The SHUFFLE_DISTINCT_EXPRS query option controls the shuffling behavior when a query has both grouping and distinct expressions. Impala can optionally include the distinct expressions in the hash exchange to spread the data among more nodes. However, this plan requires one more hash exchange phase.

It is recommended that you turn off this option if the NDVs of the grouping expressions are high.

Type: Boolean; recognized values are 1 and 0, or true and false; any other value interpreted as false

Default: false