[jira] [Assigned] (ARROW-15318) [C++][Python] Regression reading partition keys of large batches.

["Weston Pace (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-15318?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Weston Pace reassigned ARROW-15318:
-----------------------------------

    Assignee: Weston Pace

> [C++][Python] Regression reading partition keys of large batches.
> -----------------------------------------------------------------
>
>                 Key: ARROW-15318
>                 URL: https://issues.apache.org/jira/browse/ARROW-15318
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: C++, Python
>    Affects Versions: 7.0.0
>            Reporter: A. Coady
>            Assignee: Weston Pace
>            Priority: Blocker
>
> In a partitioned dataset with chunks larger than the default 1Mi batch size, reading _only_ the partition keys is hanging, and consuming unbounded memory. The bug first appeared in nightly build `7.0.0.dev468`.
> {code:python}
> In [1]: import pyarrow as pa, pyarrow.parquet as pq, numpy as np
> In [2]: pa.__version__
> Out[2]: '7.0.0.dev468'
> In [3]: table = pa.table({'key': pa.repeat(0, 2 ** 20 + 1), 'value': np.arange(2 ** 20 + 1)})
> In [4]: pq.write_to_dataset(table[:2 ** 20], 'one', partition_cols=['key'])
> In [5]: pq.write_to_dataset(table[:2 ** 20 + 1], 'two', partition_cols=['key'])
> In [6]: pq.read_table('one', columns=['key'])['key'].num_chunks
> Out[6]: 1
> In [7]: pq.read_table('two', columns=['key', 'value'])['key'].num_chunks
> Out[7]: 2
> In [8]: pq.read_table('two', columns=['key'])['key'].num_chunks
> zsh: killed     ipython # hangs; kllled
> {code}



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