fapifta commented on pull request #3579:
URL: https://github.com/apache/hadoop/pull/3579#issuecomment-962377604


   @symious I would say yes, and no :)
   
   We have 3 levels in the communication, the DfsClient which connects to HDFS, 
and is one of many users of the SASL protocol layer (SaslRpcClient), which uses 
the basic network communication layer the ipc client. (At least as I understand 
the system so far, so correct me if I am wrong.)
   
   In our problem scenario, we have two DfsClient which uses two separate 
SaslRpcClient, but under the hood they are using the same ipc client, as ipc 
clients are cached in the RpcEngine, regardless of whether we cache the 
DfsClient or not in a higher layer.
   
   Your suggestion is this as I understand:
   In order to distinguish between two DfsClient, we would need to add a client 
id into the ConnectionId in the ipc layer, which would distinguish between the 
users of the ipc client class inside the ipc client layer.
   This would require to add a bunch of new methods in the RpcEngine layer, to 
get the protobuf protocol proxies with a proper ConnectionId set, and may 
affect not just DfsClient, but every other client of the ipc client layer.
   
   I believe it is already unfortunate that the ipc layer decides and controls 
whether the SASL layer uses SASL or falls back to simple auth based 
communication, if we even add client ids from one more layer up, then the 
behaviour of the SASL layer would be defined by the layer above SASL via the 
layer under SASL that does not seem better at all.
   
   In my view, the high level client id does not, and should not distinguish 
between connections, the connection itself is a socket with one end on a port 
on the local machine, and the other end on a port on a remote machine. It does 
not really matter who uses the connection, also it should not really matter who 
uses the connection, until the user wants to use the connection between the two 
ports on the local and remote machine with the same settings. So if you look at 
it this way, the things in the equals method all qualify to differentiate 
between two connection, while the id of the user really does not.


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