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ποΈ BITMAP
BITMAP is often used to accelerate count distinct. It is similar but more accurate in count distinct than HyperLogLog (HLL). BITMAP consumes more memory and disk resources. It supports only aggregation of INT data. If you want to apply bitmap to string data, you must map the data using the low-cardinality dictionary.
ποΈ HLL (HyperLogLog)
Description