On 5/19/25 20:01, Robert Haas wrote:
> Hi,
>
> A couple of people at pgconf.dev seemed to want to know more about my
> ongoing plan shape work, so here are the patches I have currently.
> This is a long way from something that actually looks like a usable
> feature, but these are bits of infrastructure that I think will be
> necessary to get to a usable feature. As a recap, my overall goal here
> is to make it so that you can examine a finished plan, figure out what
> decisions the planner made, and then somehow get the planner to make
> those same decisions over again in a future planning cycle. Since
> doing this for all types of planner decisions seems too difficult for
> an initial goal, I'm focusing on scans and joins for now. A further
> goal is that I want it to be possible for extensions to use this
> infrastructure to implement a variety of different policies that they
> might feel to be beneficial, so I'm looking to minimize the amount of
> stuff that has to be done in core PostgreSQL or can only be used by
> core PostgreSQL.
>
> ...
Thanks for the overview. I don't have any immediate feedback, but it
sounds like it might be related to the "making planner decisions clear"
session from the unconference ...
The basic premise of that session was about how to give users better
info about the planner decisions - why paths were selected/rejected,
etc. A simple example would be "why was the index not used", and the
possible answers include "dominated by cost by another path" or "does
not match the index keys" etc.
I wonder if this work might be useful for something like that.
regards
--
Tomas Vondra
