分支和内容更新

一个在任何缓存机制的问题涉及到数据的波动性。当数据发生变化，也已经过时缓存的风险。我们已经看到了这个潜在的后果，从浏览器缓存到DNS缓存技术。分支，分支办公室的能力，从而从中央服务器上的数据是在分支机构机缓存，避免了客户通过强制执行与原来的内容服务器检查接收从缓存中的陈旧数据的问题。那原来的服务器（比如，在公司总部运行Server 2008 R2的框）创建64KB内容块的密码散列。这些散列在分支机构返回给请求的客户端。Now, the requesting client – assuming it’s running Windows 7, and assuming that one or more BranchCache hosts has been set up at the branch office – will next query the local branch (e.g. a Server 2008 R2 box running BranchCache) to see if it has a copy of the desired content. If it does, great, but the client doesn’t just accept that because the first content chunk matches the stored hash, the entire file is current. Each retrieved chunk of content must match the stored hashes received from the original content server. If any one of them fails to match up, then the client looks for another caching server. If that also fails, then the client gets the content from the origin server at corporate headquarters, and subsequently advertises the content to the local branch server, which then caches the new content. With this scheme, retrieving a stale file in BranchCache should be pretty close to impossible, and clients can be confident they aren’t getting any outdated information. Makes sense to me!