Purpose of ZooKeeper?

[Divya Sai Teja Pamarthi]

Hi,

Can we create Clickhouse cluster without Zookeeper. I would like to just create a clickhouse cluster with persistent volume. 

What am I going to lose if I don't have a Zookeeper. 

Thanks,

Sai Teja

[Michael Smitasin]

Hello Sai Teja,

Indeed, you can run a cluster without ZooKeeper:

"ZooKeeper is not a strict requirement: in some simple cases, you can duplicate the data by writing it into all the replicas from your application code. This approach is not recommended, in this case, ClickHouse won’t be able to guarantee data consistency on all replicas. Thus it becomes the responsibility of your application."

From: https://clickhouse.com/docs/en/getting-started/tutorial/#cluster-deployment

So for example, if you don't use replicas but just use shards, and ingest your data on each node independently, you won't strictly need ZooKeeper. We have a use case for this - our data in ClickHouse is redundant to its original dataset anyway and just provided as a (fast!) convenience, so losing a node wouldn't be critical.

Michael Smitasin
Cyber Security
Information Technology Division
Lawrence Berkeley National Laboratory

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