Distributed Concurrency Control
As we discussed in Chapter 10, concurrency control deals with the isolation and consistency properties of transactions. The distributed concurrency control mechanism of a distributed DBMS ensures that the consistency of the database, as defined in Section 10.2.2, is maintained in a multiuser distributed environment. If transactions are internally consistent (i.e., do not violate any consistency constraints), the simplest way of achieving this objective is to execute each transaction alone, one after another. It is obvious that such an alternative is only of theoretical interest and would not be implemented in any practical system, since it minimizes the system throughput. The level of concurrency (i.e., the number of concurrent transactions) is probably the most important parameter in distributed systems [Balter et al., 1982]. Therefore, the concurrency control mechanism attempts to find a suitable trade-off between maintaining the consistency of the database and maintaining a high level of concurrency.
KeywordsData Item Concurrency Control Transaction Manager Deadlock Detector Snapshot Isolation
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