[PIG-1065] In-determinate behaviour of Union when there are 2 non-matching schema's

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.6.0
• Fix Version/s: 0.9.0
• Assignee: Alan Gates
• Reporter: Viraj Bhat
• Created: 30/Oct/09 03:05
• Updated: 04/Aug/11 00:34
• Resolved: 24/Dec/10 01:33

Description

I have a script which first does a union of these schemas and then does a ORDER BY of this result.

f1 = LOAD '1.txt' as (key:chararray, v:chararray);
f2 = LOAD '2.txt' as (key:chararray);
u0 = UNION f1, f2;
describe u0;
dump u0;

u1 = ORDER u0 BY $0;
dump u1;

When I run in Map Reduce mode I get the following result:
$java -cp pig.jar:$HADOOP_HOME/conf org.apache.pig.Main broken.pig
====================
Schema for u0 unknown.
====================
(1,2)
(2,3)
(1)
(2)
====================
org.apache.pig.impl.logicalLayer.FrontendException: ERROR 1066: Unable to open iterator for alias u1
at org.apache.pig.PigServer.openIterator(PigServer.java:475)
at org.apache.pig.tools.grunt.GruntParser.processDump(GruntParser.java:532)
at org.apache.pig.tools.pigscript.parser.PigScriptParser.parse(PigScriptParser.java:190)
at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:166)
at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:142)
at org.apache.pig.tools.grunt.Grunt.exec(Grunt.java:89)
at org.apache.pig.Main.main(Main.java:397)
====================
Caused by: java.io.IOException: Type mismatch in key from map: expected org.apache.pig.impl.io.NullableBytesWritable, recieved org.apache.pig.impl.io.NullableText
at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:415)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapReduce$Map.collect(PigMapReduce.java:108)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapBase.runPipeline(PigMapBase.java:251)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapBase.map(PigMapBase.java:240)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapReduce$Map.map(PigMapReduce.java:93)
at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:47)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:227)
====================

When I run the same script in local mode I get a different result, as we know that local mode does not use any Hadoop Classes.
$java -cp pig.jar org.apache.pig.Main -x local broken.pig
====================
Schema for u0 unknown
====================
(1,2)
(1)
(2,3)
(2)
====================
(1,2)
(1)
(2,3)
(2)
====================

Here are some questions
1) Why do we allow union if the schemas do not match
2) Should we not print an error message/warning so that the user knows that this is not allowed or he can get unexpected results?

Viraj

Issue Links

• blocks: PIG-998 revisit frontend logic and pig-latin semantics
• duplicates: PIG-1277 Pig should give error message when cogroup on tuple keys of different inner type