add metrics for depth of state trie access

core/blockchain.go

@@ -112,6 +112,9 @@ var (
 	errChainStopped         = errors.New("blockchain is stopped")
 	errInvalidOldChain      = errors.New("invalid old chain")
 	errInvalidNewChain      = errors.New("invalid new chain")
+
+	avgAccessDepthInBlock = metrics.NewRegisteredGauge("trie/access/depth/avg", nil)
+	minAccessDepthInBlock = metrics.NewRegisteredGauge("trie/access/depth/min", nil)
 )
 
 var (
@@ -2083,6 +2086,7 @@ func (bc *BlockChain) processBlock(parentRoot common.Hash, block *types.Block, s
 			return nil, fmt.Errorf("stateless self-validation receipt root mismatch (cross: %x local: %x)", crossReceiptRoot, block.ReceiptHash())
 		}
 	}
+
 	xvtime := time.Since(xvstart)
 	proctime := time.Since(startTime) // processing + validation + cross validation
 
@@ -2118,6 +2122,24 @@ func (bc *BlockChain) processBlock(parentRoot common.Hash, block *types.Block, s
 	if err != nil {
 		return nil, err
 	}
+
+	// If witness was generated, update metrics regarding the access paths.
+	if witness != nil {
+		paths := witness.Paths
+		totaldepth, pathnum, mindepth := 0, 0, -1
+		if len(paths) > 0 {
+			for path, _ := range paths {
+				if len(path) < mindepth || mindepth < 0 {
+					mindepth = len(path)
+				}
+				totaldepth += len(path)
+				pathnum++
+			}
+			avgAccessDepthInBlock.Update(int64(totaldepth) / int64(pathnum))
+			minAccessDepthInBlock.Update(int64(mindepth))
+		}
+	}
+
 	// Update the metrics touched during block commit
 	accountCommitTimer.Update(statedb.AccountCommits)   // Account commits are complete, we can mark them
 	storageCommitTimer.Update(statedb.StorageCommits)   // Storage commits are complete, we can mark them

core/state/database.go

@@ -132,6 +132,10 @@ type Trie interface {
 	// The returned map could be nil if the witness is empty.
 	Witness() map[string]struct{}
 
+	// WitnessPaths returns a set of paths for all trie nodes. For future reference,
+	// witness can be deprecated and used as a replacement to witness.
+	WitnessPaths() map[string]struct{}
+
 	// NodeIterator returns an iterator that returns nodes of the trie. Iteration
 	// starts at the key after the given start key. And error will be returned
 	// if fails to create node iterator.

core/state/statedb.go

@@ -841,7 +841,7 @@ func (s *StateDB) IntermediateRoot(deleteEmptyObjects bool) common.Hash {
 				// If witness building is enabled and the state object has a trie,
 				// gather the witnesses for its specific storage trie
 				if s.witness != nil && obj.trie != nil {
-					s.witness.AddState(obj.trie.Witness())
+					s.witness.AddState(obj.trie.Witness(), obj.trie.WitnessPaths())
 				}
 			}
 			return nil
@@ -858,9 +858,9 @@ func (s *StateDB) IntermediateRoot(deleteEmptyObjects bool) common.Hash {
 				continue
 			}
 			if trie := obj.getPrefetchedTrie(); trie != nil {
-				s.witness.AddState(trie.Witness())
+				s.witness.AddState(trie.Witness(), trie.WitnessPaths())
 			} else if obj.trie != nil {
-				s.witness.AddState(obj.trie.Witness())
+				s.witness.AddState(obj.trie.Witness(), obj.trie.WitnessPaths())
 			}
 		}
 		// Pull in only-read and non-destructed trie witnesses
@@ -874,9 +874,9 @@ func (s *StateDB) IntermediateRoot(deleteEmptyObjects bool) common.Hash {
 				continue
 			}
 			if trie := obj.getPrefetchedTrie(); trie != nil {
-				s.witness.AddState(trie.Witness())
+				s.witness.AddState(trie.Witness(), trie.WitnessPaths())
 			} else if obj.trie != nil {
-				s.witness.AddState(obj.trie.Witness())
+				s.witness.AddState(obj.trie.Witness(), obj.trie.WitnessPaths())
 			}
 		}
 	}
@@ -942,7 +942,7 @@ func (s *StateDB) IntermediateRoot(deleteEmptyObjects bool) common.Hash {
 
