[jira] Commented: (HDFS-1295) Improve namenode restart times by short-circuiting the first block reports from datanodes

["Konstantin Shvachko (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-1295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12887618#action_12887618 ] 

Konstantin Shvachko commented on HDFS-1295:
-------------------------------------------

Could you please explain what happens with blocks in the first block report from a DN that do not belong to any file. Are they also inserted to the blocksMap?

> Improve namenode restart times by short-circuiting the first block reports from datanodes
> -----------------------------------------------------------------------------------------
>
>                 Key: HDFS-1295
>                 URL: https://issues.apache.org/jira/browse/HDFS-1295
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>             Fix For: 0.22.0
>
>         Attachments: shortCircuitBlockReport_1.txt
>
>
> The namenode restart is dominated by the performance of processing block reports. On a 2000 node cluster with 90 million blocks,  block report processing takes 30 to 40 minutes. The namenode "diffs" the contents of the incoming block report with the contents of the blocks map, and then applies these diffs to the blocksMap, but in reality there is no need to compute the "diff" because this is the first block report from the datanode.
> This code change improves block report processing time by 300%.

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