Horton

Re: Redundant Result node

Peter Eisentraut <peter@eisentraut.org>

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From: Peter Eisentraut <peter@eisentraut.org>
To: Richard Guo <guofenglinux@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2024-08-22T11:32:43Z
Lists: pgsql-hackers

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  1. Avoid unnecessary post-sort projection

On 22.08.24 09:34, Richard Guo wrote:
> I looked into this a little bit and found that in function
> create_ordered_paths, we decide whether a projection step is needed
> based on a simple pointer comparison between sorted_path->pathtarget
> and final_target.
> 
>      /* Add projection step if needed */
>      if (sorted_path->pathtarget != target)
>          sorted_path = apply_projection_to_path(root, ordered_rel,
>                                                 sorted_path, target);
> 
> This does not seem right to me, as PathTargets are not canonical, so
> we cannot guarantee that two identical PathTargets will have the same
> pointer.  Actually, for the query above, the two PathTargets are
> identical but have different pointers.
> 
> I wonder if we need to invent a function to compare two PathTargets.

Wouldn't the normal node equal() work?