Does Jena TDB load all data into memory every time? - sparql

Question

I am a newbie of Jena. I try to deal with the Yoga dataset using TDB. The dataset is about 200M and everytime I run the same query, it will have to take about 5 minutes to load the data then give out the results. I am wondering do I misunderstand any part of TDB? The following are my codes.
String directory = "tdb";
Dataset dataset = TDBFactory.createDataset(directory);
dataset.begin(ReadWrite.WRITE);
Model tdb = dataset.getDefaultModel();
//String source = "yagoMetaFacts.ttl";
//FileManager.get().readModel(tdb, source);
String queryString = "SELECT DISTINCT ?p WHERE { ?s ?p ?o. }";
Query query = QueryFactory.create(queryString);
try(QueryExecution qexec = QueryExecutionFactory.create(query, tdb)){
ResultSet results = qexec.execSelect();
ResultSetFormatter.out(System.out, results, query) ;
}
dataset.commit();
dataset.end();

Answer 1

There are two ways to load data into tdb, either by API or CMD. Much thanks to #ASKW and #AndyS
1 Load data via API
These codes need to be executed only once especially the readModel line which will takes long time.
String directory = "tdb";
Dataset dataset = TDBFactory.createDataset(directory);
dataset.begin(ReadWrite.WRITE);
Model tdb = dataset.getDefaultModel();
String source = "yagoMetaFacts.ttl";
FileManager.get().readModel(tdb, source);
dataset.commit(); //Important!! This is to commit the data to tdb.
dataset.end();
After the data is loaded into tdb, we can use following codes to query. And it is not necessary to load data again.
String directory = "path\\to\\tdb";
Dataset dataset = TDBFactory.createDataset(directory);
Model tdb = dataset.getDefaultModel();
String queryString = "SELECT DISTINCT ?p WHERE { ?s ?p ?o. }";
Query query = QueryFactory.create(queryString);
try(QueryExecution qexec = QueryExecutionFactory.create(query, tdb)){
ResultSet results = qexec.execSelect();
ResultSetFormatter.out(System.out, results, query) ;
}
2 Load data via CMD
To load data
>tdbloader --loc=path\to\tdb path\to\dataset.ttl
To query
>tdbquery --loc=path\to\tdb --query=q1.rq
q1.rq is the file which stores the query
Should get results like this
-------------------------------------------------------
| p |
=======================================================
| <http://yago-knowledge.org/resource/hasGloss> |
| <http://yago-knowledge.org/resource/occursSince> |
| <http://yago-knowledge.org/resource/occursUntil> |
| <http://yago-knowledge.org/resource/byTransport> |
| <http://yago-knowledge.org/resource/hasPredecessor> |
| <http://yago-knowledge.org/resource/hasSuccessor> |
| <http://www.w3.org/2000/01/rdf-schema#comment> |
-------------------------------------------------------