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From: Tom Lane <[email protected]>
To: Anthonin Bonnefoy <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Add ALL_CANDIDATES option to EXPLAIN
Date: Fri, 26 Jul 2024 13:13:54 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAO6_Xqoke6qntHS8odYXT_P2Lrj7dNXgsCds+C8zLOXBbNefvg@mail.gmail.com>
References: <CAO6_Xqoke6qntHS8odYXT_P2Lrj7dNXgsCds+C8zLOXBbNefvg@mail.gmail.com>

Anthonin Bonnefoy <[email protected]> writes:
> I have a prototype for an ALL_CANDIDATES option for EXPLAIN. The goal
> of this option is to print all plan candidates instead of only the
> cheapest plan. It will output the plans from the most expensive at the
> top to the cheapest.

This doesn't seem feasible at all to me.  If we don't prune plans
fairly aggressively at lower plan levels, we'll have a combinatorial
explosion in the amount of work the planner has to do.  Have you
tried this on even slightly complex plans --- say, a dozen-way join?
I do not think you'll like the runtime, the amount of memory consumed,
or the verboseness of the output.  (I wonder how it interacts with
GEQO, too.)

			regards, tom lane

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