Re: Redundant Result node

Richard Guo <guofenglinux@gmail.com>

From: Richard Guo <guofenglinux@gmail.com>

To: Peter Eisentraut <peter@eisentraut.org>

Cc: Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2024-08-27T03:29:52Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Avoid unnecessary post-sort projection
- 9626068f1333 18.0 landed

Attachments

v2-0001-Avoid-unnecessary-post-sort-projection.patch (application/octet-stream) patch v2-0001

On Mon, Aug 26, 2024 at 8:58 PM Peter Eisentraut <peter@eisentraut.org> wrote:
> On 23.08.24 10:27, Richard Guo wrote:
> > Fair point.  After looking at the code for a while, I believe it is
> > sufficient to compare PathTarget.exprs after we've checked that the
> > two targets have different pointers.
>
> -               if (sorted_path->pathtarget != target)
> +               if (sorted_path->pathtarget != target &&
> +                       !equal(sorted_path->pathtarget->exprs, target->exprs))
>                         sorted_path = apply_projection_to_path(root, ordered_rel,
>
> equal() already checks whether both pointers are equal, so I think this
> could be simplified to just
>
>      if (!equal(sorted_path->pathtarget->exprs, target->exprs))

Indeed.  If the target pointers are equal, the PathTarget.exprs
pointers must be equal too.

Attached is the updated patch with this change.

Thanks
Richard