[DRILL-4147] Union All operator runs in a single fragment

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.8.0
• Assignee: Aman Sinha
• Reporter: amit hadke
• Reviewer: Robert Hou
• Created: 01/Dec/15 03:20
• Updated: 16/Jun/22 16:35
• Resolved: 08/Aug/16 04:51

Description

A User noticed that running select from a single directory is much faster than union all on two directories.
(https://drill.apache.org/blog/2014/12/09/running-sql-queries-on-amazon-s3/#comment-2349732267)

It seems like UNION ALL operator doesn't parallelize sub scans (its using SINGLETON for distribution type). Everything is ran in single fragment.

We may have to use SubsetTransformer in UnionAllPrule.

Issue Links

• links to: GitHub Pull Request #555