[DRILL-6872] Add support for Join with small build side table between Lateral & Unnest subquery.

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: Execution - Flow
• Assignee: Unassigned
• Reporter: Sorabh Hamirwasia
• Created: 27/Nov/18 18:23
• Updated: 28/Nov/18 23:24

Description

We want to support Hash Join in Lateral & Unnest subquery for special case of small table on build side of the Hash Join. In this case basically build side is a small table which is scanned once by Hash Join and then for each left side batch with EMIT outcome, same build side information is used. The example plan will look like below: 

             LJ
              /    \
        Scan    HashJoin
                     /      \
            Unnest    Scan (Build)

 
Here we should also think about sniffing logic in Hash Join operator which can cause deadlock for this scenario.