Grokbase Groups Hive user June 2011
FAQ
Hmmm, I think this might be a bug which is only exposed when one of the mappers gets zero rows of input.

If you have a Hive build, can you try adding this before line 238 of GenericUDAFnGrams.java?

if (n == 0) {
return;
}

Just before this line:

if(myagg.n > 0 && n > 0 && myagg.n != n) {

If that fixes it, create a new JIRA issue so we can get a fix committed.

JVS
On Jun 20, 2011, at 8:06 AM, Matthew Rathbone wrote:

Hoping someone with more expertise could help on this:

I have no idea what's causing this to happen, but here is the exception:

java.lang.RuntimeException: org.apache.hadoop.hive.ql.metadata.HiveException: Hive Runtime Error while processing row (tag=0) {"key":{},"value":{"_col0":["0","0","0","0"]},"alias":0}
at org.apache.hadoop.hive.ql.exec.ExecReducer.reduce(ExecReducer.java:268)
at org.apache.hadoop.mapred.ReduceTask.runOldReducer(ReduceTask.java:467)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:415)
at org.apache.hadoop.mapred.Child.main(Child.java:170)
Caused by: org.apache.hadoop.hive.ql.metadata.HiveException: Hive Runtime Error while processing row (tag=0) {"key":{},"value":{"_col0":["0","0","0","0"]},"alias":0}
at org.apache.hadoop.hive.ql.exec.ExecReducer.reduce(ExecReducer.java:256)
... 3 more
Caused by: org.apache.hadoop.hive.ql.metadata.HiveException: GenericUDAFnGramEvaluator: mismatch in value for 'n', which usually is caused by a non-constant expression. Found '0' and '1'.
at org.apache.hadoop.hive.ql.udf.generic.GenericUDAFnGrams$GenericUDAFnGramEvaluator.merge(GenericUDAFnGrams.java:239)
at org.apache.hadoop.hive.ql.udf.generic.GenericUDAFEvaluator.aggregate(GenericUDAFEvaluator.java:142)
at org.apache.hadoop.hive.ql.exec.GroupByOperator.updateAggregations(GroupByOperator.java:592)
at org.apache.hadoop.hive.ql.exec.GroupByOperator.processAggr(GroupByOperator.java:816)
at org.apache.hadoop.hive.ql.exec.GroupByOperator.processOp(GroupByOperator.java:716)
at org.apache.hadoop.hive.ql.exec.Operator.process(Operator.java:470)
at org.apache.hadoop.hive.ql.exec.ExecReducer.reduce(ExecReducer.java:247)


What does 'mismatch in value for n' mean?
My query is super simple:
select ngrams(sentences(text), 1, 50) from messages


--
Matthew Rathbone
Foursquare | Software Engineer | Server Engineering Team
matthew@foursquare.com | @rathboma | 4sq

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postedJun 20, '11 at 3:07p
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