How Does Cassandra Database Work? Explained

Apache Cassandra is a distributed NoSQL database management system known for its scalability and high availability. In this article, we will explore how Cassandra works and its key features.

Key Concepts

• Distributed Architecture: Cassandra is designed to be distributed across multiple nodes in a cluster, allowing for horizontal scalability.
• No Single Point of Failure: Data is replicated across multiple nodes, ensuring high availability even if some nodes fail.
• Peer-to-Peer Communication: Nodes in a Cassandra cluster communicate with each other using a peer-to-peer protocol, eliminating the need for a central coordinator.
• Data Replication: Cassandra replicates data across multiple nodes based on the replication factor, ensuring data durability and fault tolerance.
• Partitioning: Data in Cassandra is partitioned using a partition key, and each node is responsible for a range of data partitions.

Architecture

Cassandra has a masterless architecture where all nodes in the cluster are equal. Data is distributed across nodes using consistent hashing, and each node communicates with other nodes to perform read and write operations.

Write Path

When a write request is received, the data is first written to an in-memory data structure called the memtable. Once the memtable reaches a certain threshold, it is flushed to disk in a data structure called an SSTable. The write is then acknowledged to the client.

Read Path

When a read request is received, Cassandra first checks the memtable for the latest data. If the data is not found in the memtable, it looks up the data in the SSTables on disk. Cassandra uses an efficient mechanism called Bloom filters to quickly determine if the data may exist in an SSTable.

Consistency

Cassandra offers tunable consistency levels to allow developers to choose between strong consistency and high availability. Consistency levels can be set per operation, enabling developers to make trade-offs based on their application requirements.

Compaction

Over time, SSTables may accumulate deleted or obsolete data. Compaction is the process of merging and compacting SSTables to reclaim disk space and improve read performance. Cassandra performs background compaction to ensure optimal performance.

Conclusion

Apache Cassandra’s distributed architecture, high availability, and tunable consistency make it a popular choice for applications requiring scalability and fault tolerance. Understanding how Cassandra works under the hood can help developers design efficient and reliable data solutions.