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https://issues.apache.org/jira/browse/CALCITE-4264?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17198433#comment-17198433
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Vladimir Sitnikov commented on CALCITE-4264:
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{quote} Low impact proposal: Compare first the row cost, and only if the row
cost is equal, compare by CPU cost.{quote}
It would rarely be useful in practice: row cost almost always differ, so the
approach of "sort by rows first, then by CPU" would be almost the same as "sort
by rows only".
> 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
> Priority: Major
>
> 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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