From: Chao Li <li.evan.chao@gmail.com>
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Subject: Prevent remote libpq notices from being sent to clients
Message-Id: <396C3BEE-CD4D-450A-8D28-E708E9AA4075@gmail.com>
Date: Fri, 5 Jun 2026 17:31:31 +0800
Cc: Fujii Masao <masao.fujii@gmail.com>,
 vignesh C <vignesh21@gmail.com>
To: Postgres hackers <pgsql-hackers@lists.postgresql.org>
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 <https://www.postgresql.org/message-id/396C3BEE-CD4D-450A-8D28-E708E9AA4075%40gmail.com>
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Hi,

This is another issue with =E2=80=9C[112faf137] Log remote NOTICE, =
WARNING, and similar messages using ereport()=E2=80=9D. =46rom the =
commit message, the intention of the feature is to log remote messages =
with ereport() to get better formatting:
```
    Log remote NOTICE, WARNING, and similar messages using ereport().

    Previously, NOTICE, WARNING, and similar messages received from =
remote
    servers over replication, postgres_fdw, or dblink connections were =
printed
    directly to stderr on the local server (e.g., the subscriber). As a =
result,
    these messages lacked log prefixes (e.g., timestamp), making them =
harder
    to trace and correlate with other log entries.

    This commit addresses the issue by introducing a custom notice =
receiver
    for replication, postgres_fdw, and dblink connections. These =
messages
    are now logged via ereport(), ensuring they appear in the logs with =
proper
    formatting and context, which improves clarity and aids in =
debugging.
```

So remote messages should only be output to the server log, but =
currently they can leak to the client if client_min_messages is set to =
log.

This is a simple repro:
```
evantest=3D# set client_min_messages=3Dlog;
SET
evantest=3D# select * from dblink('host=3Dlocalhost dbname=3Dpostgres=E2=80=
=99,
'do $$ begin raise warning ''hello, client!!!''; end $$; select 1=E2=80=99=
)
as t(x int);
LOG:  received message via remote connection: WARNING:  hello, client!!!
 x
---
 1
(1 row)
```

The one-line fix is straightforward, just change the ereport() level =
from LOG to LOG_SERVER_ONLY. I also added a test in the patch.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/


