Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> writes:
> This looks like an invisible correlation problem.
Yeah --- the planner has no idea that the join rows satisfying
newdata.* *= newdata2.* are likely to be exactly the ones not
satisfying newdata.ctid <> newdata2.ctid. It's very accidental
that we got a good plan before.
I've not looked to see where this query is generated, but I wonder
if we could make things better by dropping the LIMIT 1 and instead
using an executor count parameter to stop early.
regards, tom lane