[jira] [Created] (JENA-506) SPARQL "ORDER BY RAND()" may lead to a "Comparison method violates its general contract!" exception

["Pasquale Minervini (JIRA)" <ji...@apache.org>]

Pasquale Minervini created JENA-506:
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             Summary: SPARQL "ORDER BY RAND()" may lead to a "Comparison method violates its general contract!" exception 
                 Key: JENA-506
                 URL: https://issues.apache.org/jira/browse/JENA-506
             Project: Apache Jena
          Issue Type: Bug
          Components: ARQ
    Affects Versions: Jena 2.10.1
         Environment: OpenJDK 1.7.0_21 (64)
            Reporter: Pasquale Minervini
            Priority: Critical


It seems like the SPARQL "SELECT [..] ORDER BY RAND()" query construct can cause troubles when retrieving results; here's a complete stacktrace (Specifically, I've been querying the DBLP RDF dataset: http://sw.deri.org/~aharth/2004/07/dblp/). I think the construct can be quite useful for randomly sampling nodes from the RDF graph, that's the reason for the 'Critical'.

ARQ:        VERSION: 2.10.1
ARQ:        BUILD_DATE: 2013-05-11T22:05:51+0100
Exception in thread "main" java.lang.IllegalArgumentException: Comparison method violates its general contract!
        at java.util.TimSort.mergeLo(TimSort.java:747)
        at java.util.TimSort.mergeAt(TimSort.java:483)
        at java.util.TimSort.mergeCollapse(TimSort.java:408)
        at java.util.TimSort.sort(TimSort.java:214)
        at java.util.TimSort.sort(TimSort.java:173)
        at java.util.Arrays.sort(Arrays.java:659)
        at org.apache.jena.atlas.data.SortedDataBag.iterator(SortedDataBag.java:204)
        at org.apache.jena.atlas.data.SortedDataBag.iterator(SortedDataBag.java:189)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterSort$SortedBindingIterator.initializeIterator(QueryIterSort.java:99)
        at org.apache.jena.atlas.iterator.IteratorDelayedInitialization.init(IteratorDelayedInitialization.java:40)
        at org.apache.jena.atlas.iterator.IteratorDelayedInitialization.hasNext(IteratorDelayedInitialization.java:50)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterPlainWrapper.hasNextBinding(QueryIterPlainWrapper.java:54)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterSlice.hasNextBinding(QueryIterSlice.java:76)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:40)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:40)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.ResultSetStream.hasNext(ResultSetStream.java:75)

I can easily provide a snippet if you really need it.

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