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Re: Support logical replication of DDLs, take2

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Vitaly Davydov <v.davydov@postgrespro.ru>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-04-28T06:57:17Z
Lists: pgsql-hackers, pgsql-general 
On Mon, Apr 27, 2026 at 11:45 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> On Tue, Apr 21, 2026 at 4:45 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > The overall idea of the previous patch set was to implement DDL
> > deparsing and utilize it for DDL replication. It converted a parse
> > tree into a JSON string. For instance, if a user executes "DROP TABLE
> > t1", the deparser generates from its parse tree:
> >
> > {DROPSTMT :objects (("t1")) :removeType 41 :behavior 0 :missing_ok
> > false :concurrent false}
> >
> > to:
> >
> > {"fmt": "DROP TABLE %{objidentity}s", "objidentity": "public.t1"}
> >
> > This JSON string is self-documenting, meaning someone who gets it can
> > easily reconstruct the original DDL with schema-qualified object
> > names. In a dedicated event trigger for logical replication, we
> > deparsed the parse tree of a DDL, wrote it into a WAL record, and then
> > the logical decoding processed it similarly to DML changes.
>
> I think there was also a discussion on whether to use JSON vs the
> existing infrastructure of converting nodes to strings.  Although the
> JSON is standard format and might provide more flexibility using
> existing format avoid extra maintence burden.
>

Yes, the discussion related to node-to-string and the pros and cons of
the deparse approach are detailed in email [1]. I think some of these
points could be also related to the new approach as well.

[1] - https://www.postgresql.org/message-id/OS0PR01MB571684CBF660D05B63B4412C94AB9%40OS0PR01MB5716.jpnprd01.prod.outlook.com

-- 
With Regards,
Amit Kapila.

Commits

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

  1. Add a run_as_owner option to subscriptions.

  2. Refactor pgoutput_change().

  3. Print the correct aliases for DML target tables in ruleutils.

  4. Fix object identity string for transforms

  5. Add grantable MAINTAIN privilege and pg_maintain role.

  6. Get rid of recursion-marker values in enum AlterTableType

  7. Release cache tuple when no longer needed

  8. Empty search_path in logical replication apply worker and walsender.

  9. Refactor format_type APIs to be more modular

  10. Use wrappers of PG_DETOAST_DATUM_PACKED() more.