Which statement about high watermark is true?

Which statement about high watermark is true?

• A. It marks the offset of the oldest message
• B. It is the offset of the last message copied to all replicas
• C. It indicates the current end offset of the log
• D. It sets the retention window for messages

Answer: (B)

High watermark represents the last offset that has been replicated to all in-sync replicas, and it defines the safe read boundary for consumers. This means consumers can rely on data up to that offset being durable across the cluster; anything beyond may still be in flight or at risk if a replica lags or fails. The high watermark advances only when every in-sync replica has acknowledged up to that offset, ensuring the data up to that point won’t be lost due to a replica failure. It is not the offset of the oldest message, nor the current end of the log, and it does not set the retention window.

High watermark represents the last offset that has been replicated to all in-sync replicas, and it defines the safe read boundary for consumers. This means consumers can rely on data up to that offset being durable across the cluster; anything beyond may still be in flight or at risk if a replica lags or fails. The high watermark advances only when every in-sync replica has acknowledged up to that offset, ensuring the data up to that point won’t be lost due to a replica failure. It is not the offset of the oldest message, nor the current end of the log, and it does not set the retention window.