How does BigtableIO achieves exactly once writes?

Question

Dataflow guarantees exactly once processing and delivery as well. Is this guaranteed at sinks by not allowing mutations to the existing records and only allowing idempotent overwrite?

Answer 1

You're correct. The BigtableIO Dataflow/Beam connector will only write Put and Delete mutations, ignoring Append and Increment ones. See Note in the documentation for the class.