Horton

Re: [PoC] pg_upgrade: allow to upgrade publisher node

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, vignesh C <vignesh21@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Peter Smith <smithpb2250@gmail.com>, Andres Freund <andres@anarazel.de>, Dilip Kumar <dilipbalaut@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Bruce Momjian <bruce@momjian.us>, Julien Rouhaud <rjuju123@gmail.com>
Date: 2023-11-30T09:49:11Z
Lists: pgsql-hackers 
On Wed, Nov 29, 2023 at 7:33 AM Hayato Kuroda (Fujitsu)
<kuroda.hayato@fujitsu.com> wrote:
>
> > > Actually, we do not expect that it won't input NULL. IIUC all of slots have
> > > slot_name, and subquery uses its name. But will it be kept forever? I think we
> > > can avoid any risk.
> > >
> > > > I've not tested it yet but even if it returns NULL, perhaps
> > > > get_old_cluster_logical_slot_infos() would still set curr->caught_up
> > > > to false, no?
> > >
> > > Hmm. I checked the C99 specification [1] of strcmp, but it does not define the
> > > case when the NULL is input. So it depends implementation.
> >
> > I think PQgetvalue() returns an empty string if the result value is null.
> >
>
> Oh, you are right... I found below paragraph from [1].
>
> > An empty string is returned if the field value is null. See PQgetisnull to distinguish
> > null values from empty-string values.
>
> So I agree what you said - current code can accept NULL.
> But still not sure the error message is really good or not.
> If we regard an empty string as false, the slot which has empty name will be reported like:
> "The slot \"\" has not consumed the WAL yet" in check_old_cluster_for_valid_slots().
> Isn't it inappropriate?
>

I see your point that giving a better message (which would tell the
actual problem) to the user in this case also has a value. OTOH, as
you said, this case won't happen in practical scenarios, so I am fine
either way with a slight tilt toward retaining a better error message
(aka the current way). Sawada-San/Bharath, do you have any suggestions
on this?

-- 
With Regards,
Amit Kapila.

Commits

  1. Fix issues in binary_upgrade_logical_slot_has_caught_up().

  2. Fix a random failure in 003_logical_slots.pl.

  3. Fix a test in 003_logical_slots.

  4. Fix uninitialized slot array access during the upgrade.

  5. Fix the test 003_logical_slots.

  6. Commit b195e6d482 forgot to update meson.build.

  7. Use shorter file names in the upgrade logical slots test.

  8. Migrate logical slots to the new node during an upgrade.

  9. Flush logical slots to disk during a shutdown checkpoint if required.

  10. Prevent possibility of panics during shutdown checkpoint.