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
CONNECTION_ADMIN
privilege and
the deprecated SUPER
privilege:
Without
CONNECTION_ADMIN
orSUPER
, you can kill only your own threads and statements.With
CONNECTION_ADMIN
orSUPER
, you can kill all threads and statements, except that to affect a thread or statement that is executing with theSYSTEM_USER
privilege, your own session must additionally have theSYSTEM_USER
privilege.
You can also use the mysqladmin processlist and mysqladmin kill commands to examine and kill threads.
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.
EXPLAIN ANALYZE
aborts and prints the first row of output.
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).