[ https://issues.apache.org/jira/browse/HADOOP-14919?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
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. -- This message was sent by Atlassian JIRA (v6.4.14#64029) --------------------------------------------------------------------- To unsubscribe, e-mail: common-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: common-issues-h...@hadoop.apache.org