InvisibleWriteRule: the sufficient condition for safely omittable write operations in concurrency control
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Concurrency Control (CC) is the heart of the correctness and is the current bottleneck of OLTP databases. Many schedulers for CC are proposed to reduce coordination between transaction processing. In fact, they only improve concurrency for read operations. Generally, databases based on conventional schedulers execute transactions with lock and wait. Thus, in write intensive and contended workload, all conventional schedulers cannot scale enough in many-core environments. To reduce coordination between write operations, we propose an InvisibleWrite (IW) operation which is an omittable write operation under the specific condition. Omitting IW operations result in reducing coordination between write operations. However, a schedule including IW operations sometimes violates the correctness conditions of OLTP databases such as serializability. To guarantee serializability and other correctness conditions, we propose InvisibileWriteRule (IWR) which is the sufficient condition for schedulers. All IWR schedulers, which satisfy IWR and generate IW operations, have the guarantee of serializability, recoverability, and linearizability. We can extend all conventional schedulers to IWR schedulers with tiny overhead and implementation cost. To indicate the efficiency and extensibility of IWR schedulers, we extend three conventional schedulers such as Silo, TicToc, and MVTO. Our experimental results show that every IWR scheduler achieves significant performance, especially in write intensive and contended workload. In the best case, Silo-based IWR scheduler achieves about 6.5x faster throughput than the original scheduler.
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