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help / color / mirror / Atom feedFrom: Chao Li <li.evan.chao@gmail.com>
To: vignesh C <vignesh21@gmail.com>
Cc: Fujii Masao <masao.fujii@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Set notice receiver before libpq connection startup
Date: Thu, 21 May 2026 15:26:27 +0800
Message-ID: <6B9A85F9-B632-4286-98AF-9EC435019055@gmail.com> (raw)
In-Reply-To: <CALDaNm3UyoQ91gW2bRP4PXnnfAv3GfmCik614-AtQCiEUAjQYw@mail.gmail.com>
References: <A2B8B7DE-C119-492F-A9FA-14CF86849777@gmail.com>
<CAHGQGwHnz7FoSx+qQsAHBx_j8Tks+SC-kAPTevrKYfrL08Ee9Q@mail.gmail.com>
<978D8971-08C3-4AAD-AE8B-976D753C882A@gmail.com>
<CALDaNm3UyoQ91gW2bRP4PXnnfAv3GfmCik614-AtQCiEUAjQYw@mail.gmail.com>
> On May 21, 2026, at 13:03, vignesh C <vignesh21@gmail.com> wrote:
>
> On Thu, 21 May 2026 at 07:40, Chao Li <li.evan.chao@gmail.com> wrote:
>>
>>
>>
>>> On May 20, 2026, at 17:19, Fujii Masao <masao.fujii@gmail.com> wrote:
>>>
>>> On Wed, May 20, 2026 at 4:21 PM Chao Li <li.evan.chao@gmail.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> While testing “Log remote NOTICE, WARNING, and similar messages using ereport()”, I noticed that libpqsrv_notice_receiver is only installed after libpqsrv_connect() finishes. As a result, NOTICE messages generated during connection establishment are missed by ereport() and are still printed to stderr.
>>>>
>>>> To reproduce the issue, I created a separate database called remotedb and defined a login trigger that emits a NOTICE message:
>>>> ```
>>>> CREATE DATABASE remotedb;
>>>>
>>>> \c remotedb
>>>>
>>>> CREATE OR REPLACE FUNCTION repro_login_notice()
>>>> RETURNS event_trigger
>>>> LANGUAGE plpgsql AS $$
>>>> BEGIN
>>>> RAISE NOTICE 'startup notice from remotedb login trigger';
>>>> END;
>>>> $$;
>>>>
>>>> CREATE EVENT TRIGGER repro_login_notice_trg
>>>> ON login
>>>> EXECUTE FUNCTION repro_login_notice();
>>>>
>>>> ALTER EVENT TRIGGER repro_login_notice_trg ENABLE ALWAYS;
>>>> ```
>>>>
>>>> Then, from another database:
>>>> ```
>>>> evantest=# create extension dblink;
>>>> CREATE EXTENSION
>>>> evantest=# SELECT dblink_connect('host=127.0.0.1 port=5432 dbname=remotedb user=chaol sslmode=disable gssencmode=disable');
>>>> dblink_connect
>>>> ----------------
>>>> OK
>>>> (1 row)
>>>> ```
>>>>
>>>> In the system log, the NOTICE message is printed directly:
>>>> ```
>>>> 2026-05-20 13:02:19.350 CST [24909] STATEMENT: SELECT dblink_connect('host=127.0.0.1 port=5432 dbname=remotedb user=chaol sslmode=disable gssencmode=disable');
>>>> NOTICE: startup notice from remotedb login trigger
>>>> ```
>>>>
>>>> To fix that, I think we should install libpqsrv_notice_receiver before libpqsrv_connect_internal(). In the attached patch, I added two helpers: libpqsrv_connect_with_notice_receiver() and libpqsrv_connect_params_with_notice_receiver().
>>>>
>>>> With the fix, the NOTICE message now looks like this:
>>>> ```
>>>> 2026-05-20 14:44:49.296 CST [45567] LOG: received message via remote connection: NOTICE: startup notice from remotedb login trigger
>>>> 2026-05-20 14:44:49.296 CST [45567] STATEMENT: SELECT dblink_connect('host=127.0.0.1 port=5432 dbname=remotedb user=chaol sslmode=disable gssencmode=disable');
>>>> ```
>>>>
>>>> Please see the attached patch for details.
>>>
>>> Thanks for the report and patch!
>>>
>>> I'd prefer to avoid adding notice-receiver-specific wrappers such as
>>> libpqsrv_connect_with_notice_receiver(). Instead, how about splitting
>>> libpqsrv_connect() into two steps: libpqsrv_connect_start(), which performs
>>> libpqsrv_connect_prepare() and PQconnectStart(), and
>>> libpqsrv_connect_complete(), which runs libpqsrv_connect_internal()?
