>I need this because I do not want to trust namenode's ordering. For >applications where network congestion is rare, we should let the >client to decide which data node to load from.
If this is the case, then providing a method to re-order the datanode list shouldnt be hard. May be open a JIRA (https://issues.apache.org/jira/secure/CreateIssue!default.jspa) as improvement request and continue the discussion there? -Lohit ----- Original Message ---- From: Kevin <[EMAIL PROTECTED]> To: core-user@hadoop.apache.org Sent: Wednesday, August 6, 2008 10:37:44 AM Subject: Re: DFS. How to read from a specific datanode Thank you for the suggestion. I looked at DFSClient. It appears that chooseDataNode method decides which data node to connect to. Currently it chooses the first non-dead data node returned by namenode, which have sorted the nodes by proximity to the client. However, chooseDataNode is private, so overriding it seems infeasible. Neither are the callers of chooseDataNode public or protected. I need this because I do not want to trust namenode's ordering. For applications where network congestion is rare, we should let the client to decide which data node to load from. -Kevin On Tue, Aug 5, 2008 at 7:57 PM, lohit <[EMAIL PROTECTED]> wrote: > I havent tried it, but see if you can create DFSClient object and use its > open() and read() calls to get the job done. Basically you would have to > force currentNode to be your node of interest in there. > Just curious, what is the use case for your request? > > Thanks, > Lohit > > > > ----- Original Message ---- > From: Kevin <[EMAIL PROTECTED]> > To: "core-user@hadoop.apache.org" <core-user@hadoop.apache.org> > Sent: Tuesday, August 5, 2008 6:59:55 PM > Subject: DFS. How to read from a specific datanode > > Hi, > > This is about dfs only, not to consider mapreduce. It may sound like a > strange need, but sometimes I want to read a block from a specific > data node which holds a replica. Figuring out which datanodes have the > block is easy. But is there an easy way to specify which datanode I > want to load from? > > Best, > -Kevin > >
