google app engine NDB records counts from NDB model

问题

How many records we can get from google app engine from single query so that we can display count to user and is we can increase timeout limit 3 seconds to 5 seconds

回答1:

In my experience, ndb cannot pull more than 1000 records at a time. Here is an example of what happens if I try to use .count() on a table that contains ~500,000 records.

s~project-id> models.Transaction.query().count()
WARNING:root:suspended generator _count_async(query.py:1330) raised AssertionError()
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/ext/ndb/utils.py", line 160, in positional_wrapper
    return wrapped(*args, **kwds)
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/ext/ndb/query.py", line 1287, in count
    return self.count_async(limit, **q_options).get_result()
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/ext/ndb/tasklets.py", line 383, in get_result
    self.check_success()
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/ext/ndb/tasklets.py", line 427, in _help_tasklet_along
    value = gen.throw(exc.__class__, exc, tb)
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/ext/ndb/query.py", line 1330, in _count_async
    batch = yield rpc
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/ext/ndb/tasklets.py", line 513, in _on_rpc_completion
    result = rpc.get_result()
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 614, in get_result
    return self.__get_result_hook(self)
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/datastore/datastore_query.py", line 2910, in __query_result_hook
    self._batch_shared.conn.check_rpc_success(rpc)
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/datastore/datastore_rpc.py", line 1377, in check_rpc_success
    rpc.check_success()
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 580, in check_success
    self.__rpc.CheckSuccess()
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/api/apiproxy_rpc.py", line 157, in _WaitImpl
    self.request, self.response)
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/ext/remote_api/remote_api_stub.py", line 308, in MakeSyncCall
    handler(request, response)
  File "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/google/appengine/ext/remote_api/remote_api_stub.py", line 362, in _Dynamic_Next
    assert next_request.offset() == 0
AssertionError

To by pass this, you can do something like:

objs = []
q = None
more = True
while more:
    _objs, q, more = models.Transaction.query().fetch_page(300, start_cursor=q)
    objs.extend(_objs)

But even that will eventually hit memory/timeout limits.

Currently I use Google Dataflow to pre-compute these values and store the results in Datastore as the models DaySummaries & StatsPerUser

EDIT:

snakecharmerb is correct. I was able to use .count() in the production environment, but the more entities it has to count, the longer it seems to take. Here's a screenshot of my logs viewer where it took ~15 seconds to count ~330,000 records

When I tried adding a filter to that query which returned a count of ~4500, it took about a second to run instead.

EDIT #2:

Ok I had another app engine project with a kind with ~8,000,000 records. I tried to do .count() on that in my http request handler and the request timed-out after running for 60 seconds.

来源：https://stackoverflow.com/questions/52946950/google-app-engine-ndb-records-counts-from-ndb-model