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How does Snowflake handle schema changes in the source tables used by dynamic tables?

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How does Snowflake handle schema changes in the source tables used by dynamic tables?

Daniel Steinhold Asked question March 15, 2024

Snowflake employs a mechanism called change tracking to handle schema changes in the source tables used by dynamic tables. Here's a breakdown of how it works:

Automatic Change Tracking:

  • When you create a dynamic table, Snowflake automatically attempts to enable change tracking on all underlying objects (tables and views) referenced in the defining SQL statement. This means Snowflake starts monitoring those source tables for any modifications to their schema.

Benefits of Change Tracking:

  • Automatic Refresh Adaptation: If a schema change occurs in a source table, Snowflake detects it through change tracking. This triggers a refresh of the dependent dynamic table, ensuring the transformation logic considers the updated schema during the next refresh cycle.
  • Data Consistency: By automatically refreshing dynamic tables, Snowflake helps maintain consistency between the transformed data and the underlying source data, even when schema modifications occur.

Important Considerations:

  • Enabling Change Tracking: For change tracking to work effectively, the user creating the dynamic table must have the OWNERSHIP privilege on all referenced source objects. This allows Snowflake to modify the source tables and enable change tracking.
  • Retention Period: You can define a time frame (retention period) for how long Snowflake stores historical data related to the schema changes in the source tables. This information is crucial for ensuring the dynamic table can adapt to past modifications during refreshes.

Troubleshooting Schema Changes:

  • Manual Verification: While change tracking automates much of the process, it's still recommended to manually verify the impact of schema changes on your dynamic table's functionality, especially for complex transformations.
  • Error Handling: Consider incorporating error handling mechanisms into your dynamic table logic to gracefully handle potential issues arising from schema changes in source tables.

Here's an additional point to remember:

  • Recreating Objects: If you need to completely recreate a source table used by a dynamic table, change tracking won't automatically re-enable itself on the new object. You'll need to manually enable change tracking on the recreated table to ensure it's monitored for future modifications.

In essence, Snowflake's change tracking functionality helps dynamic tables adapt to schema changes in source tables, promoting data consistency and automation within your data pipelines.

Daniel Steinhold Changed status to publish March 15, 2024

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