Horton

Re: Reordering DISTINCT keys to match input path's pathkeys

Laurenz Albe <laurenz.albe@cybertec.at>

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From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Richard Guo <guofenglinux@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2024-01-23T08:04:22Z
Lists: pgsql-hackers 
On Tue, 2024-01-23 at 13:55 +0800, Richard Guo wrote:
> Similar to what we did to GROUP BY keys in 0452b461bc, I think we can do
> the same to DISTINCT keys, i.e. reordering DISTINCT keys to match input
> path's pathkeys, which can help reduce cost by avoiding unnecessary
> re-sort, or allowing us to use incremental-sort to save efforts.
> 
> Attached is a patch for this optimization.  Any thoughts?

I didn't scrutinize the code, but that sounds like a fine optimization.

Yours,
Laurenz Albe

Commits

  1. Fix test case from a8ccf4e93

  2. Reordering DISTINCT keys to match input path's pathkeys