Does Fivetran Lock SQL Server Tables During Incremental CDC Syncs?

Question

Does Fivetran lock SQL Server tables during incremental syncs using the change data capture (CDC) sync method?

Environment

• Connector: SQL Server
• Sync method: CDC

Answer

Fivetran does not lock your SQL Server source tables during incremental syncs that use the CDC sync method. Instead, we query the SQL Server internal CDC change tables, such as cdc.<schema>_<table>_CT.

We use the default READ COMMITTED isolation level for these reads. We don't require WITH (NOLOCK) or READ UNCOMMITTED. During syncs, SQL Server may place brief read locks on the CDC change tables, but this has no impact on your application's normal inserts, updates, or deletes on the source tables.

In some cases, we may also briefly take a schema stability (SCH-S) lock while detecting new columns. This lock typically lasts only milliseconds and does not affect normal database operations.