AppEngine MapReduce NDB，DeadlineExceededError

Question

我們正在嘗試在我們的項目中大量使用MapReduce 。 現在我們有了這個問題，日志中有很多' DeadlineExceededError '錯誤...

它的一個示例（回溯每次都會有所不同）：

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

我的問題是：

• 我們如何避免這個錯誤？
• 這項工作會發生什么，是否會對其進行重試（如果可以，我們如何控制它？）？
• 到底會導致數據不一致嗎？

Answer 1

顯然，您進行的看跌期權太多，無法插入一個數據存儲區調用中。 您在這里有多種選擇：

1. 如果這是相對罕見的事件，請忽略它。 Mapreduce將重試切片，並降低放置池的大小。 確保您的地圖是冪等的。
2. 看看http://code.google.com/p/appengine-mapreduce/source/browse/trunk/python/src/mapreduce/context.py-在main.py中，您可以將DATASTORE_DEADLINE ， MAX_ENTITY_COUNT或MAX_POOL_SIZE到降低整個mapreduce池的大小。

Answer 2

如果您使用的是InputReader，則可以調整默認的batch_size來減少每個任務處理的實體數。

我相信任務隊列會重試任務，但您可能不希望這樣做，因為它很可能會擊中相同的DeadlineExceededError。

數據不一致是可能的。

也請參閱此問題。 App Engine-使用Mapper API的任務隊列重試計數