GH-5231: fix poor query performance for hasStatements() in FedX (#5232)

tools/federation/src/main/java/org/eclipse/rdf4j/federated/FedXConnection.java

@@ -337,6 +337,27 @@ protected SailException convert(RuntimeException e) {
 		}
 	}
 
+	@Override
+	protected boolean hasStatementInternal(Resource subj, IRI pred, Value obj, boolean includeInferred,
+			Resource[] contexts) {
+		try {
+			Dataset dataset = new SimpleDataset();
+			FederationEvalStrategy strategy = federationContext.createStrategy(dataset);
+			QueryInfo queryInfo = new QueryInfo(subj, pred, obj, 0, includeInferred, federationContext, strategy,
+					dataset);
+			federationContext.getMonitoringService().monitorQuery(queryInfo);
+			return strategy.hasStatements(queryInfo, subj, pred, obj, contexts);
+
+		} catch (RuntimeException e) {
+			throw e;
+		} catch (Exception e) {
+			if (e instanceof InterruptedException) {
+				Thread.currentThread().interrupt();
+			}
+			throw new SailException(e);
+		}
+	}
+
 	@Override
 	protected void addStatementInternal(Resource subj, IRI pred, Value obj, Resource... contexts) throws SailException {
 		try {

tools/federation/src/main/java/org/eclipse/rdf4j/federated/evaluation/FederationEvalStrategy.java

@@ -17,6 +17,7 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.stream.Collectors;
 
+import org.eclipse.rdf4j.common.annotation.Experimental;
 import org.eclipse.rdf4j.common.iteration.CloseableIteration;
 import org.eclipse.rdf4j.common.iteration.EmptyIteration;
 import org.eclipse.rdf4j.common.iteration.SingletonIteration;
@@ -574,7 +575,7 @@ public CloseableIteration<Statement> getStatements(QueryInfo queryInfo, Resource
 			IRI pred, Value obj, Resource... contexts)
 			throws RepositoryException, MalformedQueryException, QueryEvaluationException {
 
-		List<Endpoint> members = federationContext.getFederation().getMembers();
+		List<Endpoint> members = getAccessibleFederationMembers(queryInfo);
 
 		// a bound query: if at least one fed member provides results
 		// return the statement, otherwise empty result
@@ -617,6 +618,53 @@ public CloseableIteration<Statement> getStatements(QueryInfo queryInfo, Resource
 		return union;
 	}
 
+	/**
+	 * Returns true if the federation has statements
+	 *
+	 * @param queryInfo information about the query
+	 * @param subj      the subject or <code>null</code>
+	 * @param pred      the predicate or <code>null</code>
+	 * @param obj       the object or <code>null</code>
+	 * @param contexts  optional list of contexts
+	 * @return the statement iteration
+	 *
+	 * @throws RepositoryException
+	 * @throws MalformedQueryException
+	 * @throws QueryEvaluationException
+	 */
+	public boolean hasStatements(QueryInfo queryInfo, Resource subj,
+			IRI pred, Value obj, Resource... contexts)
+			throws RepositoryException, MalformedQueryException, QueryEvaluationException {
+
+		List<Endpoint> members = getAccessibleFederationMembers(queryInfo);
+
+		// form the union of results from relevant endpoints
+		List<StatementSource> sources = CacheUtils.checkCacheForStatementSourcesUpdateCache(cache, members, subj, pred,
+				obj, queryInfo, contexts);
+
+		if (sources.isEmpty()) {
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * Returns the accessible federation members in the context of the query. By default this is all federation members.
+	 * <p>
+	 * Specialized implementations of the {@link FederationEvalStrategy} may override and define custom behavior (e.g.,
+	 * to support resilience).
+	 * </p>
+	 *
+	 *
+	 * @param queryInfo
+	 * @return
+	 */
+	@Experimental
+	protected List<Endpoint> getAccessibleFederationMembers(QueryInfo queryInfo) {
+		return federationContext.getFederation().getMembers();
+	}
+
 	public CloseableIteration<BindingSet> evaluateService(FedXService service,
 			BindingSet bindings) throws QueryEvaluationException {
 

tools/federation/src/test/java/org/eclipse/rdf4j/federated/BasicTests.java

@@ -139,6 +139,61 @@ public void testBindClause() throws Exception {
 		execute("/tests/basic/query_bind.rq", "/tests/basic/query_bind.srx", false, true);
 	}
 
