Re: BUG #19007: Planner fails to choose partial index with spurious 'not null'

On Wed, Aug 20, 2025 at 6:37 PM Richard Guo <guofenglinux(at)gmail(dot)com> wrote:
> I've had some time to look at this issue again. There are several
> cases in plancat.c where specific expressions need to be run through
> eval_const_expressions because the planner will be comparing them to
> similarly-processed qual clauses. This includes constraint
> expressions, statistics expressions, index expressions and index
> predicates -- as highlighted by this bug report.

I've split the patch into two. 0001 fixes const-simplification for
constraint expressions and statistics expressions by ensuring that
Vars are updated to have the correct varno before
const-simplification, and that a valid root is passed to
eval_const_expressions. 0002 fixes const-simplification for index
expressions and predicate by running eval_const_expressions a second
time after the Vars have been fixed and with a valid root.

I think 0001 is in pretty good shape. I'm concerned that in 0002 we
have to run eval_const_expressions twice. I once considered caching
the untransformed index expressions and predicate, and running
const-simplification outside of relcache.c. However, that doesn't
seem like a better solution, since we would need to re-run
const-simplification every time we fetch the index expressions and
predicate. Any suggestions?

Thanks
Richard