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https://issues.apache.org/jira/browse/HDFS-14870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16968665#comment-16968665
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Wei-Chiu Chuang commented on HDFS-14870:
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FWIW Ambari disables access time by default for HDP clusters. So that does look
like a reasonable trade-off.
Access time cause other problems with snapshots too: HDFS-12191.
> [SBN read] Client Settings to ObserverReadProxyProvider read a file request,
> due to the file atime time needs to be modified, lead to request to be
> processed twice
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-14870
> URL: https://issues.apache.org/jira/browse/HDFS-14870
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs
> Affects Versions: 2.10.0, 3.3.0, 3.2.1
> Reporter: huhaiyang
> Priority: Major
> Attachments: test_case
>
>
> Client Settings agent refers to ObserverReadProxyProvider class, read the RPC
> request will be forwarded to the ONN, but involves the need to modify the
> file, the request will be processed twice, cause the request time is too long;
> When ONN received from the client to read a file, will call FSNamesystem
> getBlockLocations method to get the list of file information, and the current
> atime decided the current file needs to be updated
> (dfs.namenode.accesstime.precision, HDFS file access time is accurate, The
> default value is 1 hour）. The ONN does not currently support write
> operations. This logic throws StandbyException and the client retries the RPC
> request and forwards it to ANN for execution. As a result, the current file
> getBlockLocations method will be called twice, lengthening the entire RPC
> request.
>
>
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