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https://issues.apache.org/jira/browse/CALCITE-4351?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Caizhi Weng updated CALCITE-4351:
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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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