Blazegraph's query optimizer orders operations in a way that leads to a timeout in some cases where disabling the optimizer returns a result within seconds.
The query below currently works, though it had the problem before:
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX wikibase: <http://wikiba.se/ontology#>
SELECT DISTINCT ?result WHERE {
{
{ ?subject0 rdfs:label "United States"@en . } UNION { ?subject0 skos:altLabel "United States"@en . }
}
{
{ ?predicate1 rdfs:label "president"@en . } UNION { ?predicate1 skos:altLabel "president"@en . }
}
?predicate1 a wikibase:Property .
?predicate1 wikibase:directClaim ?directPredicate2 .
?subject0 ?directPredicate2 ?result .
}This url helped us identify what problem caused the timeout. Blazegraph explain feature
The query works with optimizer disabled:
PREFIX hint: <http://www.bigdata.com/queryHints#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX wikibase: <http://wikiba.se/ontology#>
SELECT DISTINCT ?result WHERE {
hint:Query hint:optimizer "None" .
{
{ ?subject0 rdfs:label "United States"@en . } UNION { ?subject0 skos:altLabel "United States"@en . }
}
{
{ ?predicate1 rdfs:label "president"@en . } UNION { ?predicate1 skos:altLabel "president"@en . }
}
?predicate1 a wikibase:Property .
?predicate1 wikibase:directClaim ?directPredicate2 .
?subject0 ?directPredicate2 ?result .
}