MySQL 5.6 Reference Manual Including MySQL NDB Cluster 7.3-7.4 Reference Guide
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 as
KILL
with no modifier: It
terminates the connection associated with the given
processlist_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, for
ORDER BY
and GROUP 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
or
DELETE
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 returns
NULL
.
An INSERT DELAYED
thread
quickly flushes (inserts) all rows it has in memory and then
terminates.
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).