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: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Dilip Kumar <dilipbalaut@gmail.com>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Bruce Momjian <bruce@momjian.us>, Julien Rouhaud <rjuju123@gmail.com>, vignesh C <vignesh21@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>
Date: 2023-10-07T00:09:34Z
Lists: pgsql-hackers 
On Thu, Oct 5, 2023 at 6:43 PM Bharath Rupireddy
<bharath.rupireddyforpostgres@gmail.com> wrote:
>
> On Thu, Oct 5, 2023 at 1:48 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
>
> > The other potential problem Andres pointed out is that during shutdown
> > if due to some reason, the walreceiver goes down, we won't be able to
> > send the required WAL and users won't be able to ensure that because
> > even after restart the same situation can happen. The ideal way is to
> > have something that puts the system in READ ONLY state during shutdown
> > and then we can probably allow walreceivers to reconnect and receive
> > the required WALs. As we don't have such functionality available and
> > it won't be easy to achieve the same, we can leave this for now.
> >
> > Thoughts?
>
> You mean walreceiver for streaming replication? Or the apply workers
> going down for logical replication?
>

Apply workers.

>
> If there's yet-to-be-sent-out WAL,
> pg_upgrade will fail no? How does the above scenario a problem for
> pg_upgrade of a cluster with just logical replication slots?
>

Even, if there is a WAL yet to be sent, the walsender will simply exit
as it will receive PqMsg_Terminate ('X') from standby. See
ProcessRepliesIfAny(). After that shutdown checkpoint will finish. So,
in this case upgrade can fail due to slots. But, I think the server
should be able to succeed in consecutive runs. Does this make sense?

-- 
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.