[DRILL-5304] Queries fail intermittently when there is skew in data distribution

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.10.0
• Fix Version/s: 1.10.0
• Component/s: Query Planning & Optimization
• Labels: ready-to-commit
• Assignee: Padma Penumarthy
• Reporter: Abhishek Girish
• Reviewer: Abhishek Girish
• Created: 28/Feb/17 21:56
• Updated: 10/Apr/17 17:33
• Resolved: 02/Mar/17 22:51

Description

In a distributed environment, we've observed certain queries to fail execution intermittently, with an assignment logic issue, when the underlying data is skewed w.r.t distribution.

For example the TPC-H query 7 failed with the below error:

java.sql.SQLException: SYSTEM ERROR: IllegalArgumentException: MinorFragmentId 105 has no read entries assigned
...
  (org.apache.drill.exec.work.foreman.ForemanException) Unexpected exception during fragment initialization: MinorFragmentId 105 has no read entries assigned
    org.apache.drill.exec.work.foreman.Foreman.run():281
    java.util.concurrent.ThreadPoolExecutor.runWorker():1145
    java.util.concurrent.ThreadPoolExecutor$Worker.run():615
    java.lang.Thread.run():744
  Caused By (java.lang.IllegalArgumentException) MinorFragmentId 105 has no read entries assigned

Log containing full stack trace is attached.

And for this query, the underlying TPC-H SF100 Parquet dataset was observed to be located mostly only on 2-3 nodes on an 8 node DFS environment. The data distribution skew on this cluster is most likely the triggering factor for this case, as the same query, on the same dataset does not show this failure on a different test cluster (with possibly different data distribution).

Also, another query failed with a similar error when slice target was set to 1.

Failed with exception
java.sql.SQLException: SYSTEM ERROR: IllegalArgumentException: MinorFragmentId 66 has no read entries assigned
...
  (org.apache.drill.exec.work.foreman.ForemanException) Unexpected exception during fragment initialization: MinorFragmentId 66 has no read entries assigned

Issue Links

• links to: GitHub Pull Request #766