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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-512) Set block id as the key to Block
Date Tue, 04 Aug 2009 22:19:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12739212#action_12739212
] 

Hairong Kuang commented on HDFS-512:
------------------------------------

> Why does ReplicaInfo need genStamp field. Don't we always have it in Block? If we do
could you please add a comment clarifying what this field actually is.
Now the key is block id so the returned entry from the map may have a different generation
stamp but there is no efficient way to get the key in the map so I add the generation stamp
to the value field.

> 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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