I haven't been following this thread closely, so pardon if this has been
discussed already.
The patch doesn't seem to change the cost estimates in the planner at
all. Without that, I'd imagine that the planner rarely chooses a
multi-batch hash join to begin with.
Joshua, in the tests that you've been running, did you have to rig the
planner with "enable_mergjoin=off" or similar, to get the queries to use
hash joins?
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com