Re: Is exec_simple_check_node still doing anything?

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I'm a little mystified by exec_simple_check_node().
> ...
> Did that, possibly, remove the last way in which a simple expression
> could be could become non-simple? If so, between that and the new
> hasTargetSRFs test, it might now be impossible for
> exec_simple_check_node() to fail.

I think you might be right. The other way that I'm aware of that
could cause interesting things to happen is if someone redefines
a SQL function that had been inlined in the originally-compiled
version of the expression. However, it should be the case that
inline_function() will refuse to inline if the new definition
contains anything "scary", so that the expression as seen by
plpgsql is still simple; any non-simplicity will just be hidden
under a function call.

In fact, I suspect we could get rid of exec_simple_recheck_plan
altogether. It could use a bit more study, but the empty-rtable
check plus the other checks in exec_simple_check_plan (particularly,
hasAggs, hasWindowFuncs, hasTargetSRFs, hasSubLinks) seem like
they are enough to guarantee that what comes out of the planner
will be "simple".

If I recall things correctly, originally there were only the
post-planning simplicity checks that are now embodied in
exec_simple_recheck_plan/exec_simple_check_node. I think I added
on the pre-planning checks in exec_simple_check_plan in order to
try to save some planning cycles. Since the SRF checks were
clearly still necessary at the time, I didn't think hard about
whether any of the other post-planning checks could be got rid of.

regards, tom lane