Re: Add contrib/pg_logicalsnapinspect

On Fri, Mar 7, 2025 at 2:42 AM Bertrand Drouvot
<bertranddrouvot.pg@gmail.com> wrote:
>
> Hi,
>
> On Fri, Mar 07, 2025 at 10:26:23AM +0530, Amit Kapila wrote:
> > On Fri, Mar 7, 2025 at 3:19 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > >
> > > On Wed, Mar 5, 2025 at 4:05 AM Bertrand Drouvot
> > > <bertranddrouvot.pg@gmail.com> wrote:
> > > >
> > > > Hi,
> > > >
> > > > On Wed, Mar 05, 2025 at 02:42:15PM +0530, Amit Kapila wrote:
> > > > > On Wed, Mar 5, 2025 at 12:47 PM Bertrand Drouvot
> > > > > <bertranddrouvot.pg@gmail.com> wrote:
> > > > > >
> > > > > > Agree, PFA a patch doing so.
> > > > > >
> > > > >
> > > > > It would be better if you could add a few comments atop the
> > > > > permutation line to explain the working of the test.
> > > >
> > > > yeah makes sense. Done in the attached, and bonus point I realized that the
> > > > test could be simplified (so, removing useless steps in passing).
> > > >
> > >
> > > Thank you for the patch.
> > >
> > > The new simplified test case can be pretty-formatted as:
> > >
> > > init
> > > begin
> > > savepoint
> > > truncate
> > >                 checkpoint-1
> > >                 get_changes-1
> > > commit
> > >                 checkpoint-2
> > >                 get_changes-2
> > >                 info_catchange check
> > >                 info_committed check
> > >                 meta check
>
> Yes.
>
> > > IIUC if another checkpoint happens between get_change-2 and the
> > > subsequent checks, the first snapshot would be removed during the
> > > checkpoint, resulting in a test failure.
>
> Good catch! Yeah you're right, thanks!
>
> > I think we could check the
> > > snapshot files while one transaction keeps open. The more simplified
> > > test case would be:
> > >
> > > init
> > > begin
> > > savepoint
> > > insert(cat-change)
> > >                 begin
> > >                 insert(cat-change)
> > >                 commit
> > >                 checkpoint
> > >                 get_changes
> > >                 info_catchange check
> > >                 info_committed check
> > >                 meta check
> > > commit
> > >
> > > In this test case, we would have at least one serialized snapshot that
> > > has both cat-changes and committed txns. What do you think?
>
> Indeed, I think that would prevent snapshots to be removed.
>
> The attached ends up doing:
>
> init
> begin
> savepoint
> truncate table1
>                        create table table2
>                checkpoint
>                get_changes
>                info check
>                meta check
> commit
>
> As the 2 ongoing catalog changes and the committed catalog change are part of the
> same snapshot, then I grouped the catchanges and committed changes checks in the
> same "info check".
>
> > Your proposed change in the test sounds better than what we have now
> > but I think we should also avoid autovacuum to perform analyze as that
> > may add additional counts. For test_decoding, we keep
> > autovacuum_naptime = 1d in logical.conf file, we can either use the
> > same here or simply keep autovacuum off.
>
> When writing the attached, I initially added extra paranoia in the tests by
> using ">=", does that also address your autovacuum concern?
>

Thank you for updating the patch. It looks mostly good to me. I've
made some cosmetic changes and attached the updated version.

Regards,

-- 
Masahiko Sawada
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