Importance

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Abstract

The present invention provides client-selected consistency guarantees to clients of a weakly consistent replicated database on a per 'session' basis. The clients have access to utilities which allow the clients to, individually or collectively, define a 'session' over which the selected guarantees are enforced. A 'session' is broadly defined as a sequence of logically related Reads and Writes to the database. Sessions are initiated and terminated substantially independently of other sessions which may exist concurrently. Clients are allowed, however, to clone sessions and/or merge sessions with other clients. Clients select a minimum relevant subset of guarantees from among a set of pre-defined consistency guarantees, where 'relevancy' is a client determined factor. At any given time, the system may be enforcing a number of different combinations of consistency guarantees. The guarantees ensure that all clients participating in a particular session view the database as having certain conditions of data consistency--the consistency of which is only provided with respect to the participants' Read and Write requests. Clients are allowed to downgrade their selected guarantees during the course of their sessions. One implementation of the present invention permits the selection of any one of four consistency guarantees.

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First Claim