使用高复制数据存储+ NDB进行写入/读取 [英] Write/Read with High Replication Datastore + NDB

问题描述

因此，我最近一直在阅读关于HRD和NDB的大量文档，但我仍然对NDB如何缓存内容有所怀疑。
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示例案例：假设一个用户写入数据的情况，并且应用程序需要在写入后立即获取数据。例如。用户创建组（类似于Facebook / Linkedin组），并在创建后立即重定向到组。 （现在，我创建了一个组，并且没有将其分配给祖先）

结果：

在本地测试此类功能时（启用高复制），新创建的组的立即获取失败。返回NoneType。

问题：

docs和Google IO视频，我知道写入延迟较高，但是，NDB缓存不应该考虑这一点吗？即写缓存，然后异步实际写入磁盘，因此，立即读取将从缓存读取，因此应该没有问题。我需要执行一些其他设置吗？

解决方案

很确定您正在运行HRD功能，其中查询最终一致 。 NDB的缓存与此行为无关。

So I have been reading a lot of documentation on HRD and NDB lately, yet I still have some doubts regarding how NDB caches things.

Example case:

Imagine a case where a users writes data and the app needs to fetch it immediately after the write. E.g. A user creates a "Group" (similar to a Facebook/Linkedin group) and is redirected to the group immediately after creating it. (For now, I'm creating a group without assigning it an ancestor)

Result:

When testing this sort of functionality locally (having enabled high replication), the immediate fetch of the newly created group fails. A NoneType is returned.

Question:

Having gone through the High Replication docs and Google IO videos, I understand that there is a higher write latency, however, shouldn't NDB caching take care of this? I.e. A write is cached, and then asynchronously actually written on disk, therefore, an immediate read would be reading from cache and thus there should be no problem. Do I need to enforce some other settings?

解决方案

Pretty sure you are running into the HRD feature where queries are "eventually consistent". NDB's caching has nothing to do with this behavior.

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