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| <meta name="DC.Title" content="PREFETCH_MODE Query Option (Impala 2.6 or higher only)" /> |
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| <title>PREFETCH_MODE Query Option (Impala 2.6 or higher only)</title> |
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| <h1 class="title topictitle1" id="ariaid-title1">PREFETCH_MODE Query Option (<span class="keyword">Impala 2.6</span> or higher only)</h1> |
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| <p class="p"> |
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| Determines whether the prefetching optimization is applied during |
| join query processing. |
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| <strong class="ph b">Type:</strong> numeric (0, 1) |
| or corresponding mnemonic strings (<code class="ph codeph">NONE</code>, <code class="ph codeph">HT_BUCKET</code>). |
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| <strong class="ph b">Default:</strong> 1 (equivalent to <code class="ph codeph">HT_BUCKET</code>) |
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| <p class="p"> |
| <strong class="ph b">Added in:</strong> <span class="keyword">Impala 2.6.0</span> |
| </p> |
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| <p class="p"> |
| <strong class="ph b">Usage notes:</strong> |
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| The default mode is 1, which means that hash table buckets are |
| prefetched during join query processing. |
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| <strong class="ph b">Related information:</strong> |
| </p> |
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| <p class="p"> |
| <a class="xref" href="impala_joins.html#joins">Joins in Impala SELECT Statements</a>, |
| <a class="xref" href="impala_perf_joins.html#perf_joins">Performance Considerations for Join Queries</a>. |
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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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