Which Delta Lake feature reduces the number of files as data is written?

• A. OptimizeWrite function
• B. CompactFiles operation
• C. Data Skipping Index
• D. File Coalescing

Answer: (A)

As data is written, you want to avoid creating many tiny files, which can hurt read performance and add metadata overhead. OptimizeWrite is a write-time optimization that coalesces small files into larger ones as data is being written. This means fewer files end up in the Delta table, improving both write throughput and query performance when the data is read later. The other options don’t achieve this on-the-fly file reduction: CompactFiles cleans up small files after data has been written, Data Skipping Index helps skip irrelevant data during reads, and the term File Coalescing isn’t the write-time optimization Delta Lake uses for reducing file counts during writes.