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https://issues.apache.org/jira/browse/HDFS-17156?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Takanobu Asanuma resolved HDFS-17156.
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Fix Version/s: 3.4.0
Resolution: Fixed
> Client may receive old state ID which will lead to inconsistent reads
> ---------------------------------------------------------------------
>
> Key: HDFS-17156
> URL: https://issues.apache.org/jira/browse/HDFS-17156
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: rbf
> Reporter: Chunyi Yang
> Assignee: Chunyi Yang
> Priority: Minor
> Labels: Observer, RBF, pull-request-available
> Fix For: 3.4.0
>
>
> While executing a mapreduce job in an environment utilizing Router-Based
> Federation with Observer read enabled, there is an estimated 1% chance of
> encountering the following error.
> {code:java}
> "java.io.IOException: Resource
> hdfs://XXXX/user/XXXX/.staging/job_XXXXXX/.tez/application_XXXXXX/tez-conf.pb
> changed on src filesystem - expected: \"2023-07-07T12:41:16.801+0900\", was:
> \"2023-07-07T12:41:16.822+0900\", current time:
> \"2023-07-07T12:41:22.386+0900\"",
> {code}
> This error happens in function verifyAndCopy inside FSDownload.java when
> nodemanager tries to download a file right after the file has been written to
> the HDFS. The write operation runs on active namenode and read operation runs
> on observer namenode as expected.
> The edits file and hdfs-audit files indicate that the expected timestamp
> mentioned in the error message aligns with the OP_CLOSE MTIME of the
> 'tez-conf.pb' file (which is correct). However, the actual timestamp
> retrieved from the read operation corresponds to the OP_ADD MTIME of the
> target 'tez-conf.pf' file (which is incorrect). This inconsistency suggests
> that the observer namenode responds to the client before its edits file is
> updated with the latest stateId.
> Further troubleshooting has revealed that during write operations, the router
> responds to the client before receiving the latest stateId from the active
> namenode. Consequently, the outdated stateId is then used in the subsequent
> read operation on the observer namenode, leading to inaccuracies in the
> information provided by the observer namenode.
> To resolve this issue, it is essential to ensure that the router sends a
> response to the client only after receiving the latest stateId from the
> active namenode.
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