[
https://issues.apache.org/jira/browse/ARROW-1983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16730844#comment-16730844
]
Matthew Rocklin commented on ARROW-1983:
----------------------------------------
> If I understand correctly, we need to combine all of the row group metadata
> for all files in a directory.
Yes. Ideally when writing a row group we would get some metadata object in
memory. We would then collect all of those objects and hand them to some
`write_metadata` function afterwards.
> When a new file is written, does this file have to be updated?
Yes, or it can be removed/invalidated.
As a side note, this is probably one of a small number of issues that stop Dask
Dataframe from using PyArrow by default. Metadata files with full row group
information are especially valuable for us, particularly with remote/cloud
storage. (I'm going through Dask's parquet handling now)
> [Python] Add ability to write parquet `_metadata` file
> ------------------------------------------------------
>
> Key: ARROW-1983
> URL: https://issues.apache.org/jira/browse/ARROW-1983
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Python
> Reporter: Jim Crist
> Assignee: Robert Gruener
> Priority: Major
> Labels: beginner, parquet
> Fix For: 0.13.0
>
>
> Currently {{pyarrow.parquet}} can only write the {{_common_metadata}} file
> (mostly just schema information). It would be useful to add the ability to
> write a {{_metadata}} file as well. This should include information about
> each row group in the dataset, including summary statistics. Having this
> summary file would allow filtering of row groups without needing to access
> each file beforehand.
> This would require that the user is able to get the written RowGroups out of
> a {{pyarrow.parquet.write_table}} call and then give these objects as a list
> to new function that then passes them on as C++ objects to {{parquet-cpp}}
> that generates the respective {{_metadata}} file.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
