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| <h1 class="title topictitle1" id="ariaid-title1">DISABLE_STREAMING_PREAGGREGATIONS Query Option (<span class="keyword">Impala 2.5</span> or higher only)</h1> |
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| <div class="body conbody"> |
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| <p class="p"> |
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| Turns off the <span class="q">"streaming preaggregation"</span> optimization that is available in <span class="keyword">Impala 2.5</span> |
| and higher. This optimization reduces unnecessary work performed by queries that perform aggregation |
| operations on columns with few or no duplicate values, for example <code class="ph codeph">DISTINCT <var class="keyword varname">id_column</var></code> |
| or <code class="ph codeph">GROUP BY <var class="keyword varname">unique_column</var></code>. 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> |
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| <p class="p"> |
| <strong class="ph b">Type:</strong> Boolean; recognized values are 1 and 0, or <code class="ph codeph">true</code> and |
| <code class="ph codeph">false</code>; any other value interpreted as <code class="ph codeph">false</code> |
| </p> |
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| <p class="p"> |
| <strong class="ph b">Default:</strong> <code class="ph codeph">false</code> (shown as 0 in output of <code class="ph codeph">SET</code> |
| statement) |
| </p> |
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| <div class="note note"><span class="notetitle">Note:</span> |
| In <span class="keyword">Impala 2.5.0</span>, only the value 1 enables the option, and the value |
| <code class="ph codeph">true</code> is not recognized. This limitation is tracked by the issue |
| <a class="xref" href="https://issues.apache.org/jira/browse/IMPALA-3334" target="_blank">IMPALA-3334</a>, which shows the releases where the |
| problem is fixed. |
| </div> |
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| <p class="p"> |
| <strong class="ph b">Usage notes:</strong> |
| </p> |
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| <p class="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> |
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| <p class="p"> |
| <strong class="ph b">Added in:</strong> <span class="keyword">Impala 2.5.0</span> |
| </p> |
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| </div> |
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| <div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_set.html">SET Statement</a></div> |
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