How to analyze SPARQL execution plans using Jena 4.7.0

[chenkuncloud]

Hello,

How to analyze SPARQL execution plans using Jena 4.7.0, could you give me a complete code sample?

By the way, can Jena analyze the execution plan for SPARQL federated queries? For example:

SELECT * WHERE {
    SERVICE <https://dbpedia.org/sparql> {
        ?s ?p ?o .
        FILTER ( ?o = 'water'@en )
    }
}

[kinow]

Hi @chenkun19960427 have you seen this page in the docs already? https://jena.apache.org/documentation/query/explain.html

It contains some information about the ARQ query parse explain command, arq.qparse --explain 'SELECT * { ?s ?p ?o }'. See if that helps 👍

[chenkuncloud]

Hi, @kinow I got the analysis results through the tutorial, thank you!

Java code:

Model model = ModelFactory.createDefaultModel();
try (QueryExecution qExec = QueryExecution.create().model(model).query("SELECT * WHERE {\n" +
        "    SERVICE <https://dbpedia.org/sparql> {\n" +
        "        ?s ?p ?o .\n" +
        "        FILTER ( ?o = 'water'@en )\n" +
        "    }\n" +
        "}").set(ARQ.symLogExec, Explain.InfoLevel.ALL).build()) {
    ResultSet rs = qExec.execSelect();
}

Output:

[main] INFO org.apache.jena.arq.exec - QUERY
  SELECT  *
  WHERE
    { SERVICE <https://dbpedia.org/sparql>
        { ?s  ?p  ?o
          FILTER ( ?o = "water"@en )
        }
    }
[main] INFO org.apache.jena.arq.exec - ALGEBRA
  (service <https://dbpedia.org/sparql>
    (filter (= ?o "water"@en)
      (bgp (triple ?s ?p ?o))))

[rvesse]

By the way, can Jena analyze the execution plan for SPARQL federated queries?

No

If you analyse the query as a whole you'll see Jena has a service operator for evaluating the SERVICE portion of the query. Everything within that operator is passed to the remote endpoint mostly as-is (possibly with some value substitution to restrict the remote query where appropriate) and how the remote endpoint chooses to evaluate its portion of the query is entirely beyond Jena's control

[chenkuncloud]

Hi, @rvesse does that mean Jena Explain only works on local TDB databases, not on any remote endpoints (Virtuoso, Fuseki)?

[chenkuncloud]

@kinow Sorry, by the way, Is there any information on how to interpret the EXPLAIN results?

[kinow]

Hmm, there's some info about the SSE (SPARQL Syntax Expressions) output here:

• https://jena.apache.org/documentation/notes/sse.html
• https://en.wikipedia.org/wiki/SPARQL_Syntax_Expressions

And you can find some presentations/videos/docs if you search for "bgp" "algebra" "sparql" "jena", for instance:

• http://events17.linuxfoundation.org/sites/events/files/slides/SPARQL%20Optimisation%20101%20Tutorial.pdf

Some commands may have been renamed or its syntaxes may have changed, but you should be able to follow it after reading Jena's docs and trying some basic queries.

[chenkuncloud]

Thank you. These are very useful!