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Posted to issues@calcite.apache.org by "Caizhi Weng (Jira)" <ji...@apache.org> on 2020/10/23 08:00:29 UTC
[jira] [Updated] (CALCITE-4351) The result of
RelMdUtil#numDistinctVals is incorrect when inputs are large
[ https://issues.apache.org/jira/browse/CALCITE-4351?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Caizhi Weng updated CALCITE-4351:
---------------------------------
Description:
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.
was:
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, {{domainSize = 1e18}} and {{numSelected = 1e10}}) 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.
> The result of RelMdUtil#numDistinctVals is incorrect when inputs are large
> --------------------------------------------------------------------------
>
> 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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