SHOW [FULL] PROCESSLIST
SHOW PROCESSLIST shows you which
threads are running. You can also get this information from the
INFORMATION_SCHEMA
PROCESSLIST table or the
mysqladmin processlist command. If you have
the PROCESS privilege, you can
see all threads. Otherwise, you can see only your own threads
(that is, threads associated with the MySQL account that you are
using). If you do not use the FULL keyword,
only the first 100 characters of each statement are shown in the
Info field.
Process information is also available from the
performance_schema.threads table.
However, 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.
The SHOW PROCESSLIST statement is
very useful if you get the “too many connections”
error message and want to find out what is going on. MySQL
reserves one extra connection to be used by accounts that have
the SUPER privilege, to ensure
that administrators should always be able to connect and check
the system (assuming that you are not giving this privilege to
all your users).
Threads can be killed with the
KILL statement. See
Section 13.7.6.4, “KILL Syntax”.
Here is an example of SHOW
PROCESSLIST output:
mysql> SHOW FULL PROCESSLIST\G
*************************** 1. row ***************************
Id: 1
User: system user
Host:
db: NULL
Command: Connect
Time: 1030455
State: Waiting for master to send event
Info: NULL
*************************** 2. row ***************************
Id: 2
User: system user
Host:
db: NULL
Command: Connect
Time: 1004
State: Has read all relay log; waiting for the slave
I/O thread to update it
Info: NULL
*************************** 3. row ***************************
Id: 3112
User: replikator
Host: artemis:2204
db: NULL
Command: Binlog Dump
Time: 2144
State: Has sent all binlog to slave; waiting for binlog to be updated
Info: NULL
*************************** 4. row ***************************
Id: 3113
User: replikator
Host: iconnect2:45781
db: NULL
Command: Binlog Dump
Time: 2086
State: Has sent all binlog to slave; waiting for binlog to be updated
Info: NULL
*************************** 5. row ***************************
Id: 3123
User: stefan
Host: localhost
db: apollon
Command: Query
Time: 0
State: NULL
Info: SHOW FULL PROCESSLIST
5 rows in set (0.00 sec)
The columns produced by SHOW
PROCESSLIST have the following meanings:
The connection identifier. This is the same type of value
displayed in the ID column of the
INFORMATION_SCHEMA.PROCESSLIST
table, the PROCESSLIST_ID column of the
Performance Schema threads
table, and returned by the
CONNECTION_ID() function.
The MySQL user who issued the statement. If this is
system user, it 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. 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. For system
user, there is no host specified in the
Host column.
The host name of the client issuing the statement (except
for system user where there is no host).
SHOW PROCESSLIST reports the
host name for TCP/IP connections in
host_name:client_port
The default database, if one is selected, otherwise
NULL.
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_
commands of the client/server protocol and
xxxCom_ status
variables. See Section 5.1.7, “Server Status Variables”
xxx
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 17.2.1, “Replication Implementation Details”.
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.
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.