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https://issues.apache.org/jira/browse/CALCITE-3460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16963260#comment-16963260
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Julian Hyde commented on CALCITE-3460:
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It's important to write a test. It doesn't have to hard fail if there is a
regression, but it does have to demonstrate significant performance difference
(100x or more) before and after the fix. {{SqlValidatorTest.testLarge()}} is an
example.
> Poor performance in RexReplacer for large queries
> -------------------------------------------------
>
> Key: CALCITE-3460
> URL: https://issues.apache.org/jira/browse/CALCITE-3460
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Haisheng Yuan
> Priority: Major
> Labels: pull-request-available
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> We have queries that have tens of thousands of RexCalls.
> reducibleExps.indexOf(call) is an O(n) operation, which takes 50% of the
> running time, causing the query runs for ever until timed out.
> In RexShuttle, ImmutableList iterator creation in {{visitList}} takes another
> 5~7% of running time, and it is creating millions of temporary iterator
> object, not only time consuming, but also memory consuming.
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