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From "Yi Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8033) Erasure coding: stateful (non-positional) read from files in striped layout
Date Tue, 21 Apr 2015 06:24:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14504428#comment-14504428
] 

Yi Liu commented on HDFS-8033:
------------------------------

Thanks [~zhz] for working on this.  The patch is good, my comments:
*1.* 
In DFSInputStream, the stateful read is not to read fully for the output *buf*,  {{readWithStrategy}}
will call {{readBuffer}} and return on success.  In {{DFSStripedInputStream}} we override
{{readBuffer}}, but we only read in one striped block, so the returned result should be something
like (cell_0, cell_3, ....).  
This is not incorrect,  in the test, you have tested stateful read, but you do fully read
and the data size is *BLOCK_GROUP_SIZE*, so the result coincidentally is correct. 
I suggest we try to do fully read in {{readBuffer}} of {{DFSStripedInputStream}} unless we
find the end of file, of course, the final read length could be less than the input buf length
if we get eof.

*2.* In {{blockSeekTo}}, we need to handle refetchToken and refetchEncryptionKey. And for
other IOException, we can throw it.

*3.* 
For the test, do stateful read: read once and fully read (please make the data size large
than groupSize * cellSize), as I said in #1,

*4.* 
{{connectFailedOnce}} in {{blockSeekTo}} is not necessary.

*5.* 
Why you modify {{SimulatedFSDataset}}?

> Erasure coding: stateful (non-positional) read from files in striped layout
> ---------------------------------------------------------------------------
>
>                 Key: HDFS-8033
>                 URL: https://issues.apache.org/jira/browse/HDFS-8033
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>         Attachments: HDFS-8033.000.patch, HDFS-8033.001.patch
>
>




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