We keep a precomputed cityhash64 value for a few columns we know are going to be used for aggregations. Rather than relying on ClickHouse to do it internally, this explicity behavior I've found is faster.
Especially if it's a multi tenant architecture, it helps to have the cityHash64 caclulated as a combination of tenant ID and another column, so the overall amount of data scanned is lowered too.
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[ 3.0 ms ] story [ 11.1 ms ] threadEspecially if it's a multi tenant architecture, it helps to have the cityHash64 caclulated as a combination of tenant ID and another column, so the overall amount of data scanned is lowered too.