Re: Pathify RHS unique-ification for semijoin planning

On Wed, Aug 13, 2025 at 11:27 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Richard Guo <guofenglinux@gmail.com> writes:
> > In this patch, the only instance that doesn't follow the "unique-ify"
> > form is the macro IS_UNIQUEIFIED_REL, as dashes are not allowed in C
> > identifiers.  Maybe a better alternative is IS_RELATION_UNIQUE?  Any
> > suggestions?

> Hm ... to my ear, "unique-ified" implies that we took some positive
> action to make the path's output unique, such as running it through
> a hashagg or Unique node.  IS_RELATION_UNIQUE only implies that the
> output is unique, so for example a scan of a primary key should
> satisfy such a predicate.  Not having read the patch (I do hope
> to get to that), I'm not sure which connotation you have in mind.
> If it's the latter, IS_RELATION_UNIQUE seems like a fine name.
> If it's the former, maybe something like "RELATION_WAS_MADE_UNIQUE"?
> That's not very pretty though ...

It's the former: this macro is to signal that we've explicitly taken
steps to make the output of the relation unique.  IMO, "unique-ified"
best describes this, but we cannot use it directly in the macro name
because of the dash.

Hmm, I think "RELATION_WAS_MADE_UNIQUE" works well because it clearly
conveys that the relation has been explicitly unique-ified.  It's a
bit verbose, but I found that we have similar names in our codebase,
such as VAC_BLK_WAS_EAGER_SCANNED.

Thanks
Richard