Abstract
Concurrency control mechanisms including the wait, time-stamp and rollback mechanisms have been briefly discussed. The concepts of validation in optimistic approach are summarized in a detailed view. Various algorithms have been discussed regarding the degree of concurrency and classes of serializability. Practical questions relating arrival rate of transactions have been presented. Performance evaluation of concurrency control algorithms including degree of concurrency and system behavior have been briefly conceptualized. At last, ideas like multidimensional timestamps, relaxation of two-phase locking, system defined prewrites, flexible transactions and adaptability for increasing concurrency have been summarized.
Highlights
Database systems are important for managing the data efficiently and allowing users to perform multiple tasks on it with the ease
We include some ideas that have been used for designing concurrency control algorithms and evaluated these algorithm’s performance
The approach in (Bhargava & Riedl, 1989) is a variation of the optimistic concurrency control for global transactions while allowing individual sites to maintain their autonomy. Another concept that has been studied in the Reliable, Adaptable, Interoperable Distributed (RAID) database system (Bhargava & Riedl, 1989) involves facilities to switch concurrency control methods
Summary
Database systems are important for managing the data efficiently and allowing users to perform multiple tasks on it with the ease. The sequence number is appended to the write set of the transaction and is used to order the update of the new values into the database at each node. If a transaction succeeds in the validation phase, its write set is made global and the values of the write set become values of entities in the database at each node. Tj must follow Tj in any serial history since Π(Wi) > Π(Rj) This possibility is illustrated as follows: For a set of concurrent transactions, we proceed as follows: For each transaction that is validated and enters the list of committed transactions, we draw a directed edge according to the following rules:. If none of the transactions conflict with the validating transaction, it is considered to have succeeded in the validation and to have committed This obviously requires updating a given entity of the read set many times and is inefficient. Care should be taken to restart (or invalidate) all active transactions Ti for which Π(Ri) < Π(Wj) before Tj is deleted
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