Exactly-Once Final State vs At-Least-Once CDC

April 2026

The real CDC question is not just whether events arrive. It is whether the destination ends up in the right final state.

Short Answer

At-least-once CDC means events may be delivered more than once. Exactly-once final state means the destination still ends up with the right row state even if retries happen along the way.

For warehouse pipelines, final state is the part that matters. Analysts query tables, not delivery logs.

Why Teams Struggle with This

A lot of CDC marketing stops at event delivery language. That hides the harder question: what does the destination look like after retries, replays, deletes, and ordering edge cases?

• A tool can replay events correctly and still leave duplicates in the destination.
• Delete handling often breaks when retries happen out of order.
• Teams assume event delivery guarantees automatically imply clean warehouse tables.
• The destination contract gets left for downstream dbt models to fix.

How Skippr Handles It

Skippr talks about exactly-once final state because the warehouse is the thing people query. CDC semantics only matter if they produce a destination table you can trust.

That is why the docs focus on merge behavior, order tokens, and tombstone handling instead of vague delivery claims.

• CDC semantics are tied to the destination contract.
• Final-state merge behavior is explicit.
• Order-token guards matter more than pretty event diagrams.
• The dbt project starts on top of cleaner tables.

What the First Useful Version Looks Like

If you are evaluating CDC tooling, ask what the destination looks like after retries and deletes.

That question cuts through a lot of marketing fast.