Fine-Grained Lazy Replication with Strict Freshness and Correctness Guarantees

Abstract

Eager replication management is known to generate unacceptable performance as soon as the update rate or the number of replicas increases. Lazy replication protocols tackle this problem by decoupling transaction execution from the propagation of new values to replica sites while guaranteeing a correct and more efficient transaction processing and replica maintenance. However, they impose several restrictions on transaction models that are often not valid in practical database settings, e.g., they require that each transaction executes at its initiation site and/or are restricted to full replication schemes. Also, the protocols cannot guarantee that the transactions will always see the freshest available replicas. This paper presents a new lazy replication protocol called PDBREP that is free of these restrictions while ensuring one copy serializable executions. The protocol exploits the distinction between read-only and general transactions and works with arbitrary physical data organizations such as partitioning and striping as well as different replica granularities. It does not require that each read-only transaction executes entirely at its initiation site. Hence, each read-only site need not contain a fully replicated database. PDBREP furthermore generalizes the notion of freshness to finer data granules than entire databases. Beside its architectural advantages, experiments revealed that PDBREP outperforms related lazy replication techniques.