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Added an option to disable the creation of savepoints in atomic.

This commit is contained in:
Aymeric Augustin 2013-03-08 15:44:41 +01:00
parent 189fb4e294
commit 107d9b1d97
4 changed files with 156 additions and 30 deletions
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3
django/db/backends/__init__.py
View File

@ -52,6 +52,9 @@ class BaseDatabaseWrapper(object):
self._dirty = False
# Tracks if the connection is in a transaction managed by 'atomic'
self.in_atomic_block = False
# Tracks if the transaction should be rolled back to the next
# available savepoint because of an exception in an inner block.
self.needs_rollback = False
# List of savepoints created by 'atomic'
self.savepoint_ids = []
# Hack to provide compatibility with legacy transaction management

72
django/db/transaction.py
View File

@ -188,8 +188,11 @@ class Atomic(object):
__exit__ commits the transaction or releases the savepoint on normal exit,
and rolls back the transaction or to the savepoint on exceptions.
It's possible to disable the creation of savepoints if the goal is to
ensure that some code runs within a transaction without creating overhead.
A stack of savepoints identifiers is maintained as an attribute of the
connection. None denotes a plain transaction.
connection. None denotes the absence of a savepoint.
This allows reentrancy even if the same AtomicWrapper is reused. For
example, it's possible to define `oa = @atomic('other')` and use `@ao` or
@ -198,8 +201,9 @@ class Atomic(object):
Since database connections are thread-local, this is thread-safe.
"""
def __init__(self, using):
def __init__(self, using, savepoint):
self.using = using
self.savepoint = savepoint
def _legacy_enter_transaction_management(self, connection):
if not connection.in_atomic_block:
@ -228,9 +232,15 @@ class Atomic(object):
"'atomic' cannot be used when autocommit is disabled.")
if connection.in_atomic_block:
# We're already in a transaction; create a savepoint.
# We're already in a transaction; create a savepoint, unless we
# were told not to or we're already waiting for a rollback. The
# second condition avoids creating useless savepoints and prevents
# overwriting needs_rollback until the rollback is performed.
if self.savepoint and not connection.needs_rollback:
sid = connection.savepoint()
connection.savepoint_ids.append(sid)
else:
connection.savepoint_ids.append(None)
else:
# We aren't in a transaction yet; create one.
# The usual way to start a transaction is to turn autocommit off.
@ -244,13 +254,23 @@ class Atomic(object):
else:
connection.set_autocommit(False)
connection.in_atomic_block = True
connection.savepoint_ids.append(None)
connection.needs_rollback = False
def __exit__(self, exc_type, exc_value, traceback):
connection = get_connection(self.using)
if exc_value is None and not connection.needs_rollback:
if connection.savepoint_ids:
# Release savepoint if there is one
sid = connection.savepoint_ids.pop()
if exc_value is None:
if sid is None:
if sid is not None:
try:
connection.savepoint_commit(sid)
except DatabaseError:
connection.savepoint_rollback(sid)
