[jira] [Commented] (SPARK-17153) [Structured streams] readStream ignores partition columns

["Yin Huai (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-17153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15613705#comment-15613705 ] 

Yin Huai commented on SPARK-17153:
----------------------------------

This change needs a release note because {{spark.readStream.json('/a.file')}} (create a stream on a single file) will not work anymore (https://github.com/apache/spark/pull/14803/files#diff-e82a44dc550d2a0a92e44d1ec2ecabccR52).

> [Structured streams] readStream ignores partition columns
> ---------------------------------------------------------
>
>                 Key: SPARK-17153
>                 URL: https://issues.apache.org/jira/browse/SPARK-17153
>             Project: Spark
>          Issue Type: Bug
>          Components: Streaming
>    Affects Versions: 2.0.0
>            Reporter: Dmitri Carpov
>            Assignee: Liang-Chi Hsieh
>              Labels: release_notes
>             Fix For: 2.0.2, 2.1.0
>
>
> When parquet files are persisted using partitions, spark's `readStream` returns data with all `null`s for the partitioned columns.
> For example:
> {noformat}
> case class A(id: Int, value: Int)
> val data = spark.createDataset(Seq(
>   A(1, 1), 
>   A(2, 2), 
>   A(2, 3))
> )
> val url = "/mnt/databricks/test"
> data.write.partitionBy("id").parquet(url)
> {noformat}
> when data is read as stream:
> {noformat}
> spark.readStream.schema(spark.read.load(url).schema).parquet(url)
> {noformat}
> it reads:
> {noformat}
> id, value
> null, 1
> null, 2
> null, 3
> {noformat}
> A possible reason is `readStream` reads parquet files directly but when those are stored the columns they are partitioned by are excluded from the file itself. In the given example the parquet files contain `value` information only since `id` is partition.



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