Scott Cain <cain(at)cshl(dot)org> writes:
> [ much stuff ]
Could we see EXPLAIN ANALYZE, not just EXPLAIN, output for all these
alternatives? Your question boils down to "why is the planner
misestimating these queries" ... which is a difficult question to
answer when given only the estimates and not the reality.
A suggestion though is that you might need to raise the statistics
target on the indexed columns, so that ANALYZE will collect
finer-grained statistics. (See ALTER TABLE ... SET STATISTICS.)
Try booting it up to 100 (from the default 10), re-analyze, and
then see if/how the plans change.
regards, tom lane