Create only one snapshot for persist

src/neo/IO/Caching/DataCache.cs

@@ -314,6 +314,12 @@ public TValue TryGet(TKey key)
             }
         }
 
+        public void AddAndCommit(TKey key, TValue value)
+        {
+            Add(key, value);
+            Commit();
+        }
+
         protected abstract TValue TryGetInternal(TKey key);
 
         protected abstract void UpdateInternal(TKey key, TValue value);

src/neo/Ledger/Blockchain.cs

@@ -488,6 +488,8 @@ private void Persist(Block block)
                     }
                 }
                 snapshot.Blocks.Add(block.Hash, block.Trim());
+                StoreView clonedSnapshot = snapshot.Clone();
+                // Warning: Do not write into variable snapshot directly. Write into variable clonedSnapshot and commit instead.
                 foreach (Transaction tx in block.Transactions)
                 {
                     var state = new TransactionState
@@ -496,15 +498,19 @@ private void Persist(Block block)
                         Transaction = tx
                     };
 
-                    snapshot.Transactions.Add(tx.Hash, state);
+                    clonedSnapshot.Transactions.AddAndCommit(tx.Hash, state);
 
-                    using (ApplicationEngine engine = new ApplicationEngine(TriggerType.Application, tx, snapshot.Clone(), tx.SystemFee))
+                    using (ApplicationEngine engine = new ApplicationEngine(TriggerType.Application, tx, clonedSnapshot, tx.SystemFee))
                     {
                         engine.LoadScript(tx.Script);
                         state.VMState = engine.Execute();
                         if (state.VMState == VMState.HALT)
                         {
-                            engine.Snapshot.Commit();
+                            clonedSnapshot.Commit();
+                        }
+                        else
+                        {
+                            clonedSnapshot = snapshot.Clone();
                         }
                         ApplicationExecuted application_executed = new ApplicationExecuted(engine);
                         Context.System.EventStream.Publish(application_executed);

tests/neo.UnitTests/IO/Caching/UT_DataCache.cs

@@ -343,5 +343,12 @@ public void TestTryGet()
             myDataCache.TryGet(new MyKey("key2")).Should().Be(new MyValue("value2"));
             myDataCache.TryGet(new MyKey("key3")).Should().BeNull();
         }
+
+        [TestMethod]
+        public void TestAddAndCommit()
+        {
+            myDataCache.AddAndCommit(new MyKey("key1"), new MyValue("value1"));
+            myDataCache.InnerDict[new MyKey("key1")].Should().Be(new MyValue("value1"));
+        }
     }
 }