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From Doug Cutting <cutt...@apache.org>
Subject Re: Fwd: hadoop file permissions
Date Thu, 19 Apr 2007 21:15:27 GMT
Kurtis Heimerl wrote:
> ok, I have an architectural question. I think I get the client-side stack.
> DFSClient creates a proxy, which connects to the namenode. This all uses
> ClientProtocol. So, to implement what I need I'll probably need to modify
> ClientProtocol and NameNode.

Yes, ClientProtocol will need to be modified to pass the username.

> Now we have the whole DistributedFileSystem and FileSystem stuff. I see the
> cache in FileSystem, I just don't see where in the stack this is. It's
> server-side I assume. I see where we instantiate the NameNode on the 
> server,
> but it seemingly just deals with blocks. Where's the filesystem at?

FileSystem instances are created by user code when to access the 
FileSystem.  So a map InputFormat implementation uses a FileSystem to 
open input files, a reduce OutputFormat implementation uses a FileSystem 
to open output files, and the 'bin/hadoop fs' commands create a 
FileSystem, etc.  Does that make more sense?

Doug

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