Fixed #3460 -- Added an ability to enable true autocommit for psycopg2 backend.

Ensure to read the documentation before blindly enabling this: requires some
code audits first, but might well be worth it for busy sites.

Thanks to nicferrier, iamseb and Richard Davies for help with this patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10029 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/__init__.py

@@ -41,6 +41,21 @@ class BaseDatabaseWrapper(local):
         if self.connection is not None:
             return self.connection.rollback()
 
+    def _enter_transaction_management(self, managed):
+        """
+        A hook for backend-specific changes required when entering manual
+        transaction handling.
+        """
+        pass
+
+    def _leave_transaction_management(self, managed):
+        """
+        A hook for backend-specific changes required when leaving manual
+        transaction handling. Will usually be implemented only when
+        _enter_transaction_management() is also required.
+        """
+        pass
+
     def _savepoint(self, sid):
         if not self.features.uses_savepoints:
             return
@@ -81,6 +96,8 @@ class BaseDatabaseFeatures(object):
     update_can_self_select = True
     interprets_empty_strings_as_nulls = False
     can_use_chunked_reads = True
+    can_return_id_from_insert = False
+    uses_autocommit = False
     uses_savepoints = False
     # If True, don't use integer foreign keys referring to, e.g., positive
     # integer primary keys.
@@ -230,6 +247,15 @@ class BaseDatabaseOperations(object):
         """
         return 'DEFAULT'
 
+    def return_insert_id(self):
+        """
+        For backends that support returning the last insert ID as part of an
+        insert query, this method returns the SQL to append to the INSERT
+        query. The returned fragment should contain a format string to hold
+        hold the appropriate column.
+        """
+        pass
+
     def query_class(self, DefaultQueryClass):
         """
         Given the default Query class, returns a custom Query class

django/db/backends/postgresql_psycopg2/base.py

@@ -4,6 +4,7 @@ PostgreSQL database backend for Django.
 Requires psycopg 2: http://initd.org/projects/psycopg2
 """
 
+from django.conf import settings
 from django.db.backends import *
 from django.db.backends.postgresql.operations import DatabaseOperations as PostgresqlDatabaseOperations
 from django.db.backends.postgresql.client import DatabaseClient
@@ -28,7 +29,7 @@ psycopg2.extensions.register_adapter(SafeUnicode, psycopg2.extensions.QuotedStri
 
 class DatabaseFeatures(BaseDatabaseFeatures):
     needs_datetime_string_cast = False
-    uses_savepoints = True
+    can_return_id_from_insert = True
 
 class DatabaseOperations(PostgresqlDatabaseOperations):
     def last_executed_query(self, cursor, sql, params):
@@ -37,6 +38,9 @@ class DatabaseOperations(PostgresqlDatabaseOperations):
         # http://www.initd.org/tracker/psycopg/wiki/psycopg2_documentation#postgresql-status-message-and-executed-query
         return cursor.query
 
+    def return_insert_id(self):
+        return "RETURNING %s"
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     operators = {
         'exact': '= %s',
@@ -59,6 +63,12 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         super(DatabaseWrapper, self).__init__(*args, **kwargs)
 
