Re: Reduce "Var IS [NOT] NULL" quals during constant folding

On Thu, May 1, 2025 at 4:33 AM Richard Guo <guofenglinux@gmail.com> wrote:
> Here is the patchset that implements this optimization.  0001 moves
> the expansion of virtual generated columns to occur before sublink
> pull-up.  0002 introduces a new function, preprocess_relation_rtes,
> which scans the rangetable for relation RTEs and performs inh flag
> updates and virtual generated column expansion in a single loop, so
> that only one table_open/table_close call is required for each
> relation.  0003 collects NOT NULL attribute information for each
> relation within the same loop, stores it in a relation OID based hash
> table, and uses this information to reduce NullTest quals during
> constant folding.
>
> I think the code now more closely resembles the phase 1 and phase 2
> described earlier: it collects all required early-stage catalog
> information within a single loop over the rangetable, allowing each
> relation to be opened and closed only once.  It also avoids the
> has_subclass() call along the way.

Before we commit to something along these lines, I think we need to
understand whether Tom intends to press Peter for some bigger change
around expand_virtual_generated_columns.

If Tom doesn't respond right away, I suggest that we need to add an
open item for http://postgr.es/m/602561.1744314879@sss.pgh.pa.us

--
Robert Haas
EDB: http://www.enterprisedb.com