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没有事务时 GAE 上的 TransactionFailedError

本文介绍了没有事务时 GAE 上的 TransactionFailedError的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我收到此错误:

TransactionFailedError:对这些数据存储实体的争用过多.请再试一次.

即使我没有进行任何交易.导致错误的代码行是

ndb.put_multi(entity_list) # entity_list 是 100 个实体的列表

这个错误并不经常发生，所以没什么大不了的，但我很好奇为什么会出现这个错误.有什么想法吗?

这里是大部分的回溯:

回溯(最近一次调用最后一次):...文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/deferred/deferred.py"，第 318 行，在帖子中self.run_from_request()run_from_request 中的文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/deferred/deferred.py"，第 313 行运行(self.request.body)运行中的文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/deferred/deferred.py"，第 155 行返回 func(*args, **kwds)文件/base/data/home/apps/s~opavote/2017-09-15.404125237783169549/tasks.py"，第70行，在start_electionmodels.Voter.create(e.eid，块)文件/base/data/home/apps/s~opavote/2017-09-15.404125237783169549/models.py"，第2426行，在创建ndb.put_multi(选民+ vbs)文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/model.py"，第 3958 行，在 put_multi 中未来在 put_multi_async(entities, **ctx_options)]文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py"，第 383 行，在 get_result 中self.check_success()文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py"，第 427 行，在 _help_tasklet_alongvalue = gen.throw(exc.__class__, exc, tb)文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/context.py"，第 824 行，输入key = yield self._put_batcher.add(entity, options)文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py"，第 427 行，在 _help_tasklet_alongvalue = gen.throw(exc.__class__, exc, tb)_put_tasklet 中的文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/context.py"，第 358 行键 = 产量 self._conn.async_put(options, datastore_entities)文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py"，第 513 行，_on_rpc_completion结果 = rpc.get_result()get_result 中的文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py"，第 928 行结果 = rpc.get_result()get_result 中的文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/api/apiproxy_stub_map.py"，第 613 行返回 self.__get_result_hook(self)文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py"，第 1893 行，在 __put_hookself.check_rpc_success(rpc)check_rpc_success 中的文件/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py"，第 1385 行引发 _ToDatastoreError(err)TransactionFailedError:这些数据存储实体的争用过多.请再试一次.
解决方案

请注意，错误实际上是从数据存储本身接收到的，在 RPC 响应中:self.check_rpc_success(rpc).>

这让我怀疑在数据存储方面，为了确保支持它的冗余基础设施之间的操作一致性/可靠性，每个写操作实际上都使用与事务操作相同/相似的机制.不同之处在于，它们在客户端、RPC 交换之前/之后也有一些事务检查，可能还有数据存储的显式 RPC 事务开始/结束触发器.

来自 数据存储写入的生命，引述了一些常见机制无论操作是否是事务性的都被使用(强调我的):

如果提交阶段成功但应用阶段失败，则数据存储将前滚以将更改应用于两个下的索引情况:

  1. 下次您对该实体组执行读取或写入或启动事务时，数据存储区将首先滚动转发并完全应用此已提交但未应用的写入，基于日志中的数据.

失败的可能原因之一就是对同一实体的并行访问过多，即使它们只是只读的.请参阅 Google App Engine 中的争用问题，但在这种情况下它们用于客户端的交易.

请注意，这只是一个理论;)

I got this error:

TransactionFailedError: too much contention on these datastore entities. please try again.

Even though I'm not doing any transactions. The line of my code that causes the error is

ndb.put_multi(entity_list) # entity_list is a list of 100 entities

This error doesn't happen often so it isn't a big deal, but I'm curious why I get this error. Any ideas?

Here is most of the traceback:

Traceback (most recent call last):
  ...
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/deferred/deferred.py", line 318, in post
    self.run_from_request()
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/deferred/deferred.py", line 313, in run_from_request
    run(self.request.body)
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/deferred/deferred.py", line 155, in run
    return func(*args, **kwds)
  File "/base/data/home/apps/s~opavote/2017-09-15.404125237783169549/tasks.py", line 70, in start_election
    models.Voter.create(e.eid, chunk)
  File "/base/data/home/apps/s~opavote/2017-09-15.404125237783169549/models.py", line 2426, in create
    ndb.put_multi(voters + vbs)
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 3958, in put_multi
    for future in put_multi_async(entities, **ctx_options)]
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 383, in get_result
    self.check_success()
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 427, in _help_tasklet_along
    value = gen.throw(exc.__class__, exc, tb)
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/context.py", line 824, in put
    key = yield self._put_batcher.add(entity, options)
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 427, in _help_tasklet_along
    value = gen.throw(exc.__class__, exc, tb)
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/context.py", line 358, in _put_tasklet
    keys = yield self._conn.async_put(options, datastore_entities)
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 513, in _on_rpc_completion
    result = rpc.get_result()
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 928, in get_result
    result = rpc.get_result()
  File "/base/data/home/runtimes/python27_experiment/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_experiment/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1893, in __put_hook
    self.check_rpc_success(rpc)
  File "/base/data/home/runtimes/python27_experiment/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1385, in check_rpc_success
    raise _ToDatastoreError(err)
TransactionFailedError: too much contention on these datastore entities. please try again.
解决方案

Note that the error is actually received from the datastore itself, in the RPC response: self.check_rpc_success(rpc).

Which makes me suspect that on the datastore side, to ensure operation consistency/reliability across the redundant pieces of infra supporting it, every write operation is actually using the same/similar mechanisms as for transactional operations. The difference would be that those also have some transactional checks on the client side, before/after the RPC exchange and maybe explicit RPC transaction start/end triggers for the datastore.

From Life of a Datastore Write, a quote suggesting that some common mechanisms are being used regardless of the operations being transactional or not (emphasis mine):

And one of the possible reasons for failures would be simply too many parallel accesses to the same entities, even if they're just read-only. See Contention problems in Google App Engine, though in that case they're for transactions on the client side.

Note that this is just a theory ;)

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08-22 12:10
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