> ## Documentation Index
> Fetch the complete documentation index at: https://docs.e6data.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Backfill historical windows

> Preview historical schedule windows before creating runs. Use a saved cron or interval batch workload with data windows enabled and no incremental cursor.

How-to guideApplies to: Unified engine deployments

Preview historical schedule windows before creating runs. Use a saved cron or interval batch workload with data windows enabled and no incremental cursor.

### Preview and start historical windows

Use an active daily midnight UTC workload with window filtering enabled. Inspect the preview before creating execution work.

| Placeholder | Value |
| - | - |
| `{{workload_id}}` | Your environment value. |
| `{{revision}}` | `1` |
| `{{backfill_submission}}` | A new UUID for this request; reuse it when recovering the same submission. |

Replace the placeholders in your client. Keep returned IDs for later requests. Paths below use the native API prefix; adjust it for your deployment.

#### 1. Preview complete windows

```http theme={"theme":{"light":"github-light","dark":"github-dark"}}
POST /api/v1/workloads/{{workload_id}}/backfills/preview
Host: <ENGINE_HOST>
Content-Type: application/json

{
  "submission_id": "{{backfill_submission}}",
  "expected_revision": {{revision}},
  "from_unix_millis": 1767225600000,
  "to_unix_millis": 1767398400000,
  "parameters": {},
  "reprocess": "missing",
  "max_active_runs": 1
}
```

[Endpoint reference](https://docs.e6data.com/transformation/http/reference/preview-backfill.md).

#### 2. Create the reviewed backfill

```http theme={"theme":{"light":"github-light","dark":"github-dark"}}
POST /api/v1/workloads/{{workload_id}}/backfills
Host: <ENGINE_HOST>
Content-Type: application/json

{
  "submission_id": "{{backfill_submission}}",
  "expected_revision": {{revision}},
  "from_unix_millis": 1767225600000,
  "to_unix_millis": 1767398400000,
  "parameters": {},
  "reprocess": "missing",
  "max_active_runs": 1
}
```

From the response, keep `backfill_id` from `/id`.

[Endpoint reference](https://docs.e6data.com/transformation/http/reference/create-backfill.md).

#### 3. Inspect windows and run IDs

```http theme={"theme":{"light":"github-light","dark":"github-dark"}}
GET /api/v1/workloads/{{workload_id}}/backfills/{{backfill_id}}
Host: <ENGINE_HOST>
```

Repeat this read until `/status` reaches a terminal state: `succeeded`, `failed`, `cancelled`.

[Endpoint reference](https://docs.e6data.com/transformation/http/reference/get-backfill.md).

Enter the workload ID and current revision under Example values. The example range covers January 1 and January 2, 2026, in UTC. It must align with the saved schedule's complete windows. Use a daily midnight UTC schedule for these exact boundaries.

Read every preview window and its exclusion reason. Missing, failed, and all have different reprocessing rules. Active or uncertain executions are not safe evidence for replay.

Creating the backfill uses the reviewed request and a stable submission ID. Follow its window list and resulting run IDs. Cancelling a backfill stops further materialization and requests cancellation of submitted runs. Confirm final run states and commits.

See [Workload backfills](https://docs.e6data.com/transformation/workloads/backfills.md) for a complete inline-data workload and expected daily totals.


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