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How Are Joins Performed In Impala? |
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Answer» By DEFAULT, Impala automatically determines the most efficient order in which to join tables using a cost-BASED method, based on their overall size and NUMBER of rows. (This is a new feature in Impala 1.2.2 and higher.) The COMPUTE STATS statement gathers information about each table that is crucial for efficient join performance. Impala CHOOSES between two techniques for join queries, known as "broadcast joins" and "partitioned joins". By default, Impala automatically determines the most efficient order in which to join tables using a cost-based method, based on their overall size and number of rows. (This is a new feature in Impala 1.2.2 and higher.) The COMPUTE STATS statement gathers information about each table that is crucial for efficient join performance. Impala chooses between two techniques for join queries, known as "broadcast joins" and "partitioned joins". |
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