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https://issues.apache.org/jira/browse/ARROW-8733?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17105223#comment-17105223
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Joris Van den Bossche commented on ARROW-8733:
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> but more importantly because it may or not map to what the real physical
> FileMetaData holds
Do you mean because the {{_metadata}} file might not be correct (I think we can
assume it is, responsibility of the user to ensure the integrity f the
dataset?), or rather that the metadata might not map anymore to the exact
fragment for other reasons? (eg we might already have filtered out some
fragment / parts of fragments)
The file paths contained in the metadata of a {{_metadata}} file will of course
also not map to the one in the physical metadata of the actual data file.
> I plan to expose the statistics probably via shared_ptr<Expression>.
The idea here would then be to expose statistics of a Fragment in a file
format-agnostic way?
> What about serialization for dask? That's another potential issue.
The FileMetadata itself are already serializable in Python, as well as
expressions.
> [C++][Dataset][Python] ParquetFileFragment should provide access to parquet
> FileMetadata
> ----------------------------------------------------------------------------------------
>
> Key: ARROW-8733
> URL: https://issues.apache.org/jira/browse/ARROW-8733
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++, Python
> Reporter: Joris Van den Bossche
> Priority: Major
> Labels: dataset
> Fix For: 1.0.0
>
>
> Related to ARROW-8062 (as there we will also need a way to expose the global
> FileMetadata). But independently, it would be useful to get access to the
> FileMetadata on each {{ParquetFileFragment}} (eg to get access to the
> statistics).
> This would be relatively simple to code on the Python/R side, since we have
> access to the file path, and could read the metadata from the file backing
> the fragment, and return this as a FileMetadata object.
> I am wondering if we want to integrate this with ARROW-8062, since when the
> fragments were created from a {{_metadata}} file, a
> {{ParquetFileFragment.metadata}} attribute would not need to read it from the
> parquet file in this case, but from the global metadata (at least for eg the
> row group data).
> Another question: what for a ParquetFileFragment that maps to a single row
> group?
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