Ok, here is my story.

GAE has some never officially exposed contention problem with Tasks within 
Transactions<http://code.google.com/appengine/docs/java/taskqueue/overview.html#Tasks_Within_Transactions>
 and 
I have already wrote about this problem 
here<https://groups.google.com/forum/#!topic/google-appengine/8RNu4EeQvmM>
. 

I have collected some test data. This problem exists on M/S and HR datastore 
app version and it doesn't matter if you do some datastore operation or not 
with task enqueuing in transaction. Also it doesn't matter if you enqueue 
two tasks in transaction in same task queue or in two different task queues. 
It isn't also related to task request in some strange class name or 
seialversionid related way.

This contention is related in some nonsense and unreasonable way (from my 
point) to application. Maybe to some service part that gives task queue job 
name (Transactional tasks must not have user-specified names) or something 
strange like that.

Ok. We have some new limit that I didn't noticed before. It's fine. You 
(Googlers) won't speak about it because you are embarrassed :D, have more 
important task to do or simply you don't care. It's fine. This is preview, 
alpha, beta or what ever and we agreed to this. We don't have official 
support and we are fine with that.

But, I want to reduce the consequences of this situation in a way to lower 
number of seconds of task queue to wait before retrying a task after it 
fails and I can't. For some strange reason it is always 20 second. I have 
tried almost every possible variation of task queue parameters but I won't 
work.

If I set parameters in this way should I not get maximum 10 second backoff 
period, or 20 second is minimum ? What is minimum for max-backoff-seconds? 
Is this 20 seconds somehow related to GAE task queue backend speed ?

<retry-parameters>
  <min-backoff-seconds>5</min-backoff-seconds>
  <max-backoff-seconds>10</max-backoff-seconds>
  <max-doublings>0</max-doublings>
</retry-parameters>

2011-04-18 05:20:46.146 /_ah/queue/testni 200 117ms 99cpu_ms 0kb 
AppEngine-Google; 
(+http://code.google.com/appengine)... task_name=7241583885447122407
2011-04-18 05:20:26.008 /_ah/queue/testni 500 1193ms 240cpu_ms 0kb 
AppEngine-Google; 
(+http://code.google.com/appengine)... task_name=7241583885447122407

Thank you for your time, MATijA.

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