[1.6.x] Fixed #21109 -- made db cursor error wrapping faster

Backpatch of 94001421321bd8808c4027a72aa32a1eef005764 from master.

3 files changed, 18 insertions, 12 deletions

diff --git a/django/db/backends/__init__.py b/django/db/backends/__init__.py
index a0813cceb0..3184c11f48 100644
--- a/django/db/backends/__init__.py
+++ b/django/db/backends/__init__.py
@@ -120,29 +120,29 @@ class BaseDatabaseWrapper(object):
         Guarantees that a connection to the database is established.
         """
         if self.connection is None:
-            with self.wrap_database_errors():
+            with self.wrap_database_errors:
                 self.connect()
 
     ##### Backend-specific wrappers for PEP-249 connection methods #####
 
     def _cursor(self):
         self.ensure_connection()
-        with self.wrap_database_errors():
+        with self.wrap_database_errors:
             return self.create_cursor()
 
     def _commit(self):
         if self.connection is not None:
-            with self.wrap_database_errors():
+            with self.wrap_database_errors:
                 return self.connection.commit()
 
     def _rollback(self):
         if self.connection is not None:
-            with self.wrap_database_errors():
+            with self.wrap_database_errors:
                 return self.connection.rollback()
 
     def _close(self):
         if self.connection is not None:
-            with self.wrap_database_errors():
+            with self.wrap_database_errors:
                 return self.connection.close()
 
     ##### Generic wrappers for PEP-249 connection methods #####
@@ -482,6 +482,7 @@ class BaseDatabaseWrapper(object):
 
     ##### Miscellaneous #####
 
+    @cached_property
     def wrap_database_errors(self):
         """
         Context manager and decorator that re-throws backend-specific database
diff --git a/django/db/backends/util.py b/django/db/backends/util.py
index aa2601277a..43ceff095b 100644
--- a/django/db/backends/util.py
+++ b/django/db/backends/util.py
@@ -19,13 +19,17 @@ class CursorWrapper(object):
         self.cursor = cursor
         self.db = db
 
+    SET_DIRTY_ATTRS = frozenset(['execute', 'executemany', 'callproc'])
+    WRAP_ERROR_ATTRS = frozenset([
+        'callproc', 'close', 'execute', 'executemany',
+        'fetchone', 'fetchmany', 'fetchall', 'nextset'])
+
     def __getattr__(self, attr):
-        if attr in ('execute', 'executemany', 'callproc'):
+        if attr in CursorWrapper.SET_DIRTY_ATTRS:
             self.db.set_dirty()
         cursor_attr = getattr(self.cursor, attr)
-        if attr in ('callproc', 'close', 'execute', 'executemany',
-                    'fetchone', 'fetchmany', 'fetchall', 'nextset'):
-            return self.db.wrap_database_errors()(cursor_attr)
+        if attr in CursorWrapper.WRAP_ERROR_ATTRS:
+            return self.db.wrap_database_errors(cursor_attr)
         else:
             return cursor_attr
 
@@ -39,7 +43,7 @@ class CursorDebugWrapper(CursorWrapper):
         self.db.set_dirty()
         start = time()
         try:
-            with self.db.wrap_database_errors():
+            with self.db.wrap_database_errors:
                 if params is None:
                     # params default might be backend specific
                     return self.cursor.execute(sql)
@@ -60,7 +64,7 @@ class CursorDebugWrapper(CursorWrapper):
         self.db.set_dirty()
         start = time()
         try:
-            with self.db.wrap_database_errors():
+            with self.db.wrap_database_errors:
                 return self.cursor.executemany(sql, param_list)
         finally:
             stop = time()
diff --git a/django/db/utils.py b/django/db/utils.py
index bd7e10d24c..4afc592e64 100644
--- a/django/db/utils.py
+++ b/django/db/utils.py
@@ -99,7 +99,8 @@ class DatabaseErrorWrapper(object):
                 six.reraise(dj_exc_type, dj_exc_value, traceback)
 
     def __call__(self, func):
-        @wraps(func)
+        # Note that we are intentionally not using @wraps here for performance
+        # reasons. Refs #21109.
         def inner(*args, **kwargs):
             with self:
                 return func(*args, **kwargs)