Fixed #18130 -- Made the isolation level configurable on PostgreSQL.

Thanks limscoder for the report and niwi for the draft patch.

django/db/backends/postgresql_psycopg2/base.py

@@ -83,7 +83,8 @@ def __init__(self, *args, **kwargs):
         if autocommit:
             level = psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT
         else:
-            level = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
+            level = self.settings_dict["OPTIONS"].get('isolation_level',
+                psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED)
         self._set_isolation_level(level)
         self.ops = DatabaseOperations(self)
         self.client = DatabaseClient(self)
@@ -104,6 +105,8 @@ def get_connection_params(self):
         conn_params.update(settings_dict['OPTIONS'])
         if 'autocommit' in conn_params:
             del conn_params['autocommit']
+        if 'isolation_level' in conn_params:
+            del conn_params['isolation_level']
         if settings_dict['USER']:
             conn_params['user'] = settings_dict['USER']
         if settings_dict['PASSWORD']:
@@ -170,7 +173,9 @@ def _enter_transaction_management(self, managed):
         the same transaction is visible across all the queries.
         """
         if self.features.uses_autocommit and managed and not self.isolation_level:
-            self._set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED)
+            level = self.settings_dict["OPTIONS"].get('isolation_level',
+                psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED)
+            self._set_isolation_level(level)
 
     def _leave_transaction_management(self, managed):
         """

docs/ref/databases.txt

@@ -143,8 +143,11 @@ autocommit behavior is enabled by setting the ``autocommit`` key in
 the :setting:`OPTIONS` part of your database configuration in
 :setting:`DATABASES`::
 
-    'OPTIONS': {
-        'autocommit': True,
+    DATABASES = {
+        # ...
+        'OPTIONS': {
+            'autocommit': True,
+        },
     }
 
 In this configuration, Django still ensures that :ref:`delete()
@@ -168,6 +171,34 @@ You should also audit your existing code for any instances of this behavior
 before enabling this feature. It's faster, but it provides less automatic
 protection for multi-call operations.
 
+Isolation level
+~~~~~~~~~~~~~~~
+
+.. versionadded:: 1.6
+
+Like PostgreSQL itself, Django defaults to the ``READ COMMITTED`` `isolation
+level <postgresql-isolation-levels>`_. If you need a higher isolation level
+such as ``REPEATABLE READ`` or ``SERIALIZABLE``, set it in the
+:setting:`OPTIONS` part of your database configuration in
+:setting:`DATABASES`::
+
+    import psycopg2.extensions
+
+    DATABASES = {
+        # ...
+        'OPTIONS': {
+            'isolation_level': psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE,
+        },
+    }
+
+.. note::
+
+    Under higher isolation levels, your application should be prepared to
+    handle exceptions raised on serialization failures. This option is
+    designed for advanced uses.
+
+.. _postgresql-isolation-levels: http://www.postgresql.org/docs/devel/static/transaction-iso.html
+
 Indexes for ``varchar`` and ``text`` columns
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

docs/releases/1.6.txt

@@ -125,6 +125,8 @@ Minor features
 * The admin list columns have a ``column-<field_name>`` class in the HTML
   so the columns header can be styled with CSS, e.g. to set a column width.
 
+* The isolation level can be customized under PostgreSQL.
+
 Backwards incompatible changes in 1.6
 =====================================
 

tests/transactions_regress/tests.py

@@ -242,17 +242,18 @@ def test_commit_unless_managed_in_managed(self):
 
 @skipUnless(connection.vendor == 'postgresql',
             "This test only valid for PostgreSQL")
-class TestPostgresAutocommit(TransactionTestCase):
+class TestPostgresAutocommitAndIsolation(TransactionTestCase):
     """
-    Tests to make sure psycopg2's autocommit mode is restored after entering
-    and leaving transaction management. Refs #16047.
+    Tests to make sure psycopg2's autocommit mode and isolation level
+    is restored after entering and leaving transaction management.
+    Refs #16047, #18130.
     """
     def setUp(self):
         from psycopg2.extensions import (ISOLATION_LEVEL_AUTOCOMMIT,
-                                         ISOLATION_LEVEL_READ_COMMITTED,
+                                         ISOLATION_LEVEL_SERIALIZABLE,
                                          TRANSACTION_STATUS_IDLE)
         self._autocommit = ISOLATION_LEVEL_AUTOCOMMIT
-        self._read_committed = ISOLATION_LEVEL_READ_COMMITTED
+        self._serializable = ISOLATION_LEVEL_SERIALIZABLE
         self._idle = TRANSACTION_STATUS_IDLE
 
         # We want a clean backend with autocommit = True, so
@@ -261,6 +262,7 @@ def setUp(self):
         settings = self._old_backend.settings_dict.copy()
         opts = settings['OPTIONS'].copy()
         opts['autocommit'] = True
+        opts['isolation_level'] = ISOLATION_LEVEL_SERIALIZABLE
         settings['OPTIONS'] = opts
         new_backend = self._old_backend.__class__(settings, DEFAULT_DB_ALIAS)
         connections[DEFAULT_DB_ALIAS] = new_backend
@@ -279,29 +281,29 @@ def test_initial_autocommit_state(self):
     def test_transaction_management(self):
         transaction.enter_transaction_management()
         transaction.managed(True)
-        self.assertEqual(connection.isolation_level, self._read_committed)
+        self.assertEqual(connection.isolation_level, self._serializable)
 
         transaction.leave_transaction_management()
         self.assertEqual(connection.isolation_level, self._autocommit)
 
     def test_transaction_stacking(self):
         transaction.enter_transaction_management()
         transaction.managed(True)
-        self.assertEqual(connection.isolation_level, self._read_committed)
+        self.assertEqual(connection.isolation_level, self._serializable)
 
         transaction.enter_transaction_management()
-        self.assertEqual(connection.isolation_level, self._read_committed)
+        self.assertEqual(connection.isolation_level, self._serializable)
 
         transaction.leave_transaction_management()
-        self.assertEqual(connection.isolation_level, self._read_committed)
+        self.assertEqual(connection.isolation_level, self._serializable)
 
         transaction.leave_transaction_management()
         self.assertEqual(connection.isolation_level, self._autocommit)
 
     def test_enter_autocommit(self):
         transaction.enter_transaction_management()
         transaction.managed(True)
-        self.assertEqual(connection.isolation_level, self._read_committed)
+        self.assertEqual(connection.isolation_level, self._serializable)
         list(Mod.objects.all())
         self.assertTrue(transaction.is_dirty())
         # Enter autocommit mode again.
@@ -314,7 +316,7 @@ def test_enter_autocommit(self):
         list(Mod.objects.all())
         self.assertFalse(transaction.is_dirty())
         transaction.leave_transaction_management()
-        self.assertEqual(connection.isolation_level, self._read_committed)
+        self.assertEqual(connection.isolation_level, self._serializable)
         transaction.leave_transaction_management()
         self.assertEqual(connection.isolation_level, self._autocommit)