Turns off the "streaming preaggregation" optimization that is available in CDH 5.7 / Impala 2.5 and higher. This optimization reduces unnecessary work performed by queries that perform aggregation operations on columns with few or no duplicate values, for example DISTINCT id_column or GROUP BY unique_column. If the optimization causes regressions in existing queries that use aggregation functions, you can turn it off as needed by setting this query option.

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

Default: false (shown as 0 in output of SET statement)

  Note: In CDH 5.7.0 / Impala 2.5.0, only the value 1 enables the option, and the value true is not recognized. This limitation is tracked by the issue IMPALA-3334, which shows the releases where the problem is fixed.

Usage notes:

Typically, queries that would require enabling this option involve very large numbers of aggregated values, such as a billion or more distinct keys being processed on each worker node.

Added in: CDH 5.7.0 (Impala 2.5.0)