[SPARK-20593] Writing Parquet: Cannot build an empty group

• Type: Question
• Status: Closed
• Priority: Minor
• Resolution: Not A Problem
• Affects Version/s: 2.1.1
• Component/s: Spark Core, Spark Shell

Environment

I use Apache Spark 2.1.1 (used 2.1.0 and it was the same, switched today). Tested only on Mac

• Assignee: Unassigned
• Reporter: Viktor Khristenko
• Created: 04/May/17 05:47
• Updated: 26/Jul/22 01:33
• Resolved: 04/May/17 07:12

Description

Hi,

This is my first ticket and I apologize for/if I'm doing certain things in an improper way.

I have a dataset:

root
|-- muons: array (nullable = true)
|    |-- element: struct (containsNull = true)
|    |    |-- reco::Candidate: struct (nullable = true)
|    |    |-- qx3_: integer (nullable = true)
|    |    |-- pt_: float (nullable = true)
|    |    |-- eta_: float (nullable = true)
|    |    |-- phi_: float (nullable = true)
|    |    |-- mass_: float (nullable = true)
|    |    |-- vertex_: struct (nullable = true)
|    |    |    |-- fCoordinates: struct (nullable = true)
|    |    |    |    |-- fX: float (nullable = true)
|    |    |    |    |-- fY: float (nullable = true)
|    |    |    |    |-- fZ: float (nullable = true)
|    |    |-- pdgId_: integer (nullable = true)
|    |    |-- status_: integer (nullable = true)
|    |    |-- cachePolarFixed_: struct (nullable = true)
|    |    |-- cacheCartesianFixed_: struct (nullable = true)

As you can see, there are 3 empty structs in this schema. I know 100% that I can read/manipulate/do whatever. However, when I try writing to disk in parquet, I get the following Exception:

ds.write.format("parquet").save(outputPathName):

java.lang.IllegalStateException: Cannot build an empty group
at org.apache.parquet.Preconditions.checkState(Preconditions.java:91)
at org.apache.parquet.schema.Types$BaseGroupBuilder.build(Types.java:622)
at org.apache.parquet.schema.Types$BaseGroupBuilder.build(Types.java:497)
at org.apache.parquet.schema.Types$Builder.named(Types.java:286)
at org.apache.spark.sql.execution.datasources.parquet.ParquetSchemaConverter.convertField(ParquetSchemaConverter.scala:535)
at org.apache.spark.sql.execution.datasources.parquet.ParquetSchemaConverter.convertField(ParquetSchemaConverter.scala:321)
at org.apache.spark.sql.execution.datasources.parquet.ParquetSchemaConverter$$anonfun$convertField$1.apply(ParquetSchemaConverter.scala:534)
at org.apache.spark.sql.execution.datasources.parquet.ParquetSchemaConverter$$anonfun$convertField$1.apply(ParquetSchemaConverter.scala:533)
So, basically I would like to understand if it's a bug or an intended behavior??? I also assume that it's related to the empty structs. Any help would be really appreciated!

I've quickly created stripped version and that one works without any issues!
For reference, I put a link to the original question on SO[1]

VK

[1] http://stackoverflow.com/questions/43767358/apache-spark-parquet-cannot-build-an-empty-group

Issue Links

• relates to: DRILL-8272 Skip MAP column without children when creating parquet tables
• relates to: DRILL-8261 Make the XML format plugin's attributes MAP an implicit column