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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-512) Set block id as the key to Block
Date Wed, 05 Aug 2009 20:39:15 GMT

    [ https://issues.apache.org/jira/browse/HDFS-512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12739734#action_12739734
] 

Tsz Wo (Nicholas), SZE commented on HDFS-512:
---------------------------------------------

> We cannot have semantically different implementations of compareTo() and equals() methods.
...
We indeed could have two implementations of compareTo() since we may pass a Comparator object.
 See [this TreeMap constructor|http://java.sun.com/javase/6/docs/api/java/util/TreeMap.html#TreeMap%28java.util.Comparator%29
API].

> 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: Append Branch
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: Append Branch
>
>         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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