explain_regress, explain(MACHINE), and default to explain(BUFFERS) (was: BUFFERS enabled by default in EXPLAIN (ANALYZE))

I'm renaming this thread for better visibility, since buffers is a small,
optional part of the patches I sent.

I made a CF entry here.
https://commitfest.postgresql.org/36/3409/

On Wed, Dec 01, 2021 at 06:58:20PM -0600, Justin Pryzby wrote:
> On Mon, Nov 15, 2021 at 01:09:54PM -0600, Justin Pryzby wrote:
> > Some time ago, I had a few relevant patches:
> > 1) add explain(REGRESS) which is shorthand for (BUFFERS OFF, TIMING OFF, COSTS OFF, SUMMARY OFF)
> > 2) add explain(MACHINE) which elides machine-specific output from explain;
> > for example, Heap Fetches, sort spaceUsed, hash nbuckets, and tidbitmap stuff.
> >
> > https://www.postgresql.org/message-id/flat/20200306213310(dot)GM684(at)telsasoft(dot)com
>
> The attached patch series now looks like this (some minor patches are not
> included in this list):
>
> 1. add GUC explain_regress, which disables TIMING, SUMMARY, COSTS;
> 2. enable explain(BUFFERS) by default (but disabled by explain_regress);
> 3. Add explain(MACHINE) - which is disabled by explain_regress.
> This elides various machine-specific output like Memory and Disk use.
> Maybe it should be called something else like "QUIET" or "VERBOSE_MINUS_1"
> or ??
>
> The regression tests now automatically run with explain_regress=on, which is
> shorthand for TIMING OFF, SUMMARY OFF, COSTS OFF, and then BUFFERS OFF.
>
> There's a further option called explain(MACHINE) which can be disabled to hide
> portions of the output that are unstable, like Memory/Disk/Batches/
> Heap Fetches/Heap Blocks. This allows "explain analyze" to be used more easily
> in regression tests, and simplifies some existing tests that currently use
> plpgsql functions to filter the output. But it doesn't handle all the
> variations from parallel workers.
>
> (3) is optional, but simplifies some regression tests. The patch series could
> be rephrased with (3) first.
>
> Unfortunately, "COSTS OFF" breaks postgres_fdw remote_estimate. If specifying
> "COSTS ON" in postgres_fdw.c is considered to be a poor fix , then I suppose
> this patch series could do as suggested and enable buffers by default only when
> ANALYZE is specified. Then postgres_fdw is not affected, and the
> explain_regress GUC is optional: instead, we'd need to specify BUFFERS OFF in
> ~100 regression tests which use EXPLAIN ANALYZE. (3) still seems useful on its
> own.