Do you know about copy‑on‑write and merge‑on‑read strategies? Which are available?

Copy‑on‑write (CoW) and merge‑on‑read (MoR) are two data storage strategies used in modern data lakes and file systems.

• Copy‑on‑write rewrites the entire file when an update occurs. It is simple and provides strong consistency, but can be expensive for large files because the whole file must be rewritten. It is common in HDFS and older data lake formats like Parquet.
• Merge‑on‑read writes updates as separate delta files and merges them only when reading. This reduces write amplification and is efficient for workloads with frequent updates. It is used in systems like Apache Hudi and Delta Lake.

Both strategies are available in many big‑data platforms; the choice depends on write frequency, consistency requirements, and performance trade‑offs.