[jira] [Commented] (PARQUET-1950) Define core features / compliance level

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PARQUET-1950?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17276187#comment-17276187 ] 

ASF GitHub Bot commented on PARQUET-1950:
-----------------------------------------

gszadovszky commented on pull request #164:
URL: https://github.com/apache/parquet-format/pull/164#issuecomment-770716726


   @emkornfield, in parquet-mr there was another reason to use the `file_path` in the footer. The feature is called _summary files_. The idea was to have a separate file containing a summarized footer of several parquet files so you might do filtering and pruning without even checking a file's own footer. As far as I know this implementation exists in parquet-mr only and there are no specification for it in parquet-format.
   This feature is more or less abandoned meaning during the development of some newer features (e.g. column indexes, bloom filters) the related parts might not updated properly. There were a couple of discussions about this topic in the dev list: [here](https://lists.apache.org/thread.html/fb232d024d3ca0f3900b76fb884b55fad11dffafb182d6f336b37a69%40%3Cdev.parquet.apache.org%3E) and [here](https://lists.apache.org/thread.html/r2e539c50c1cc818304de2b7dc28a4109aaa529955a42664e3073f811%40%3Cdev.parquet.apache.org%3E).
   
   Because non of the ideas of _external column chunks_ nor the _summary files_ were spread across the different implementations (because of the lack of specification) I think we should not include the usage of the field `file_path` in this document or even explicitly specify that this field is not supported.
   
   I am open to specify such features properly and after the required demonstration we may include them in a later version of the core features. However, I think these requirements (e.g. snapshot API, summary files) are not necessarily needed by all of our clients or already implemented in some ways (e.g. storing statistics in HMS, Iceberg).
   
   


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> Define core features / compliance level
> ---------------------------------------
>
>                 Key: PARQUET-1950
>                 URL: https://issues.apache.org/jira/browse/PARQUET-1950
>             Project: Parquet
>          Issue Type: New Feature
>          Components: parquet-format
>            Reporter: Gabor Szadovszky
>            Assignee: Gabor Szadovszky
>            Priority: Major
>
> Parquet format is getting more and more features while the different implementations cannot keep the pace and left behind with some features implemented and some are not. In many cases it is also not clear if the related feature is mature enough to be used widely or more an experimental one.
> These are huge issues that makes hard ensure interoperability between the different implementations.
> The following idea came up in a [discussion|https://lists.apache.org/thread.html/rde5cba8443487bccd47593ddf5dfb39f69c729d260165cb936a1a289%40%3Cdev.parquet.apache.org%3E]. Create a now document in the parquet-format repository that lists the "core features". This document is versioned by the parquet-format releases. This way a certain version of "core features" defines a level of compatibility between the different implementations. This version number can be written to a new field (e.g. complianceLevel) in the footer. If an implementation writes a file with a version in the field it must implement all the related "core features" (read and write) and must not use any other features at write because it makes the data unreadable by another implementation if only the same level of "core features" are implemented.
> For example if we have encoding A listed in the version 1 "core features" but encoding B is not then at "complianceLevel = 1" we can use encoding A but we cannot use encoding B because it would make the related data unreadable.



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