Horton

Re: making EXPLAIN extensible

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Thom Brown <thom@linux.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-03-05T17:52:29Z
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 →

  1. pg_overexplain: Use PG_MODULE_MAGIC_EXT.

  2. pg_overexplain: Call previous hooks as appropriate.

  3. pg_overexplain: Additional EXPLAIN options for debugging.

  4. Add an additional hook for EXPLAIN option validation.

  5. Add some new hooks so extensions can add details to EXPLAIN.

  6. Make it possible for loadable modules to add EXPLAIN options.

It would be good to clarify whether this is for (a) experimenting with
explain options that might be useful in core some day; or (b) special
developer-only options that would never be useful in core; or (c)
production-grade explain options specific to an extension.

On Tue, 2025-03-04 at 16:23 -0500, Robert Haas wrote:
> Where I see this being more useful is for people who want to display
> additional information for plan nodes that they did not implement.
> For
> example, my EXPLAIN (RANGE_TABLE) option dumps every
> range-table-related fact it can find in the Plan tree.

That sounds like (b) or maybe (a).

But the first motivation you listed when introducing the patch was: "It
wouldn't make sense for core to have an EXPLAIN option whose whole
purpose is to cater to the needs of some extension, so that made me
think of providing some extensibility infrastructure."

which sounds like (c).

And if (c) is part of the intended use, but not CustomScan or TableAM,
then what kind of extensions would need extension-specific explain
options?

I am not trying to push the patch in any particular direction. On the
contrary, I'd just like to know the scope of the feature so that I can
stop accidentally pushing it in some direction by asking questions
about out-of-scope use cases.

Regards,
	Jeff Davis