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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-202) Add a bulk FIleSystem.getFileBlockLocations
Date Wed, 04 Aug 2010 04:55:19 GMT

    [ https://issues.apache.org/jira/browse/HDFS-202?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895142#action_12895142
] 

Hadoop QA commented on HDFS-202:
--------------------------------

-1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12451084/hdfsListFiles3.patch
  against trunk revision 982091.

    +1 @author.  The patch does not contain any @author tags.

    +1 tests included.  The patch appears to include 15 new or modified tests.

    -1 patch.  The patch command could not apply the patch.

Console output: http://hudson.zones.apache.org/hudson/job/Hdfs-Patch-h2.grid.sp2.yahoo.net/228/console

This message is automatically generated.

> Add a bulk FIleSystem.getFileBlockLocations
> -------------------------------------------
>
>                 Key: HDFS-202
>                 URL: https://issues.apache.org/jira/browse/HDFS-202
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>            Reporter: Arun C Murthy
>            Assignee: Hairong Kuang
>             Fix For: 0.22.0
>
>         Attachments: hdfsListFiles.patch, hdfsListFiles1.patch, hdfsListFiles2.patch,
hdfsListFiles3.patch
>
>
> Currently map-reduce applications (specifically file-based input-formats) use FileSystem.getFileBlockLocations
to compute splits. However they are forced to call it once per file.
> The downsides are multiple:
>    # Even with a few thousand files to process the number of RPCs quickly starts getting
noticeable
>    # The current implementation of getFileBlockLocations is too slow since each call
results in 'search' in the namesystem. Assuming a few thousand input files it results in that
many RPCs and 'searches'.
> It would be nice to have a FileSystem.getFileBlockLocations which can take in a directory,
and return the block-locations for all files in that directory. We could eliminate both the
per-file RPC and also the 'search' by a 'scan'.
> When I tested this for terasort, a moderate job with 8000 input files the runtime halved
from the current 8s to 4s. Clearly this is much more important for latency-sensitive applications...

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