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We will not provide the ability to operate in either a pure cluster mode or hybrid mode. Cluster mode will be the only mode. (This would not preclude non-cluster clients capable of interpreting MOVED responses from working).

Solution

Redis enables data sharding by partitioning data into 16384 slots. Keys are hashed using a well defined hashing algorithm (CRC16/XMODEM) the result of which is then modded with 16384 to determine the slot. Each primary server is responsible for hosting a non-overlapping set of slots. Various cluster commands provide information on slot-to-server allocation. Thus, given a key, a client is able to determine which server is hosting that data and direct the command to the correct server. See also Redis Cluster Specification.

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Although not currently implemented, this change will greatly ease the ability to develop transactional support using Redis' MULTI/EXEC commands. Redis transactions require all keys, participating in a transaction, to be colocated in the same slot. The current implementation would require a much more complicated locking scheme allowing multiple keys to be locked across multiple members.

Additional CLUSTER commands may also be implemented in the future - for example CLUSTER REPLICAS , CLUSTER INFO  and CLUSTER GETKEYSINSLOT .

Changes and Additions to Public Interfaces

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