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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 Thu, 06 Aug 2009 02:19:15 GMT

    [ https://issues.apache.org/jira/browse/HDFS-512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12739878#action_12739878

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

> I want to see at least one example where current the implementation (id+gs) of the block
key is critical.
I did not say that I got a good example for using id+gs.

> (1) is too dangerous to get everything correct
Typo: it should be "(1) is too dangerous: it is very difficult to get everything correct"
I mean (1) involves too much.  I even have a hard time to list out all the affected components
in [my previous comment|https://issues.apache.org/jira/browse/HDFS-512?focusedCommentId=12737395&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_12737395].

BTW, I am not against (1) and I am not the assignee of this issue.  Please go ahead if you
have fully considered other alternatives.  I think the assignee has the freedom to choose
a solution.

> 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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