Re: pgsql: Add better handling of redundant IS [NOT] NULL quals

Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> On 2024-Jan-23, David Rowley wrote:
>> Until now PostgreSQL has not been very smart about optimizing away IS
>> NOT NULL base quals on columns defined as NOT NULL.

> Hmm, what happens if a NOT NULL constraint is dropped and you have such
> a plan in plancache?  As I recall, lack of a mechanism to invalidate
> such plans was the main reason for Postgres not to have this.

IIRC, we realized that that concern was bogus.  Removal of such
constraints would cause pg_attribute.attnotnull to change, leading
to a relcache invalidation on the table, forcing replan.  If anyone
tried to get rid of attnotnull or make it incompletely reliable,
then we'd have problems; but AFAIK that's not being contemplated.

            regards, tom lane