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From "Jing Zhao (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8453) Erasure coding: properly handle start offset for internal blocks in a block group
Date Tue, 02 Jun 2015 22:50:50 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14569924#comment-14569924
] 

Jing Zhao commented on HDFS-8453:
---------------------------------

The patch looks pretty good to me. +1 after making the test change.

> Erasure coding: properly handle start offset for internal blocks in a block group
> ---------------------------------------------------------------------------------
>
>                 Key: HDFS-8453
>                 URL: https://issues.apache.org/jira/browse/HDFS-8453
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>         Attachments: HDFS-8453-HDFS-7285.00.patch
>
>
> {code}
>   void actualGetFromOneDataNode(final DNAddrPair datanode,
>     ...
>       LocatedBlock block = getBlockAt(blockStartOffset);
>     ...
>       fetchBlockAt(block.getStartOffset());
> {code}
> The {{blockStartOffset}} here is from inner block. For parity blocks, the offset will
overlap with the next block group, and we may end up with fetching wrong block. So we have
to assign a meaningful start offset for internal blocks in a block group, especially for parity
blocks.



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