[LRUG] Rails after_create transaction queueing problem

[David Salgado]

Hi Pat

Many thanks - these look like just what I need.

Cheers

David


On 16 Jun 2008, at 18:03, Pat Allan wrote:

> Hi David
>
> I've come across this before... there's two very similar solutions I  
> can point you to - both adding an after_commit callback.
> First off - the original source:
> http://elimiller.blogspot.com/2007/06/proper-cache-expiry-with-aftercommit.html
>
> My modifications, to make it more friendly with 2.0 and 2.1:
> http://github.com/freelancing-god/thinking-sphinx/tree/master/lib/thinking_sphinx/active_record/delta.rb
>
> And a more rounded solution, that handles nested transactions (so  
> I'll be pulling this plugin into my own in the near future):
> http://github.com/GUI/after_commit/tree/master
>
> Hope this is helpful.
>
> Cheers
>
> -- 
> Pat
> e: pat at freelancing-gods.com    || m: 0413 273 337
> w: http://freelancing-gods.com || p: 03 9386 0928
> discworld: http://ausdwcon.org || skype: patallan
>
> On 16/06/2008, at 9:56 AM, David Salgado wrote:
>
>> Hi Folks
>>
>> I've come across an odd quirk when trying to use beanstalk to manage
>> my tasks, and I'm wondering how other people have handled this.
>>
>> I've got an 'add_to_beanstalk' method which gets called in an
>> after_create hook on a Rails model. All it does is to put the ID of
>> the newly-created model instance onto the appropriate beanstalk  
>> queue.
>> A separate process consumes this queue.
>>
>> The trouble is that the after_create callback is called before the
>> 'COMMIT' which finalises the INSERT. So, what happens is;
>>
>> 1. The after_create method gets the ID of the current record and puts
>> it on the beanstalk queue.
>> 2. The agent which is processes the beanstalk queue gets the ID and
>> does a find to retrieve the record
>> 3. The model class calls COMMIT to finish the model create.
>>
>> This means that step 2 fails with a 'record not found' exception. In
>> theory, I would expect this issue to crop up with any queuing system,
>> not just beanstalk.
>>
>> I've hacked around this by calling
>> self.class.connection.commit_db_transaction inside my after_create
>> method. This works, but it smells really bad.
>>
>> Has anyone else come across this issue, and if so, how did you get  
>> around it?
>>
>> Any help will be gratefully received and rewarded with a pint at the
>> next LRUG/LRUG Nights.
>>
>> Cheers
>>
>> David
>> _______________________________________________
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>
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