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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