[OAK-2023] Optimal index usage for XPath queries with "order by" combined with "or"

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Fix Version/s: 1.3.4, 1.4
• Component/s: query
• Labels: performance
• Assignee: Thomas Mueller
• Reporter: Thomas Mueller
• Created: 11/Aug/14 13:05
• Updated: 02/Mar/16 15:33
• Resolved: 22/Jul/15 11:50

Description

XPath queries with "or" are converted to union, even if there is an "order by" clause. In such cases, sorting is done in memory. See also OAK-2022.

For some queries, it might be better to not use union, but use an ordered index instead. This is tricky to decide up-front, but it would be possible to estimate the cost of both variants and pick the one that seems better.

Issue Links

• is related to: OAK-2022 XPath queries with "order by" are never converted to "union"