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https://issues.apache.org/jira/browse/HADOOP-14919?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jason Lowe reassigned HADOOP-14919:
-----------------------------------
Assignee: Jason Lowe
Affects Version/s: 2.8.0
2.7.3
3.0.0-alpha1
Priority: Critical (was: Major)
Upgrading the priority since this involves silent data loss.
> BZip2 drops records when reading data in splits
> -----------------------------------------------
>
> Key: HADOOP-14919
> URL: https://issues.apache.org/jira/browse/HADOOP-14919
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 2.8.0, 2.7.3, 3.0.0-alpha1
> Reporter: Aki Tanaka
> Assignee: Jason Lowe
> Priority: Critical
> Attachments: 250000.bz2, HADOOP-14919-test.patch
>
>
> BZip2 can drop records when reading data in splits. This problem was already
> discussed before in HADOOP-11445 and HADOOP-13270. But we still have a
> problem in corner case, causing lost data blocks.
>
> I attached a unit test for this issue. You can reproduce the problem if you
> run the unit test.
>
> First, this issue happens when position of newly created stream is equal to
> start of split. Hadoop has some test cases for this (blockEndingInCR.txt.bz2
> file for TestLineRecordReader#testBzip2SplitStartAtBlockMarker, etc).
> However, the issue I am reporting does not happen when we run these tests
> because this issue happens only when the start of split byte block includes
> both block marker and compressed data.
>
> BZip2 block marker - 0x314159265359
> (001100010100000101011001001001100101001101011001)
>
> blockEndingInCR.txt.bz2 (Start of Split - 136504):
> {code:java}
> $ xxd -l 6 -g 1 -b -seek 136498
> ./hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/target/test-classes/blockEndingInCR.txt.bz2
> 0021532: 00110001 01000001 01011001 00100110 01010011 01011001 1AY&SY
> {code}
>
> Test bz2 File (Start of Split - 203426)
> {code:java}
> $ xxd -l 7 -g 1 -b -seek 203419 250000.bz2
> 0031a9b: 11100110 00101000 00101011 00100100 11001010 01101011 .(+$.k
> 0031aa1: 00101111 /
> {code}
>
> Let's say a job splits this test bz2 file into two splits at the start of
> split (position 203426).
> The former split does not read records which start position 203426 because
> BZip2 says the position of these dropped records is 203427. The latter split
> does not read the records because BZip2CompressionInputStream read the block
> from position 320955.
> Due to this behavior, records between 203427 and 320955 are lost.
> Also, if we reverted the changes in HADOOP-13270, we will not see this issue.
> We will see HADOOP-13270 issue though.
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