Doug Eck <deck1(at)yahoo(dot)com> writes:
> Any ideas as to what could the first db to opt for the slower subquery rather than the merge?
Not from the information given. Presumably db1 thinks that the
mergejoin plan would be slower, but why it thinks that isn't clear yet.
Try setting enable_nestloop = off (and enable_hashjoin = off if it then
wants a hashjoin) and then post the EXPLAIN ANALYZE results.
regards, tom lane