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https://issues.apache.org/jira/browse/CALCITE-4577?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17325474#comment-17325474
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Haisheng Yuan commented on CALCITE-4577:
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See comments in CALCITE-4578, since 1.24.0, the issue should exist anymore.
> RelDigestWriter#done has performance issue when node's inputs is large
> ----------------------------------------------------------------------
>
> Key: CALCITE-4577
> URL: https://issues.apache.org/jira/browse/CALCITE-4577
> Project: Calcite
> Issue Type: Bug
> Components: core
> Reporter: Jiatao Tao
> Assignee: Jiatao Tao
> Priority: Critical
> Attachments: image-2021-04-11-16-53-35-466.png,
> image-2021-04-11-16-53-58-757.png
>
>
> Example like that: insert xxx VALUES (1, 'one'), (2, 'two'), (3,
> 'three')...(10000, 'ten thousand');
> It generates a Union node with 10000 inputs, and the performance is poor,
> here's the profile:
>
> !image-2021-04-11-16-53-58-757.png|width=735,height=109!
> A point that affects performance is the array copy of StringBuilder, current
> we just new StringBuilder with default capacity, my proposal is to consider
> the node's input size, like that(we can discuss the strategy):
> org.apache.calcite.rel.AbstractRelNode.RelDigestWriter#done
> {code:java}
> StringBuilder sb = new StringBuilder((values.size() + 1) * 16);{code}
> It's about 20% performance improvement and mem is more smooth.
>
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