What is the technical principle behind Cassandra?

Cassandra is a distributed, open-source NoSQL database, with its technical principles mainly including the following aspects:

1. A distributed architecture: Cassandra uses a distributed architecture where data is distributed across multiple nodes, allowing each node to independently handle read and write requests. This architecture provides high availability, scalability, and fault tolerance.
2. Data Model: Cassandra employs a column-based data model where data is organized in tables, each table can contain multiple rows and columns. Compared to traditional relational databases, this model is more flexible, able to support a large number of columns and highly variable data structures.
3. Data distribution: Cassandra utilizes a distributed hash algorithm to distribute data to different nodes. By calculating the hash function of the data key, it is mapped to a node and stored on that node. This approach ensures even data distribution and load balancing.
4. Replication and Consistency: Cassandra replicates data to multiple nodes to enhance data reliability and fault tolerance. Users can configure a replication factor to specify the number of replicas. Cassandra employs a consistent hashing algorithm to determine data distribution among multiple copies.
5. Distributed transactions: In a distributed environment, Cassandra adopts a model of eventual consistency for its distributed transactions. Data inconsistency may exist for a period of time in replicas on different nodes, but eventually all replicas will reach a consistent state. To achieve eventual consistency, Cassandra uses vector clocks and repair mechanisms.
6. Writing and reading: Cassandra uses a Log-Structured Merge (LSM) tree to handle write operations. All write operations are appended to a commit log in memory, then asynchronously written to disk. When reading data, Cassandra retrieves it from memory and disk to return to the client.

In summary, Cassandra’s technical principles include distributed architecture, column-based data model, data distribution, replication and consistency, distributed transactions, and handling of write and read operations. These principles enable Cassandra to provide a distributed storage solution with high availability, scalability, and fault tolerance.