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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-642) Support pipeline close and close recovery
Date Mon, 28 Sep 2009 18:41:16 GMT

    [ https://issues.apache.org/jira/browse/HDFS-642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12760330#action_12760330
] 

Suresh Srinivas commented on HDFS-642:
--------------------------------------

# Some of the changed code goes beyond 80 chars
# DFSClient.java - can the following check be made in a separate method {{(!streamerClosed
&& !hasError && clientRunning)}}
# DFSClient.java - waiting for ack (ack size to become zero) can become a separate method
# DFSClient readChunk() - {{( dataLen <= 0 && !lastPacketInBlock )}} should the
first part be just datalen == 0?
# DFSClient.Packet - An optimization that could be made in future is to not to allocate any
memory to Packet.buf for zero length packet
# Nit: FSDatasetInterface.java - Change comment {and returns the meta info of the replica}
to {and return ...}
# DFSClient.java not sure why the waiting for ack queue to become zero len was moved out of
previous try catch?


> Support pipeline close and close recovery
> -----------------------------------------
>
>                 Key: HDFS-642
>                 URL: https://issues.apache.org/jira/browse/HDFS-642
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: Append Branch
>
>         Attachments: closePipeline.patch
>
>
> This jira intends to implement the third stage of block construction: close. The main
ideas are:
> 1. A client notifies the datanodes in the pipeline to finalize a replica and then shuts
down the pipeline by sending a special end-of-block message.
> 2. The end-of-block message does not get sent until the client finishes sending all packets
belong to the block and have received all their acks.
> 3. If close fails, the client recovers the failures by setting up a new pipeline with
the remaining datanodes and a newer generation stamp.
> 4. I plan to use an empty packet as the end-of-block message.

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