[jira] [Commented] (CALCITE-4351) RelMdUtil#numDistinctVals always returns 0 for large inputs

["lincoln lee (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-4351?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17307648#comment-17307648 ] 

lincoln lee commented on CALCITE-4351:
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[~fan_li_ya] When domainSize is in range  (0, 1), the new formula will produce Double.NaN result which may cause unexcepted exceptions，so at least we should add protection for the code? {code}Math.log(1.0 - 1.0 / dSize){code} 

> RelMdUtil#numDistinctVals always returns 0 for large inputs
> -----------------------------------------------------------
>
>                 Key: CALCITE-4351
>                 URL: https://issues.apache.org/jira/browse/CALCITE-4351
>             Project: Calcite
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 1.26.0
>            Reporter: Caizhi Weng
>            Priority: Major
>
> Previous implementation of {{RelMdUtil#numDistinctVals}} uses the approximation {{ln(1 + x) ~= x}} when {{x}} is small.
> However CALCITE-4132 remove this approximation to make the result more accurate. This causes the function to calculate an incorrect result for large inputs (for example, when {{domainSize = 1e18}} and {{numSelected = 1e10}} the result is 0) due to precision problems.
> What I would suggest is to treat small and large inputs in different ways. For small inputs we use the new, more precise function and for large inputs we use the old, approximated function.



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