[GitHub] [hadoop] ZanderXu commented on pull request #4813: HDFS-16748. DFSClient should uniquely identify writing files by namespace id and iNodeId via RBF

[GitBox <gi...@apache.org>]

ZanderXu commented on PR #4813:
URL: https://github.com/apache/hadoop/pull/4813#issuecomment-1233896312

   @Hexiaoqiao Thanks for your review. This improvement is not used to help Router to forward renewLease to only one or certain Namenode.
   
   One DFSClient may be writing some files from different namespace but with the same file id via RBF. The current `filesBeingWritten` is only use iNodeId to identify the written file, it cannot cover the case that two written files from different namespace with the same iNodeId. 
   
   For example:
   
   - RBF contains two mount point, /ns0 -> ns0 and /ns1 -> ns1
   - One DFSClient create one file /ns0/file0 via RBF, the RBF will forward this create rpc to ns0, and suppose the file with iNodeId 1000
   - DFSClient will put this outputStream into `filesBeingWritten` with iNodeId 1000
   - Then this DFSClient create one new file /ns1/file1 via RBF, the RBF will forward this create RPC to NS1, and the response of this RPC may with one 1000 iNodeId, because they are from different namespace
   - Then this DFSClient will put the new outputStream into `filesBeingWritten` with iNodeId 1000 again. It will overwrite the previous outputStream with path /ns0/file0 and iNodeId 1000 from NS0
   
   It may caused this DFSClient cannot renew the lease of /ns0/file0


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