Refs #16614 -- Made QuerySet.iterator() use server-side cursors on PostgreSQL.

Thanks to Josh Smeaton for the idea of implementing server-side cursors
in PostgreSQL from the iterator method, and Anssi Kääriäinen and Kevin
Turner for their previous work. Also Simon Charette and Tim Graham for
review.

1 files changed, 23 insertions, 2 deletions

diff --git a/django/db/backends/postgresql/base.py b/django/db/backends/postgresql/base.py
index b4008532ee..91dee6a722 100644
--- a/django/db/backends/postgresql/base.py
+++ b/django/db/backends/postgresql/base.py
@@ -4,6 +4,7 @@ PostgreSQL database backend for Django.
 Requires psycopg 2: http://initd.org/projects/psycopg2
 """
 
+import threading
 import warnings
 
 from django.conf import settings
@@ -145,6 +146,10 @@ class DatabaseWrapper(BaseDatabaseWrapper):
     introspection_class = DatabaseIntrospection
     ops_class = DatabaseOperations
 
+    def __init__(self, *args, **kwargs):
+        super(DatabaseWrapper, self).__init__(*args, **kwargs)
+        self._named_cursor_idx = 0
+
     def get_connection_params(self):
         settings_dict = self.settings_dict
         # None may be used to connect to the default 'postgres' db
@@ -206,11 +211,27 @@ class DatabaseWrapper(BaseDatabaseWrapper):
             if not self.get_autocommit():
                 self.connection.commit()
 
-    def create_cursor(self):
-        cursor = self.connection.cursor()
+    def create_cursor(self, name=None):
+        if name:
+            # In autocommit mode, the cursor will be used outside of a
+            # transaction, hence use a holdable cursor.
+            cursor = self.connection.cursor(name, scrollable=False, withhold=self.connection.autocommit)
+        else:
+            cursor = self.connection.cursor()
         cursor.tzinfo_factory = utc_tzinfo_factory if settings.USE_TZ else None
         return cursor
 
+    def chunked_cursor(self):
+        self._named_cursor_idx += 1
+        db_cursor = self._cursor(
+            name='_django_curs_%d_%d' % (
+                # Avoid reusing name in other threads
+                threading.current_thread().ident,
+                self._named_cursor_idx,
+            )
+        )
+        return self._prepare_cursor(db_cursor)
+
     def _set_autocommit(self, autocommit):
         with self.wrap_database_errors:
             self.connection.autocommit = autocommit