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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1783) Ability for HDFS client to write replicas in parallel
Date Thu, 14 Jun 2012 11:01:43 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1783?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13294951#comment-13294951
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Lars Hofhansl commented on HDFS-1783:
-------------------------------------

@Ted: The first method is overridden in DistributedFileSystem (to avoid having to change method
signatures in each subclass for FileSystem).

PrimitiveCreate is called from FileContext. There seem to be some general inconsistencies
in FileSystem. For example calling FileSystem.create(..., APPEND, ...) will not append. FileContext.create(...,
APPEND, ...) on the other hand will do the right thing.

This patch does not affect that. The patch will naturally work with FileContext.create(...,
APPEND, ...) I'll add a few more tests for this.
When I'm back in the US, I'll get some performance numbers (judging from my micro benchmarks,
I'd expect some nice improvements as long as the client's network-link is not saturated).

                
> 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-v5.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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