ClickHouse, in production

I build analytics and reporting systems for a supermarket chain — mostly React and Node on top of ClickHouse, where the tables are large enough that a careless query takes the server with it.

This is where I write down what actually worked: the query patterns, the schema decisions, and the mistakes that cost me an afternoon so they don't cost you one. Real numbers, measured from system.query_log, not vibes.

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