我们的应用程序有多个在大多数情况下只和数据库“A”打交道的服务层方法；它们偶尔也会从数据库“B”中获取只读数据。
Our application has several service layer methods which only deal with database “A” in most instances; however occasionally they also retrieve read-only data from database “B”.
以这种方式编写我们的查询可以最小化数据库和应用程序服务器层之间传输的数据总量。
Writing our query in this manner minimizes the amount of data transferred between the database and application server tiers.
清单3给出包含两个服务器组的数据库层的xml片段。
Listing 3 shows XML fragment for a database tier with two server groups.
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