[jira] [Resolved] (ARROW-5140) [Bug?][Parquet] Can write a jagged array column of strings to disk, but hit `ArrowNotImplementedError` on read

["Neal Richardson (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-5140?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Neal Richardson resolved ARROW-5140.
------------------------------------
    Resolution: Not A Problem

> [Bug?][Parquet] Can write a jagged array column of strings to disk, but hit `ArrowNotImplementedError` on read
> --------------------------------------------------------------------------------------------------------------
>
>                 Key: ARROW-5140
>                 URL: https://issues.apache.org/jira/browse/ARROW-5140
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Python
>    Affects Versions: 0.12.0
>         Environment: Debian 8
>            Reporter: Zachary Jablons
>            Priority: Blocker
>             Fix For: 0.14.0
>
>
> h1. Description
> I encountered an issue on a proprietary dataset where we have a schema that looks roughly like:
> {\{ |-- ids: array (nullable = true) | |-- element: string (containsNull = true) }}
> I was able to write this dataset to parquet no problem (using {{pq.write_table}}), but upon reading it (using {{pq.read_table}}) I encountered the following error: {{ArrowNotImplementedError: Nested data conversions not implemented for chunked array outputs}} (a full stacktrace is attached below)
> I believe that this is pretty confusing because I was able to serialize but not deserialize this table. I was able to also find that this does not happen with all sizes of the dataset - a smaller sample did not encounter this issue! So I built a small reproduction harness and checked out where this could happen:
> h2. Further investigation
>  * If I set the maximum number of elements per row of {{ids}}, I found that reducing it allows me to serialize/deserialize more rows
>  * At a setting of maximum 15 elements per row, each element being at most 20 characters, I fail at about 1.3e5 rows
>  * At the limit of my willingness to spend time building giant dataframes to investigate this, I haven't been able to reproduce this issue for e.g. longs instead of strings
>  * Another column in this dataset consists of much longer strings than this column's strings (when concatenated), and the total sum of all characters is ~3x in _that_ column versus this trouble column (when the strings in each row are just simply concatenated). I have no issue serializing / deserializing that column.
>  * The fact that each array is of a different length doesn't seem to matter - if I change it so as to force everything to be ~14 elements, it fails with the same error even at 1e5 rows.
> h1. Reproduction code
> This [gist|https://gist.github.com/zmjjmz/1bf738966d2df147a4fae7268ee3d812] should have both a stacktrace and reproduction code.
> h2. Version info
> {\{pyarrow==0.12.0 parquet==1.2 }}
> h1. Mea culpa
> I copy-pasted this from Github on request ([https://github.com/apache/arrow/issues/4115]), and Jira formatting is a nightmare compared to markdown, so I apologize.



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