[jira] [Commented] (HDFS-5031) BlockScanner scans the block multiple times and on restart scans everything

["Arpit Agarwal (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-5031?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13763413#comment-13763413 ] 

Arpit Agarwal commented on HDFS-5031:
-------------------------------------

Hi Vinay, thanks for the explanation! I apologize for the delay in reviewing this.

# I ran {{TestDatanodeBlockScanner#testDuplicateScans}} without the rest of the code changes and it continues to pass. Do you see the same?
# I did not understand how the {{isNewPeriod}} check works. I will continue to take a look but meanwhile if someone more familiar with this code wants to chime in please do so.

Minor points:
# {{BlockScanInfo#equals}} looks redundant now. Can we just remove it?
# In {{Reader#next}}, should the assignment to {{lastReadFile}} happen after the call to {{readNext}}?


                
> BlockScanner scans the block multiple times and on restart scans everything
> ---------------------------------------------------------------------------
>
>                 Key: HDFS-5031
>                 URL: https://issues.apache.org/jira/browse/HDFS-5031
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>    Affects Versions: 3.0.0, 2.1.0-beta
>            Reporter: Vinay
>            Assignee: Vinay
>         Attachments: HDFS-5031.patch
>
>
> BlockScanner scans the block twice, also on restart of datanode scans everything.
> Steps:
> 1. Write blocks with interval of more than 5 seconds. write new block on completion of scan for written block.
> Each time datanode scans new block, it also scans, previous block which is already scanned. 
> Now after restart, datanode scans all blocks again.

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