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https://issues.apache.org/jira/browse/HADOOP-1079?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12496443
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dhruba borthakur commented on HADOOP-1079:
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A short discussion with Sameer revealed that the case where admin/rogue-process
manually deleted some blk-xxx files cannot be dealt with by an daily block
report. A proposal is to do make the datanode compare its in-memory data
structures with what is on disk. If it finds inconsistencies, then it send s a
complete block report to the namenode.
In response to Raghu's comments: I agree that sending a block report
"immediately" after a successful heartbeat (that was preceeded by a failed
heartbeat) could add more load on the namenode. It is enough if we can "hasten"
the next block report rather than sending it immediately. I will work on this
fix.
> DFS Scalability: optimize processing time of block reports
> ----------------------------------------------------------
>
> Key: HADOOP-1079
> URL: https://issues.apache.org/jira/browse/HADOOP-1079
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Reporter: dhruba borthakur
> Assigned To: dhruba borthakur
> Attachments: blockReportPeriod.patch
>
>
> I have a cluster that has 1800 datanodes. Each datanode has around 50000
> blocks and sends a block report to the namenode once every hour. This means
> that the namenode processes a block report once every 2 seconds. Each block
> report contains all blocks that the datanode currently hosts. This makes the
> namenode compare a huge number of blocks that practically remains the same
> between two consecutive reports. This wastes CPU on the namenode.
> The problem becomes worse when the number of datanodes increases.
> One proposal is to make succeeding block reports (after a successful send of
> a full block report) be incremental. This will make the namenode process only
> those blocks that were added/deleted in the last period.
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