[jira] [Commented] (ARROW-12264) [C++][Dataset] Handle NaNs correctly in Parquet predicate push-down

["Antoine Pitrou (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-12264?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17644354#comment-17644354 ] 

Antoine Pitrou commented on ARROW-12264:
----------------------------------------

cc @westonpace

> [C++][Dataset] Handle NaNs correctly in Parquet predicate push-down
> -------------------------------------------------------------------
>
>                 Key: ARROW-12264
>                 URL: https://issues.apache.org/jira/browse/ARROW-12264
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: C++, Parquet
>            Reporter: Antoine Pitrou
>            Priority: Major
>
> The Parquet spec (in parquet.thrift) says the following about handling of floating-point statistics:
> {code}
>    * (*) Because the sorting order is not specified properly for floating
>    *     point values (relations vs. total ordering) the following
>    *     compatibility rules should be applied when reading statistics:
>    *     - 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.
>    *     - When looking for NaN values, min and max should be ignored.
> {code}
> It appears that the dataset code uses the following filter expression when doing Parquet predicate push-down (in {{file_parquet.cc}}):
> {code:c++}
>     return and_(greater_equal(field_expr, literal(min)),
>                 less_equal(field_expr, literal(max)));
> {code}
> A NaN value will fail that filter and yet may be found in the given Parquet column chunk.
> We may instead need a "greater_equal_or_nan" comparison that returns true if either value is NaN.



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