Terminating Queries and Disconnecting Sessions: KILL Command Guide

The KILL command cancels a running query or disconnects a specified session. Before using it, obtain the identifier of the target query (Query ID, Connection ID, or Trace ID), then execute the corresponding KILL statement.

Obtain Query Identifiers

The KILL command supports the following three query identifiers:

Identifier Type	Description	How to Obtain
Query ID	A unique identifier that the system automatically generates for each query	SHOW PROCESSLIST or information_schema.processlist
Connection ID	A unique identifier of a session connection	SHOW PROCESSLIST or information_schema.processlist
Trace ID	A user-defined query identifier (supported from 2.1.11 / 3.0.7)	Set through the session_context variable

View Through PROCESSLIST

SHOW PROCESSLIST displays all current session connections and the queries they are running, including Query ID and Connection ID.

SHOW PROCESSLIST;

Example output:

+------------------+------+------+---------------------+---------------------+----------+------+---------+------+-------+----------------------------------+------------------+---------------+--------------+
| CurrentConnected | Id   | User | Host                | LoginTime           | Catalog  | Db   | Command | Time | State | QueryId                          | Info             | FE            | CloudCluster |
+------------------+------+------+---------------------+---------------------+----------+------+---------+------+-------+----------------------------------+------------------+---------------+--------------+
| No               |    2 | root | 172.20.32.136:54850 | 2025-05-11 10:41:52 | internal |      | Query   |    6 | OK    | 12ccf7f95c1c4d2c-b03fa9c652757c15| select sleep(20) | 172.20.32.152 | NULL         |
| Yes              |    3 | root | 172.20.32.136:54862 | 2025-05-11 10:41:55 | internal |      | Query   |    0 | OK    | b710ed990d4144ee-8b15bb53002b7710| show processlist | 172.20.32.152 | NULL         |
| No               |    1 | root | 172.20.32.136:47964 | 2025-05-11 10:41:54 | internal |      | Sleep   |   11 | EOF   | b60daa992bac4fe4-b29466aacce67d27|                  | 172.20.32.153 | NULL         |
+------------------+------+------+---------------------+---------------------+----------+------+---------+------+-------+----------------------------------+------------------+---------------+--------------+

Key field descriptions:

• CurrentConnected: Yes indicates the connection that corresponds to the current session.
• Id: Connection ID, the unique identifier of the connection.
• QueryId: Query ID, the unique identifier of the most recently executed or currently running SQL.

Default behavior: SHOW PROCESSLIST only displays sessions on the FE node that the current connection is attached to, and does not include other FE nodes. To view sessions on all FE nodes, set the following variable before running the query:

SET show_all_fe_connection = true;
SHOW PROCESSLIST;

You can also use the information_schema system table, which displays sessions on all FE nodes by default and requires no additional setup:

SELECT * FROM information_schema.processlist;

Identify Queries by Trace ID

This feature is supported from versions 2.1.11 and 3.0.7.

A Trace ID is a custom identifier that you assign to a query in advance. It lets a management tool record the unique identifier of a query before submission, so the query can be canceled at any time by Trace ID afterward.

Set the Trace ID for the current session as follows:

SET session_context = "trace_id:your_trace_id";

• your_trace_id: A custom string that must not contain the ; character. A UUID is recommended to ensure uniqueness.
• The Trace ID is a session-level parameter and only applies to the current session. Once set, all subsequent queries in this session map to this Trace ID.

You can also set it through a Hint on a single query statement, without modifying the session variable:

SELECT /*+SET_VAR(session_context=trace_id:your_trace_id)*/ * FROM table ...;

Execute the KILL Operation

Permission notes: Regular users can only terminate queries that they submitted themselves. ADMIN users can terminate queries of any user.

Kill a Query

KILL QUERY cancels a specified running query without disconnecting the session.

KILL QUERY "query_id" | "trace_id" | connection_id;

Comparison of the three forms:

Parameter Type	Example	Scope
"query_id"	KILL QUERY "d36417cc05ff41ab-9d3afe49be251055";	Searches all FE nodes and cancels the matching query
"trace_id"	KILL QUERY "your_trace_id";	Searches all FE nodes and cancels the matching query
connection_id	KILL QUERY 55;	Only cancels the query running on this connection, on the FE node that the current connection is attached to

Notes:

• Query ID and Trace ID must be enclosed in quotation marks. Connection ID must be an integer greater than 0 and must not be enclosed in quotation marks.
• KILL QUERY by Connection ID only takes effect on the FE node that the current connection is attached to.

Kill a Connection

KILL CONNECTION disconnects a specified session and also cancels the query running on that connection.

KILL [CONNECTION] connection_id;

The CONNECTION keyword can be omitted. The following two forms are equivalent:

KILL CONNECTION 55;
KILL 55;

Note: Connection IDs on different FE nodes may collide. This operation only takes effect on the FE node that the current connection is attached to.

Best Practice: Manage Queries by Trace ID

In a management system or business platform, using Trace IDs is recommended for marking queries in advance and canceling them precisely. The workflow is:

1. Before submitting the query, generate a unique Trace ID (UUID recommended) and bind it to the query.
2. While the query is running, the system can issue a KILL request at any time through the Trace ID.

There are two ways to bind the Trace ID:

• Set the session variable before the query (suitable for single-connection scenarios):

  SET session_context = "trace_id:your_trace_id";
  SELECT * FROM table ...;

• Embed a Hint in the query statement (suitable for connection-pool reuse scenarios):

  SELECT /*+SET_VAR(session_context=trace_id:your_trace_id)*/ * FROM table ...;

Once bound, cancel the query at any time with the following command:

KILL QUERY "your_trace_id";