Re: plan shape work

On Mon, Sep 29, 2025 at 4:52 AM Richard Guo <guofenglinux@gmail.com> wrote:
> It seems no one has attempted to code up the approach I suggested, so
> I went ahead and did it; please see the attached PoC patch.  It's just
> a proof of concept to show what I have in mind, so please excuse the
> lack of comments and necessary assertions for now.

I think that if there are subqueries named expr_1 and expr_3, this
will assign the name expr_4 next, whereas the previous patch assigns
the name expr_2. That might not be a bug, but it's different and I
don't like it as well.

I also think that if there are subqueries named expr_1a and expr_2a,
this will assign the name expr_3 next, whereas the previous patch
assigns the name expr_1. I would consider that a clear bug.

Your code will also see expr_01 and decide that the next name should
be expr_2 rather than expr_1. I don't think that's right, either.

I also think that it's a bug that your function sometimes returns a
value different from the one it appends to canon_names.

I don't really understand why you're so fixed on this point. I think
that the code as I wrote it is quite a normal way to write code for
that kind of thing. Sure, there are other things that we could do, but
I wrote the code that way I did precisely in order to avoid behaviors
like the ones I mention above. It would be possible to rearrange the
code so that the termination condition for the loop was something like
"!found", or to rewrite the loop as a do { ... } while (!found)
construct as we do in set_rtable_names() for a very similar problem to
the code that this is solving, but I think the generated machine code
would be exactly the same and the code would not look as intuitive for
a human to read. Somebody else might have had a different stylistic
preference, but if you are going to object every time I write for (;;)
or while (1), you're going to hate an awful lot of my code for, IMHO,
very little reason. It's reasonable to be concerned about whether a
loop will ever terminate, but the mere fact of putting the loop exit
someplace other than the top of the loop isn't enough to say that
there's a problem.

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