# Remove this when the legacy transaction management goes away.
self._legacy_leave_transaction_management(connection)
raise
else:
# Commit transaction
connection.in_atomic_block = False
try:
@ -266,16 +286,18 @@ class Atomic(object):
else:
connection.set_autocommit(True)
else:
# Release savepoint
try:
connection.savepoint_commit(sid)
except DatabaseError:
connection.savepoint_rollback(sid)
# Remove this when the legacy transaction management goes away.
self._legacy_leave_transaction_management(connection)
raise
else:
# This flag will be set to True again if there isn't a savepoint
# allowing to perform the rollback at this level.
connection.needs_rollback = False
if connection.savepoint_ids:
# Roll back to savepoint if there is one, mark for rollback
# otherwise.
sid = connection.savepoint_ids.pop()
if sid is None:
connection.needs_rollback = True
else:
connection.savepoint_rollback(sid)
else:
# Roll back transaction
connection.in_atomic_block = False
try:
@ -285,9 +307,6 @@ class Atomic(object):
connection.autocommit = True
else:
connection.set_autocommit(True)
else:
# Roll back to savepoint
connection.savepoint_rollback(sid)
# Remove this when the legacy transaction management goes away.
self._legacy_leave_transaction_management(connection)
@ -301,17 +320,17 @@ class Atomic(object):
return inner
def atomic(using=None):
def atomic(using=None, savepoint=True):
# Bare decorator: @atomic -- although the first argument is called
# `using`, it's actually the function being decorated.
if callable(using):
return Atomic(DEFAULT_DB_ALIAS)(using)
return Atomic(DEFAULT_DB_ALIAS, savepoint)(using)
# Decorator: @atomic(...) or context manager: with atomic(...): ...
else:
return Atomic(using)
return Atomic(using, savepoint)
def atomic_if_autocommit(using=None):
def atomic_if_autocommit(using=None, savepoint=True):
# This variant only exists to support the ability to disable transaction
# management entirely in the DATABASES setting. It doesn't care about the
# autocommit state at run time.
@ -319,7 +338,7 @@ def atomic_if_autocommit(using=None):
autocommit = get_connection(db).settings_dict['AUTOCOMMIT']
if autocommit:
return atomic(using)
return atomic(using, savepoint)
else:
# Bare decorator: @atomic_if_autocommit
if callable(using):
@ -447,7 +466,7 @@ def commit_manually(using=None):
return _transaction_func(entering, exiting, using)
def commit_on_success_unless_managed(using=None):
def commit_on_success_unless_managed(using=None, savepoint=False):
"""
Transitory API to preserve backwards-compatibility while refactoring.
@ -455,10 +474,13 @@ def commit_on_success_unless_managed(using=None):
simply be replaced by atomic_if_autocommit. Until then, it's necessary to
avoid making a commit where Django didn't use to, since entering atomic in
managed mode triggers a commmit.
Unlike atomic, savepoint defaults to False because that's closer to the
legacy behavior.
"""
connection = get_connection(using)
if connection.autocommit or connection.in_atomic_block:
return atomic_if_autocommit(using)
return atomic_if_autocommit(using, savepoint)
else:
def entering(using):
pass

