TransactionFailedError from contention issues

[mwfarb]

Both issues are from updating records, a back-off retry could help here.

too much contention on these datastore entities. please try again.
Traceback (most recent call last):
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1511, in call
rv = self.handle_exception(request, response, e)
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1505, in call
rv = self.router.dispatch(request, response)
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1253, in default_dispatcher
return route.handler_adapter(request, response)
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1077, in call
return handler.dispatch()
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 547, in dispatch
return self.handle_exception(e, self.app.debug)
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 545, in dispatch
return method(_args, *_kwargs)
File "/base/data/home/apps/s~safeslinger-messenger/01060000p.383466187135273271/postRegistration.py", line 155, in post
reg_old.put()
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/db/init.py", line 1073, in put
return datastore.Put(self._entity, *_kwargs)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/api/datastore.py", line 605, in Put
return PutAsync(entities, *_kwargs).get_result()
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/api/apiproxy_stub_map.py", line 613, in get_result
return self.__get_result_hook(self)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1827, in __put_hook
self.check_rpc_success(rpc)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1342, in check_rpc_success
raise _ToDatastoreError(err)
TransactionFailedError: too much contention on these datastore entities. please try again.

too much contention on these datastore entities. please try again.
Traceback (most recent call last):
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1511, in call
rv = self.handle_exception(request, response, e)
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1505, in call
rv = self.router.dispatch(request, response)
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1253, in default_dispatcher
return route.handler_adapter(request, response)
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1077, in call
return handler.dispatch()
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 547, in dispatch
return self.handle_exception(e, self.app.debug)
File "/base/data/home/runtimes/python27/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 545, in dispatch
return method(_args, *_kwargs)
File "/base/data/home/apps/s~safeslinger-messenger/01060000p.383466187135273271/getMessage.py", line 102, in post
item.put()
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/db/init.py", line 1073, in put
return datastore.Put(self._entity, *_kwargs)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/api/datastore.py", line 605, in Put
return PutAsync(entities, *_kwargs).get_result()
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/api/apiproxy_stub_map.py", line 613, in get_result
return self.__get_result_hook(self)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1827, in __put_hook
self.check_rpc_success(rpc)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1342, in check_rpc_success
raise _ToDatastoreError(err)
TransactionFailedError: too much contention on these datastore entities. please try again.