#18557: get_or_create() causes a race condition with MySQL
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Reporter: foxwhisper | Owner: nobody
Type: Uncategorized | Status: new
Component: Core (URLs) | Version: 1.4
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Hi,
When using MySQL, get_or_create() has a race condition under high load
scenarios.
Up until now, the only fix was to use READ COMMITED transaction isolation,
but this can break legacy apps.
Instead - we have been using the following fix in production, and it works
great under high load or multi threaded / multi node job queues.
{{{
# This needs uploading tomorrow
class ExtendedManager( Manager ):
@transaction.commit_on_success
def get_or_create(self, *args, **kwargs):
transaction.commit()
created = None
try:
return super(ExtendedManager, self).get_or_create(*args,
**kwargs)
except IntegrityError, e:
transaction.commit()
print "RACE 3: %s, %s" % ( str(e) , kwargs)
# Ensure the error code matches 1062 (duplicate entry)
if not e.args[0] == 1062:
raise e
_res = self.all().filter(**kwargs)
if not _res:
raise Exception, "Object busy or not yet ready: %s" % ( e
)
if len(_res) > 1:
raise Exception, "get_or_create(): duplicate object found,
this should never happen"
return _res[0], False
}}}
This has been discussed here:
http://stackoverflow.com/questions/2235318/how-do-i-deal-with-this-race-
condition-in-django
And here:
https://groups.google.com/forum/?fromgroups#!topic/django-developers/VNpt-
sxSmho
Is there any chance this patch would make it into the core?
Cal
--
Ticket URL: <https://code.djangoproject.com/ticket/18557>
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