Hi,
I'm maintaining a multi-threaded application which uses sqlalchemy to
access mysql db. Some time ago we decided to upgrade
sqlalchemy version from 1.1.18 to 1.2.14 and since then we started
observing strange problems, the application started
throwing IntegrityError in code like that:
translation = item.translation # translation is a relation
if translation is None:
session.add(Translation(item=item)) # this throws error
Strange thing was that these errors happened rather rarely, there were a
few hundred application processes running and only
a few of them were throwing such errors. Restarting those processed made
the errors vanish.
I started debugging faulty processes and noticed that sql query generated
looked like this:
SELECT <truncated list of columns>
FROM ebay_translations
WHERE NULL = ebay_translations.item_id
Further debugging led me to LazyLoader._emit_lazyload and BackedQuery
thingy where I believe problem lays:
if a thread switch occurs inside _memoized_attr__simple_lazy_clause it
could happen that BindParameter keys and
cached relation query will not match each other.
Since that discovery I've been running the application with patched version
of sqlalchemy for two months now,
IntegrityErrors are gone.
Can you please take a look at this patch? Or maybe this issue is known and
there exists workaround for it although I searched
the mailing list archive and found nothing.
best regards
Krzysztof Sulejczak
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http://www.sqlalchemy.org/
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diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index d7597d3b2..d265f570b 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -8,6 +8,8 @@
"""sqlalchemy.orm.interfaces.LoaderStrategy
implementations, and related MapperOptions."""
+import threading
+
from .. import exc as sa_exc, inspect
from .. import util, log, event
from ..sql import util as sql_util, visitors
@@ -446,7 +448,7 @@ class LazyLoader(AbstractRelationshipLoader, util.MemoizedSlots):
'_lazywhere', '_rev_lazywhere', 'use_get', '_bind_to_col',
'_equated_columns', '_rev_bind_to_col', '_rev_equated_columns',
'_simple_lazy_clause', '_raise_always', '_raise_on_sql',
- '_bakery')
+ '_bakery', '_lock')
def __init__(self, parent, strategy_key):
super(LazyLoader, self).__init__(parent, strategy_key)
@@ -483,6 +485,8 @@ class LazyLoader(AbstractRelationshipLoader, util.MemoizedSlots):
self.logger.info("%s will use query.get() to "
"optimize instance loads", self)
+ self._lock = threading.Lock()
+
def init_class_attribute(self, mapper):
self.is_class_level = True
@@ -531,7 +535,8 @@ class LazyLoader(AbstractRelationshipLoader, util.MemoizedSlots):
return criterion, params
def _generate_lazy_clause(self, state, passive):
- criterion, param_keys = self._simple_lazy_clause
+ with self._lock:
+ criterion, param_keys = self._simple_lazy_clause
if state is None:
return sql_util.adapt_criterion_to_null(
