Horton

Re: making EXPLAIN extensible

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Sami Imseih <samimseih@gmail.com>, Andrei Lepikhov <lepihov@gmail.com>, Jeff Davis <pgsql@j-davis.com>, Thom Brown <thom@linux.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-03-21T19:54:12Z
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.

Attachments

On Fri, Mar 21, 2025 at 2:37 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I took a look through v8, and have just a couple of trivial nits:

Thank you!

> +static void overexplain_debug_handler(ExplainState *, DefElem *,
> +                                      ParseState *);
> +static void overexplain_range_table_handler(ExplainState *, DefElem *,
> +                                            ParseState *);
>
> I cordially hate this parameter-name-less style of function
> declaration, and consider it Stroustrup's single worst idea in C++.
> It rests on the assumption that parameter names convey zero
> information, which is wrongheaded for any function more complex than,
> say, addition.  Also, even if you like this style, clang-tidy probably
> won't (cf for example 035ce1feb).

I don't hate the style but I didn't use it intentionally. Fixed now, I hope.

> pgoverexplain.sgml seems to have been formatted to fit in about an
> 85-column window.  Please don't do that --- you might as well have
> made it 99 columns wide or any other random number, it still looks
> like heck in 80 columns.

Oops. Fixed. Also, I tried to disclaim stability and comprehensibility
a little better and fixed a dumb mistake in the page title.

> Other than that, there's room to debate exactly what to show.
> But as long as we're agreed that we won't hold this module to
> high cross-version compatibility standards, that doesn't seem
> like a problem.  I'm okay with this as a starting point.

Great news, thanks again!

Here's v9, which also adds 'SET debug_parallel_query = off' to the
pg_overexplain tests, per CI, because the test results are not (and
cannot realistically be made) stable under under that option.

--
Robert Haas
EDB: http://www.enterprisedb.com