[GitHub] [parquet-format] gszadovszky commented on pull request #164: PARQUET-1950: Define core features

[GitBox <gi...@apache.org>]

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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