Horton

Re: logical decoding and replication of sequences, take 2

Christophe Pettus <xof@thebuild.com>

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From: Christophe Pettus <xof@thebuild.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Masahiko Sawada <sawada.mshk@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Date: 2023-12-19T12:54:32Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

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

  2. Make test_decoding ddl.out shorter

  3. Fix snapshot handling in logicalmsg_decode

  4. doc: Adjust a few more references to "postmaster"

  5. Revert "Logical decoding of sequences"

Hi,

I wanted to hop in here on one particular issue:

> On Dec 12, 2023, at 02:01, Tomas Vondra <tomas.vondra@enterprisedb.com> wrote:
> - desirability of the feature: Random IDs (UUIDs etc.) are likely a much
> better solution for distributed (esp. active-active) systems. But there
> are important use cases that are likely to keep using regular sequences
> (online upgrades of single-node instances, existing systems, ...).

+1.

Right now, the lack of sequence replication is a rather large foot-gun on logical replication upgrades.  Copying the sequences over during the cutover period is doable, of course, but:

(a) There's no out-of-the-box tooling that does it, so everyone has to write some scripts just for that one function.
(b) It's one more thing that extends the cutover window.

I don't think it is a good idea to make it mandatory: for example, there's a strong use case for replicating a table but not a sequence associated with it.  But it's definitely a missing feature in logical replication.