ClickHouse Keeper is an open-source component that serves as a fast and resource-efficient alternative to ZooKeeper for ClickHouse. It provides a reliable metadata store and coordination and synchronization mechanisms. The development of ClickHouse Keeper started in 2021 and has been deployed at scale in ClickHouse Cloud. ClickHouse Keeper offers easier setup and operation, consumes less disk space, and has no limitations on data size compared to ZooKeeper. It provides the same consistency guarantees as ZooKeeper and is more resource-efficient, using up to 46 times less memory for the same volume of data while maintaining performance. ClickHouse Keeper has been extensively benchmarked and compared to ZooKeeper, consistently showing superior performance and memory usage.
https://clickhouse.com/blog/clickhouse-keeper-a-zookeeper-alternative-written-in-cpp