[Wikidata-bugs] [Maniphest] [Created] T172113: ConcurrentModificationException on non-grouping query with aggregates in SELECT

[Lucas_Werkmeister_WMDE]

Lucas_Werkmeister_WMDE created this task. Lucas_Werkmeister_WMDE added projects: Wikidata, Wikidata-Query-Service. Herald added subscribers: PokestarFan, Aklapper. Herald added a project: Discovery.

TASK DESCRIPTION

The following query (link) results in an exception:

SELECT (COUNT(*) AS ?a) (COUNT(?x) AS ?b) (?b/?a AS ?r) {}

java.util.ConcurrentModificationException

	at java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:719)
	at java.util.LinkedHashMap$LinkedKeyIterator.next(LinkedHashMap.java:742)
	at com.bigdata.rdf.sparql.ast.StaticAnalysis.gatherVarsToMaterialize(StaticAnalysis.java:2058)
	at com.bigdata.rdf.sparql.ast.StaticAnalysis.gatherVarsToMaterialize(StaticAnalysis.java:2009)
	at com.bigdata.rdf.sparql.ast.eval.AST2BOpUtility.addAggregation(AST2BOpUtility.java:4679)
	at com.bigdata.rdf.sparql.ast.AST2BOpUtility.convertQueryBaseWithScopedVars(AST2BOpUtility.java:534)
	at com.bigdata.rdf.sparql.ast.eval.AST2BOpUtility.convert(AST2BOpUtility.java:287)
	at com.bigdata.rdf.sparql.ast.eval.ASTEvalHelper.optimizeQuery(ASTEvalHelper.java:426)
	…

I think the query is legal, according to SPARQL, because GROUP BY is not a requirement for using aggregates (“By default a solution set consists of a single group, containing all solutions.”). If you remove the last projection (?b/?a AS ?r), it works.

Here’s the non-reduced query where I found the error: ratio of mandatory constraints

SELECT (COUNT(*) AS ?total) (COUNT(?status) AS ?mandatory) (?mandatory/?total AS ?ratio) WHERE {
  ?property p:P2302 ?statement.
  OPTIONAL { ?statement pq:P2316 ?status. }
}

TASK DETAIL

https://phabricator.wikimedia.org/T172113

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To: Lucas_Werkmeister_WMDE
Cc: Aklapper, Smalyshev, Lucas_Werkmeister_WMDE, PokestarFan, GoranSMilovanovic, QZanden, EBjune, merbst, Avner, debt, Gehel, Jonas, FloNight, Xmlizer, Izno, jkroll, Wikidata-bugs, Jdouglas, aude, Tobias1984, Manybubbles, Mbch331

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