mpt: don't flush nodes already present in the DB

It's just a waste of time.

pkg/core/mpt/base.go

@@ -14,6 +14,8 @@ type BaseNode struct {
 	bytes      []byte
 	hashValid  bool
 	bytesValid bool
+
+	isFlushed bool
 }
 
 // BaseNodeIface abstracts away basic Node functions.
@@ -21,6 +23,8 @@ type BaseNodeIface interface {
 	Hash() util.Uint256
 	Type() NodeType
 	Bytes() []byte
+	IsFlushed() bool
+	SetFlushed()
 }
 
 // getHash returns a hash of this BaseNode.
@@ -60,6 +64,17 @@ func (b *BaseNode) updateBytes(n Node) {
 func (b *BaseNode) invalidateCache() {
 	b.bytesValid = false
 	b.hashValid = false
+	b.isFlushed = false
+}
+
+// IsFlushed checks for node flush status.
+func (b *BaseNode) IsFlushed() bool {
+	return b.isFlushed
+}
+
+// SetFlushed sets 'flushed' flag to true for this node.
+func (b *BaseNode) SetFlushed() {
+	b.isFlushed = true
 }
 
 // encodeNodeWithType encodes node together with it's type.

pkg/core/mpt/trie.go

@@ -318,6 +318,9 @@ func (t *Trie) Flush() {
 }
 
 func (t *Trie) flush(node Node) {
+	if node.IsFlushed() {
+		return
+	}
 	switch n := node.(type) {
 	case *BranchNode:
 		for i := range n.Children {
@@ -336,6 +339,7 @@ func (t *Trie) putToStore(n Node) {
 		panic("can't put hash node in trie")
 	}
 	_ = t.Store.Put(makeStorageKey(n.Hash().BytesBE()), n.Bytes()) // put in MemCached returns no errors
+	n.SetFlushed()
 }
 
 func (t *Trie) getFromStore(h util.Uint256) (Node, error) {