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https://issues.apache.org/jira/browse/PARQUET-1222?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Zoltan Ivanfi updated PARQUET-1222:
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Attachment: ordering.png
> Definition of float and double sort order is ambigious
> ------------------------------------------------------
>
> Key: PARQUET-1222
> URL: https://issues.apache.org/jira/browse/PARQUET-1222
> Project: Parquet
> Issue Type: Bug
> Components: parquet-format
> Reporter: Zoltan Ivanfi
> Priority: Critical
> Fix For: format-2.5.0
>
> Attachments: ordering.png
>
>
> Currently parquet-format specifies the sort order for floating point numbers
> as follows:
> {code:java}
> * FLOAT - signed comparison of the represented value
> * DOUBLE - signed comparison of the represented value
> {code}
> The problem is that the comparison of floating point numbers is only a
> partial ordering with strange behaviour in specific corner cases. For
> example, according to IEEE 754, -0 is neither less nor more than \+0 and
> comparing NaN to anything always returns false. This ordering is not suitable
> for statistics. Additionally, the Java implementation already uses a
> different (total) ordering that handles these cases correctly but differently
> than the C\+\+ implementations, which leads to interoperability problems.
> TypeDefinedOrder for doubles and floats should be deprecated and a new
> TotalFloatingPointOrder should be introduced. The default for writing doubles
> and floats would be the new TotalFloatingPointOrder. The proposed ordering is
> the following:
> * -∞
> * negative numbers in their natural order
> * -0 and +0 in the same equivalence class \(!)
> * positive numbers in their natural order
> * +∞
> * all NaN values, including the negative ones \(!), in the same equivalence
> class \(!)
> This ordering should be effective and easy to implement in all programming
> languages.
> For reading existing stats created using TypeDefinedOrder, the following
> compatibility rules should be applied:
> * When looking for NaN values, min and max should be ignored.
> * If the min is a NaN, it should be ignored.
> * If the max is a NaN, it should be ignored.
> * If the min is \+0, the row group may contain -0 values as well.
> * If the max is -0, the row group may contain \+0 values as well.
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