Re: POC, WIP: OR-clause support for indexes

Hi!

Let me join the review process.

I am no expert in execution plans, so there would not be much help in doing
even better optimization. But I can read the code, as a person who is not
familiar
with this area and help making it clear even to a person like me.

So, I am reading v25-0001-Transform-OR-clauses-to-ANY-expression.patch that
have been posted some time ago, and especially transform_or_to_any function.

> @@ -38,7 +45,6 @@
> int from_collapse_limit;
> int join_collapse_limit;
>
> -
> /*
> * deconstruct_jointree requires multiple passes over the join tree,
because we
> * need to finish computing JoinDomains before we start distributing quals.

Do not think that removing empty line should be part of the patch

> + /*
> + * If the const node's (right side of operator
expression) type
> + * don't have “true” array type, then we cannnot
do the
> + * transformation. We simply concatenate the
expression node.
> + */
Guess using unicode double quotes is not the best idea here...

Now to the first part of `transform_or_to_any`:

> + List *entries = NIL;
I guess the idea of entries should be explained from the start. What kind of
entries are accomulated there... I see they are added there all around the
code, but what is the purpose of that is not quite clear when you read it.

At the first part of `transform_or_to_any` function, you costanly repeat two
lines, like a mantra:

> + entries = lappend(entries, rinfo);
> + continue;

"If something is wrong -- do that mantra"

From my perspective, if you have to repeat same code again and again, then
most probably you have some issues with architecture of the code. If you
repeat some code again and again, you need to try to rewrite the code, the
way, that part is repeated only once.

In that case I would try to move the most of the first loop of
`transform_or_to_any` to a separate function (let's say its name is
prepare_single_or), that will do all the checks, if this or is good for us;
return NULL if it does not suits our purposes (and in this case we do "entries
= lappend(entries, rinfo); continue" in the main code, but only once) or
return pointer to some useful data if this or clause is good for our purposes.

This, I guess will make that part more clear and easy to read, without
repeating same "lappend mantra" again and again.

Will continue digging into the code tomorrow.

P.S. Sorry for sending partly finished email. Pressed Ctrl+Enter
accidentally... With no way to make it back :-(((