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https://issues.apache.org/jira/browse/HDFS-13923?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16691154#comment-16691154
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xiangheng commented on HDFS-13923:
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Hey [~csun],that's a intreasting ideas,I'm studying this question.if you like,
please assign this question to me,i will try to solve this problem,thank you
very much.
> Add a configuration to turn on/off observer reads
> -------------------------------------------------
>
> Key: HDFS-13923
> URL: https://issues.apache.org/jira/browse/HDFS-13923
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Chao Sun
> Priority: Major
>
> In some situations having a config to turn on/off observer reads dynamically
> may be useful. For instance, some applications may be sensitive for data
> freshness and want to always reach directly to active NN. In a more complex
> scenario, services such as Presto may want to apply observer reads for
> different types of queries. In this case, simply change
> {{dfs.client.failover.proxy.provider.<nameservice>}} may not be enough, since
> with FileSystem cache (which is usually turned on) will ignore the change and
> still use the same FileSystem object.
> Here I'm proposing to add a flag in {{HdfsClientConfigKeys}}, such as
> {{dfs.client.observer.reads.enabled}}, that can be used to dynamically turn
> on/off observer reads. The FileSystem cache key should also take account of
> this flag in its {{hashCode}} and {{equals}} impl, so that different
> FileSystem objects will be used depending on the flag.
>
> cc [~shv], [~xkrogen], [~vagarychen], [~zero45] for discussion.
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