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	filename=v1-0001-Avoid-sending-remote-libpq-notices-back-to-client.patch
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=46rom=20be744e8ca867626f721ad146214cde9db395834e=20Mon=20Sep=2017=20=
00:00:00=202001=0AFrom:=20"Chao=20Li=20(Evan)"=20<lic@highgo.com>=0A=
Date:=20Fri,=205=20Jun=202026=2017:18:11=20+0800=0ASubject:=20[PATCH=20=
v1]=20Avoid=20sending=20remote=20libpq=20notices=20back=20to=20clients=0A=
=0ACommit=20112faf137=20added=20a=20custom=20libpq=20notice=20receiver=20=
so=20that=20remote=0ANOTICE,=20WARNING,=20and=20similar=20messages=20=
from=20dblink,=20postgres_fdw,=20and=0Areplication=20connections=20are=20=
logged=20via=20ereport().=20The=20receiver=20used=20LOG,=0Awhich=20=
preserves=20server=20logging,=20but=20LOG=20can=20also=20be=20sent=20to=20=
the=20local=20SQL=0Aclient=20when=20client_min_messages=20is=20set=20to=20=
log.=0A=0AThat=20exposes=20remote=20notices=20to=20the=20client=20as=20=
local=20LOG=20messages,=20unlike=20the=0Aprevious=20libpq=20default=20=
notice=20processor=20behavior,=20which=20printed=20them=20only=20to=0A=
backend=20stderr.=0A=0AUse=20LOG_SERVER_ONLY=20instead.=20This=20keeps=20=
the=20messages=20in=20the=20server=20log=20while=0Apreventing=20them=20=
from=20being=20sent=20to=20the=20SQL=20client.=20Add=20a=20dblink=20=
regression=0Atest=20for=20the=20client-visible=20case.=0A=0AAuthor:=20=
Chao=20Li=20<lic@highgo.com>=0A---=0A=20=
contrib/dblink/expected/dblink.out=20=20=20=20=20=20|=2012=20=
++++++++++++=0A=20contrib/dblink/sql/dblink.sql=20=20=20=20=20=20=20=20=20=
=20=20|=20=208=20++++++++=0A=20src/include/libpq/libpq-be-fe-helpers.h=20=
|=20=202=20+-=0A=203=20files=20changed,=2021=20insertions(+),=201=20=
deletion(-)=0A=0Adiff=20--git=20a/contrib/dblink/expected/dblink.out=20=
b/contrib/dblink/expected/dblink.out=0Aindex=201d2759def9e..835367b3668=20=
100644=0A---=20a/contrib/dblink/expected/dblink.out=0A+++=20=
b/contrib/dblink/expected/dblink.out=0A@@=20-176,6=20+176,18=20@@=20=
WHERE=20t.a=20>=207;=0A=20=209=20|=20j=20|=20{a9,b9,c9}=0A=20(2=20rows)=0A=
=20=0A+--=20remote=20notices=20should=20be=20logged=20server-side=20only=0A=
+SET=20client_min_messages=20=3D=20log;=0A+SELECT=20*=0A+FROM=20=
dblink(connection_parameters(),=0A+=20=20=20=20=20=20=20=20=20=20=20=20=
$$DO=20$do$=20BEGIN=20RAISE=20NOTICE=20'remote=20notice';=20END=20$do$;=20=
SELECT=201$$)=0A+=20=20AS=20t(x=20int);=0A+=20x=20=0A+---=0A+=201=0A+(1=20=
row)=0A+=0A+RESET=20client_min_messages;=0A=20--=20should=20generate=20=
"connection=20not=20available"=20error=0A=20SELECT=20*=0A=20FROM=20=
dblink('SELECT=20*=20FROM=20foo')=20AS=20t(a=20int,=20b=20text,=20c=20=
text[])=0Adiff=20--git=20a/contrib/dblink/sql/dblink.sql=20=
b/contrib/dblink/sql/dblink.sql=0Aindex=20d67a0a5992e..4c043a3ef87=20=
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b/contrib/dblink/sql/dblink.sql=0A@@=20-128,6=20+128,14=20@@=20SELECT=20=
*=0A=20FROM=20dblink(connection_parameters(),'SELECT=20*=20FROM=20foo')=20=
AS=20t(a=20int,=20b=20text,=20c=20text[])=0A=20WHERE=20t.a=20>=207;=0A=20=
=0A+--=20remote=20notices=20should=20be=20logged=20server-side=20only=0A=
+SET=20client_min_messages=20=3D=20log;=0A+SELECT=20*=0A+FROM=20=
dblink(connection_parameters(),=0A+=20=20=20=20=20=20=20=20=20=20=20=20=
$$DO=20$do$=20BEGIN=20RAISE=20NOTICE=20'remote=20notice';=20END=20$do$;=20=
SELECT=201$$)=0A+=20=20AS=20t(x=20int);=0A+RESET=20client_min_messages;=0A=
+=0A=20--=20should=20generate=20"connection=20not=20available"=20error=0A=
=20SELECT=20*=0A=20FROM=20dblink('SELECT=20*=20FROM=20foo')=20AS=20t(a=20=
int,=20b=20text,=20c=20text[])=0Adiff=20--git=20=
a/src/include/libpq/libpq-be-fe-helpers.h=20=
b/src/include/libpq/libpq-be-fe-helpers.h=0Aindex=20=
cff68cd1c37..05b15118284=20100644=0A---=20=
a/src/include/libpq/libpq-be-fe-helpers.h=0A+++=20=
b/src/include/libpq/libpq-be-fe-helpers.h=0A@@=20-498,7=20+498,7=20@@=20=
libpqsrv_notice_receiver(void=20*arg,=20const=20PGresult=20*res)=0A=20=09=
if=20(len=20>=200=20&&=20message[len=20-=201]=20=3D=3D=20'\n')=0A=20=09=09=
len--;=0A=20=0A-=09ereport(LOG,=0A+=09ereport(LOG_SERVER_ONLY,=0A=20=09=09=
=09errmsg_internal("%s:=20%.*s",=20prefix,=20len,=20message));=0A=20}=0A=20=
=0A--=20=0A2.50.1=20(Apple=20Git-155)=0A=0A=

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