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

Fujii Masao <masao.fujii@gmail.com>

From: Fujii Masao <masao.fujii@gmail.com>

To: Amit Kapila <amit.kapila16@gmail.com>

Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>

Date: 2025-12-19T07:55:19Z

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 →

Add TAP test for GUC settings passed via CONNECTION in logical replication.
- ec8d91c7e78c 15.16 landed
- 67edd54f0639 16.12 landed
- 358784645eb8 17.8 landed
- 6ec596815125 18.2 landed
- 5f13999aa11d 19 (unreleased) landed
Honor GUC settings specified in CREATE SUBSCRIPTION CONNECTION.
- f7eb44e0f087 15.16 landed
- 75f3428f2436 16.12 landed
- 7a990e801a72 17.8 landed
- 797fc5d1b38d 18.2 landed
- d926462d8190 19 (unreleased) landed
Ensure consistent logical replication of datetime and float8 values.
- f3d4019da5d0 15.0 cited

Attachments

v5-0001-PG15-PG16-Honor-GUC-settings-specified-in-CREATE-SUBSCRIPTI.txt (text/plain)
v5-0002-Add-TAP-test-for-GUC-settings-passed-via-CONNECTI.patch (application/octet-stream) patch v5-0002
v5-0001-Honor-GUC-settings-specified-in-CREATE-SUBSCRIPTI.patch (application/octet-stream) patch v5-0001

On Wed, Dec 3, 2025 at 2:45 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Tue, Dec 2, 2025 at 8:30 PM Fujii Masao <masao.fujii@gmail.com> wrote:
> >
> > On Tue, Dec 2, 2025 at 9:08 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > > Is it possible that we append the predefined options to the options
> > > given by the user to avoid extra round-trip?
> >
> > One idea is to add a function, similar to libpqrcv_get_dbname_from_conninfo()
> > in libpqwalreceiver.c, that extracts the options string from the conninfo,
> > to append the required fixed settings, and then to use the combined string as
> > the value of the options parameter.
> >
>
> Yes, but libpqrcv_get_dbname_from_conninfo() is an exposed function,
> we can implement something internal for libpqwalreceiver.c like
> conninfo_add_defaults() present in fe-connect.c.
>
> > Do you think implementing this is worthwhile
> > to avoid the extra round trip?
> >
>
> I think so. Today, we have three variables, tomorrow there could be
> more such variables as well and apart from avoiding extra round trips,
> the idea to append options to provided options (if any) sounds more
> logical to me.

OK, I've implemented the idea discussed upthread. The patch updates
libpqrcv_connect() so that, for logical replication, it extracts the options
string from the conninfo, appends the required fixed settings, and passes
the combined string as the options parameter to libpq.

For example, if the conninfo specifies -c wal_sender_timeout=10s,
the resulting options value becomes:

        -c wal_sender_timeout=10s -c datestyle=ISO -c
intervalstyle=postgres -c extra_float_digits=3.

Patch attached.

Regards,

-- 
Fujii Masao