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Re: Add contrib/pg_logicalsnapinspect

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Andres Freund <andres@anarazel.de>, Peter Smith <smithpb2250@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, shveta malik <shveta.malik@gmail.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2025-03-06T21:48:46Z
Lists: pgsql-hackers

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  1. Fix indentation issue

  2. pg_logicalinspect: Stabilize isolation tests.

  3. Add contrib/pg_logicalinspect.

  4. Move SnapBuild and SnapBuildOnDisk structs to snapshot_internal.h.

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

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. 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?

Regards,

-- 
Masahiko Sawada
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