Avoiding Blocking During Consensus Blocking problem of 2PC is a serious concern ■ Idea:involve multiple nodes in decision process,so failure of a few nodes does not cause blocking as long as majority don't fail More general form:distributed consensus problem A set of n nodes need to agree on a decision Inputs to make the decision are provided to all the nodes,and then each node votes on the decision ·The decision should be made in such a way that all nodes will“learn” the same value for the even if some nodes fail during the execution of the protocol,or there are network partitions. Further,the distributed consensus protocol should not block,as long as a majority of the nodes participating remain alive and can communicate with each other ■ Several consensus protocols,Paxos and Raft are popular More later in this chapter Database System Concepts-7th Edition 23.15 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 23.15 ©Silberschatz, Korth and Sudarshan th Edition Avoiding Blocking During Consensus ▪ Blocking problem of 2PC is a serious concern ▪ Idea: involve multiple nodes in decision process, so failure of a few nodes does not cause blocking as long as majority don’t fail ▪ More general form: distributed consensus problem • A set of n nodes need to agree on a decision • Inputs to make the decision are provided to all the nodes, and then each node votes on the decision • The decision should be made in such a way that all nodes will “learn” the same value for the even if some nodes fail during the execution of the protocol, or there are network partitions. • Further, the distributed consensus protocol should not block, as long as a majority of the nodes participating remain alive and can communicate with each other ▪ Several consensus protocols, Paxos and Raft are popular • More later in this chapter