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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