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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-898) Sequential generation of block ids
Date Fri, 05 Feb 2010 00:58:28 GMT

    [ https://issues.apache.org/jira/browse/HDFS-898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12829894#action_12829894
] 

Tsz Wo (Nicholas), SZE commented on HDFS-898:
---------------------------------------------


This is not a birthday problem.  There is no limitation on the number of people having the
same birthday but there is a limitation on block ids.

For 365 days and 2^26 people, all 2^26 people could have the same birthday.

However, for 2^(64-b) id space and B=2^26 blocks, at most two blocks could share the same
block id after removing 1 bit.

> Sequential generation of block ids
> ----------------------------------
>
>                 Key: HDFS-898
>                 URL: https://issues.apache.org/jira/browse/HDFS-898
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>    Affects Versions: 0.20.1
>            Reporter: Konstantin Shvachko
>            Assignee: Konstantin Shvachko
>             Fix For: 0.22.0
>
>         Attachments: DuplicateBlockIds.patch, HighBitProjection.pdf
>
>
> This is a proposal to replace random generation of block ids with a sequential generator
in order to avoid block id reuse in the future.

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