In this chapter we've discussed what operations Cassandra performs internally when doing a Read or a Write operation. We discussed various key data structures which Cassandra maintains internally. We also discussed how these data structures and processes affects a read/write operation. We discussed the role of CommitLog to make a write operation durable also how it can be used to recover a data that is not flushed to disk yet and the node dies. Cassandra maintains different caches and employs various techniques like BloomFilter to make its read/write operation fast. It has various data consistency levels that can be tuned as per our needs. We've discussed how it first writes to memory to make write operation ultra-fast and then later on flushes that data to disk in the form of immutable SSTables. Since SSTables are immutables so over the time multiple SSTables are formed over a Cassandra node. Multiple SSTable for a column family could lead to multiple disks seeks for a read operation...