On Mon, Feb 26, 2018 at 2:54 PM, Cecil Rock <cecil.r...@gmail.com> wrote:
> Hi,
>
> I have a question about some ORM internal state tracking stuff. If this
> isn't the right venue for this type of question my apologies.
>
> I've run into what looks like a race condition using the ORM during some our
> production workloads. I am trying to figure out if our code has a bug or if
> we are hitting a bug inside the ORM. We are occasionally getting a
> FlushError with this message "Over 100 subsequent flushes have occurred
> within session.commit() - is an after_flush() hook creating new objects?"(
> we are not using any event hooks.)
>
> I've managed to track this down to what looks like the session.identity_map
> has an InstanceState in its modified list (i.e. the session is dirty) but
> the InstanceState is not in the sessions.identity_map._dict (i.e not in the
> session?). The InstanceState is showing that it is attached to the session.
>
> e.g. the WeakInstanceDict looks like this for the session...
> _dict = {} # is empty
> _modified = ( TheModifiedInstanceState )
>
>
> This is a difficult bug to reproduce, but seems more likely to occur if we
> hold the session open longer like so...
>
> my_model = MyModel.query.filter('...').first()
> my_model.attr = 'something'
> sleep(1)
> session.commit() <-- flush error "occasionally"
>
>
> I was hoping someone could confirm for me that this is "never a valid state"
> for the identity map to be in. (Or if I'm super lucky someone will
> recognize this as a known bug or something).
try doing a gc.collect() there instead of a sleep since it looks
related to the object being garbage collected.
but no, that is never a valid state and I cannot imagine how you would
get that error without using any flush hooks. that error was put in
after observing very specifically end-user event hooks that would add
more things to the dirty state within the scope of a flush. There is
no way that can happen otherwise.
>
> Thanks for the help,
>
> Cecil
>
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> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
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