KILL [CONNECTION | QUERY] thread_id

每个与mysqld的连接都在一个独立的线程里运行，您可以使用SHOW PROCESSLIST语句查看哪些线程正在运行，并使用KILL thread_id语句终止一个线程。

KILL允许自选的CONNECTION或QUERY修改符：

·  KILL CONNECTION与不含修改符的KILL一样：它会终止与给定的thread_id有关的连接。

·  KILL QUERY会终止连接当前正在执行的语句，但是会保持连接的原状。

如果您拥有PROCESS权限，则您可以查看所有线程。如果您拥有SUPER权限，您可以终止所有线程和语句。否则，您只能查看和终止您自己的线程和语句。

您也可以使用mysqladmin processlist和mysqladmin kill命令来检查和终止线程。

注释：您不能同时使用KILL和Embedded MySQL Server库，因为内植的服务器只运行主机应用程序的线程。它不能创建任何自身的连接线程。

当您进行一个KILL时，对线程设置一个特有的终止标记。在多数情况下，线程终止可能要花一些时间，这是因为终止标记只会在在特定的间隔被检查：

·  在SELECT, ORDER BY和GROUP BY循环中，在读取一组行后检查标记。如果设置了终止标记，则该语句被放弃。

·  在ALTER TABLE过程中，在每组行从原来的表中被读取前，检查终止标记。如果设置了终止标记，则语句被放弃，临时表被删除。

·  在UPDATE或DELETE运行期间，在每个组读取之后以及每个已更行或已删除的行之后，检查终止标记。如果终止标记被设置，则该语句被放弃。注意，如果您正在使用事务，则变更不会被 回滚。

·  GET_LOCK()会放弃和返回NULL。

·  INSERT DELAYED线程会快速地刷新（插入）它在存储器中的所有的行，然后终止。

·  如果线程在表锁定管理程序中（状态：锁定），则表锁定被快速地放弃。

·  如果在写入调用中，线程正在等待空闲的磁盘空间，则写入被放弃，并伴随"disk full"错误消息。

·  警告：对MyISAM表终止一个REPAIR TABLE或OPTIMIZE TABLE操作会导致出现一个被损坏的没有用的表。对这样的表的任何读取或写入都会失败，直到您再次优化或修复它（不中断）。

下面MySQL5.6的官方说明：

http://dev.mysql.com/doc/refman/5.6/en/kill.html

KILL [CONNECTION | QUERY] processlist_id

Each connection to mysqld runs in a separate thread. You can kill a thread with the KILL processlist_id statement.

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.

If you have the PROCESS privilege, you can see all threads. If you have the SUPER privilege, you can kill all threads and statements. Otherwise, you can see and kill only your own threads and statements.

You can also use the mysqladmin processlist and mysqladmin kill commands to examine and kill threads.

Note

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.

During ALTER TABLE operations, the kill flag is checked before each block of rows are read from the original table. If the kill flag was set, the statement is aborted and the temporary table is deleted.

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.

Warning

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).