Which statement about high watermark is accurate?

Which statement about high watermark is accurate?

• A. It indicates the oldest retained offset
• B. It defines the end offset of the log
• C. It is the offset of the last message copied to all replicas
• D. It determines the flush point for consumers

Answer: (C)

High watermark represents the highest offset that has been replicated to all in-sync replicas, making those messages durable and safe to read. This boundary defines what both the broker and consumers can rely on: messages at offsets up to this point are committed, while anything beyond may still be in flight to some replicas and not yet guaranteed. It’s not the oldest retained offset—that would be the log start offset, which is determined by retention and log trimming. It’s not the end offset of the log—the end offset is where new messages will be appended, not where the replication boundary stands. It’s also not a consumer flush point—consumers track their own progress and can lag or advance independently of the high watermark. For example, if offsets up to 95 have been replicated to all in-sync replicas, the high watermark is 95; consumers can safely read up to that point with the assurance of durability.

High watermark represents the highest offset that has been replicated to all in-sync replicas, making those messages durable and safe to read. This boundary defines what both the broker and consumers can rely on: messages at offsets up to this point are committed, while anything beyond may still be in flight to some replicas and not yet guaranteed.

It’s not the oldest retained offset—that would be the log start offset, which is determined by retention and log trimming. It’s not the end offset of the log—the end offset is where new messages will be appended, not where the replication boundary stands. It’s also not a consumer flush point—consumers track their own progress and can lag or advance independently of the high watermark.

For example, if offsets up to 95 have been replicated to all in-sync replicas, the high watermark is 95; consumers can safely read up to that point with the assurance of durability.