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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="enable_expr_rewrites"> |
| |
| <title>ENABLE_EXPR_REWRITES Query Option</title> |
| |
| <titlealts audience="PDF"> |
| |
| <navtitle>ENABLE_EXPR_REWRITES</navtitle> |
| |
| </titlealts> |
| |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Query Options"/> |
| <data name="Category" value="Troubleshooting"/> |
| <data name="Category" value="Performance"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| The <codeph>ENABLE_EXPR_REWRITES</codeph> query option controls whether to enable or |
| disable the query compile time optimizations. These optimizations rewrite the expression |
| trees to a more compact and optimized form that helps avoid redundant expression |
| evaluation at run time. Performance optimizations controlled by this query option include: |
| </p> |
| |
| <ul> |
| <li> |
| Constant folding (added in <keyword keyref="impala28">)</keyword> |
| </li> |
| |
| <li> |
| Extracting common conjuncts from disjunctions (added in |
| <keyword |
| keyref="impala28">)</keyword> |
| </li> |
| |
| <li> |
| Simplify conditionals with constant conditions (added in |
| <keyword |
| keyref="impala29">)</keyword> |
| </li> |
| </ul> |
| |
| <p> |
| Set the option to <codeph>false</codeph> or <codeph>0</codeph> to disable the performance |
| optimizations. |
| </p> |
| |
| <p> |
| <b>Type: </b><codeph>boolean</codeph> |
| </p> |
| |
| <p> |
| <b>Default:</b> <codeph>true</codeph> (<codeph>1</codeph>) |
| </p> |
| |
| <p> |
| <b>Added in:</b> <keyword keyref="impala28"/> |
| </p> |
| |
| </conbody> |
| |
| </concept> |