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.py
URL: http://mesonstreaming.appspot.com/admin/collectStats
Stacktrace:
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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