AI / Apache Paimon Interview questions
What is the difference between the input and lookup changelog producers?
Both aim to give downstream consumers a full before/after changelog, but they get the "before" value from different places:
| Producer | Where the before value comes from | Requirement |
| input | Passed straight through from the input stream, unmodified. | The input must already be a complete changelog (e.g. CDC), or this breaks silently. |
| lookup | Paimon looks up the current on-disk value for that key before committing the new one. | Works for any input, including plain append/insert-only sources, at the cost of a lookup on write. |
Use input when you're confident the source is already a proper changelog and want to avoid extra lookup cost; use lookup when the source doesn't carry before-values itself (or you're not sure it does) and you need Paimon to reconstruct them.
The input changelog producer assumes:
The lookup changelog producer gets the "before" value by:
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