[SPARK-3963] Support getting task-scoped properties from TaskContext

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Incomplete
• Component/s: Spark Core
• Labels: bulk-closed
• Assignee: Unassigned
• Reporter: Patrick Wendell
• Created: 16/Oct/14 03:55
• Updated: 21/May/19 05:36
• Resolved: 21/May/19 05:36

Description

This is a proposal for a minor feature. Given stabilization of the TaskContext API, it would be nice to have a mechanism for Spark jobs to access properties that are defined based on task-level scope by Spark RDD's. I'd like to propose adding a simple properties hash map with some standard spark properties that users can access. Later it would be nice to support users setting these properties, but for now to keep it simple in 1.2. I'd prefer users not be able to set them.

The main use case is providing the file name from Hadoop RDD's, a very common request. But I'd imagine us using this for other things later on. We could also use this to expose some of the taskMetrics, such as e.g. the input bytes.

val data = sc.textFile("s3n//..2014/*/*/*.json")
data.mapPartitions { 
  val tc = TaskContext.get
  val filename = tc.getProperty(TaskContext.HADOOP_FILE_NAME)
  val parts = fileName.split("/")
  val (year, month, day) = (parts[3], parts[4], parts[5])
  ...
}

Internally we'd have a method called setProperty, but this wouldn't be exposed initially. This is structured as a simple (String, String) hash map for ease of porting to python.

Issue Links

• is related to: SPARK-7171 Allow for more flexible use of metric sources