MySQL :: MySQL 8.0 Reference Manual :: 15.7.8.4 KILL Statement (original) (raw)

15.7.8.4 KILL Statement

KILL [CONNECTION | QUERY] processlist_id

Each connection to mysqld runs in a separate thread. You can kill a thread with the KILL_`processlistid`_ statement.

Thread processlist identifiers can be determined from theID column of theINFORMATION_SCHEMA PROCESSLIST table, theId column of SHOW PROCESSLIST output, and thePROCESSLIST_ID column of the Performance Schema threads table. The value for the current thread is returned by theCONNECTION_ID() function.

KILL permits an optionalCONNECTION or QUERY modifier:

• KILL CONNECTION is the same asKILL with no modifier: It terminates the connection associated with the given_processlistid_, 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:

• Without PROCESS, you can see only your own threads.
• With PROCESS, you can see all threads.

The ability to kill threads and statements depends on theCONNECTION_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 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 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. This works in MySQL 8.0.20 and later.

Warning

Killing a REPAIR TABLE orOPTIMIZE TABLE operation on aMyISAM 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).