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ClickHouse is OLAP (analytics), this one is OLTP (transactional)

Hence the focus on multi-AZ. This makes completely sense for transactional.

I believe that something like AZure CosmosDB, AWS Aurora/DynamoDB but open-sourced, which is great.

or cockroachdb and spanner ?

Yes, YDB plays in this category.

I think YDB's architecture is more like TiDB

YDB can work in a single AZ and such setups exist. Most of our users want to handle AZ downtime, so it's a major case.