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Date: Tue, 10 Jan 2017 15:12:58 +0000 (UTC)
From: "Kihwal Lee (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12783789.1426893424000.697534.1484061178707@Atlassian.JIRA>
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Subject: [jira] [Commented] (HDFS-7967) Reduce the performance impact of the
 balancer
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archived-at: Tue, 10 Jan 2017 15:13:00 -0000


    [ https://issues.apache.org/jira/browse/HDFS-7967?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15815227#comment-15815227 ] 

Kihwal Lee commented on HDFS-7967:
----------------------------------

I have reviewed the patch and am fine with it. We have used a variant of this over a year and this is the latest improved version. 

We can commit this to branch-2 and 2.8 now, but then we will likely forget about the remaining work and move on.  So I think we need to discuss what we are going to do for trunk. [~daryn], would you share your thoughts and concerns on the state of trunk and possible solutions?

> Reduce the performance impact of the balancer
> ---------------------------------------------
>
>                 Key: HDFS-7967
>                 URL: https://issues.apache.org/jira/browse/HDFS-7967
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>    Affects Versions: 2.0.0-alpha
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Critical
>         Attachments: HDFS-7967-branch-2.8.patch, HDFS-7967-branch-2.patch, HDFS-7967.branch-2-1.patch, HDFS-7967.branch-2.001.patch, HDFS-7967.branch-2.002.patch, HDFS-7967.branch-2.8-1.patch, HDFS-7967.branch-2.8.001.patch, HDFS-7967.branch-2.8.002.patch
>
>
> The balancer needs to query for blocks to move from overly full DNs.  The block lookup is extremely inefficient.  An iterator of the node's blocks is created from the iterators of its storages' blocks.  A random number is chosen corresponding to how many blocks will be skipped via the iterator.  Each skip requires costly scanning of triplets.
> The current design also only considers node imbalances while ignoring imbalances within the nodes's storages.  A more efficient and intelligent design may eliminate the costly skipping of blocks via round-robin selection of blocks from the storages based on remaining capacity.


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