神马文学网[Bernstein09] 9.6. Other Replication Techniques
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9.6. Other Replication Techniques
Replicationalgorithms have been an active area of database research for over threedecades. Many algorithms have been published beyond those describedhere, which are the ones that are primarily used in today’s databasesystems. Some interesting other approaches include:
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Nontransactional replication, based on timestamped updates. That is, each original update executes as an atomic action outside the context of any transaction. These algorithms often are used for distributed system services, such as a directory service, where multimaster replication is needed but not transactions.
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Quorum consensus applied to every transaction. Each transaction reads a quorum of copies of each data item it accesses, and uses the most up-to-date value among those copies as input. This approach avoids elections and other reconfiguration algorithms, at the cost of more work for each transaction. It is also one of the first correct replication algorithms published.
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Read-one-write-all-available, where instead of using a primary copy, each transaction writes to all available copies of every data item it updates. One well-known algorithm, called Virtual Partitions, uses this approach along with quorum consensus, to ensure a data item is updatable only if the set of connected sites have a quorum of copies of that item.
See the Bibliographic Notes for further reading.