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Denormalizing Data
Denormalization in ClickHouse means storing related data together in the same table instead of using JOINs. This is often the right approach for analytics workloads because JOINs can be expensive, and ClickHouse's columnar storage makes denormalization efficient. Denormalize when you frequently need related data together, when JOINs are slow, or when data relationships are stable.
In traditional relational databases, normalization is the norm. In ClickHouse, denormalization is often the better choice for analytics workloads. Understanding when and how to denormalize is key to writing efficient queries.
Why Denormalize in ClickHouse?
JOINs in ClickHouse can be expensive: they're memory intensive (right table loaded into memory), CPU intensive (hash table construction and lookups), slower execution, and performance degrades with table size.
Denormalization stores related data together, eliminating the need for JOINs:
✗ Slow: JOINs user data for each event