Why are sequence numbers used in fault-tolerant data logging?

Why are sequence numbers used in fault-tolerant data logging?

• A. To compress data.
• B. To encrypt data.
• C. To provide authentication.
• D. To detect missing entries and preserve correct ordering across multiple media.

Answer: (D)

Sequence numbers act as a reliable timeline for log records. In fault-tolerant data logging, entries can be written to different media or be interrupted; giving each entry a monotonically increasing number lets the system verify that every intended entry is present and place records in the correct order when they are read back. If a gap appears in the sequence, the reader knows an entry was lost and can take steps to recover or flag the gap. When multiple media are involved, sequence numbers provide a common ordering key so data from different sources can be merged consistently without misordering. This makes the log resilient to failures and easier to replay or reconstruct. Compressing, encrypting, or authenticating data serves other purposes and does not address ordering and gap detection.

Sequence numbers act as a reliable timeline for log records. In fault-tolerant data logging, entries can be written to different media or be interrupted; giving each entry a monotonically increasing number lets the system verify that every intended entry is present and place records in the correct order when they are read back. If a gap appears in the sequence, the reader knows an entry was lost and can take steps to recover or flag the gap. When multiple media are involved, sequence numbers provide a common ordering key so data from different sources can be merged consistently without misordering. This makes the log resilient to failures and easier to replay or reconstruct. Compressing, encrypting, or authenticating data serves other purposes and does not address ordering and gap detection.