Explain why allowing backups to process read operations leads to sequentially consistent rather than linearizable executions in a passive replication system.

What will be an ideal response?



Due to delays in update propagation, a read operation processed at a backup could retrieve results that are older than those at the primary – that is, results that are older than those of an earlier operation requested by another process. So the execution is not linearizable.

The system is sequentially consistent, however: the primary totally orders all updates, and each process sees some consistent interleaving of reads between the same series of updates.

Computer Science & Information Technology

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