Cassandra中的哈希表

青禾华丽

谢谢分享

jieforest

When Cassandra receives a key for either a read or a write, the hash function is applied to the key to determine where it lies in the range. Since all nodes in the cluster are aware of the other nodes' ranges, any node can handle a request for any other node's range. The node receiving the request is called the coordinator, and any node can act in this role. If a key does not belong to the coordinator's range, it forwards the request to replicas in the correct range.

Following the previous example, we can now examine how our names might map to a hash, using the Murmur3 hash algorithm. Once the values are computed, they can be matched to the range of one of the nodes in the cluster, as follows:

————————————————————————————————————————————
Name                Hash value                                  Node assignment
————————————————————————————————————————————
John              -3916187946103363496                   3
————————————————————————————————————————————
Jane              4290246218330003133                    5
————————————————————————————————————————————
George          -7281444397324228783                   2
————————————————————————————————————————————
Sue               -8489302296308032607                   2
————————————————————————————————————————————

jieforest

The placement of these keys might be easier to understand by visualizing their position in the ring.

jieforest

The hash value of the name keys determines their placement in the cluster

Now that you understand the basics of consistent hashing, let's turn our focus to the mechanism by which Cassandra assigns data ranges.

青禾华丽

谢谢分享！