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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="delete_stats_in_truncate"> |
| |
| <title>DELETE_STATS_IN_TRUNCATE Query Option</title> |
| <titlealts audience="PDF"><navtitle>DELETE STATS IN TRUNCATE</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="Querying"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| This query option <codeph>DELETE_STATS_IN_TRUNCATE</codeph> can be used to delete or retain |
| table statistics. The default value of this option is 1 or true which means table statistics will |
| be deleted as part of truncate operation. However the default may not be an ideal solution in |
| case of non-transactional tables when the table and column statistics for the table are also |
| deleted by default. This can be an expensive operation especially when many truncate table |
| commands are running concurrently. In cases where truncate operation is used to remove the |
| existing data and then reload new data, it is likely that you will compute stats again as soon as |
| the new data is reloaded. This would overwrite the existing statistics and hence the additional |
| time spent by the truncate operation to delete column and table statistics becomes obsolete. To |
| avoid this expensive operation and to improve performance, you can set this query option to false |
| or 0. When set to false, a truncate operation will not delete the table and column statistics for |
| the table. |
| </p> |
| |
| <p> |
| <b>Type:</b><codeph>BOOLEAN</codeph>; recognized values are 1 and 0, or true and false; |
| </p> |
| |
| <p> |
| <b>Default:</b><codeph>TRUE</codeph> (shown as 1 in output of SET statement). |
| </p> |
| |
| <p><b>Added in:</b> |
| <keyword keyref="impala40"/></p> |
| |
| </conbody> |
| </concept> |