Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access)

Hello Melanie and Andres,

20.04.2026 19:18, Melanie Plageman wrote:
>> but I wonder if there are other queries,
>> which plans can change due to the same reason.
> I think we'll have to take this on a case-by-case basis when we see
> failures. While it is certainly possible other tests just rely on
> autovacuum not having run and set the page all-visible, many of them
> probably have already had to account for that.

Thank you for paying attention to this!

I think, I found another test which suffers from autoanalyze with the new
behavior: [1], [2].

Initially I reproduced this diff on a slow armv7 device after many
iterations of `make check` with:
autovacuum_naptime = 1
autovacuum_analyze_threshold = 1
debug_parallel_query = 'regress'

But now I see that it can be reproduced on an ordinary machine with just:
--- a/src/test/regress/sql/plancache.sql
+++ b/src/test/regress/sql/plancache.sql
@@ -208,2 +208,3 @@ execute test_mode_pp(1); -- 2x
 execute test_mode_pp(1); -- 3x
+analyze test_mode;
 execute test_mode_pp(1); -- 4x
(and expected/plancache.out updated)

and `make check` running in a loop. It failed for me on iterations 5, 4,
10 (as far as I can see, analyze updates relallvisible not every time):
# parallel group (18 tests):  prepare xml conversion plancache limit returning copy2 polymorphism sequence rowtypes
largeobject temp rangefuncs with truncate domain plpgsql alter_table
# diff -U3 .../src/test/regress/expected/plancache.out .../src/test/regress/results/plancache.out
# --- .../src/test/regress/expected/plancache.out    2026-04-20 21:35:30.677775398 +0300
# +++ .../src/test/regress/results/plancache.out     2026-04-20 21:43:49.324492302 +0300
# @@ -374,11 +374,11 @@
#
#  -- we should now get a really bad plan
#  explain (costs off) execute test_mode_pp(2);
# -         QUERY PLAN
# ------------------------------
# +                        QUERY PLAN
# +----------------------------------------------------------
#   Aggregate
# -   ->  Seq Scan on test_mode
# -         Filter: (a = $1)
# +   ->  Index Only Scan using test_mode_a_idx on test_mode
# +         Index Cond: (a = $1)
#  (3 rows)
#
#  -- but we can force a custom plan

The same modified test survived 50 iterations at 378a21618~1.

[1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=dodo&dt=2026-04-07%2012%3A45%3A07
[2] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=dodo&dt=2026-04-12%2022%3A45%3A06

Best regards,
Alexander