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From "Chao Sun (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-13924) Handle BlockMissingException when reading from observer
Date Tue, 16 Oct 2018 00:32:00 GMT

     [ https://issues.apache.org/jira/browse/HDFS-13924?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Chao Sun updated HDFS-13924:
----------------------------
    Status: Patch Available  (was: Open)

> Handle BlockMissingException when reading from observer
> -------------------------------------------------------
>
>                 Key: HDFS-13924
>                 URL: https://issues.apache.org/jira/browse/HDFS-13924
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Chao Sun
>            Assignee: Chao Sun
>            Priority: Major
>         Attachments: HDFS-13924-HDFS-12943.000.patch
>
>
> Internally we found that reading from ObserverNode may result to {{BlockMissingException}}.
This may happen when the observer sees a smaller number of DNs than active (maybe due to communication
issue with those DNs), or (we guess) late block reports from some DNs to the observer. This
error happens in [DFSInputStream#chooseDataNode|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java#L846],
when no valid DN can be found for the {{LocatedBlock}} got from the NN side.
> One potential solution (although a little hacky) is to ask the {{DFSInputStream}} to
retry active when this happens. The retry logic already present in the code - we just have
to dynamically set a flag to ask the {{ObserverReadProxyProvider}} try active in this case.
> cc [~shv], [~xkrogen], [~vagarychen], [~zero45] for discussion.



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