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https://issues.apache.org/jira/browse/HDFS-10702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16164158#comment-16164158
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Ming Ma commented on HDFS-10702:
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[~csun], the long checkpoint duration could cause the following issue:
* Checkpointer holding {{cpLock}} takes a long time to finish for a large
namespace.
* edit log tailer blocked by {{cpLock}} can't update namespace. Thus the
namespace becomes stale.
* An application deletes a file. StandbyNN receives incremental block report
indicating the blocks have been removed and update its blockmap.
* StandbyNN's stale namespace still has the file but without block locations.
> Add a Client API and Proxy Provider to enable stale read from Standby
> ---------------------------------------------------------------------
>
> Key: HDFS-10702
> URL: https://issues.apache.org/jira/browse/HDFS-10702
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Jiayi Zhou
> Assignee: Sean Mackrory
> Priority: Minor
> Attachments: HDFS-10702.001.patch, HDFS-10702.002.patch,
> HDFS-10702.003.patch, HDFS-10702.004.patch, HDFS-10702.005.patch,
> HDFS-10702.006.patch, HDFS-10702.007.patch, HDFS-10702.008.patch,
> StaleReadfromStandbyNN.pdf
>
>
> Currently, clients must always talk to the active NameNode when performing
> any metadata operation, which means active NameNode could be a bottleneck for
> scalability. One way to solve this problem is to send read-only operations to
> Standby NameNode. The disadvantage is that it might be a stale read.
> Here, I'm thinking of adding a Client API to enable/disable stale read from
> Standby which gives Client the power to set the staleness restriction.
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