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https://issues.apache.org/jira/browse/HDFS-12943?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17015234#comment-17015234
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Chen Liang commented on HDFS-12943:
-----------------------------------

[~lindy_hopper] access time update is a write call so it can not be processed 
by Observer. Access time should be turned off on Observer, as mentioned in 
HDFS-14959.

> Consistent Reads from Standby Node
> ----------------------------------
>
>                 Key: HDFS-12943
>                 URL: https://issues.apache.org/jira/browse/HDFS-12943
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: hdfs
>            Reporter: Konstantin Shvachko
>            Assignee: Konstantin Shvachko
>            Priority: Major
>             Fix For: 2.10.0, 3.3.0, 3.1.4, 3.2.2
>
>         Attachments: ConsistentReadsFromStandbyNode.pdf, 
> ConsistentReadsFromStandbyNode.pdf, HDFS-12943-001.patch, 
> HDFS-12943-002.patch, HDFS-12943-003.patch, HDFS-12943-004.patch, 
> TestPlan-ConsistentReadsFromStandbyNode.pdf
>
>
> StandbyNode in HDFS is a replica of the active NameNode. The states of the 
> NameNodes are coordinated via the journal. It is natural to consider 
> StandbyNode as a read-only replica. As with any replicated distributed system 
> the problem of stale reads should be resolved. Our main goal is to provide 
> reads from standby in a consistent way in order to enable a wide range of 
> existing applications running on top of HDFS.



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