What is replication in ClickHouse?

Replication in ClickHouse is the process of creating and maintaining copies of data across multiple servers (nodes) to ensure fault tolerance and scalability.

Key features of replication in ClickHouse:

• Replicated tables: ClickHouse supports special table types (e.g., ReplicatedMergeTree) that automatically synchronize data between replicas.
• Consistency: Replicas maintain a consistent state using ZooKeeper, which coordinates write operations and guarantees that data is not lost.
• Fault tolerance: When one replica fails, requests can be served by others, increasing data availability.
• Load balancing: Replication allows distributing read requests across multiple servers, improving performance.

Thus, replication in ClickHouse provides reliable data storage and quick access in a distributed environment.