ClickHouse Hashes Map Keys into Buckets So a One-Key Read Touches One Stream
A Map column is an Array(Tuple(keys, values)) with offsets, and since 26.3 its serialization can hash the keys into buckets so m[âkâ] reads one substream.
A Map column is an Array(Tuple(keys, values)) with offsets, and since 26.3 its serialization can hash the keys into buckets so m[âkâ] reads one substream.