每一次请求都要在网络上传输一些数据;如果请求未在服务器上发现任何更新,那么这个数据传输就是浪费的。
Each request carries some data over the network; if the request does not find any updates on the server, this data transfer is a waste.
相反,您必须发起一个传输请求将数据复制到本地存储中。
Instead, you must initiate a transfer request to copy data into your local store.
在普通HTTP通信中,客户端始终通过打开到服务器的连接并发送请求来发起数据传输。
In normal HTTP communication, the client always initiates the data transfer by opening a connection to the server and sending a request.
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