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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 Mon, 19 Oct 2009 18:03:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12767427#action_12767427
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Hairong Kuang commented on HDFS-512:
------------------------------------

FSNamesystem.java has code that removes a blockinfo entry from the blocksMap, changes its
generation stamp, and adds it back, for example, in updatePipeline and commitBlockSynchronization.
Now that the generation stamp is not the part of the key, those code are not necessary.

> 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: Konstantin Shvachko
>             Fix For: 0.21.0
>
>         Attachments: blockIdAsKey.patch, 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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