Horton

Re: Allow GUC settings in CREATE SUBSCRIPTION CONNECTION to take effect

Jelte Fennema-Nio <postgres@jeltef.nl>

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From: Jelte Fennema-Nio <postgres@jeltef.nl>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Chao Li <li.evan.chao@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-11-24T05:54:54Z
Lists: pgsql-hackers

Commits

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  1. Add TAP test for GUC settings passed via CONNECTION in logical replication.

  2. Honor GUC settings specified in CREATE SUBSCRIPTION CONNECTION.

  3. Ensure consistent logical replication of datetime and float8 values.

On Fri, Nov 21, 2025, 00:47 Fujii Masao <masao.fujii@gmail.com> wrote:

> On Thu, Nov 20, 2025 at 3:54 PM Chao Li <li.evan.chao@gmail.com> wrote:
> > Before this patch, all user specified options are silently discarded,
>
> The GUC settings in CREATE SUBSCRIPTION were honored up through v14;
> the behavior changed in commit f3d4019da5d, so some might view this
> as a regression.
>

FWIW, I definitely view it as a regression. I used this in citus to make
the logical replication sender of the shard rebalancer use a higher CPU
priority[1]. I had no clue, until now, that that logic got completely
broken in PG15 (which we coincidentally added support for in the same
release).

I'm not entirely sure if it's worth a backpatch. This citus feature
probably isn't the most critical. So if that's the only usecase in the wild
that got broken, then that might be fine. But I at least wanted to share
that others (i.e. me) have used this feature.

[1]:
https://github.com/citusdata/citus/blame/662b7248db2146d33a1a21227271b839355a970a/src/backend/distributed/replication/multi_logical_replication.c#L1510

>