Tuning Concurrency Control
Database systems implement concurrency control to give users the illusion that each transaction executes correctly, in isolation from all others. The concurrency-control algorithm in predominant use is two-phase locking. Tuning concurrency control consists in improving the performance of concurrent operations by reducing the number, duration and scope of the conflicts due to locking.
In 1976, Jim Gray et al. identified the fundamental concurrency control trade-off between correctness and performance. They discussed different lock granularities and introduced the notion of degrees of consistency.
Database systems attempt to give users the illusion that each transaction executes in isolation from all others. The ANSI SQL standard, for example, makes this explicit with its concept of degrees of isolation. Full isolation or serializabilityis the guarantee that each transaction that completes will appear to execute one at a...
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