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Cassandra Write Operation Performance Explained

An ☞ interesting explanation of how Cassandra write ops are happening:

  • client submits its write request to a single, random Cassandra node
  • the node behavior is similar to a proxy writing data to the cluster
  • writes are replicated to N nodes according to the replication placement strategy (the details of RackAwareStrategy are quite interesting)
  • each of the N nodes performs 2 actions when receiving a write (in the form of RowMutation):
    • append the mutation to the commit log for transactional purposes
    • update an in-memory Memtable structure with the change

There are also a couple of asynchronous operations:

  • Memtable is written to disk in a structure called SSTable
  • SSTables corresponding to a column family are merged into a raw ColumnFamily datafile.

You should definitely check the ☞ original post as there are more interesting details.