[OAK-2944] Support merge iterator for union order by queries

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.2.15, 1.3.1, 1.4
• Component/s: query
• Labels: perfomance
• Assignee: Amit Jain
• Reporter: Amit Jain
• Created: 02/Jun/15 06:16
• Updated: 08/Oct/19 15:21
• Resolved: 22/Jun/15 07:50

Description

Currently, any order by union queries (including optimized OR XPATH) scan a much larger set when returning the results even when the individual queries are sorted by the index itself.
We should have a merge iterator which would scan a much smaller set as the individual queries would be sorted.