There is no return value to enter; in some upcoming steps we'll tell you how to trigger the next state change.
没有要输入的返回值；在一些后续步骤中，我将会告诉您如何触发下一状态变化。
If no index is found, then there are no cached tweets, so there is nothing to show and no optimization can be made on the query (and you return a value of 0 to indicate this).
如果没找到任何索引，那么就没有缓存的tweet，所以就没有展示的东西，并且没有可对查询进行的优化(您返回一个0值以指示这一点)。
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