Re: Test to dump and restore objects left behind by regression

On Thu, Mar 20, 2025 at 10:09 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2025-Mar-20, vignesh C wrote:
>
> > Will it help the execution time if we use --jobs in case of pg_dump
> > and pg_restore wherever supported:
>
> As I said in another thread, I think we should enable this test to run
> without requiring any PG_TEST_EXTRA, because otherwise the only way to
> know about problems is to commit a patch and wait for buildfarm to run
> it.  Furthermore, I think running all 4 dump format modes is a waste of
> time; there isn't any extra coverage by running this test in additional
> formats.
>
> Putting those two thoughts together with yours about running with -j,
> I propose that what we should do is make this test use -Fc with no
> compression (to avoid wasting CPU on that) and use a lowish -j value for
> both pg_dump and pg_restore, probably 2, or 3 at most.  (Not more,
> because this is likely to run in parallel with other tests anyway.)

-Fc and -j are not allowed. -j is only allowed for directory format.

$ pg_dump -Fc -j2
pg_dump: error: parallel backup only supported by the directory format

Using just directory format, on my laptop with dev build (because
that's what most developers will use when running the tests)

$ meson test -C $BuildDir pg_upgrade/002_pg_upgrade | grep 002_pg_upgrade

without dump/restore test
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
33.51s   19 subtests passed
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
34.22s   19 subtests passed
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
34.64s   19 subtests passed

without -j, extra ~9 seconds
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
43.33s   28 subtests passed
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
43.25s   28 subtests passed
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
43.10s   28 subtests passed

with -j2, extra 7.5 seconds
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
42.77s   28 subtests passed
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
41.67s   28 subtests passed
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
41.88s   28 subtests passed

with -j3, extra 7 seconds
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
40.77s   28 subtests passed
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
41.05s   28 subtests passed
1/1 postgresql:pg_upgrade / pg_upgrade/002_pg_upgrade OK
41.28s   28 subtests passed

Between -j2 and -j3 there's not much difference so we could use -j2.
But it still takes 7.5 extra seconds which almost 20% extra time. Do
you think that will be acceptable? I saw somewhere Andres mentioning
that he runs this test quite frequently. Please note that I would very
much like this test to be run by default, but Tom Lane has expressed a
concern about adding even that much time [1] to run the test and
mentioned that he would like the test to be opt-in.

When I started writing the test one year before, people raised
concerns about how useful the test would be. Within a year it has
shown 4 bugs. I have similar feeling about the formats - it's doubtful
now but will prove useful soon especially with the work happening on
dump formats in nearby threads. If we run the test by default, we
could run directory with -j by default and leave other formats as
opt-in OR just forget those formats for now. But If we are going to
make it opt-in, testing all formats gives the extra coverage.

About the format coverage, consensus so far is me and Daniel are for
including all formats when running test as opt-in. Alvaro and Vignesh
are for just one format. We need a tie-breaker or someone amongst us
needs to change their vote :D.

--
Best Wishes,
Ashutosh Bapat