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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