How does HBase ensure the reliability of data?

HBase ensures data reliability primarily through the following aspects:

1. Data replication: HBase utilizes HDFS as its underlying storage, which already has built-in redundancy by storing data replicas on different nodes to ensure data reliability. HBase will replicate data to multiple nodes based on configured replica numbers, ensuring that data can still be accessed from other nodes in case of a node failure.
2. Write-Ahead-Log (WAL) : Before writing data in HBase, it is first written to the WAL log to ensure that even in the event of node failure or data loss, data can be recovered by replaying the WAL log, guaranteeing data consistency and reliability.
3. Distributed coordination: HBase uses ZooKeeper for distributed coordination and management to ensure consistency among nodes and the reliability of data. ZooKeeper facilitates coordination of node status, fault detection, and fault tolerance to maintain system availability and data consistency.
4. Data consistency: HBase ensures strong consistency in data read and write operations, guaranteeing the reliability and consistency of the data. When a client writes data, HBase first writes it to the WAL log, then to memory and HDFS. Only after all these operations are successfully completed will it return a successful write response to the client, thus ensuring data consistency.

By using the above methods, HBase can ensure the reliability and consistency of data, guaranteeing that data is not lost and that read and write operations are correct and reliable.