Re: Secondary index access optimizations

On Sun, Sep 3, 2017 at 4:34 AM, Konstantin Knizhnik
<k(dot)knizhnik(at)postgrespro(dot)ru> wrote:
> Thank you for review.
> I attached new version of the patch with
> remove_restrictions_implied_by_constraints() function.
> Concerning failed tests - this is actually result of this optimization:
> extra filter conditions are removed from query plans.
> Sorry, I have not included updated version of expected test output files to
> the patch.
> Now I did it.

A regression test under contrib/postgres_fdw now fails:

- Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T
1" WHERE (("C 1" IS NOT NULL))
+ Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1"

(("C 1" IS NOT NULL)) is indeed redundant in that case, because column
"C 1" was declared to be NOT NULL. But:

1. Do we want to go this far? Note that this is not involving
inheritance and constraint exclusion. I don't immediately see any
reason why not, but I'm not sure.

2. If yes, then this postgres_fdw test should be changed, because I
think it was trying to demonstrate that IS NOT NULL expressions are
sent to remote databases -- it would need to be changed so that it
tries that with a column that is actually nullable.

--
Thomas Munro
http://www.enterprisedb.com