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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