[LRUG] To debug the impossible bug

[Jonathan del Strother]

On 3 August 2011 14:15, Simon Coffey <simon at tribesports.com> wrote:
> Hi Tatsuya,
>
> Thanks very much for the response. Instrumenting this particular
> method is definitely next on the list - I was a bit loath to stick
> debugging code on production, but it looks like the only option.
>
> On 3 August 2011 12:59, Tatsuya Ono <ononoma at gmail.com> wrote:
>> 2) Error happened different place.
>> e.g.
>> class Question
>>   def background
>>     return @something.background # <= NoMethod error @something is nil here
>>   end
>> end
>> I know that unless you are bit careless, you wouldn't miss the backtrace.
>
> Yep, sorry for not including the backtrace - unfortunately Hoptoad
> (now AirBrake), the service we use to trap exceptions, has scrubbed
> the backtrace so I can't copy it here. However as I said in my reply
> to Murray, Question#background isn't a particularly interesting
> method, it's just an ActiveRecord attribute accessor, and not one
> we've overridden or delegated in any way.
>
> Thanks again - I'll definitely be posting back results as and when we
> get to the bottom of this. :-)

I'm not sure how helpful this is going to be - it's a bit handwavy -
but we've started migrating to 1.9.2 recently and coincidentally have
also started seeing a couple of really strange errors that seem
somewhat similar to what you're seeing.  They're pretty rare,
definitely not reproducible at will, but it does almost seem like an
object is getting swapped out and replaced with something totally
unrelated.  I haven't yet had chance to do a proper investigation of
it (and a bug like that in the ruby interpreter does seem pretty
unlikely), but I thought I'd mention it...

-Jonathan