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From "Chao Sun (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10702) Add a Client API and Proxy Provider to enable stale read from Standby
Date Tue, 05 Sep 2017 22:37:02 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16154494#comment-16154494
] 

Chao Sun commented on HDFS-10702:
---------------------------------

Thanks [~clouderajiayi] and [~mackrorysd] for this great work! we are experiencing lots of
NN issues at Uber and this could be a big help.

[~mingma] and [~zhz]: you have raised the question of potential race conditions with {{cpLock}}.
However, I'm not sure if this is possible: to my understanding the {{cpLock}} is used to protect
edit log from checkpointing and the tailer, which the read operations would not need to touch
(seems like). Please correct me if I'm wrong. :)

> 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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