Re: Object Lookup after Save

I bribed the DBA to turn on the general query log briefly (which generated 327k logs in 2 minutes and 2 seconds). Looking at the logs, I see the transaction block for the INSERT. The SELECT is definitely coming after the COMMIT in a different thread. I'll try the commit_unless_managed fix quickly and if that doesn't work, I'll post the full query trace.

On Tuesday, May 28, 2013 5:27:36 PM UTC-4, akaariai wrote:

On 28 touko, 22:20, Chris Conover <clc...@gmail.com> wrote:
> Well, you can inspect the object and see it's primary key. Surely that
> means the INSERT is completed? So the workflow goes like this:
>
> foo = Foo()
> foo.save()
> foo.pk # new primary key is available
> submit_gearman_task(foo.pk)
>
> Then in the Gearman worker:
>
> foo = Foo.objects.get(pk=foo_pk) # this causes a Foo.DoesNotExist exception
>
> That's what I don't understand. The primary key is assigned and available
> in the application layer in one place but then the lookup using that
> primary key fails in another place. Maybe it has something to do with the
> fact that the database is set to REPEATABLE-READ isolation level versus
> READ-COMMITTED. Still investigating...

Could it be that the Gearman worker is in a transaction? When you
issue Foo.objects.get(), if the transaction Gearman is in has started
before the save() you will not see the new object (as MySQL uses
REPEATABLE READ transaction).

Note that any read query will start a transaction implicitly, and ORM
writes commit implicitly started transaction. You can also use
connection.commit_unless_managed() to commit implicitly started
transaction (not part of public API!). So, even if you haven't
explicitly started any transactions in Gearman worker an earlier read
query might have started one for you. (If you find this behavior
confusing this is one of the reasons why transaction handling will be
changed in Django 1.6).

In short: try if connection.commit_unless_managed() before the get()
changes anything. If so, investigate why there is an ongoing
transaction in the worker.

 - Anssi

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