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From "Zhe Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7678) Erasure coding: DFSInputStream with decode functionality (pread)
Date Wed, 06 May 2015 23:53:03 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7678?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14531718#comment-14531718
] 

Zhe Zhang commented on HDFS-7678:
---------------------------------

bq. I think to make the test simple, we can use end-to-end tests like TestDFSStripedInputStream.

End-to-end testing is indeed simpler; in order to fake a striped file we have to add a considerable
chunk of new code (metadata first, then fake blocks on DN). But I think it's worth it because
it makes the test faster, and also more accurately test the input stream logic. The content-dismatch
failures are pretty hard to debug if we go through all levels (writing, codec); I just spent
several good hours to find out the above test failure is a codec level issue :( Once we have
this isolated test ready we don't need to worry about future bugs in output stream and codec.

> Erasure coding: DFSInputStream with decode functionality (pread)
> ----------------------------------------------------------------
>
>                 Key: HDFS-7678
>                 URL: https://issues.apache.org/jira/browse/HDFS-7678
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>    Affects Versions: HDFS-7285
>            Reporter: Li Bo
>            Assignee: Zhe Zhang
>         Attachments: BlockGroupReader.patch, HDFS-7678-HDFS-7285.002.patch, HDFS-7678-HDFS-7285.003.patch,
HDFS-7678-HDFS-7285.004.patch, HDFS-7678-HDFS-7285.005.patch, HDFS-7678-HDFS-7285.006.patch,
HDFS-7678-HDFS-7285.007.patch, HDFS-7678-HDFS-7285.008.patch, HDFS-7678-HDFS-7285.009.patch,
HDFS-7678-HDFS-7285.010.patch, HDFS-7678.000.patch, HDFS-7678.001.patch
>
>
> A block group reader will read data from BlockGroup no matter in striping layout or contiguous
layout. The corrupt blocks can be known before reading(told by namenode), or just be found
during reading. The block group reader needs to do decoding work when some blocks are found
corrupt.



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