| <?xml version="1.0" encoding="UTF-8"?> |
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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="prefetch_mode" rev="2.6.0 IMPALA-3286"> |
| |
| <title>PREFETCH_MODE Query Option (<keyword keyref="impala26"/> or higher only)</title> |
| <titlealts audience="PDF"><navtitle>PREFETCH_MODE</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="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p rev="2.6.0 IMPALA-3286"> |
| <indexterm audience="hidden">PREFETCH_MODE query option</indexterm> |
| Determines whether the prefetching optimization is applied during |
| join query processing. |
| </p> |
| |
| <p> |
| <b>Type:</b> numeric (0, 1) |
| or corresponding mnemonic strings (<codeph>NONE</codeph>, <codeph>HT_BUCKET</codeph>). |
| </p> |
| |
| <p> |
| <b>Default:</b> 1 (equivalent to <codeph>HT_BUCKET</codeph>) |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_260"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| <p> |
| The default mode is 1, which means that hash table buckets are |
| prefetched during join query processing. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/related_info"/> |
| <p> |
| <xref href="impala_joins.xml#joins"/>, |
| <xref href="impala_perf_joins.xml#perf_joins"/>. |
| </p> |
| |
| </conbody> |
| </concept> |