ClickHouse/docs/en/engines/database-engines/replicated.md

[experimental] Replicated

Supports replication of metadata via DDL log being written to ZooKeeper and executed on all of the replicas for a given database. One Clickhouse server can have multiple replicated databases running and updating at the same time. But there can't be multiple replicas of the same replicated database.

Creating a Database

    CREATE DATABASE testdb ENGINE = Replicated('zoo_path', 'shard_name', 'replica_name') [SETTINGS ...]

Engine Parameters

• zoo_path — ZooKeeper path. The same ZooKeeper path corresponds to the same database.
• shard_name — Shard name. Database replicas are grouped into shards by shard_name.
• replica_name — Replica name. Replica names must be different for all replicas of the same shard.

Using this engine, creation of Replicated tables requires no ZooKeeper path and replica name parameters. Table's replica name is the same as database replica name. Table's ZooKeeper path is a concatenation of database's ZooKeeper path, /tables/, and UUID of the table.

Specifics and recommendations

Algorithms Specifics of read and write processes Examples of tasks Recommendations for usage Specifics of data storage

Usage Example

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Input table:

Query:

Result:

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See Also

• link