AppEngine MapReduce NDB，DeadlineExceededError

Question

我们正在尝试在我们的项目中大量使用MapReduce 。 现在我们有了这个问题，日志中有很多' DeadlineExceededError '错误...

它的一个示例（回溯每次都会有所不同）：

Traceback (most recent call last):
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/runtime/wsgi.py", line 207, in Handle
    result = handler(dict(self._environ), self._StartResponse)
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1505, in __call__
    rv = self.router.dispatch(request, response)
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1253, in default_dispatcher
    return route.handler_adapter(request, response)
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1077, in __call__
    return handler.dispatch()
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 545, in dispatch
    return method(*args, **kwargs)
  File "/base/data/home/apps/s~sba/1.362471299468574812/mapreduce/base_handler.py", line 65, in post
    self.handle()
  File "/base/data/home/apps/s~sba/1.362471299468574812/mapreduce/handlers.py", line 208, in handle
    ctx.flush()
  File "/base/data/home/apps/s~sba/1.362471299468574812/mapreduce/context.py", line 333, in flush
    pool.flush()
  File "/base/data/home/apps/s~sba/1.362471299468574812/mapreduce/context.py", line 221, in flush
    self.__flush_ndb_puts()
  File "/base/data/home/apps/s~sba/1.362471299468574812/mapreduce/context.py", line 239, in __flush_ndb_puts
    ndb.put_multi(self.ndb_puts.items, config=self.__create_config())
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 3625, in put_multi
    for future in put_multi_async(entities, **ctx_options)]
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 323, in get_result
    self.check_success()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 318, in check_success
    self.wait()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 302, in wait
    if not ev.run1():
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/eventloop.py", line 219, in run1
    delay = self.run0()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/eventloop.py", line 181, in run0
    callback(*args, **kwds)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 365, in _help_tasklet_along
    value = gen.send(val)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/context.py", line 274, in _put_tasklet
    keys = yield self._conn.async_put(options, datastore_entities)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1560, in async_put
    for pbs, indexes in pbsgen:
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1350, in __generate_pb_lists
    incr_size = pb.lengthString(pb.ByteSize()) + 1
DeadlineExceededError

我的问题是：

• 我们如何避免这个错误？
• 这项工作会发生什么，是否会对其进行重试（如果可以，我们如何控制它？）？
• 到底会导致数据不一致吗？

Answer 1

显然，您进行的看跌期权太多，无法插入一个数据存储区调用中。 您在这里有多种选择：

1. 如果这是相对罕见的事件，请忽略它。 Mapreduce将重试切片，并降低放置池的大小。 确保您的地图是幂等的。
2. 看看http://code.google.com/p/appengine-mapreduce/source/browse/trunk/python/src/mapreduce/context.py-在main.py中，您可以将DATASTORE_DEADLINE ， MAX_ENTITY_COUNT或MAX_POOL_SIZE到降低整个mapreduce池的大小。

Answer 2

如果您使用的是InputReader，则可以调整默认的batch_size来减少每个任务处理的实体数。

我相信任务队列会重试任务，但您可能不希望这样做，因为它很可能会击中相同的DeadlineExceededError。

数据不一致是可能的。

也请参阅此问题。 App Engine-使用Mapper API的任务队列重试计数