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: Amit Kapila <amit.kapila16@gmail.com>
Cc: Nisha Moond <nisha.moond412@gmail.com>, shveta malik <shveta.malik@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-06-04T17:46:02Z
Lists: pgsql-hackers 
On Sun, Jun 1, 2025 at 10:25 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
>
> Yet another idea is to dump the subscription with two_phase = on and
> failover = false. We should do this when both options are 'true'
> during the dump.  As we are documenting that we always dump
> createsubscription with connect as false and let users take care (see
> [1] (When dumping logical replication subscriptions ...)), a similar
> reasoning could be given for the failover flag.

It probably would work for subscriptions but what about logical slots?
If we restore two_phase=on and failover=false, the user would have to
enable the failover via ALTER_REPLICATION_SLOT. I think we should
avoid asking users to execute the replication commands directly.

> The one more combination to consider is when someone takes a dump of
> an older version and loads it into a newer version. For example, where
> users dump from 17.5 and then restore in a newer version, say 17.6
> (which has our fix), the restore will fail due to newer restrictions
> added by this patch. Do we need to do anything about it?

A valid concern. Implementing this change could potentially render
dumps created prior to version 17.5 incompatible with version 17.6 or
later, which seems a significant backwards incompatibility to me. Do
we have any precedence of such incompatibility?

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.