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Posted to dev@calcite.apache.org by "Thomas Rebele (Jira)" <ji...@apache.org> on 2020/09/18 16:04:00 UTC

[jira] [Created] (CALCITE-4264) The query planner should take CPU cost into account

Thomas Rebele created CALCITE-4264:
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             Summary: The query planner should take CPU cost into account
                 Key: CALCITE-4264
                 URL: https://issues.apache.org/jira/browse/CALCITE-4264
             Project: Calcite
          Issue Type: Improvement
            Reporter: Thomas Rebele


Calcite only takes the row count into account when optimizing the queries. See [the relevant lines in VolcanoCost|https://github.com/apache/calcite/blob/52a57078ba081b24b9d086ed363c715485d1a519/core/src/main/java/org/apache/calcite/plan/volcano/VolcanoCost.java#L98-L116]. However, two plans might have the same row count, but differ greatly in CPU cost. This happens for example when the limit sort rule ([CALCITE-3920|https://issues.apache.org/jira/browse/CALCITE-3920]) is activated. The row cost is the same, the EnumerableLimitSort only sorts the input partially, so has a lower CPU cost.

Low impact proposal: Compare first the row cost, and only if the row cost is equal, compare by CPU cost.



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