must have the
Each process list entry contains several pieces of information:
Id is the connection identifier for the client
associated with the thread.
Host indicate the
account associated with the thread.
db is the default database for the thread, or
NULL if none is selected.
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.
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 = . 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.
Info contains the text of the statement being executed
by the thread, or
NULL if it is not executing one. By default, this value
contains only the first 100 characters of the statement. To see the complete statements, use
SHOW FULL PROCESSLIST.
The following sections list the possible
Command values, and
values grouped by category. The meaning for some of these values is self-evident. For others, additional
description is provided.