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From "Endre Major (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLUME-2973) Deadlock in hdfs sink
Date Tue, 28 Aug 2018 09:24:00 GMT

    [ https://issues.apache.org/jira/browse/FLUME-2973?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16594746#comment-16594746

Endre Major commented on FLUME-2973:

I have attached the absolute minimum patch that solves this deadlock. This is very similar
to [~adrianjian] patch.
I did some measurements with both Denes's and Yan's patches, they both work fine. 
Unfortunately Yan's deadlock reproduction test reproduces a different deadlock( one of the
locks is in the synchronized test method), but Denes's test seems fine. 
I am combining Yan's test cleanup, Denes' deadlock test and my minimal fix into a pull request.

> Deadlock in hdfs sink
> ---------------------
>                 Key: FLUME-2973
>                 URL: https://issues.apache.org/jira/browse/FLUME-2973
>             Project: Flume
>          Issue Type: Bug
>          Components: Sinks+Sources
>    Affects Versions: 1.7.0
>            Reporter: Denes Arvay
>            Assignee: Denes Arvay
>            Priority: Critical
>              Labels: hdfssink
>             Fix For: 1.9.0
>         Attachments: FLUME-2973-1.patch, FLUME-2973-min.patch, FLUME-2973.patch
> Automatic close of BucketWriters (when open file count reached {{hdfs.maxOpenFiles}})
and the file rolling thread can end up in deadlock.
> When creating a new {{BucketWriter}} in {{HDFSEventSink}} it locks {{HDFSEventSink.sfWritersLock}}
and the {{close()}} called in {{HDFSEventSink.sfWritersLock.removeEldestEntry}} tries to lock
the {{BucketWriter}} instance.
> On the other hand if the file is being rolled in {{BucketWriter.close(boolean)}} it locks
the {{BucketWriter}} instance first and in the close callback it tries to lock the {{sfWritersLock}}.
> The chances for this deadlock is higher when the {{hdfs.maxOpenFiles}}'s value is low
> Script to reproduce: https://gist.github.com/adenes/96503a6e737f9604ab3ee9397a5809ff
> (put to {{flume-ng-sinks/flume-hdfs-sink/src/main/java/org/apache/flume/sink/hdfs}})
> Deadlock usually occurs before ~30 iterations.

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