         self.features = DatabaseFeatures()
+        if settings.DATABASE_OPTIONS.get('autocommit', False):
+          self.features.uses_autocommit = True
+          self._iso_level_0()
+        else:
+          self.features.uses_autocommit = False
+          self._iso_level_1()
         self.ops = DatabaseOperations()
         self.client = DatabaseClient(self)
         self.creation = DatabaseCreation(self)
@@ -77,6 +87,8 @@ class DatabaseWrapper(BaseDatabaseWrapper):
                 'database': settings_dict['DATABASE_NAME'],
             }
             conn_params.update(settings_dict['DATABASE_OPTIONS'])
+            if 'autocommit' in conn_params:
+                del conn_params['autocommit']
             if settings_dict['DATABASE_USER']:
                 conn_params['user'] = settings_dict['DATABASE_USER']
             if settings_dict['DATABASE_PASSWORD']:
@@ -86,7 +98,6 @@ class DatabaseWrapper(BaseDatabaseWrapper):
             if settings_dict['DATABASE_PORT']:
                 conn_params['port'] = settings_dict['DATABASE_PORT']
             self.connection = Database.connect(**conn_params)
-            self.connection.set_isolation_level(1) # make transactions transparent to all cursors
             self.connection.set_client_encoding('UTF8')
         cursor = self.connection.cursor()
         cursor.tzinfo_factory = None
@@ -98,3 +109,44 @@ class DatabaseWrapper(BaseDatabaseWrapper):
                 # No savepoint support for earlier version of PostgreSQL.
                 self.features.uses_savepoints = False
         return cursor
+
+    def _enter_transaction_management(self, managed):
+        """
+        Switch the isolation level when needing transaction support, so that
+        the same transaction is visible across all the queries.
+        """
+        if self.features.uses_autocommit and managed and not self.isolation_level:
+            self._iso_level_1()
+
+    def _leave_transaction_management(self, managed):
+        """
+        If the normal operating mode is "autocommit", switch back to that when
+        leaving transaction management.
+        """
+        if self.features.uses_autocommit and not managed and self.isolation_level:
+            self._iso_level_0()
+
+    def _iso_level_0(self):
+        """
+        Do all the related feature configurations for isolation level 0. This
+        doesn't touch the uses_autocommit feature, since that controls the
+        movement *between* isolation levels.
+        """
+        try:
+            if self.connection is not None:
+                self.connection.set_isolation_level(0)
+        finally:
+            self.isolation_level = 0
+            self.features.uses_savepoints = False
+
+    def _iso_level_1(self):
+        """
+        The "isolation level 1" version of _iso_level_0().
+        """
+        try:
+            if self.connection is not None:
+                self.connection.set_isolation_level(1)
+        finally:
+            self.isolation_level = 1
+            self.features.uses_savepoints = True
+

django/db/models/query.py

@@ -447,8 +447,20 @@ class QuerySet(object):
                 "Cannot update a query once a slice has been taken."
         query = self.query.clone(sql.UpdateQuery)
         query.add_update_values(kwargs)
-        rows = query.execute_sql(None)
-        transaction.commit_unless_managed()
+        if not transaction.is_managed():
+            transaction.enter_transaction_management()
+            forced_managed = True
+        else:
+            forced_managed = False
+        try:
+            rows = query.execute_sql(None)
+            if forced_managed:
+                transaction.commit()
+            else:
+                transaction.commit_unless_managed()
+        finally:
+            if forced_managed:
+                transaction.leave_transaction_management()
         self._result_cache = None
         return rows
     update.alters_data = True
@@ -962,6 +974,11 @@ def delete_objects(seen_objs):
     Iterate through a list of seen classes, and remove any instances that are
     referred to.
     """
+    if not transaction.is_managed():
+        transaction.enter_transaction_management()
+        forced_managed = True
+    else:
+        forced_managed = False
     try:
         ordered_classes = seen_objs.keys()
     except CyclicDependency:
@@ -972,51 +989,58 @@ def delete_objects(seen_objs):
         ordered_classes = seen_objs.unordered_keys()
 
     obj_pairs = {}
-    for cls in ordered_classes:
-        items = seen_objs[cls].items()
-        items.sort()
-        obj_pairs[cls] = items
+    try:
+        for cls in ordered_classes:
+            items = seen_objs[cls].items()
+            items.sort()
+            obj_pairs[cls] = items
 
-        # Pre-notify all instances to be deleted.
-        for pk_val, instance in items:
-            signals.pre_delete.send(sender=cls, instance=instance)
+            # Pre-notify all instances to be deleted.
+            for pk_val, instance in items:
+                signals.pre_delete.send(sender=cls, instance=instance)
 
-        pk_list = [pk for pk,instance in items]
-        del_query = sql.DeleteQuery(cls, connection)
-        del_query.delete_batch_related(pk_list)
+            pk_list = [pk for pk,instance in items]
+            del_query = sql.DeleteQuery(cls, connection)
+            del_query.delete_batch_related(pk_list)
 
