DELAY/RE-READ PROTOCOL FOR CONCURRENCY CONTROL IN DATABASES.

We present a new protocol, called the Delay/ReRead Protocol, for controlling concurrent access to a database. The protocol uses a combination of preventive and corrective measures for maintaining consistency. On recognizing that a transaction has read inconsistent data, the Protocol applies a corrective measure which requires the transaction to re-read some data. Alternatively, on recognizing that a transaction is about to write data which will result in inconsistency, the Protocol applies a preventive measure which delays the Write. A Read request is always granted without delay. The Protocol is deadlock-free, requires no backup data, and supports a greater degree of concurrency than Two Phase Locking. A transaction is never aborted or delayed indefinitely by the Protocol.