[1.11.x] Fixed #28062 -- Added a setting to disable server-side cursors on PostgreSQL.

When a connection pooler is set up in transaction pooling mode, queries
relying on server-side cursors fail. The DISABLE_SERVER_SIDE_CURSORS
setting in DATABASES disables server-side cursors for this use case.

Backport of 88336fdbb5 from master

tests/backends/test_postgresql.py

@@ -1,5 +1,7 @@
+import operator
 import unittest
 from collections import namedtuple
+from contextlib import contextmanager
 
 from django.db import connection
 from django.test import TestCase
@@ -23,6 +25,18 @@ class ServerSideCursorsPostgres(TestCase):
             cursors = cursor.fetchall()
         return [self.PostgresCursor._make(c) for c in cursors]
 
+    @contextmanager
+    def override_db_setting(self, **kwargs):
+        for setting, value in kwargs.items():
+            original_value = connection.settings_dict.get(setting)
+            if setting in connection.settings_dict:
+                self.addCleanup(operator.setitem, connection.settings_dict, setting, original_value)
+            else:
+                self.addCleanup(operator.delitem, connection.settings_dict, setting)
+
+            connection.settings_dict[setting] = kwargs[setting]
+            yield
+
     def test_server_side_cursor(self):
         persons = Person.objects.iterator()
         next(persons)  # Open a server-side cursor
@@ -52,3 +66,17 @@ class ServerSideCursorsPostgres(TestCase):
         del persons
         cursors = self.inspect_cursors()
         self.assertEqual(len(cursors), 0)
+
+    def test_server_side_cursors_setting(self):
+        with self.override_db_setting(DISABLE_SERVER_SIDE_CURSORS=False):
+            persons = Person.objects.iterator()
+            next(persons)  # Open a server-side cursor
+            cursors = self.inspect_cursors()
+            self.assertEqual(len(cursors), 1)
+            del persons  # Close server-side cursor
+
+        with self.override_db_setting(DISABLE_SERVER_SIDE_CURSORS=True):
+            persons = Person.objects.iterator()
+            next(persons)  # Should not open a server-side cursor
+            cursors = self.inspect_cursors()
+            self.assertEqual(len(cursors), 0)