-        update_query = sql.UpdateQuery(cls, connection)
-        for field, model in cls._meta.get_fields_with_model():
-            if (field.rel and field.null and field.rel.to in seen_objs and
-                    filter(lambda f: f.column == field.column,
-                    field.rel.to._meta.fields)):
-                if model:
-                    sql.UpdateQuery(model, connection).clear_related(field,
-                            pk_list)
-                else:
-                    update_query.clear_related(field, pk_list)
+            update_query = sql.UpdateQuery(cls, connection)
+            for field, model in cls._meta.get_fields_with_model():
+                if (field.rel and field.null and field.rel.to in seen_objs and
+                        filter(lambda f: f.column == field.column,
+                        field.rel.to._meta.fields)):
+                    if model:
+                        sql.UpdateQuery(model, connection).clear_related(field,
+                                pk_list)
+                    else:
+                        update_query.clear_related(field, pk_list)
 
-    # Now delete the actual data.
-    for cls in ordered_classes:
-        items = obj_pairs[cls]
-        items.reverse()
+        # Now delete the actual data.
+        for cls in ordered_classes:
+            items = obj_pairs[cls]
+            items.reverse()
 
-        pk_list = [pk for pk,instance in items]
-        del_query = sql.DeleteQuery(cls, connection)
-        del_query.delete_batch(pk_list)
+            pk_list = [pk for pk,instance in items]
+            del_query = sql.DeleteQuery(cls, connection)
+            del_query.delete_batch(pk_list)
 
-        # Last cleanup; set NULLs where there once was a reference to the
-        # object, NULL the primary key of the found objects, and perform
-        # post-notification.
-        for pk_val, instance in items:
-            for field in cls._meta.fields:
-                if field.rel and field.null and field.rel.to in seen_objs:
-                    setattr(instance, field.attname, None)
+            # Last cleanup; set NULLs where there once was a reference to the
+            # object, NULL the primary key of the found objects, and perform
+            # post-notification.
+            for pk_val, instance in items:
+                for field in cls._meta.fields:
+                    if field.rel and field.null and field.rel.to in seen_objs:
+                        setattr(instance, field.attname, None)
 
-            signals.post_delete.send(sender=cls, instance=instance)
-            setattr(instance, cls._meta.pk.attname, None)
+                signals.post_delete.send(sender=cls, instance=instance)
+                setattr(instance, cls._meta.pk.attname, None)
 
-    transaction.commit_unless_managed()
+        if forced_managed:
+            transaction.commit()
+        else:
+            transaction.commit_unless_managed()
+    finally:
+        if forced_managed:
+            transaction.leave_transaction_management()
 
 
 def insert_query(model, values, return_id=False, raw_values=False):

django/db/models/sql/subqueries.py

@@ -302,9 +302,13 @@ class InsertQuery(Query):
         # We don't need quote_name_unless_alias() here, since these are all
         # going to be column names (so we can avoid the extra overhead).
         qn = self.connection.ops.quote_name
-        result = ['INSERT INTO %s' % qn(self.model._meta.db_table)]
+        opts = self.model._meta
+        result = ['INSERT INTO %s' % qn(opts.db_table)]
         result.append('(%s)' % ', '.join([qn(c) for c in self.columns]))
         result.append('VALUES (%s)' % ', '.join(self.values))
+        if self.connection.features.can_return_id_from_insert:
+            col = "%s.%s" % (qn(opts.db_table), qn(opts.pk.column))
+            result.append(self.connection.ops.return_insert_id() % col)
         return ' '.join(result), self.params
 
     def execute_sql(self, return_id=False):

django/db/transaction.py

@@ -40,7 +40,7 @@ savepoint_state = {}
 # database commit.
 dirty = {}
 
-def enter_transaction_management():
+def enter_transaction_management(managed=True):
     """
     Enters transaction management for a running thread. It must be balanced with
     the appropriate leave_transaction_management call, since the actual state is
@@ -58,6 +58,7 @@ def enter_transaction_management():
         state[thread_ident].append(settings.TRANSACTIONS_MANAGED)
     if thread_ident not in dirty:
         dirty[thread_ident] = False
+    connection._enter_transaction_management(managed)
 
 def leave_transaction_management():
     """
@@ -65,6 +66,7 @@ def leave_transaction_management():
     over to the surrounding block, as a commit will commit all changes, even
     those from outside. (Commits are on connection level.)
     """
+    connection._leave_transaction_management(is_managed())
     thread_ident = thread.get_ident()
     if thread_ident in state and state[thread_ident]:
         del state[thread_ident][-1]
@@ -216,7 +218,7 @@ def autocommit(func):
     """
     def _autocommit(*args, **kw):
         try:
-            enter_transaction_management()
+            enter_transaction_management(managed=False)
             managed(False)
             return func(*args, **kw)
         finally:

docs/ref/databases.txt

@@ -13,6 +13,8 @@ This file describes some of the features that might be relevant to Django
 usage. Of course, it is not intended as a replacement for server-specific
 documentation or reference manuals.
 
