表明返回的数据集中的第一行数据是什么。
Indicates what the first row of data should be in the set of data to be returned.
远程查询比较复杂，需要消耗较多时间，必须在执行较长时间之后才能返回第一行数据。
The remote queries are complex, time consuming and take some time to return the first row
此外，如果远程查询都是执行大约相同一段时间之后返回第一行数据，那么异步带来的好处就可以实现最大化。
In addition, if the remote operations take approximately the same amount of time to return the first row, then the benefit achieved in enabling asynchrony is maximized.
因此，能从异步中获得最多好处的联邦查询是那些其远程查询比较复杂，在返回第一行数据之前需要花费较多时间的查询。
Thus, the federated queries which benefit the most from asynchrony are those whose remote queries are complex and and for which it is time consuming to return the first row.
因此，能从异步中获得最多好处的联邦查询是那些其远程查询比较复杂，在返回第一行数据之前需要花费较多时间的查询。
Thus, the federated queries which benefit the most from asynchrony are those whose remote queries are complex and and for which it is time consuming to return the first row.
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