Distributed Database Systems, 1st Edition by Chhanda Ray

Distributed Concurrency Control

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The major benefi t of the quorum consensus protocol is that it allows to reduce the cost of read

and write operations selectively by appropriately assigning the read and write quorums to data

items. For example, a read operation on a data item with a small read quorum requires reading of

fewer replicas of the data item. But the write quorum of that data item may be higher, and hence, to

succeed, the write operation needs to obtain locks on more replicas of the data item that are avail-

able. Furthermore, if higher weights are assigned to some sites, fewer sites need to be accessed for

acquiring locks on a ...