[PHOENIX-1556] Base hash versus sort merge join decision on cost

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.14.0, 5.0.0
• Labels: CostBasedOptimization
• Assignee: Wei Xue
• Reporter: James R. Taylor
• Created: 23/Dec/14 23:44
• Updated: 26/Jul/18 01:14
• Resolved: 12/Feb/18 23:06

Description

At compile time, we know how many guideposts (i.e. how many bytes) will be scanned for the RHS table. We should, by default, base the decision of using the hash-join verus many-to-many join on this information.

Another criteria (as we've seen in PHOENIX-4508) is whether or not the tables being joined are already ordered by the join key. In that case, it's better to always use the sort merge join.