VIVO-907 make the the check for isomorphism more efficient.

Read the file graph into memory and check against that.

webapp/src/edu/cornell/mannlib/vitro/webapp/triplesource/impl/tdb/TDBTripleStoreQuirks.java

@@ -47,7 +47,7 @@ public class TDBTripleStoreQuirks extends DefaultTripleStoreQuirks {
 			Model mangled = ModelFactory.createDefaultModel();
 			mangled.read(mangleStream, null, "N-TRIPLE");
 
-			return !mangled.isIsomorphicWith(previous);
+			return !isIsomorphic(previous, mangled);
 		} catch (Exception e) {
 			log.warn("Failed to test for changes in filegraph. "
 					+ "Change assumed.", e);
@@ -55,4 +55,17 @@ public class TDBTripleStoreQuirks extends DefaultTripleStoreQuirks {
 		}
 	}
 
+	/**
+	 * If we check isomorphism with a dbModel directly, we issue many ASK
+	 * queries against the underlying RDFService.
+	 * 
+	 * It's faster to read the entire model from the RDFService and then issue
+	 * all of those ASKs against a memory-resident model.
+	 */
+	private boolean isIsomorphic(Model previous, Model mangled) {
+		Model previousInMemory = ModelFactory.createDefaultModel()
+				.add(previous);
+		return mangled.isIsomorphicWith(previousInMemory);
+	}
+
 }