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From "eric baldeschwieler (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-659) Boost the priority of re-replicating blocks that are far from their replication target
Date Thu, 02 Nov 2006 08:37:17 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-659?page=comments#action_12446507 ] 
            
eric baldeschwieler commented on HADOOP-659:
--------------------------------------------

why not maintain a total order?

> Boost the priority of re-replicating blocks that are far from their replication target
> --------------------------------------------------------------------------------------
>
>                 Key: HADOOP-659
>                 URL: http://issues.apache.org/jira/browse/HADOOP-659
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.7.2
>            Reporter: Konstantin Shvachko
>         Assigned To: Konstantin Shvachko
>
> I see two types of replications that should be accelerated compared to all others.
> 1. Blocks that have only one remaining copy (but are required to have higher replication).
> 2. Blocks that have less than 1/3 of their replicas in place.
> The latter occurs when map/reduce sets replication of certain files to 10, and we want
> it happen fast to achieve better performance on the tasks.
> So I think we should distinguish two major groups of under-replicated blocks:
> first-priority (having only 1 copy or less than 1/3 of required replicas), and the rest.
> The name-node places first-priority blocks into the beginning of the neededReplication
> list, and the rest are placed at the end. That way the first-priority blocks will be
replicated
> first and then the others.

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