Horton

Two issues with version checks in CREATE SUBSCRIPTION

Fujii Masao <masao.fujii@gmail.com>

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From: Fujii Masao <masao.fujii@gmail.com>
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-12-22T17:26:42Z
Lists: pgsql-hackers

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  1. Fix CREATE SUBSCRIPTION failure when the publisher runs on pre-PG19.

  2. Fix version check for retain_dead_tuples subscription option.

Attachments

Hi,

While looking at subscription-related code, I noticed two issues related to
version checks.

        if (walrcv_server_version(wrconn) < 19000)
            ereport(ERROR,
                errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                errmsg("cannot enable retain_dead_tuples if the
publisher is running a version earlier than PostgreSQL 19"));

First, in subscriptioncmds.c this check rejects enabling retain_dead_tuples
when the publisher is running an older version. However, the comparison uses
19000 as v19 value. Since server versions are encoded as 190000 for v19,
this appears to be a typo and allows the option to be enabled unexpectedly
on pre-v19 publishers. The attached 0001 patch fixes this by correcting
the version constant.

Second, CREATE SUBSCRIPTION with copy_data=true and origin='none' currently
fails when the publisher is running a version earlier than v19, although
this combination should be supported. The failure occurs because the command
issues a query calling pg_get_publication_sequences on the publisher,
which does not exist before v19. The attached 0002 patch fixes this
by skipping that query when the publisher runs an older version.

Thoughts?

Regards,

-- 
Fujii Masao