| <?xml version="1.0" encoding="UTF-8"?> |
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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="disable_streaming_preaggregations" rev="2.5.0 IMPALA-1305"> |
| |
| <title>DISABLE_STREAMING_PREAGGREGATIONS Query Option (<keyword keyref="impala25"/> or higher only)</title> |
| <titlealts audience="PDF"><navtitle>DISABLE_STREAMING_PREAGGREGATIONS</navtitle></titlealts> |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Query Options"/> |
| <data name="Category" value="Performance"/> |
| <data name="Category" value="Aggregate Functions"/> |
| <data name="Category" value="Troubleshooting"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p rev="2.5.0 IMPALA-1305"> |
| <indexterm audience="hidden">DISABLE_STREAMING_PREAGGREGATIONS query option</indexterm> |
| Turns off the <q>streaming preaggregation</q> optimization that is available in <keyword keyref="impala25_full"/> |
| and higher. This optimization reduces unnecessary work performed by queries that perform aggregation |
| operations on columns with few or no duplicate values, for example <codeph>DISTINCT <varname>id_column</varname></codeph> |
| or <codeph>GROUP BY <varname>unique_column</varname></codeph>. If the optimization causes regressions in |
| existing queries that use aggregation functions, you can turn it off as needed by setting this query option. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/type_boolean"/> |
| <p conref="../shared/impala_common.xml#common/default_false_0"/> |
| |
| <note conref="../shared/impala_common.xml#common/one_but_not_true"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| <p> |
| 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. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_250"/> |
| |
| </conbody> |
| </concept> |