10
docs/topics/db/transactions.txt
View File

@ -89,7 +89,7 @@ Controlling transactions explicitly
Django provides a single API to control database transactions.
.. function:: atomic(using=None)
.. function:: atomic(using=None, savepoint=True)
This function creates an atomic block for writes to the database.
(Atomicity is the defining property of database transactions.)
@ -164,6 +164,14 @@ Django provides a single API to control database transactions.
- releases or rolls back to the savepoint when exiting an inner block;
- commits or rolls back the transaction when exiting the outermost block.
You can disable the creation of savepoints for inner blocks by setting the
``savepoint`` argument to ``False``. If an exception occurs, Django will
perform the rollback when exiting the first parent block with a savepoint
if there is one, and the outermost block otherwise. Atomicity is still
guaranteed by the outer transaction. This option should only be used if
the overhead of savepoints is noticeable. It has the drawback of breaking
the error handling described above.
.. admonition:: Performance considerations
Open transactions have a performance cost for your database server. To

93
tests/transactions/tests.py
View File

@ -106,6 +106,44 @@ class AtomicTests(TransactionTestCase):
raise Exception("Oops, that's his first name")
self.assertQuerysetEqual(Reporter.objects.all(), [])
def test_merged_commit_commit(self):
with transaction.atomic():
Reporter.objects.create(first_name="Tintin")
with transaction.atomic(savepoint=False):
Reporter.objects.create(first_name="Archibald", last_name="Haddock")
self.assertQuerysetEqual(Reporter.objects.all(),
['<Reporter: Archibald Haddock>', '<Reporter: Tintin>'])
def test_merged_commit_rollback(self):
with transaction.atomic():
Reporter.objects.create(first_name="Tintin")
with six.assertRaisesRegex(self, Exception, "Oops"):
with transaction.atomic(savepoint=False):
Reporter.objects.create(first_name="Haddock")
raise Exception("Oops, that's his last name")
# Writes in the outer block are rolled back too.
self.assertQuerysetEqual(Reporter.objects.all(), [])
def test_merged_rollback_commit(self):
with six.assertRaisesRegex(self, Exception, "Oops"):
with transaction.atomic():
Reporter.objects.create(last_name="Tintin")
with transaction.atomic(savepoint=False):
Reporter.objects.create(last_name="Haddock")
raise Exception("Oops, that's his first name")
self.assertQuerysetEqual(Reporter.objects.all(), [])
def test_merged_rollback_rollback(self):
with six.assertRaisesRegex(self, Exception, "Oops"):
with transaction.atomic():
Reporter.objects.create(last_name="Tintin")
with six.assertRaisesRegex(self, Exception, "Oops"):
with transaction.atomic(savepoint=False):
Reporter.objects.create(first_name="Haddock")
raise Exception("Oops, that's his last name")
raise Exception("Oops, that's his first name")
self.assertQuerysetEqual(Reporter.objects.all(), [])
def test_reuse_commit_commit(self):
atomic = transaction.atomic()
with atomic:
@ -171,6 +209,61 @@ class AtomicInsideLegacyTransactionManagementTests(AtomicTests):
transaction.leave_transaction_management()
@skipUnless(connection.features.uses_savepoints,
"'atomic' requires transactions and savepoints.")
class AtomicMergeTests(TransactionTestCase):
"""Test merging transactions with savepoint=False."""
def test_merged_outer_rollback(self):
with transaction.atomic():
Reporter.objects.create(first_name="Tintin")
with transaction.atomic(savepoint=False):
Reporter.objects.create(first_name="Archibald", last_name="Haddock")
with six.assertRaisesRegex(self, Exception, "Oops"):
with transaction.atomic(savepoint=False):
Reporter.objects.create(first_name="Tournesol")
raise Exception("Oops, that's his last name")
# It wasn't possible to roll back
self.assertEqual(Reporter.objects.count(), 3)
# It wasn't possible to roll back
self.assertEqual(Reporter.objects.count(), 3)
# The outer block must roll back
self.assertQuerysetEqual(Reporter.objects.all(), [])
def test_merged_inner_savepoint_rollback(self):
with transaction.atomic():
Reporter.objects.create(first_name="Tintin")
with transaction.atomic():
Reporter.objects.create(first_name="Archibald", last_name="Haddock")
with six.assertRaisesRegex(self, Exception, "Oops"):
with transaction.atomic(savepoint=False):
Reporter.objects.create(first_name="Tournesol")
raise Exception("Oops, that's his last name")
# It wasn't possible to roll back
self.assertEqual(Reporter.objects.count(), 3)
# The first block with a savepoint must roll back
self.assertEqual(Reporter.objects.count(), 1)
self.assertQuerysetEqual(Reporter.objects.all(), ['<Reporter: Tintin>'])
def test_merged_outer_rollback_after_inner_failure_and_inner_success(self):
with transaction.atomic():
Reporter.objects.create(first_name="Tintin")
# Inner block without a savepoint fails
with six.assertRaisesRegex(self, Exception, "Oops"):
with transaction.atomic(savepoint=False):
Reporter.objects.create(first_name="Haddock")
raise Exception("Oops, that's his last name")
# It wasn't possible to roll back
self.assertEqual(Reporter.objects.count(), 2)
# Inner block with a savepoint succeeds
with transaction.atomic(savepoint=False):
Reporter.objects.create(first_name="Archibald", last_name="Haddock")
# It still wasn't possible to roll back
self.assertEqual(Reporter.objects.count(), 3)
# The outer block must rollback
self.assertQuerysetEqual(Reporter.objects.all(), [])
@skipUnless(connection.features.uses_savepoints,
"'atomic' requires transactions and savepoints.")
class AtomicErrorsTests(TransactionTestCase):