Two-Version Based Concurrency Control and Recovery in Real-Time Client/Server Databases
IEEE Transactions on Computers
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In this paper, we investigate the consistency requirements of read-only (RO) transactions. Since RO transactions do not update any data item, they do not need to be serializable with consistent serial ordering of update transactions. We present a new algorithm that processes real-time RO transactions separately from update transactions in a multiversion database system. The new algorithm allows non-serializable execution of RO transactions. Nevertheless, RO transactions are still guaranteed to see consistent data, which is in contrast to other non-serializable algorithms allowing RO transactions to see bounded inconsistent data. Among its advantages of eliminating data contention between RO and update transactions and of reducing the overheads of accessing old version of data items, the new algorithm explicitly attempts to let RO transactions to read the most recent data rather than stale data. It could be very important for some real-time applications where reactive actions should be based on the latest status of the system.