Re: Re: [PATCH] Caching for stable expressions with constant arguments v3

Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> I wonder if it would be better to add the CacheExpr nodes to the tree as
> a separate pass, instead of shoehorning it into eval_const_expressions?
> I think would be more readable that way, even though a separate pass
> would be more expensive.

A separate pass would be very considerably more expensive, because
(1) it would require making a whole new copy of each expression tree,
and (2) it would require looking up the volatility status of each
function and operator. eval_const_expressions already has to do the
latter, or has to do it in a lot of cases anyway, so I think it's
probably the best place to add this. If it weren't for (2) I would
suggest adding the work to setrefs.c instead, but as it is I think
we'd better suck it up and deal with any fallout in the later stages
of the planner.

regards, tom lane