[jira] [Commented] (HDFS-3512) Delay in scanning blocks at DN side when there are huge number of blocks

["Uma Maheswara Rao G (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-3512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13696266#comment-13696266 ] 

Uma Maheswara Rao G commented on HDFS-3512:
-------------------------------------------

@Amith, This is intentional from the code. If there are many blocks then it will give some random number. So, scan should happen with that period time anyway. So, I am not seeing big issue here. do you agree?
                
> Delay in scanning blocks at DN side when there are huge number of blocks
> ------------------------------------------------------------------------
>
>                 Key: HDFS-3512
>                 URL: https://issues.apache.org/jira/browse/HDFS-3512
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>    Affects Versions: 2.0.0-alpha
>            Reporter: suja s
>            Assignee: amith
>         Attachments: HDFS-3512.patch
>
>
> Block scanner maintains the full list of blocks at DN side in a map and there is no differentiation between the blocks which are already scanned and the ones not scanend. For every check (ie every 5 secs) it will pick one block and scan. There are chances that it chooses a block which is already scanned which leads to further delay in scanning of blcoks which are yet to be scanned.

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