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https://issues.apache.org/jira/browse/HDFS-1295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12986564#action_12986564
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Matt Foley commented on HDFS-1295:
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Hi Dhruba, I think this is a really important improvement to startup time, so I
will try to get some contributors here to review it.
Regarding this dangling issue, can you please describe any risks you see from
corrupt replicas, with this shortcut in place? Thanks.
> 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
> 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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