> We wanted to use Clickhouse (as "db we need" in above diagram) but its update/delete is actually done with garbage collection (it's done at some point but we

> We wanted to use Clickhouse (as "db we need" in above diagram) but its update/delete is actually done with garbage collection (it's done at some point but we don't know when). Are you saying you can't tell whether the update has completed or you can't tell when the update will complete in general? If the former, it's easy to track completion by looking at the system.mutations table. ClickHouse will have synchronous SQL DELETE later this year. My company Altinity is working on the implementation.