protected long getUpperSampleLimit(SPARQLEndpoint endpoint, Triple triplePattern)
throws SADIException, IOException {
String uri = endpoint.getURI();
log.trace("determining number of triples matching " + triplePattern + " in " + uri);
ServiceStatus status = ServiceStatus.OK;
if (getRegistry() != null) {
status = getRegistry().getServiceStatus(endpoint.getURI());
}
// check for a cached value first
if (upperSampleLimitCache.contains(endpoint, triplePattern)) {
log.trace("using previously cached value for upper sample limit");
return upperSampleLimitCache.get(endpoint, triplePattern);
}
ElementGroup whereClause = getWhereClauseWithBlankNodeFilter(triplePattern);
/*
Node s = triplePattern.getSubject();
Node o = triplePattern.getObject();
// Build a Jena representation of the WHERE clause
ElementGroup whereClause = new ElementGroup();
whereClause.addTriplePattern(triplePattern);
if(s.isVariable()) {
whereClause.addElementFilter(new ElementFilter(new E_LogicalNot(new E_IsBlank(new ExprVar(s)))));
}
if(o.isVariable()) {
whereClause.addElementFilter(new ElementFilter(new E_LogicalNot(new E_IsBlank(new ExprVar(o)))));
}
*/
if (status != ServiceStatus.SLOW) {
try {
// issue a SELECT COUNT(*) query
Query countStarQuery = new Query();
countStarQuery.setQuerySelectType();
countStarQuery.setQueryPattern(whereClause);
countStarQuery.addResultVar(countStarQuery.allocAggregate(AggCount.get()));
List<Map<String, String>> results = endpoint.selectQuery(countStarQuery.serialize());
Map<String, String> firstRow = results.iterator().next();
String firstColumn = firstRow.keySet().iterator().next();
long limit = Long.parseLong(firstRow.get(firstColumn));
upperSampleLimitCache.put(endpoint, triplePattern, limit);
log.trace(String.format("successful upper limit query: %s", countStarQuery.serialize()));
log.trace(String.format("upper limit: %d", limit));
return limit;
} catch (IOException e) {
log.warn(
"failed to COUNT number of triples matching "
+ triplePattern
+ " in "
+ uri
+ ", trying for a lower bound instead.");
}
}
Query selectStarQuery = new Query();
selectStarQuery.setQuerySelectType();
selectStarQuery.setQueryPattern(whereClause);
selectStarQuery.setQueryResultStar(true);
long limit = endpoint.getResultsCountLowerBound(selectStarQuery.serialize(), 50000);
upperSampleLimitCache.put(endpoint, triplePattern, limit);
log.trace(String.format("successful upper limit query: %s", selectStarQuery.serialize()));
log.trace(String.format("upper limit: %d", limit));
return limit;
}
