Salutations Kartik,
Contention happens when you are doing to many writes per second. This is a
great article on avoiding it.
<https://cloud.google.com/appengine/articles/scaling/contention?hl=en> If
you give some more details as to what you are doing I might be able to give
some more specific advice.
On Thursday, August 4, 2011 at 9:48:37 AM UTC-4, Joshua Smith wrote:
>
> This is a weird one.
>
> I have a cron that rolls up some data every few minutes. Nothing too
> complicated:
>
> class CollectStatsHandler(webapp.RequestHandler):
> def get(self):
> nodes = NodeModel.gql("WHERE online = :1 and procs > :2", True,
> 0).fetch(1000)
> sum = 0
> for n in nodes:
> sum = sum + n.procs
> now = datetime.datetime.now().timetuple()
> hour = datetime.datetime(now[0], now[1], now[2], now[3])
> hourly = HourlyStatsModel.gql("WHERE hour = :1", hour).get()
> if not hourly:
> hourly = HourlyStatsModel()
> hourly.hour = hour
> hourly.stats = str(sum)
> else:
> hourly.stats = hourly.stats + "," + str(sum)
> hourly.put()
>
> I'm running on M/S, so every now and then I'll get timeouts or whatever,
> but that's OK because this is really just for my internal "app health"
> dashboard.
>
> Anyway, yesterday I got this exception:
>
> google.appengine.api.datastore_errors.TransactionFailedError@/base/python_runtime/python_lib/versions/1/google/appengine/datastore/datastore_rpc.py:1074
>
> (at least 2 occurrences)Handler:main.pyURL:
> http://mesonstreaming.appspot.com/admin/collectStatsStacktrace:
>
> Traceback (most recent call last):
> File
> "/base/python_runtime/python_lib/versions/1/google/appengine/ext/webapp/__init__.py",
> line 700, in __call__
> handler.get(*groups)
> File "/base/data/home/apps/mesonstreaming/51.352130110004909428/main.py",
> line 1677, in get
> hourly.put()
> File
> "/base/python_runtime/python_lib/versions/1/google/appengine/ext/db/__init__.py",
> line 1006, in put
> return datastore.Put(self._entity, config=config)
> File
> "/base/python_runtime/python_lib/versions/1/google/appengine/api/datastore.py",
> line 467, in Put
> return PutAsync(entities, **kwargs).get_result()
> File
> "/base/python_runtime/python_lib/versions/1/google/appengine/datastore/datastore_rpc.py",
> line 658, in get_result
> results = self.__rpcs[0].get_result()
> File
> "/base/python_runtime/python_lib/versions/1/google/appengine/api/apiproxy_stub_map.py",
> line 592, in get_result
> return self.__get_result_hook(self)
> File
> "/base/python_runtime/python_lib/versions/1/google/appengine/datastore/datastore_rpc.py",
> line 1385, in __put_hook
> self.check_rpc_success(rpc)
> File
> "/base/python_runtime/python_lib/versions/1/google/appengine/datastore/datastore_rpc.py",
> line 1074, in check_rpc_success
> raise _ToDatastoreError(err)
> TransactionFailedError: too much contention on these datastore entities.
> please try again.
>
>
> So we have a transaction failed error on a put which is NOT a transaction.
>
> And we have too much contention on an entity which is written once every 5
> minutes by a cron.
>
> Huh?
>
> -Joshua
>
>
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