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From "Alexandre Normand (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-5953) DBInputFormat forces overly aggressive transaction level of SERIALIZABLE
Date Tue, 01 Jul 2014 17:38:24 GMT
Alexandre Normand created MAPREDUCE-5953:
--------------------------------------------

             Summary: DBInputFormat forces overly aggressive transaction level of SERIALIZABLE

                 Key: MAPREDUCE-5953
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5953
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
    Affects Versions: 2.4.1
            Reporter: Alexandre Normand


We are using {{DBInputFormat}} in some of our mapreduce jobs and we found issues in production
where other applications writing to the database would cause the hadoop job to fail with a
deadlock. 

On inspection of the code, we found that the transaction isolation level is set to [SERIALIZABLE|http://docs.oracle.com/javase/6/docs/api/java/sql/Connection.html#TRANSACTION_SERIALIZABLE].
This seems like it's too aggressive for most hadoop use cases. At the very minimum, this seems
like a more relaxed mode should be allowed through configuration.  

Reference stack trace (or part of it, I don't have the full map task logs at hand anymore)
when this deadlock occurs:
{code}
java.io.IOException: Deadlock found when trying to get lock; try restarting transaction at
org.apache.hadoop.mapreduce.lib.db.DBRecordReader.nextKeyValue(DBRecordReader.java:235) at
org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.nextKeyValue(MapTask.java:483) at
org.apache.hadoop.mapreduce.task.MapContextImpl.nextKeyValue(MapContextImpl.java:76) at org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context.nextKeyValue(WrappedMapper.java:85)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:139) at opower.kiji.mapreduce.DelegateKijiMapper.doRun(DelegateKijiMapper.java:29)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at
java.lang.reflect.Method.invoke(Method.java:606) at 
{code}



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