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

["Dmitri Carpov (JIRA)" <ji...@apache.org>]

Dmitri Carpov created SPARK-17153:
-------------------------------------

             Summary: [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


When parquet files are persisted using partitions, spark's `readStream` returns data with all `null`s for the partitioned columns.

For example:

```
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)
```

when data is read as stream:

```
spark.readStream.schema(spark.read.load(url).schema).parquet(url)
```

it reads:

```
id, value
null, 1
null, 2
null, 3
```

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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