+	@Test
+	public void testRepositoryConnectionApi() throws Exception {
+
+		prepareTest(
+				Arrays.asList("/tests/basic/data_emptyStore.ttl", "/tests/basic/data_emptyStore.ttl"));
+
+		Repository repo1 = getRepository(1);
+		Repository repo2 = getRepository(2);
+
+		IRI bob = Values.iri("http://example.org/bob");
+		IRI alice = Values.iri("http://example.org/alice");
+		IRI graph1 = Values.iri("http://example.org/graph1");
+		IRI graph2 = Values.iri("http://example.org/graph2");
+
+		try (RepositoryConnection conn = repo1.getConnection()) {
+			conn.add(bob, RDF.TYPE, FOAF.PERSON, graph1);
+			conn.add(bob, FOAF.NAME, Values.literal("Bob"), graph1);
+		}
+
+		try (RepositoryConnection conn = repo2.getConnection()) {
+			conn.add(alice, RDF.TYPE, FOAF.PERSON, graph2);
+			conn.add(alice, FOAF.NAME, Values.literal("Alice"), graph2);
+		}
+
+		var fedxRepo = fedxRule.getRepository();
+
+		try (var conn = fedxRepo.getConnection()) {
+
+			// hasStatement which exist
+			Assertions.assertTrue(conn.hasStatement(bob, RDF.TYPE, FOAF.PERSON, false));
+			Assertions.assertTrue(conn.hasStatement(bob, RDF.TYPE, FOAF.PERSON, false, graph1));
+			Assertions.assertTrue(conn.hasStatement(null, RDF.TYPE, FOAF.PERSON, false));
+			Assertions.assertTrue(conn.hasStatement(null, RDF.TYPE, FOAF.PERSON, false, graph1));
+			Assertions.assertTrue(conn.hasStatement(null, RDF.TYPE, null, false));
+			Assertions.assertTrue(conn.hasStatement(null, RDF.TYPE, null, false, graph1));
+			Assertions.assertTrue(conn.hasStatement(null, RDF.TYPE, null, false, graph2));
+			Assertions.assertTrue(conn.hasStatement(null, null, null, false));
+			Assertions.assertTrue(conn.hasStatement(null, null, null, false, graph1));
+
+			// hasStatement which do not exist
+			Assertions.assertFalse(conn.hasStatement(bob, RDF.TYPE, FOAF.ORGANIZATION, false));
+			Assertions.assertFalse(conn.hasStatement(bob, RDF.TYPE, FOAF.PERSON, false, graph2));
+
+			// getStatements
+			Assertions.assertEquals(Set.of(bob, alice),
+					QueryResults.asModel(conn.getStatements(null, RDF.TYPE, FOAF.PERSON, false)).subjects());
+			Assertions.assertEquals(Set.of(bob),
+					QueryResults.asModel(conn.getStatements(null, RDF.TYPE, FOAF.PERSON, false, graph1)).subjects());
+			Assertions.assertEquals(Set.of(bob, alice),
+					QueryResults.asModel(conn.getStatements(null, null, null, false)).subjects());
+			Assertions.assertEquals(Set.of(bob),
+					QueryResults.asModel(conn.getStatements(null, null, null, false, graph1)).subjects());
+		}
+	}
+
 	@Test
 	public void testFederationSubSetQuery() throws Exception {
 		String ns1 = "http://namespace1.org/";