Cassandra - Storage Layout

About

The data is automatically distributed by horizontal partition (sharding).

Request processing:

  • When data is inserted into the cluster, the first step is to apply a hash function to the partition key to get a numeric token
  • The coordinator does a token lookup and retrieve the node that owns the numeric token called a replica (Each node owns a particular ranges of tokens - numeric)
  • The coordinator assigns the data to a given partition

In a 3 replica node, if a request comes in for data, even if one of our replicas has gone down, the other two are still available to fulfill the request.

Data Storage Hierarchy

  • Table: Logical
  • Partition: Physical (one or more file)

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