>>>
>>> With this approach, callers could invoke PQsetNoticeReceiver() after
>>> libpqsrv_connect_start() returns but before libpqsrv_connect_complete() is
>>> called. This would allow startup-time notices to be handled correctly without
>>> introducing a dedicated wrapper function.
>>>
>>> Compared to the *_with_notice_receiver() approach, this design is more
>>> general because it exposes the phase between PQconnectStart() and connection
>>> completion. It could also support other kinds of per-connection setup in the
>>> future, not just notice receiver installation. Thought?
>>>
>>> Regards,
>>>
>>> --
>>> Fujii Masao
>>
>> The idea sounds good to me, so v2 is implemented following that idea.
>>
>> A few things I want to point out abut v2:
>>
>> * Since libpqsrv_connect_complete() would only wrap libpqsrv_connect_internal(), I just renamed libpqsrv_connect_internal() to libpqsrv_connect_complete().
>> * Since libpqsrv_connect() is now split into two phases, libpqsrv_connect_complete() must be called even if conn is NULL, because it may need to call ReleaseExternalFD(). I mentioned this in the header comment of libpqsrv_connect_start().
>> * In the postgres_fdw/connection.c change, I introduced a new local variable, start_conn, to keep the original logic unchanged. Because there is a PG_TRY/PG_CATCH block, conn is assigned only after libpqsrv_connect_complete() finishes successfully.
>
> Thanks for reporting this issue. I was able to reproduce the issue
> with the steps provided and your patch fixes the issue.
> Few comments:
> 1) No need of conn variable here, we can directly return
> PQconnectStart(conninfo) in this function:
> +static inline PGconn *
> +libpqsrv_connect_start(const char *conninfo)
> +{
> + PGconn *conn = NULL;
> +
> + libpqsrv_connect_prepare();
> +
> + conn = PQconnectStart(conninfo);
> +
> + return conn;
> +}
>
> 2) Similarly here too:
> +static inline PGconn *
> +libpqsrv_connect_params_start(const char *const *keywords,
> + const char *const *values,
> + int expand_dbname)
> {
> PGconn *conn = NULL;
>
> libpqsrv_connect_prepare();
>
> - conn = PQconnectStart(conninfo);
> -
> - libpqsrv_connect_internal(conn, wait_event_info);
> + conn = PQconnectStartParams(keywords, values, expand_dbname);
>
> return conn;
> }
>
> Regards,
> Vignesh
Thanks for your comment. Addressed in v3.
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
Attachments:
[application/octet-stream] v3-0001-Set-notice-receiver-before-libpq-connection-start.patch (10.3K, 2-v3-0001-Set-notice-receiver-before-libpq-connection-start.patch)
download | inline diff:
From 8549b8bfbaa48a954687c12d732f4bb4443a4d85 Mon Sep 17 00:00:00 2001
From: "Chao Li (Evan)" <lic@highgo.com>
Date: Wed, 20 May 2026 14:57:25 +0800
Subject: [PATCH v3] Set notice receiver before libpq connection startup
libpqsrv_connect() and libpqsrv_connect_params() complete the libpq
connection startup before returning the PGconn. As a result, callers that
install a notice receiver after these functions return can miss NOTICE,
WARNING, and similar messages emitted during connection establishment.
Split the connection helper API into start and complete steps, so callers
can install per-connection setup such as notice receivers after
PQconnectStart() returns but before the startup sequence is completed.
Document the resource-lifetime rule for the split API: callers must either
call libpqsrv_connect_complete(), even when the start function returns NULL,
or otherwise clean up the partially-started connection and release the
reserved external FD if an error is thrown before completion.
