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Re: Executing pg_createsubscriber with a non-compatible control file

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Postgres hackers <pgsql-hackers@lists.postgresql.org>, Euler Taveira <euler@eulerto.com>
Date: 2025-10-10T06:07:42Z
Lists: pgsql-hackers

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On Thu, Oct 09, 2025 at 11:22:47AM -0700, Masahiko Sawada wrote:
> +1, sounds like a good idea to improve user experience. I think we can
> use the API in pg_combinebackup.c too since it has a similar function,
> read_pg_version_file().

Please find attached what I am finishing with.  At the end, I have
designed an API that can be reused across the board for the following
tools that do the same things in the tree, removing some duplicated
code:
- pg_resetwal
- pg_upgrade
- pg_combinebackup

The routine that retrieves the contents gets a uint32 number, and it
is optionally possible to get the contents of PG_VERSION (pg_upgrade
wants that for tablespace paths, but that's really for pg_resetwal to
be able to show back buggy data):
extern uint32 get_pg_version(const char *datadir, char **version_str);

This support both the pre-v10 and the post-v10 version formats, for
pg_upgrade.

To ease comparisons with PG_MAJORVERSION_NUM, I have added a small
helper macro (see GET_PG_MAJORVERSION_NUM). 

I have also applied the same method to pg_createsubscriber, on top of
that, to take care of my original issue.  I have not looked at other
places where the same concept could be applied, at least it's a start.

Thoughts or comments?
--
Michael

Commits

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

  1. pg_checksums: Use new routine to retrieve data of PG_VERSION

  2. pg_createsubscriber: Use new routine to retrieve data of PG_VERSION

  3. pg_resetwal: Use new routine to retrieve data of PG_VERSION

  4. pg_combinebackup: Use new routine to retrieve data of PG_VERSION

  5. pg_upgrade: Use new routine to retrieve data of PG_VERSION

  6. Introduce frontend API able to retrieve the contents of PG_VERSION