CODEWITHSUNDEEP
performancesparqljenaowl
2Application
2Application

Reputation: 165

Decreasing Performance of Jena function "ResultSetFactory.copyResults()"

I am querying my ontology using SPARQL, but I observe a decreasing performance the more queries I request, the worse it gets. At the beginning the PC needs about 150ms to process the query, the 30. query needs 670ms and the 100. query needs over 7 seconds! It is depending on the query and/or ontology, but until now, I could find it in every ontology.

The line "ResultSetRewindable r = ResultSetFactory.copyResults(results);" is responsible for the time leak, but also work arounds by avoiding the line lead to similar behaviour.

I used the pizza ontology (https://ontohub.org/pizza/pizza.owl) and the following code. Additionally, I used the Jena version 2.13.

Has anybody an idea how to fix it?

public static void main(String[] args) throws UnsupportedEncodingException, InterruptedException{
    OntModel model = ModelFactory.createOntologyModel();
    String OWLPath = "pizza.owl";
    String queryString = "PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX owl: <http://www.w3.org/2002/07/owl#> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> PREFIX pz: <http://www.co-ode.org/ontologies/pizza/pizza.owl#> SELECT DISTINCT ?x WHERE {     ?b owl:someValuesFrom pz:MozzarellaTopping. ?x rdfs:subClassOf ?b.      ?x rdfs:subClassOf* pz:Pizza.}";
    for(int j=0; j<100;j++){
    double starttime = System.currentTimeMillis();
                InputStream in = FileManager.get().open(OWLPath);
        if (in == null) {
            throw new IllegalArgumentException("File: " + OWLPath + " not found");
        }
        model.read(in, "");

        Query query = QueryFactory.create(queryString);
        QueryExecution qe = QueryExecutionFactory.create(query, model);
        ResultSet results = qe.execSelect();

        ByteArrayOutputStream baos = new ByteArrayOutputStream();   
        PrintStream ps = new PrintStream(baos);

        double time1 = System.currentTimeMillis();
        ResultSetRewindable r = ResultSetFactory.copyResults(results);
        double time2 = System.currentTimeMillis();  

        ResultSetFormatter.out(ps, r, query);
        String queryOutput = new String(baos.toByteArray(), "UTF-8");
        String[] resultText = queryOutput.split("\n");  
        for(int i=0; i<resultText.length;i++){
            System.out.println(resultText[i]);
        }
    double endtime = System.currentTimeMillis();
    System.out.println("Time: "+ (endtime-starttime) +"     Time for ResultSetFactory.copyResults(results): "+ (time2-time1));
    }
 }

Upvotes: 0

Views: 152

Answers (1)

2Application
2Application

Reputation: 165

It is a simple error. The problem is that the model is not cleaned up, every time the ontology is read, the model size increases. The model can cleaned up with:

model.removeAll();

or the line

model.read(in, "");

can be replaces by

Model model = ModelFactory.createDefaultModel().read(in, "");

It will work without any problem in version 2.13 and 3.3.0. Additionally, the required time decreased by the factor 5, so the performance is better and it runs stable. The second version is only slightly better than the first one.

Upvotes: 5

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