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From "Jason Lowe (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HADOOP-11445) Bzip2Codec: Data block is skipped when position of newly created stream is equal to start of split
Date Tue, 06 Jan 2015 21:16:34 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-11445?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Jason Lowe updated HADOOP-11445:
            Priority: Critical  (was: Major)
    Target Version/s: 2.7.0
            Assignee: Ankit Kamboj
        Hadoop Flags: Reviewed

Nice catch, Ankit!  Increasing the severity of this bug since it involves silent data loss.

+1 the changes look good to me, and the findbug warnings are unrelated.  I agree that BZip2Codec
should not be scanning for the next block if the current block starts at the split.  Ran the
unit tests without the change and they fail, as expected.

Committing this.

> Bzip2Codec: Data block is skipped when position of newly created stream is equal to start
of split
> --------------------------------------------------------------------------------------------------
>                 Key: HADOOP-11445
>                 URL: https://issues.apache.org/jira/browse/HADOOP-11445
>             Project: Hadoop Common
>          Issue Type: Bug
>    Affects Versions: 2.4.0
>            Reporter: Ankit Kamboj
>            Assignee: Ankit Kamboj
>            Priority: Critical
>         Attachments: HADOOP-11445.001.patch
> bz2 input files are handled by FileInputFormat+LineRecordReader. In LineRecordReader,
bz2 specific compressed input stream is created to iterate over records. After every new creation,
the stream points to the beginning of next data block. The logic to find the beginning of
next block depends on start of the split. The search begins at 10 bytes behind the start of
split. If the first search creates input stream whose position is before or at start of split,
next block beginning is sought (assuming that the record reader for previous split would have
already iterated over the the data block in which current start of split lies). If the split
start is just at the byte where a newly created stream is positioned (start of data block),
attempt is made to find beginning of next data block. This doesn't seem correct because this
will result in jumping a whole block and will result in missing records.

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