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https://issues.apache.org/jira/browse/HDFS-16821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17626688#comment-17626688
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ASF GitHub Bot commented on HDFS-16821:
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simbadzina commented on PR #5078:
URL: https://github.com/apache/hadoop/pull/5078#issuecomment-1297360423
> @simbadzina Thanks for your contribution. Make sense and looks good to me.
I just realized that
[HDFS-13522](https://issues.apache.org/jira/browse/HDFS-13522) has been merged,
after looked into the relate code, I have a question and looking forward your
feedback.
>
> 1. Should Router support forwarding the read request to the Observer
NameNodes from the client not using the ObserverReadProxyProvider?
Hi @ZanderXu. Thanks for looking.
No, clients not using ObserverReadProxyProvider shouldn't have their reads
forwarded. Observer reads should be an opt-in feature since clients that
participate may need to msync. To maintain backward compatibility, using
ObserverReadProxyProvider was the method for opting in.
A future improvement that can be made is to provide an alternative flag to
opt-in.
> 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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