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From "Christian Kunz (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-508) random seeks using FSDataInputStream can become invalid such that reads return invalid data
Date Tue, 05 Sep 2006 20:48:24 GMT
random seeks using FSDataInputStream can become invalid such that reads return invalid data

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                 Key: HADOOP-508
                 URL: http://issues.apache.org/jira/browse/HADOOP-508
             Project: Hadoop
          Issue Type: Bug
    Affects Versions: 0.5.0
            Reporter: Christian Kunz


Some of my applications using Hadoop DFS  receive wrong data after certain random seeks. After
some investigation I believe (without looking at source code of java.io.BufferedInputStream)
that it basically boils down to the fact that the method 
read(byte[] b, int off, int len), when called with an external buffer larger than the internal
buffer, reads into the external buffer directly without using the internal buffer anymore,
but without invalidating the internal buffer by setting the variable 'count' to 0 such that
a subsequent seek to an offset which is closer to the 'position' of the Positioncache than
the internal buffersize will put the current position into the internal buffer containing
outdated data from somewhere else.

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