update description about compatible-kill-query configuration (#13491) (…

…#13514)

tidb-configuration-file.md

@@ -78,8 +78,12 @@ The TiDB configuration file supports more options than command-line parameters.
 
 + Determines whether to set the `KILL` statement to be MySQL compatible.
 + Default value: `false`
-+ The behavior of `KILL xxx` in TiDB differs from the behavior in MySQL. TiDB requires the `TIDB` keyword, namely, `KILL TIDB xxx`. If `compatible-kill-query` is set to `true`, the `TIDB` keyword is not needed.
-+ This distinction is important because the default behavior of the MySQL command-line client, when the user hits <kbd>Ctrl</kbd>+<kbd>C</kbd>, is to create a new connection to the backend and execute the `KILL` statement in that new connection. If a load balancer or proxy has sent the new connection to a different TiDB server instance than the original session, the wrong session could be terminated, which could cause interruption to applications using the cluster. Enable `compatible-kill-query` only if you are certain that the connection you refer to in your `KILL` statement is on the same server to which you send the `KILL` statement.
++ `compatible-kill-query` takes effect only when [`enable-global-kill`](#enable-global-kill-new-in-v610) is set to `false`.
++ When [`enable-global-kill`](#enable-global-kill-new-in-v610) is `false`, `compatible-kill-query` controls whether you need to append the `TIDB` keyword when killing a query.
+    - When `compatible-kill-query` is `false`, the behavior of `KILL xxx` in TiDB is different from that in MySQL. To kill a query in TiDB, you need to append the `TIDB` keyword, such as `KILL TIDB xxx`.
+    - When `compatible-kill-query` is `true`, to kill a query in TiDB, there is no need to append the `TIDB` keyword. It is **STRONGLY NOT RECOMMENDED** to set `compatible-kill-query` to `true` in your configuration file UNLESS you are certain that clients will be always connected to the same TiDB instance. This is because pressing <kbd>Control</kbd>+<kbd>C</kbd> in the default MySQL client opens a new connection in which `KILL` is executed. If there is a proxy between the client and the TiDB cluster, the new connection might be routed to a different TiDB instance, which possibly kills a different session by mistake.
++ When [`enable-global-kill`](#enable-global-kill-new-in-v610) is `true`, `KILL xxx` and `KILL TIDB xxx` have the same effect, but using <kbd>Control</kbd>+<kbd>C</kbd> to kill a query is not supported.
++ For more information about the `KILL` statement, see [KILL [TIDB]](/sql-statements/sql-statement-kill.md).
 
 ### `check-mb4-value-in-utf8`