+.. postgresql-notes:
+
 PostgreSQL notes
 ================
 
@@ -29,6 +31,56 @@ aggregate with an database backend falls within the affected release range.
 .. _known to be faulty: http://archives.postgresql.org/pgsql-bugs/2007-07/msg00046.php
 .. _Release 8.2.5: http://developer.postgresql.org/pgdocs/postgres/release-8-2-5.html
 
+Transaction handling
+---------------------
+
+:ref:`By default <topics-db-transactions>`, Django starts a transaction when a
+database connection if first used and commits the result at the end of the
+request/response handling. The PostgreSQL backends normally operate the same
+as any other Django backend in this respect.
+
+Autocommit mode
+~~~~~~~~~~~~~~~
+
+.. versionadded:: 1.1
+
+If your application is particularly read-heavy and doesn't make many database
+writes, the overhead of a constantly open transaction can sometimes be
+noticeable. For those situations, if you're using the ``postgresql_psycopg2``
+backend, you can configure Django to use *"autocommit"* behavior for the
+connection, meaning that each database operation will normally be in its own
+transaction, rather than having the transaction extend over multiple
+operations. In this case, you can still manually start a transaction if you're
+doing something that requires consistency across multiple database operations.
+The autocommit behavior is enabled by setting the ``autocommit`` key in the
+:setting:`DATABASE_OPTIONS` setting::
+
+    DATABASE_OPTIONS = {
+        "autocommit": True,
+    }
+
+In this configuration, Django still ensures that :ref:`delete()
+<topics-db-queries-delete>` and :ref:`update() <topics-db-queries-update>`
+queries run inside a single transaction, so that either all the affected
+objects are changed or none of them are.
+
+.. admonition:: This is database-level autocommit
+
+    This functionality is not the same as the
+    :ref:`topics-db-transactions-autocommit` decorator. That decorator is a
+    Django-level implementation that commits automatically after data changing
+    operations. The feature enabled using the :setting:`DATABASE_OPTIONS`
+    settings provides autocommit behavior at the database adapter level. It
+    commits after *every* operation.
+
+If you are using this feature and performing an operation akin to delete or
+updating that requires multiple operations, you are strongly recommended to
+wrap you operations in manual transaction handling to ensure data consistency.
+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.
+
+
 .. _mysql-notes:
 
 MySQL notes
@@ -199,7 +251,7 @@ Here's a sample configuration which uses a MySQL option file::
   DATABASE_ENGINE = "mysql"
   DATABASE_OPTIONS = {
       'read_default_file': '/path/to/my.cnf',
-      }
+  }
 
   # my.cnf
   [client]
@@ -237,9 +289,7 @@ storage engine, you have a couple of options.
       creating your tables::
 
           DATABASE_OPTIONS = {
-              # ...
              "init_command": "SET storage_engine=INNODB",
-              # ...
           }
 
       This sets the default storage engine upon connecting to the database.

docs/topics/db/queries.txt

@@ -714,6 +714,8 @@ primary key field is called ``name``, these two statements are equivalent::
     >>> some_obj == other_obj
     >>> some_obj.name == other_obj.name
 
+.. _topics-db-queries-delete:
+
 Deleting objects
 ================
 
@@ -756,6 +758,8 @@ complete query set::
 
     Entry.objects.all().delete()
 
+.. _topics-db-queries-update:
+
 Updating multiple objects at once
 =================================
 

docs/topics/db/transactions.txt

@@ -63,6 +63,8 @@ particular view function.
     Although the examples below use view functions as examples, these
     decorators can be applied to non-view functions as well.
 
+.. _topics-db-transactions-autocommit:
+
 ``django.db.transaction.autocommit``
 ------------------------------------