---
title: "Bobsled transfer backfill"
slug: "bobsled-transfers-backfill"
updated: 2025-05-12T20:29:21Z
published: 2025-05-12T20:29:21Z
canonical: "bobsled.com/bobsled-transfers-backfill"
---

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

# Bobsled transfer backfill

Backfilling helps ensure data consistency and completeness by re-syncing source data to destination shares under specific scenarios.

The Backfill process transfers all historical source data to a destination share in a single synchronization and resets the schema on the destination table when loading a data warehouse.

---

### When does a Backfill occur?

Users can manually trigger a backfill in two ways:

- Transferring data for the first time to a new share.
- Selecting **Backfill** on Next Run or **Backfill all while** editing a transfer in the Bobsled Application.

### When is a Backfill recommended?

Bobsled will alert in the application when a backfill is recommended to ensure data consistency, under the following conditions:

- Modifications to [source](/v2/docs/sources) or [destination](/v2/docs/destinations) locations.
- Changes in loading or unloading behaviors, including settings like `primaryKeys`, `deleteFlags`, or `fileOptions`.
- Updates to [glob](/v2/docs/setting-globs) filters or source view definitions.

![](https://cdn.document360.io/87a415ff-4d6a-4c0c-adbb-26c563a2d9a8/Images/Documentation/BF.png)

> [!NOTE]
> **NOTE:** Not enabling backfill when recommended may result in inconsistent data or a failed transfer. If a transfer fails as a result, you can manually trigger a backfill later from the UI.

---

#### Snowflake backfill behaviour on view change (if enabled)

![](https://cdn.document360.io/87a415ff-4d6a-4c0c-adbb-26c563a2d9a8/Images/Documentation/SNOWFLAKE.png)

> [!NOTE]
> **NOTE:** Bobsled detects if a Secure View has been recreated by inspecting ‘**created_at’** field in ‘**SHOW VIEWS’** query results.

---

### **Key Benefits**

- **Data Consistency**: Ensure [destination](/v2/docs/destinations) shares always reflect source data accurately.
- **Automation**: Bobsled detects and initiates necessary backfills to save time and effort.

### **Considerations**

- **Sources with TTL policies:** When backfilling from sources that maintain a TTL policy, any data in the share older than the TTL policy **will not be restored**.
  - Example: The share has been active for 30 days. The source bucket has a 10-day TTL policy. Once a backfill is initiated, this share will only have data from the most recent 10 days available in the source bucket.