13.7.6.4 KILL Statement
KILL [CONNECTION | QUERY] processlist_id
Each connection to mysqld runs in a separate thread. You can kill a thread with the KILL
statement. processlist_id
Thread processlist identifiers can be determined from the ID
column of the INFORMATION_SCHEMA
PROCESSLIST
table, the Id
column of SHOW PROCESSLIST
output, and the PROCESSLIST_ID
column of the Performance Schema threads
table. The value for the current thread is returned by the CONNECTION_ID()
function.
KILL
permits an optional CONNECTION
or QUERY
modifier:
KILL CONNECTION
is the same asKILL
with no modifier: It terminates the connection associated with the givenprocesslist_id
, after terminating any statement the connection is executing.KILL QUERY
terminates the statement the connection is currently executing, but leaves the connection itself intact.
The ability to see which threads are available to be killed depends on the PROCESS
privilege:
The ability to kill threads and statements depends on the SUPER
privilege:
You can also use the mysqladmin processlist and mysqladmin kill commands to examine and kill threads.
You cannot use KILL
with the Embedded MySQL Server library because the embedded server merely runs inside the threads of the host application. It does not create any connection threads of its own.
When you use KILL
, a thread-specific kill flag is set for the thread. In most cases, it might take some time for the thread to die because the kill flag is checked only at specific intervals:
During
SELECT
operations, forORDER BY
andGROUP BY
loops, the flag is checked after reading a block of rows. If the kill flag is set, the statement is aborted.ALTER TABLE
operations that make a table copy check the kill flag periodically for each few copied rows read from the original table. If the kill flag was set, the statement is aborted and the temporary table is deleted.The
KILL
statement returns without waiting for confirmation, but the kill flag check aborts the operation within a reasonably small amount of time. Aborting the operation to perform any necessary cleanup also takes some time.During
UPDATE
orDELETE
operations, the kill flag is checked after each block read and after each updated or deleted row. If the kill flag is set, the statement is aborted. If you are not using transactions, the changes are not rolled back.GET_LOCK()
aborts and returnsNULL
.If the thread is in the table lock handler (state:
Locked
), the table lock is quickly aborted.If the thread is waiting for free disk space in a write call, the write is aborted with a “disk full” error message.
Killing a REPAIR TABLE
or OPTIMIZE TABLE
operation on a MyISAM
table results in a table that is corrupted and unusable. Any reads or writes to such a table fail until you optimize or repair it again (without interruption).