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From "Tim Armstrong (JIRA)" <j...@apache.org>
Subject [jira] [Created] (IMPALA-5713) Consider always reserving memory for grouping pre-aggregations
Date Mon, 24 Jul 2017 23:06:00 GMT
Tim Armstrong created IMPALA-5713:
-------------------------------------

             Summary: Consider always reserving memory for grouping pre-aggregations
                 Key: IMPALA-5713
                 URL: https://issues.apache.org/jira/browse/IMPALA-5713
             Project: IMPALA
          Issue Type: Sub-task
          Components: Backend
    Affects Versions: Impala 2.10.0
            Reporter: Tim Armstrong


The initial IMPALA-3200 code added the ability for a grouping pre-aggregation to run with
zero reservation, passing through all of the rows. However, this is a very low performance
mode for aggregations that reduce their input a lot, since it forces everything to be sent
over the network. We would be better off in most cases requiring more memory but not allowing
perf to degrade so much.



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