Author: Chao Li <lic@highgo.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Vignesh C <vignesh21@gmail.com>
Discussion: https://postgr.es/m/A2B8B7DE-C119-492F-A9FA-14CF86849777@gmail.com
---
contrib/dblink/dblink.c | 18 ++---
contrib/postgres_fdw/connection.c | 14 ++--
.../libpqwalreceiver/libpqwalreceiver.c | 13 ++--
src/include/libpq/libpq-be-fe-helpers.h | 65 ++++++++++++++-----
4 files changed, 73 insertions(+), 37 deletions(-)
diff --git a/contrib/dblink/dblink.c b/contrib/dblink/dblink.c
index d843eee7e97..0751df9e444 100644
--- a/contrib/dblink/dblink.c
+++ b/contrib/dblink/dblink.c
@@ -222,7 +222,11 @@ dblink_get_conn(char *conname_or_str,
dblink_we_get_conn = WaitEventExtensionNew("DblinkGetConnect");
/* OK to make connection */
- conn = libpqsrv_connect(connstr, dblink_we_get_conn);
+ conn = libpqsrv_connect_start(connstr);
+ if (conn != NULL)
+ PQsetNoticeReceiver(conn, libpqsrv_notice_receiver,
+ "received message via remote connection");
+ libpqsrv_connect_complete(conn, dblink_we_get_conn);
if (PQstatus(conn) == CONNECTION_BAD)
{
@@ -235,9 +239,6 @@ dblink_get_conn(char *conname_or_str,
errdetail_internal("%s", msg)));
}
- PQsetNoticeReceiver(conn, libpqsrv_notice_receiver,
- "received message via remote connection");
-
dblink_security_check(conn, NULL, connstr);
if (PQclientEncoding(conn) != GetDatabaseEncoding())
PQsetClientEncoding(conn, GetDatabaseEncodingName());
@@ -321,7 +322,11 @@ dblink_connect(PG_FUNCTION_ARGS)
}
/* OK to make connection */
- conn = libpqsrv_connect(connstr, dblink_we_connect);
+ conn = libpqsrv_connect_start(connstr);
+ if (conn != NULL)
+ PQsetNoticeReceiver(conn, libpqsrv_notice_receiver,
+ "received message via remote connection");
+ libpqsrv_connect_complete(conn, dblink_we_connect);
if (PQstatus(conn) == CONNECTION_BAD)
{
@@ -336,9 +341,6 @@ dblink_connect(PG_FUNCTION_ARGS)
errdetail_internal("%s", msg)));
}
- PQsetNoticeReceiver(conn, libpqsrv_notice_receiver,
- "received message via remote connection");
-
/* check password actually used if not superuser */
dblink_security_check(conn, connname, connstr);
diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index 3d2a8d0519d..86178ec5fb2 100644
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -638,6 +638,7 @@ connect_pg_server(ForeignServer *server, UserMapping *user)
const char **keywords;
const char **values;
char *appname;
+ PGconn *start_conn;
construct_connection_params(server, user, &keywords, &values, &appname);
@@ -646,9 +647,13 @@ connect_pg_server(ForeignServer *server, UserMapping *user)
pgfdw_we_connect = WaitEventExtensionNew("PostgresFdwConnect");
/* OK to make connection */
- conn = libpqsrv_connect_params(keywords, values,
- false, /* expand_dbname */
- pgfdw_we_connect);
+ start_conn = libpqsrv_connect_params_start(keywords, values,
+ /* expand_dbname = */ false);
+ if (start_conn != NULL)
+ PQsetNoticeReceiver(start_conn, libpqsrv_notice_receiver,
+ "received message via remote connection");
+ libpqsrv_connect_complete(start_conn, pgfdw_we_connect);
+ conn = start_conn;
if (!conn || PQstatus(conn) != CONNECTION_OK)
ereport(ERROR,
@@ -657,9 +662,6 @@ connect_pg_server(ForeignServer *server, UserMapping *user)
server->servername),
errdetail_internal("%s", pchomp(PQerrorMessage(conn)))));
- PQsetNoticeReceiver(conn, libpqsrv_notice_receiver,
- "received message via remote connection");
-
/* Perform post-connection security checks. */
pgfdw_security_check(keywords, values, user, conn);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 9f04c9ed25d..af2734cb328 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -223,9 +223,13 @@ libpqrcv_connect(const char *conninfo, bool replication, bool logical,
conn = palloc0_object(WalReceiverConn);
conn->streamConn =
- libpqsrv_connect_params(keys, vals,
- /* expand_dbname = */ true,
- WAIT_EVENT_LIBPQWALRECEIVER_CONNECT);
+ libpqsrv_connect_params_start(keys, vals,
+ /* expand_dbname = */ true);
+ if (conn->streamConn != NULL)
+ PQsetNoticeReceiver(conn->streamConn, libpqsrv_notice_receiver,
+ "received message via replication");
+ libpqsrv_connect_complete(conn->streamConn,
+ WAIT_EVENT_LIBPQWALRECEIVER_CONNECT);
if (options_val != NULL)
pfree(options_val);
@@ -245,9 +249,6 @@ libpqrcv_connect(const char *conninfo, bool replication, bool logical,
errhint("Target server's authentication method must be changed, or set password_required=false in the subscription parameters.")));
}
- PQsetNoticeReceiver(conn->streamConn, libpqsrv_notice_receiver,
- "received message via replication");
-
/*
* Set always-secure search path for the cases where the connection is
* used to run SQL queries, so malicious users can't get control.
diff --git a/src/include/libpq/libpq-be-fe-helpers.h b/src/include/libpq/libpq-be-fe-helpers.h
index 85d8b63f019..cff68cd1c37 100644
--- a/src/include/libpq/libpq-be-fe-helpers.h
+++ b/src/include/libpq/libpq-be-fe-helpers.h
@@ -39,10 +39,28 @@
static inline void libpqsrv_connect_prepare(void);
-static inline void libpqsrv_connect_internal(PGconn *conn, uint32 wait_event_info);
+static inline void libpqsrv_connect_complete(PGconn *conn, uint32 wait_event_info);
static inline PGresult *libpqsrv_get_result_last(PGconn *conn, uint32 wait_event_info);
static inline PGresult *libpqsrv_get_result(PGconn *conn, uint32 wait_event_info);
+/*
+ * Start a connection using PQconnectStart().
