> ## Documentation Index
> Fetch the complete documentation index at: https://docs.risingwave.com/llms.txt
> Use this file to discover all available pages before exploring further.

# ALTER FRAGMENT

> The `ALTER FRAGMENT` command modifies the configuration of streaming fragments at runtime.

## Syntax

```sql theme={null}
ALTER FRAGMENT fragment_id [, ...]
    alter_option;
```

*`alter_option`* depends on the operation you want to perform on the fragment.

## Clauses

### `SET PARALLELISM`

```sql theme={null}
ALTER FRAGMENT fragment_id [, ...]
SET PARALLELISM { TO | = } { parallelism_number | ADAPTIVE | DEFAULT };
```

| Parameter or clause   | Description                                                                                                                                                                                                                                                                                      |
| :-------------------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **SET PARALLELISM**   | This clause controls the degree of [parallelism](/reference/key-concepts#parallelism) for specific streaming [fragments](/reference/key-concepts#fragments). This allows fine-grained control over fragment execution, enabling targeted scaling of individual fragments within a streaming job. |
| *fragment\_id*        | The ID of the fragment to modify. You can specify multiple fragment IDs separated by commas. To find fragment IDs, query the [`rw_fragment_parallelism`](/sql/system-catalogs/rw-catalog#available-risingwave-catalogs) system table.                                                            |
| *parallelism\_number* | A fixed number (e.g., 1, 2, 3) that locks the fragment's parallelism at that value. Setting it to 0 is equivalent to ADAPTIVE.                                                                                                                                                                   |
| **ADAPTIVE**          | Expands the fragment's parallelism to all available units in the cluster.                                                                                                                                                                                                                        |
| **DEFAULT**           | Resets the fragment's parallelism to inherit from its parent streaming job's parallelism setting.                                                                                                                                                                                                |

```sql Example theme={null}
-- Set the parallelism of fragment 5 to 4
ALTER FRAGMENT 5 SET PARALLELISM = 4;

-- Set the parallelism of multiple fragments to adaptive
ALTER FRAGMENT 10, 11, 12 SET PARALLELISM = ADAPTIVE;

-- Reset fragment parallelism to inherit from the job
ALTER FRAGMENT 7 SET PARALLELISM = DEFAULT;
```

### `SET BACKFILL_RATE_LIMIT`

```sql theme={null}
ALTER FRAGMENT fragment_id
SET BACKFILL_RATE_LIMIT { TO | = } rate_limit_number;
```

| Parameter or clause           | Description                                                                                  |
| :---------------------------- | :------------------------------------------------------------------------------------------- |
| **SET BACKFILL\_RATE\_LIMIT** | This clause controls the rate limit for backfilling operations on the specified fragment.    |
| *fragment\_id*                | The ID of the fragment to modify. Only a single fragment ID is supported for this operation. |
| *rate\_limit\_number*         | The rate limit value in records per second. Set to 0 to pause backfilling.                   |

```sql Example theme={null}
-- Set backfill rate limit for fragment 3
ALTER FRAGMENT 3 SET BACKFILL_RATE_LIMIT = 1000;

-- Pause backfilling for fragment 3
ALTER FRAGMENT 3 SET BACKFILL_RATE_LIMIT = 0;
```

## See also

* [System catalogs](/sql/system-catalogs/rw-catalog) — View fragment information using `rw_fragment_parallelism` and `rw_fragments`