GH-2998 improve performance of Changeset and reduce memory load of Li…

…nkedHashModel

core/model/src/main/java/org/eclipse/rdf4j/model/impl/LinkedHashModel.java

@@ -341,13 +341,13 @@ private static class ModelNode<V extends Value> implements Serializable {
 
 		private static final long serialVersionUID = -1205676084606998540L;
 
-		Set<ModelStatement> subjects = new LinkedHashSet<>();
+		Set<ModelStatement> subjects = new LinkedHashSet<>(1);
 
-		Set<ModelStatement> predicates = new LinkedHashSet<>();
+		Set<ModelStatement> predicates = new LinkedHashSet<>(1);
 
-		Set<ModelStatement> objects = new LinkedHashSet<>();
+		Set<ModelStatement> objects = new LinkedHashSet<>(1);
 
-		Set<ModelStatement> contexts = new LinkedHashSet<>();
+		Set<ModelStatement> contexts = new LinkedHashSet<>(1);
 
 		private final V value;
 

core/sail/base/src/main/java/org/eclipse/rdf4j/sail/base/Changeset.java

@@ -15,6 +15,7 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.ConcurrentModificationException;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.IdentityHashMap;
@@ -806,6 +807,25 @@ Iterable<Triple> getApprovedTriples(Resource subj, IRI pred, Value obj) {
 
 	void removeApproved(Statement next) {
 		assert !closed;
+
+		try {
+			Model localApproved = approved;
+			if (localApproved != null && !readWriteLock.writeLock.isWriteLocked() && !localApproved.contains(next)) {
+				boolean readLock = readWriteLock.readLock();
+				try {
+					if (approved != null && !approvedEmpty) {
+						if (!approved.contains(next)) {
+							return;
+						}
+					}
+				} finally {
+					readWriteLock.unlockReader(readLock);
+				}
+			}
+
+		} catch (ConcurrentModificationException ignored) {
+		}
+
 		long writeLock = readWriteLock.writeLock();
 		try {
 			if (approved != null) {