diff --git a/trie/trie_reader.go b/trie/trie_reader.go
index ff2db1d674..4b8ba808df 100644
--- a/trie/trie_reader.go
+++ b/trie/trie_reader.go
@@ -55,6 +55,9 @@ func newEmptyReader() *trieReader {
 // node retrieves the rlp-encoded trie node with the provided trie node
 // information. An MissingNodeError will be returned in case the node is
 // not found or any error is encountered.
+//
+// Don't modify the returned byte slice since it's not deep-copied and
+// still be referenced by database.
 func (r *trieReader) node(path []byte, hash common.Hash) ([]byte, error) {
 	// Perform the logics in tests for preventing trie node access.
 	if r.banned != nil {
diff --git a/triedb/pathdb/buffer.go b/triedb/pathdb/buffer.go
index bb591a594f..3f1d0e90ee 100644
--- a/triedb/pathdb/buffer.go
+++ b/triedb/pathdb/buffer.go
@@ -104,11 +104,6 @@ func (b *buffer) size() uint64 {
 	return b.nodes.size
 }
 
-// allocBatch returns a database batch with pre-allocated buffer.
-func (b *buffer) allocBatch(db ethdb.KeyValueStore) ethdb.Batch {
-	return db.NewBatchWithSize(b.nodes.dbsize() * 11 / 10) // extra 10% for potential pebble internal stuff
-}
-
 // flush persists the in-memory dirty trie node into the disk if the configured
 // memory threshold is reached. Note, all data must be written atomically.
 func (b *buffer) flush(db ethdb.KeyValueStore, freezer ethdb.AncientWriter, nodesCache *fastcache.Cache, id uint64) error {
@@ -120,7 +115,7 @@ func (b *buffer) flush(db ethdb.KeyValueStore, freezer ethdb.AncientWriter, node
 	// Terminate the state snapshot generation if it's active
 	var (
 		start = time.Now()
-		batch = b.allocBatch(db)
+		batch = db.NewBatchWithSize(b.nodes.dbsize() * 11 / 10) // extra 10% for potential pebble internal stuff
 	)
 	// Explicitly sync the state freezer, ensuring that all written
 	// data is transferred to disk before updating the key-value store.
diff --git a/triedb/pathdb/flush.go b/triedb/pathdb/flush.go
index 8728f47e56..baa0bfb292 100644
--- a/triedb/pathdb/flush.go
+++ b/triedb/pathdb/flush.go
@@ -24,7 +24,8 @@ import (
 	"github.com/ethereum/go-ethereum/trie/trienode"
 )
 
-// nodeCacheKey constructs the unique key of clean cache.
+// nodeCacheKey constructs the unique key of clean cache. The assumption is held
+// that zero address does not have any associated storage slots.
 func nodeCacheKey(owner common.Hash, path []byte) []byte {
 	if owner == (common.Hash{}) {
 		return path