Horton

Re: Fix slot synchronization with two_phase decoding enabled

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Nisha Moond <nisha.moond412@gmail.com>
Cc: shveta malik <shveta.malik@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-05-28T00:40:19Z
Lists: pgsql-hackers 
On Sun, May 25, 2025 at 11:34 PM Nisha Moond <nisha.moond412@gmail.com> wrote:
>
>  to
> On Fri, May 23, 2025 at 10:06 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> >
> > Here are review comments for v14 patch:
> >
>
> Thank you for the review.
>
> > I think we need to include a basic test case where we simply create a
> > subscription with two_phase=true and then enable the failover via
> > ALTER SUBSCRIPTION after making sure that slot's restart_lsn passed
> > two_phase_at. Probably if we use this case in 003_logical_slots.pl, we
> > can avoid creating regress_sub2?
> >
>
> A test has been added in 040_standby_failover_slots_sync.pl to enable
> failover via ALTER SUBSCRIPTION.

Yes but the slot is originally created via SQL API, which seems
uncommon usage in practice. I thought it would be good to have the
basic steps in the tests to enable both fields.

> Regarding regress_sub2 in 003_logical_slots.pl :
> If we use ALTER SUBSCRIPTION to set failover=true on regress_sub, it
> leads to pg_upgrade failure, as it attempts to create a slot on the
> new_node(upgraded version) with both two_phase and failover enabled,
> which is an unsupported combination.

I think that the pg_upgrade test should cover the case where it
restores logical slots with both fields enabled in the new cluster.
When I actually tried this case, I realized that pg_upgrade doesn't
handle this case; it tried to create the logical slot via SQL API but
it failed as we don't allow it to create a logical slot with enabling
both two_phase and failover. How can we handle this case?

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com

Commits

  1. Don't retreat slot's confirmed_flush LSN.

  2. Fix assertion failure during decoding from synced slots.

  3. Fix xmin advancement during fast_forward decoding.

  4. Fix slot synchronization for two_phase enabled slots.

  5. Again match pg_user_mappings to information_schema.user_mapping_options.