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https://issues.apache.org/jira/browse/HDFS-16821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17629910#comment-17629910
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ASF GitHub Bot commented on HDFS-16821:
---------------------------------------

omalley commented on PR #5078:
URL: https://github.com/apache/hadoop/pull/5078#issuecomment-1305886044

   +1 LGTM




> Fix regression in HDFS-13522 that enables observer reads by default.
> --------------------------------------------------------------------
>
>                 Key: HDFS-16821
>                 URL: https://issues.apache.org/jira/browse/HDFS-16821
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs
>            Reporter: Simbarashe Dzinamarira
>            Assignee: Simbarashe Dzinamarira
>            Priority: Major
>              Labels: pull-request-available
>
> Serving reads consistently from Observer Namenodes is a feature that was 
> introduced in HDFS-12943.
> Clients opt-into this feature by configuring the ObserverReadProxyProvider. 
> It is important that the opt-in is explicit because for third-party reads to 
> remain consistent, these clients then need to perform an msync before reads.
> In HDFS-13522, the ClientGSIContext is implicitly added to the DFSClient thus 
> enabling Observer reads for all clients by default. This breaks consistency 
> guarantees for clients that haven't opted into observer reads.
> [https://github.com/apache/hadoop/pull/4883/files#diff-a627e2c1f3e68235520d3c28092f4ae8a41aa4557cc530e4e6862c318be7e898R352-R354]
> We need to return to the old behavior of only using the ClientGSIContext when 
> users have explicitly opted into Observer reads.



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