[jira] Updated: (MAPREDUCE-1861) Raid should rearrange the replicas while raiding

["Scott Chen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MAPREDUCE-1861?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Scott Chen updated MAPREDUCE-1861:
----------------------------------

    Attachment: MAPREDUCE-1861.txt

> Raid should rearrange the replicas while raiding
> ------------------------------------------------
>
>                 Key: MAPREDUCE-1861
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1861
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: contrib/raid
>    Affects Versions: 0.22.0
>            Reporter: Scott Chen
>            Assignee: Scott Chen
>             Fix For: 0.22.0
>
>         Attachments: MAPREDUCE-1861.txt
>
>
> Raided file introduce extra dependencies on the blocks on the same stripe.
> Therefore we need a new way to place the blocks.
> It is desirable that raided file satisfies the following two conditions:
> a. Replicas on the same stripe should be on different machines (or racks)
> b. Replicas of the same block should be on different racks
> MAPREDUCE-1831 will try to delete the replicas on the same stripe and the same machine (a).
> But in the mean time, it will try to maintain the number of distinct racks of one block (b).
> We cannot satisfy (a) and (b) at the same time with the current logic in BlockPlacementPolicyDefault.chooseTarget().
> One choice we have is to change BlockPlacementPolicyDefault.chooseTarget().
> However, this placement is in general good for all files including the unraided ones.
> It is not clear to us that we can make this good for both raided and unraided files.
> So we propose this idea that when raiding the file. We create one more off-rack replica (so the replication=4 now).
> Than we delete two blocks using the policy in MAPREDUCE-1831 after that (replication=2 now).
> This way we can rearrange the replicas to satisfy (a) and (b) at the same time.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.