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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-512) Set block id as the key to Block
Date Mon, 03 Aug 2009 20:35:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12738568#action_12738568
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Konstantin Shvachko commented on HDFS-512:
------------------------------------------

I was looking at compareTo(), which is used in TreeMap. HashMap uses equals() so yes all maps
are affected.
I still think the change makes sense because we don't want to treat the same block with different
generation stamps as separate blocks.
By the way, equals() should probably be implemented via compareTo() so that they are always
in sync.

> Set block id as the key to Block
> --------------------------------
>
>                 Key: HDFS-512
>                 URL: https://issues.apache.org/jira/browse/HDFS-512
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 0.21.0
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: 0.21.0
>
>         Attachments: blockKey.patch
>
>
> Currently the key to Block is block id + generation stamp. I would propose to change
it to be only block id. This is based on the following properties of the dfs cluster:
> 1. On each datanode only one replica of block exists. Therefore there is only one generation
of a block.
> 2. NameNode has only one entry for a block in its blocks map.
> With this change, search for a block/replica's meta information is easier since most
of the time we know a block's id but may not know its generation stamp.

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