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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1783) Ability for HDFS client to write replicas in parallel
Date Fri, 08 Jun 2012 17:01:24 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1783?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13291861#comment-13291861
] 

Todd Lipcon commented on HDFS-1783:
-----------------------------------

{code}
As for the complexity, I find it manageable... The pipelining as such has not changed, only
that the client opens up N pipelines on length 1.
Once this change is in, one could get fancier (for example 2 pipelines of length 2 for 4 replicas,
etc, or maybe we could open pipelines to multiple clusters, etc).
{code}

My concern is less with the complexity of the actual writing and more with the changes that
will probably have to be done for failure handling, for the append path, etc. At the least
I'd probably want all of our write-pipeline tests to be duplicated to run once in pipelined-write
mode and once in parallel-write mode. Maybe I'm just being paranoid, happy for more opinions
here :)
                
> Ability for HDFS client to write replicas in parallel
> -----------------------------------------------------
>
>                 Key: HDFS-1783
>                 URL: https://issues.apache.org/jira/browse/HDFS-1783
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>            Reporter: dhruba borthakur
>            Assignee: Lars Hofhansl
>         Attachments: HDFS-1783-trunk-v2.patch, HDFS-1783-trunk-v3.patch, HDFS-1783-trunk-v4.patch,
HDFS-1783-trunk.patch
>
>
> The current implementation of HDFS pipelines the writes to the three replicas. This introduces
some latency for realtime latency sensitive applications. An alternate implementation that
allows the client to write all replicas in parallel gives much better response times to these
applications. 

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