Allow dbname in pg_basebackup/pg_receivewal connstring

As physical replication work at the cluster level and not database level, any dbname in the connection string is ignored. Proxies and middleware used in connecting to the cluster might however need to know the dbname in order to make the correct routing decision for the connection. With this the startup packet will include the dbname parameter. Author: Jelte Fennema-Nio <[email protected]> Reviewed-by: Tristen Raab <[email protected]> Reviewed-by: Jim Jones <[email protected]> Discussion: https://postgr.es/m/CAGECzQTw-dZkVT_RELRzfWRzY714-VaTjoBATYfZq93R8C-auA@mail.gmail.com
neondatabase · Sep 21, 2023 · cca97ce · cca97ce
1 parent c621467
commit cca97ce
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Showing 3 changed files with 27 additions and 14 deletions.
diff --git a/doc/src/sgml/ref/pg_basebackup.sgml b/doc/src/sgml/ref/pg_basebackup.sgml
@@ -778,7 +778,10 @@ PostgreSQL documentation
         The option is called <literal>--dbname</literal> for consistency with other
         client applications, but because <application>pg_basebackup</application>
         doesn't connect to any particular database in the cluster, any database
-        name in the connection string will be ignored.
+        name in the connection string will be ignored
+        by <productname>PostgreSQL</productname>. Middleware, or proxies, used in
+        connecting to <productname>PostgreSQL</productname> might however
+        utilize the value.
        </para>
       </listitem>
      </varlistentry>

diff --git a/doc/src/sgml/ref/pg_receivewal.sgml b/doc/src/sgml/ref/pg_receivewal.sgml
@@ -316,8 +316,11 @@ PostgreSQL documentation
        <para>
         The option is called <literal>--dbname</literal> for consistency with other
         client applications, but because <application>pg_receivewal</application>
-        doesn't connect to any particular database in the cluster, database
-        name in the connection string will be ignored.
+        doesn't connect to any particular database in the cluster, any database
+        name in the connection string will be ignored by
+        <productname>PostgreSQL</productname>. Middleware, or proxies, used in
+        connecting to <productname>PostgreSQL</productname> might however
+        utilize the value.
        </para>
       </listitem>
      </varlistentry>

diff --git a/src/bin/pg_basebackup/streamutil.c b/src/bin/pg_basebackup/streamutil.c
@@ -79,9 +79,6 @@ GetConnection(void)
 	/*
 	 * Merge the connection info inputs given in form of connection string,
 	 * options and default values (dbname=replication, replication=true, etc.)
-	 * Explicitly discard any dbname value in the connection string;
-	 * otherwise, PQconnectdbParams() would interpret that value as being
-	 * itself a connection string.
 	 */
 	i = 0;
 	if (connection_string)
@@ -92,18 +89,24 @@ GetConnection(void)
 
 		for (conn_opt = conn_opts; conn_opt->keyword != NULL; conn_opt++)
 		{
-			if (conn_opt->val != NULL && conn_opt->val[0] != '\0' &&
-				strcmp(conn_opt->keyword, "dbname") != 0)
+			if (conn_opt->val != NULL && conn_opt->val[0] != '\0')
 				argcount++;
 		}
 
 		keywords = pg_malloc0((argcount + 1) * sizeof(*keywords));
 		values = pg_malloc0((argcount + 1) * sizeof(*values));
 
+		/*
+		 * Set dbname here already, so it can be overridden by a dbname in the
+		 * connection string.
+		 */
+		keywords[i] = "dbname";
+		values[i] = "replication";
+		i++;
+
 		for (conn_opt = conn_opts; conn_opt->keyword != NULL; conn_opt++)
 		{
-			if (conn_opt->val != NULL && conn_opt->val[0] != '\0' &&
-				strcmp(conn_opt->keyword, "dbname") != 0)
+			if (conn_opt->val != NULL && conn_opt->val[0] != '\0')
 			{
 				keywords[i] = conn_opt->keyword;
 				values[i] = conn_opt->val;
@@ -115,11 +118,11 @@ GetConnection(void)
 	{
 		keywords = pg_malloc0((argcount + 1) * sizeof(*keywords));
 		values = pg_malloc0((argcount + 1) * sizeof(*values));
+		keywords[i] = "dbname";
+		values[i] = dbname;
+		i++;
 	}
 
-	keywords[i] = "dbname";
-	values[i] = dbname == NULL ? "replication" : dbname;
-	i++;
 	keywords[i] = "replication";
 	values[i] = dbname == NULL ? "true" : "database";
 	i++;
@@ -171,7 +174,11 @@ GetConnection(void)
 			values[i] = NULL;
 		}
 
-		tmpconn = PQconnectdbParams(keywords, values, true);
+		/*
+		 * Only expand dbname when we did not already parse the argument as a
+		 * connection string ourselves.
+		 */
+		tmpconn = PQconnectdbParams(keywords, values, !connection_string);
 
 		/*
 		 * If there is too little memory even to allocate the PGconn object