[SPARK-2294] TaskSchedulerImpl and TaskSetManager do not properly prioritize which tasks get assigned to an executor

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.0.0, 1.0.1
• Fix Version/s: 1.1.0
• Component/s: Spark Core
• Assignee: Nan Zhu
• Reporter: Kay Ousterhout
• Created: 26/Jun/14 17:43
• Updated: 06/Aug/14 06:03
• Resolved: 06/Aug/14 06:03

Description

If an executor E is free, a task may be speculatively assigned to E when there are other tasks in the job that have not been launched (at all) yet. Similarly, a task without any locality preferences may be assigned to E when there was another NODE_LOCAL task that could have been scheduled.

This happens because TaskSchedulerImpl calls TaskSetManager.resourceOffer (which in turn calls TaskSetManager.findTask) with increasing locality levels, beginning with PROCESS_LOCAL, followed by NODE_LOCAL, and so on until the highest currently allowed level. Now, supposed NODE_LOCAL is the highest currently allowed locality level. The first time findTask is called, it will be called with max level PROCESS_LOCAL; if it cannot find any PROCESS_LOCAL tasks, it will try to schedule tasks with no locality preferences or speculative tasks. As a result, speculative tasks or tasks with no preferences may be scheduled instead of NODE_LOCAL tasks.

cc matei

Issue Links

• links to: [Github] Pull Request #1313 (CodingCat)