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From "Wei-Chiu Chuang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-13985) Clearer error message for ReplicaNotFoundException
Date Wed, 31 Oct 2018 16:33:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-13985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16670351#comment-16670351

Wei-Chiu Chuang commented on HDFS-13985:

FWIW, this message is logged when client attempts to access a block on a DataNode. However,
DN doesn't have that block in its blockMap, so there's no way for it to tell the corresponding
block file path and such.

Possible reasons for this condition include: a balancer was run and the block was removed
from DN (essentially a race condition) Or the block was removed because a client reduced replication
factor. Usually this is harmless.

Perhaps you can update the message and say: "The block may have been removed recently by balancer
or by a reducing replication factor intentionally. This is usually harmless. Check previous
DataNode log messages to make sure"

> Clearer error message for ReplicaNotFoundException
> --------------------------------------------------
>                 Key: HDFS-13985
>                 URL: https://issues.apache.org/jira/browse/HDFS-13985
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs
>            Reporter: Adam Antal
>            Priority: Major
> The issue is that we came across a ReplicaNotFoundException in a bug report, the most
informative thing we could get is "Replica not found for [ExtendedBlock]". If someone tries
to investigate cases including ReplicaNotFoundExceptions should review diagnostic bundles,
dig through logs, but as a starting point enhancing the exception message would boost this
process, and be beneficial in the long run.
> More concretely, it would be helpful if any of the following information was displayed
along with the exception: file's name, replication factor or block location.

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