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 18.104.22.168, “SHOW PROCESSLIST Syntax”
Section 20.16, “The 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 mutex.
threads also shows information
about background threads, which
SHOW PROCESSLIST do not. This
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
Each process list entry contains several pieces of information:
Id is the connection identifier for the
client associated with the thread.
the account associated with the thread.
db is the default database for the
NULL if none is selected.
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.
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
= . 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
Info contains the text of the statement
being executed by the thread, or
it is not executing one. By default, this value contains
only the first 100 characters of the statement. To see the
complete statements, use
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.