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ClusterMain is the main class in the cluster module, which performs some developer-level customization and start a MetaClusterServer, which will further initialize the Raft logics and the underlying IoTDB.

Coordinator :  route database operations to the responsible DataMember with the help of its partition table.

Servers

Servers are implementations of Thrift RPC servers, their main concerns are network transport and protocol parsing. Each of them listens on a port and an IP address, accept connection from clients, wrap connections with certain types of Thrift transports, read requests from the transports, parse them with specific protocols, and send the requests to associated RaftMembers. Each node only has one each server.

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• RaftMember: an abstraction of common Raft procedures, like log generation, log replication, heartbeat, election, and catch-up of falling behind nodes.
• MetaMember: an extension of RaftMember, representing a member in the MetaGroup, where cluster configuration, authentication info, and storage groups are managed. It holds the partition table, processes operations that may modify the partition table, and also acts as a coordinator to route database operations to the responsible DataMember with the help of its partition table. One node has only one MetaMember.
• DataMember: an extension of RaftMember, representing a member in one DataGroup, where timeseries schemas and timeseries data of one cluster-level partition are managed. It also handles data queries and thus manages query resources. One node may have multiple DataMembers, depending on how many data partition it manages, which is further decided by the number of replications and partitioning strategy.

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