A county archives cold historical 311 tickets for rare compliance reads while keeping active silver tickets ready for ACID merges. Which format choice fits?

Using Parquet for the cold historical 311 archive and Delta for the active silver tables that need ACID merges is the correct format choice. Cold civic archives optimized for infrequent compliance reads benefit from compact Parquet storage, while active silver 311 tickets that undergo concurrent merges need Delta Lake transactionality, versioning, and ACID guarantees.

Using Delta for the cold historical 311 archive and Parquet for the active silver tables that need ACID merges is the wrong split because Delta imposes transactional overhead on cold, rarely read files, while Parquet cannot deliver the ACID merge semantics that active silver requires. Using Parquet for the cold historical 311 archive and Parquet for the active silver tables that need ACID merges fails because Parquet fits the cold archive but supplies no transaction log, versioning, or atomic merge support for active silver tables. Using Avro for the cold historical 311 archive and ORC for the active silver tables that need ACID merges is a poor fit because Avro’s row-oriented layout is inefficient for cold compliance scans, and ORC alone lacks the ACID transaction and merge guarantees that active silver demands.

Exam caveat: Format follows workload: Delta (or similar transactional lake formats) for mutable, merge-heavy silver; Parquet or similarly compact files for cold, rarely updated archives. You can still govern both via Unity Catalog external or managed patterns appropriate to the platform, but the exam distinction is ACID-active versus cold-archive efficiency. Do not confuse “archive in Parquet” with “abandon all metadata and retention controls.”

Operational check: Confirm active silver 311 tables are Delta and successfully run merge operations, confirm cold historical tickets live in Parquet (or equivalent) optimized for rare compliance scans, run a sample compliance read against the archive, and reject swapped Delta/Parquet, uniform Parquet, or Avro/ORC combinations for either path.