Amazon Redshift will no longer support the creation of new Python UDFs starting Patch 198. Existing Python UDFs will continue to function until June 30, 2026. For more information, see the [ blog post ](https://amazonaws-china.com/blogs/big-data/amazon-redshift-python-user-defined-functions-will-reach-end-of-support-after-june-30-2026/). 

# PG\$1CANCEL\$1BACKEND
<a name="PG_CANCEL_BACKEND"></a>

Cancels a query. PG\$1CANCEL\$1BACKEND is functionally equivalent to the [CANCEL](r_CANCEL.md) command. You can cancel queries currently being run by your user. Superusers can cancel any query.

## Syntax
<a name="PG_CANCEL_BACKEND-synopsis"></a>

```
pg_cancel_backend( pid )
```

## Arguments
<a name="PG_CANCEL_BACKEND-arguments"></a>

 *pid*   
The process ID (PID) of the query to be canceled. You cannot cancel a query by specifying a query ID; you must specify the query's process ID. Requires an `INTEGER` value.

## Return type
<a name="PG_CANCEL_BACKEND-return-type"></a>

None

## Usage notes
<a name="PG_CANCEL_BACKEND-usage-notes"></a>

If queries in multiple sessions hold locks on the same table, you can use the [PG\$1TERMINATE\$1BACKEND](PG_TERMINATE_BACKEND.md) function to terminate one of the sessions, which forces any currently running transactions in the terminated session to release all locks and roll back the transaction. Query the PG\$1\$1LOCKS catalog table to view currently held locks. If you cannot cancel a query because it is in transaction block (BEGIN … END), you can terminate the session in which the query is running by using the PG\$1TERMINATE\$1BACKEND function. 

## Examples
<a name="PG_CANCEL_BACKEND-example"></a>

To cancel a currently running query, first retrieve the process ID for the query that you want to cancel. To determine the process IDs for all currently running queries, run the following command. 

```
SELECT pid, TRIM(starttime) AS start, 
duration, TRIM(user_name) AS user,
SUBSTRING(query,1,40) AS querytxt
FROM stv_recents
WHERE status = 'Running';

+-----+------------------------+----------+--------+-----------------------------+
| pid |       starttime        | duration |  user  |          querytxt           |
+-----+------------------------+----------+--------+-----------------------------+
| 802 | 2013-10-14 09:19:03.55 |      132 | dwuser | select venuename from venue |
| 834 | 2013-10-14 08:33:49.47 |  1250414 | dwuser | select * from listing;      |
| 964 | 2013-10-14 08:30:43.29 |   326179 | dwuser | select sellerid from sales  |
+-----+------------------------+----------+--------+-----------------------------+
```

To cancel the query with process ID 802, use the following example.

```
SELECT PG_CANCEL_BACKEND(802);
```