#24810: Reopen database connection automatically when no transaction is active
-------------------------------------+-------------------------------------
Reporter: aaugustin | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by binary):
Replying to [comment:6 aaugustin]:
> Yes, these are the reasons why this ticket exists. Patches *that do not
ignore transactional integrity* welcome.
So I gave it a humble try.
There is no problem in case the trouble happened inside a transaction
because in case error happened and was caught by the Atomic, the
connection will be closed in one of the places like
[https://github.com/django/django/blob/master/django/db/transaction.py#L230
this]. And next transaction will work without any problem as connection
will be re-established because django is now aware that the current one is
not an option any more.
It's still a problem in autocommit mode though because in this case
connection won't be closed and will remain in a broken state, so in case
we try to obtain a cursor again, we'll get the InterfaceError exception.
So the code like:
{{{
def do_query():
return Model.objects.first()
def loop():
while True:
try:
print do_query()
except:
print 'shit happened'
sleep(5)
}}}
will stop working after first disconnect.
At first I tried to intercept InterfaceError at the moment we are
obtaining a cursor and OperationalErorr at the execute method, but then I
realized that such a problem may happen in other methods, like fetchone or
anywhere else, so eventually I came to just intercept it in the
DatabaseErrorWrapper and close the connection if one of those errors
occured but only in case we are not inside a transaction, as this case is
covered already and it may break that code. Here's the commit:
https://github.com/jbinary/django/commit/568a4eb573c7fce2fdec2d1578b2db4f3d0e51fd
After that, that code above starts to work even after disconnect.
I have no any idea if this is the right approach, and I have no idea how
to write tests for this yet. But if anyone will tell this one is a worthy
approach, I'll try to think about tests too. (but advices are welcome,
ofc)
--
Ticket URL: <https://code.djangoproject.com/ticket/24810#comment:7>
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