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From "Zhe Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9918) Erasure Coding: Sort located striped blocks based on decommissioned states
Date Tue, 29 Mar 2016 21:13:25 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15216846#comment-15216846

Zhe Zhang commented on HDFS-9918:

Thanks for the discussion [~walter.k.su] and [~rakeshr]. Below is my analysis:

Now we have 3 dimensions to consider in the sorting algorithm:
# Index in the logical block group
# Decomm status
# Distance to the {{targethost}}

I think Walter's suggestion was to consider 3) only if 1) and 2) are the same. That's my understanding
too. For striped blocks I don't think we care too much about the distance because locality
is mostly broken anyway. I think it's more important to preserve the index ordering. LMK if
 you agree. 

> Erasure Coding: Sort located striped blocks based on decommissioned states
> --------------------------------------------------------------------------
>                 Key: HDFS-9918
>                 URL: https://issues.apache.org/jira/browse/HDFS-9918
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Rakesh R
>            Assignee: Rakesh R
>         Attachments: HDFS-9918-001.patch, HDFS-9918-002.patch, HDFS-9918-003.patch, HDFS-9918-004.patch,
HDFS-9918-005.patch, HDFS-9918-006.patch, HDFS-9918-007.patch
> This jira is a follow-on work of HDFS-8786, where we do decommissioning of datanodes
having striped blocks.
> Now, after decommissioning it requires to change the ordering of the storage list so
that the decommissioned datanodes should only be last node in list.
> For example, assume we have a block group with storage list:-
> d0, d1, d2, d3, d4, d5, d6, d7, d8, d9
> mapping to indices
> 0, 1, 2, 3, 4, 5, 6, 7, 8, 2
> Here the internal block b2 is duplicated, locating in d2 and d9. If d2 is a decommissioning
node then should switch d2 and d9 in the storage list.
> Thanks [~jingzhao] for the [discussions|https://issues.apache.org/jira/browse/HDFS-8786?focusedCommentId=15180415&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15180415]

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