| <?xml version="1.0" encoding="UTF-8"?> |
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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="shuffle_distinct_exprs"> |
| |
| <title>SHUFFLE_DISTINCT_EXPRS Query Option</title> |
| |
| <titlealts audience="PDF"> |
| |
| <navtitle>SHUFFLE_DISTINCT_EXPRS</navtitle> |
| |
| </titlealts> |
| |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Query Options"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| The <codeph>SHUFFLE_DISTINCT_EXPRS</codeph> 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. |
| </p> |
| |
| <p> |
| It is recommended that you turn off this option if the NDVs of the grouping |
| expressions are high. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/type_boolean"/> |
| |
| <p conref="../shared/impala_common.xml#common/default_false"/> |
| |
| </conbody> |
| |
| </concept> |