 	// If witness building is enabled, gather the account trie witness
 	if s.witness != nil {
-		s.witness.AddState(s.trie.Witness())
+		s.witness.AddState(s.trie.Witness(), nil)
 	}
 	return hash
 }

core/stateless/database.go

@@ -63,5 +63,6 @@ func (w *Witness) MakeHashDB() ethdb.Database {
 
 		rawdb.WriteLegacyTrieNode(memdb, common.BytesToHash(hash), blob)
 	}
+
 	return memdb
 }

core/stateless/witness.go

@@ -41,6 +41,7 @@ type Witness struct {
 	Headers []*types.Header     // Past headers in reverse order (0=parent, 1=parent's-parent, etc). First *must* be set.
 	Codes   map[string]struct{} // Set of bytecodes ran or accessed
 	State   map[string]struct{} // Set of MPT state trie nodes (account and storage together)
+	Paths   map[string]struct{} // Set of MPT trie paths (i.e. all accessed nodes, not just the ones in state)
 
 	chain HeaderReader // Chain reader to convert block hash ops to header proofs
 	lock  sync.Mutex   // Lock to allow concurrent state insertions
@@ -58,13 +59,15 @@ func NewWitness(context *types.Header, chain HeaderReader) (*Witness, error) {
 		}
 		headers = append(headers, parent)
 	}
-	// Create the wtness with a reconstructed gutted out block
+	// Create the witness with a reconstructed gutted out block
 	return &Witness{
 		context: context,
 		Headers: headers,
 		Codes:   make(map[string]struct{}),
 		State:   make(map[string]struct{}),
-		chain:   chain,
+		Paths:   make(map[string]struct{}),
+
+		chain: chain,
 	}, nil
 }
 
@@ -88,7 +91,7 @@ func (w *Witness) AddCode(code []byte) {
 }
 
 // AddState inserts a batch of MPT trie nodes into the witness.
-func (w *Witness) AddState(nodes map[string]struct{}) {
+func (w *Witness) AddState(nodes map[string]struct{}, paths map[string]struct{}) {
 	if len(nodes) == 0 {
 		return
 	}
@@ -96,6 +99,9 @@ func (w *Witness) AddState(nodes map[string]struct{}) {
 	defer w.lock.Unlock()
 
 	maps.Copy(w.State, nodes)
+	if paths != nil {
+		maps.Copy(w.Paths, paths)
+	}
 }
 
 // Copy deep-copies the witness object.  Witness.Block isn't deep-copied as it
@@ -105,6 +111,7 @@ func (w *Witness) Copy() *Witness {
 		Headers: slices.Clone(w.Headers),
 		Codes:   maps.Clone(w.Codes),
 		State:   maps.Clone(w.State),
+		Paths:   maps.Clone(w.Paths),
 		chain:   w.chain,
 	}
 	if w.context != nil {

trie/secure_trie.go

@@ -277,6 +277,11 @@ func (t *StateTrie) Witness() map[string]struct{} {
 	return t.trie.Witness()
 }
 
+// Witness returns a set containing all trie nodes that have been accessed.
+func (t *StateTrie) WitnessPaths() map[string]struct{} {
+	return t.trie.WitnessPaths()
+}
+
 // Commit collects all dirty nodes in the trie and replaces them with the
 // corresponding node hash. All collected nodes (including dirty leaves if
 // collectLeaf is true) will be encapsulated into a nodeset for return.

trie/tracer.go

@@ -154,6 +154,10 @@ func (t *prevalueTracer) values() [][]byte {
 	return slices.Collect(maps.Values(t.data))
 }
 
+func (t *prevalueTracer) keys() []string {
+	return slices.Collect(maps.Keys(t.data))
+}
+
 // reset resets the cached content in the prevalueTracer.
 func (t *prevalueTracer) reset() {
 	t.lock.Lock()

trie/trie.go

@@ -762,11 +762,26 @@ func (t *Trie) Witness() map[string]struct{} {
 	if len(values) == 0 {
 		return nil
 	}
-	witness := make(map[string]struct{}, len(values))
+	witnessStates := make(map[string]struct{}, len(values))
 	for _, val := range values {
-		witness[string(val)] = struct{}{}
+		witnessStates[string(val)] = struct{}{}
 	}
-	return witness
+
+	return witnessStates
+}
+
+func (t *Trie) WitnessPaths() map[string]struct{} {
+	// Return the paths of all nodes that have been accessed.
+	// The paths are the keys of the prevalue tracer.
+	keys := t.prevalueTracer.keys()
+	if len(keys) == 0 {
+		return nil
+	}
+	witnessPaths := make(map[string]struct{}, len(keys))
+	for _, key := range keys {
+		witnessPaths[string(key)] = struct{}{}
+	}
+	return witnessPaths
 }
 
 // Reset drops the referenced root node and cleans all internal state.

trie/verkle.go

@@ -455,3 +455,8 @@ func (t *VerkleTrie) nodeResolver(path []byte) ([]byte, error) {
 func (t *VerkleTrie) Witness() map[string]struct{} {
 	panic("not implemented")
 }
+
+// Witness returns a set containing all trie nodes that have been accessed.
+func (t *VerkleTrie) WitnessPaths() map[string]struct{} {
+	panic("not implemented")
+}