Hi Matija,
I put together a simple python handler that can demonstrate your
problem. It also shows a potential solution. What seems to be
happening is that when your transaction is not interacting with an
entity group, the transactions run on the same entity group. If you
cause an entity group to be set, the problem should disappear -- at
least it does in my testing.
This little handler can demonstrate this. Call it with a 'limit'
of, say, 7. You'll get a ton of transaction collisions. Then call it
again (with the same limit) but with the set_group parameter set to 1.
The collisions should go away.
In this example I'm setting the connection's entity group by
building a key, then trying to read that entity. No need for it to
exist. In Python it is possible to set the "connection's" entity
group -- not sure how to do this in Java.
Robert
class InsertTaskHandler(webapp.RequestHandler):
def get(self):
self.post()
def post(self):
task_id = self.request.get('task_id', '')
limit = int(self.request.get('limit', 2))
depth = int(self.request.get('depth', 0))
if depth > limit:
log.debug('Task (%s) reached limit (%d, %d)', task_id, depth, limit)
return
tasks_to_add = int(self.request.get('tasks_to_add', 2))
set_group = self.request.get('set_group')
def add_tasks():
if set_group:
group = self.request.headers.get('X-AppEngine-TaskName', 'a')
db.get(db.Key.from_path('T', group))
log.debug('Setting group: %s.', group)
for task in range(tasks_to_add):
log.debug('Adding task %s%d.', task_id, task)
taskqueue.add(url=self.request.path,
params={'set_group': set_group,
'limit': limit,
'depth': depth + 1,
'tasks_to_add': tasks_to_add,
'task_id': '%s%d' % (task_id, task)},
transactional=True)
db.run_in_transaction(add_tasks)
log.debug('Task %s done.', task_id)
On Thu, Apr 21, 2011 at 06:06, Matija <[email protected]> wrote:
> I want two tasks to be enqueued or none. There are some get datastore
> operations in this first task, but no put operation. These two tasks do
> their entity group datastore put operations.
> There is much more beside this, but core usage is multiple entity group
> eventual consistency.
> Matija.
>
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