我正在对Google App Engine的分片计数器实现进行一些诊断，我不确定其他RPC的来源。
当获得20个计数器的非缓存计数时，带有20个分片的开箱即用版本在Appstats中提供以下信息：
RPCs
memcache.get 100
memcache.set 80
memcache.del 0
datastore.get 60
datastore_commit 0
datastore_put 0
datastore_begin_transaction 0
Billed Ops
datastore_read 420
datastore_write 0
Cost 29,400
供参考，这是计数器代码：
class GeneralCounterShard(ndb.Model):
"""Shards for each named counter."""
count = ndb.IntegerProperty(default=0)
def get_count(name):
"""Retrieve the value for a given sharded counter.
Args:
name: The name of the counter.
Returns:
Integer; the cumulative count of all sharded counters for the given
counter name.
"""
total = memcache.get(name)
if total is None:
total = 0
all_keys = GeneralCounterShardConfig.all_keys(name)
for counter in ndb.get_multi(all_keys):
if counter is not None:
total += counter.count
memcache.add(name, total, 60)
return total
当我更改分片计数器代码以使get_count成为GeneralCounterShard类的“classmethod”时，RPC会发生巨大变化：
RPCs
memcache.get 100
memcache.set 80
memcache.del 20
datastore.get 80
datastore_commit 20
datastore_put 20
datastore_begin_transaction 20
Billed Ops
datastore_read 440
datastore_write 60
Cost 36,800
供参考，以下是更改：
class GeneralShardedCounter(ndb.Model):
count = ndb.IntegerProperty(default=0)
@classmethod
def get_count(name):
total = memcache.get(name)
if total is None:
total = 0
all_keys = GeneralShardedCounterConfig.all_keys(name)
for counter in ndb.get_multi(all_keys):
if counter is not None:
total += counter.count
memcache.add(name, total, 60)
return total
在回顾中，两者之间的区别是：
RPCs
memcache.get +0
memcache.set +0
memcache.del +20
datastore.get +20
datastore_commit +20
datastore_put +20
datastore_begin_transaction +20
Billed Ops
datastore_read +20
datastore_write +60
Cost +7,400
只需将一个方法作为ndb模型的类方法，会导致RPC和读写的跳转是什么？