+ *
+ * The returned connection has not yet completed its startup sequence. Callers
+ * may perform per-connection setup, such as installing a notice receiver,
+ * before calling libpqsrv_connect_complete().
+ *
+ * Callers must call libpqsrv_connect_complete(), even if this function returns
+ * NULL, because libpqsrv_connect_prepare() may already have reserved an
+ * external FD that must be released.
+ */
+static inline PGconn *
+libpqsrv_connect_start(const char *conninfo)
+{
+ libpqsrv_connect_prepare();
+
+ return PQconnectStart(conninfo);
+}
/*
* PQconnectdb() wrapper that reserves a file descriptor and processes
@@ -55,17 +73,30 @@ static inline PGresult *libpqsrv_get_result(PGconn *conn, uint32 wait_event_info
static inline PGconn *
libpqsrv_connect(const char *conninfo, uint32 wait_event_info)
{
- PGconn *conn = NULL;
+ PGconn *conn;
- libpqsrv_connect_prepare();
-
- conn = PQconnectStart(conninfo);
+ conn = libpqsrv_connect_start(conninfo);
- libpqsrv_connect_internal(conn, wait_event_info);
+ libpqsrv_connect_complete(conn, wait_event_info);
return conn;
}
+/*
+ * Start a connection using PQconnectStartParams().
+ *
+ * See libpqsrv_connect_start() for the resource-lifetime rules.
+ */
+static inline PGconn *
+libpqsrv_connect_params_start(const char *const *keywords,
+ const char *const *values,
+ int expand_dbname)
+{
+ libpqsrv_connect_prepare();
+
+ return PQconnectStartParams(keywords, values, expand_dbname);
+}
+
/*
* Like libpqsrv_connect(), except that this is a wrapper for
* PQconnectdbParams().
@@ -76,13 +107,11 @@ libpqsrv_connect_params(const char *const *keywords,
int expand_dbname,
uint32 wait_event_info)
{
- PGconn *conn = NULL;
+ PGconn *conn;
- libpqsrv_connect_prepare();
+ conn = libpqsrv_connect_params_start(keywords, values, expand_dbname);
- conn = PQconnectStartParams(keywords, values, expand_dbname);
-
- libpqsrv_connect_internal(conn, wait_event_info);
+ libpqsrv_connect_complete(conn, wait_event_info);
return conn;
}
@@ -90,8 +119,9 @@ libpqsrv_connect_params(const char *const *keywords,
/*
* PQfinish() wrapper that additionally releases the reserved file descriptor.
*
- * It is allowed to call this with a NULL pgconn iff NULL was returned by
- * libpqsrv_connect*.
+ * It is allowed to call this with NULL only when the external FD reservation
+ * has already been released, for example after calling
+ * libpqsrv_connect_complete() with a NULL connection.
*/
static inline void
libpqsrv_disconnect(PGconn *conn)
@@ -101,7 +131,7 @@ libpqsrv_disconnect(PGconn *conn)
* already released it). This rule makes it easier to write PG_CATCH()
* handlers for this facility's users.
*
- * See also libpqsrv_connect_internal().
+ * See also libpqsrv_connect_complete().
*/
if (conn == NULL)
return;
@@ -111,7 +141,7 @@ libpqsrv_disconnect(PGconn *conn)
}
-/* internal helper functions follow */
+/* lower-level connection helper functions follow */
/*
@@ -144,10 +174,11 @@ libpqsrv_connect_prepare(void)
}
/*
- * Helper function for all connection establishment functions.
+ * Complete a connection started by libpqsrv_connect_start() or
+ * libpqsrv_connect_params_start().
*/
static inline void
-libpqsrv_connect_internal(PGconn *conn, uint32 wait_event_info)
+libpqsrv_connect_complete(PGconn *conn, uint32 wait_event_info)
{
/*
* With conn == NULL libpqsrv_disconnect() wouldn't release the FD. So do
--
2.50.1 (Apple Git-155)
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To: pgsql-hackers@postgresql.org
Cc: li.evan.chao@gmail.com, vignesh21@gmail.com, masao.fujii@gmail.com
Subject: Re: Set notice receiver before libpq connection startup
In-Reply-To: <6B9A85F9-B632-4286-98AF-9EC435019055@gmail.com>
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