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From "John George (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-1907) BlockMissingException upon concurrent read and write: reader was doing file position read while writer is doing write without hflush
Date Wed, 01 Jun 2011 03:42:47 GMT

     [ https://issues.apache.org/jira/browse/HDFS-1907?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

John George updated HDFS-1907:
------------------------------

    Attachment: HDFS-1907.patch

In cases where a request for data from a file that has blocks that are yet to be finalized
is made, DFSInputStream, assumes that the request that was made included the unfinalized block
as well. This causes the offset to go negative.

> BlockMissingException upon concurrent read and write: reader was doing file position
read while writer is doing write without hflush
> ------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-1907
>                 URL: https://issues.apache.org/jira/browse/HDFS-1907
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs client
>    Affects Versions: 0.23.0
>         Environment: Run on a real cluster. Using the latest 0.23 build.
>            Reporter: CW Chung
>            Assignee: John George
>         Attachments: HDFS-1907.patch
>
>
> BlockMissingException is thrown under this test scenario:
> Two different processes doing concurrent file r/w: one read and the other write on the
same file
>   - writer keep doing file write
>   - reader doing position file read from beginning of the file to the visible end of
file, repeatedly
> The reader is basically doing:
>   byteRead = in.read(currentPosition, buffer, 0, byteToReadThisRound);
> where CurrentPostion=0, buffer is a byte array buffer, byteToReadThisRound = 1024*10000;
> Usually it does not fail right away. I have to read, close file, re-open the same file
a few times to create the problem. I'll pose a test program to repro this problem after I've
cleaned up a bit my current test program.

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