diff --git a/db/common_test.go b/db/common_test.go
index 5afec28b3..7f9d10e9b 100644
--- a/db/common_test.go
+++ b/db/common_test.go
@@ -107,11 +107,11 @@ func (mdb *mockDB) SetNoLockSync([]byte, []byte) {
 	mdb.calls["SetNoLockSync"] += 1
 }
 
-func (mdb *mockDB) Delete([]byte, []byte) {
+func (mdb *mockDB) Delete([]byte) {
 	mdb.calls["Delete"] += 1
 }
 
-func (mdb *mockDB) DeleteSync([]byte, []byte) {
+func (mdb *mockDB) DeleteSync([]byte) {
 	mdb.calls["DeleteSync"] += 1
 }
 
@@ -144,7 +144,7 @@ func (mdb *mockDB) NewBatch() Batch {
 
 func (mdb *mockDB) Print() {
 	mdb.calls["Print"] += 1
-	fmt.Sprintf("mockDB{%v}", mdb.Stats())
+	fmt.Printf("mockDB{%v}", mdb.Stats())
 }
 
 func (mdb *mockDB) Stats() map[string]string {
diff --git a/db/db_test.go b/db/db_test.go
index 8884cea2d..3d6ac38c4 100644
--- a/db/db_test.go
+++ b/db/db_test.go
@@ -111,7 +111,8 @@ func TestDBIteratorNonemptyBeginAfter(t *testing.T) {
 
 func TestDBBatchWrite1(t *testing.T) {
 	mdb := newMockDB()
-	batch := mdb.NewBatch()
+	ddb := NewDebugDB(t.Name(), mdb)
+	batch := ddb.NewBatch()
 
 	batch.Set(bz("1"), bz("1"))
 	batch.Set(bz("2"), bz("2"))
@@ -131,7 +132,8 @@ func TestDBBatchWrite1(t *testing.T) {
 
 func TestDBBatchWrite2(t *testing.T) {
 	mdb := newMockDB()
-	batch := mdb.NewBatch()
+	ddb := NewDebugDB(t.Name(), mdb)
+	batch := ddb.NewBatch()
 
 	batch.Set(bz("1"), bz("1"))
 	batch.Set(bz("2"), bz("2"))
@@ -151,7 +153,8 @@ func TestDBBatchWrite2(t *testing.T) {
 
 func TestDBBatchWriteSync1(t *testing.T) {
 	mdb := newMockDB()
-	batch := mdb.NewBatch()
+	ddb := NewDebugDB(t.Name(), mdb)
+	batch := ddb.NewBatch()
 
 	batch.Set(bz("1"), bz("1"))
 	batch.Set(bz("2"), bz("2"))
@@ -171,7 +174,8 @@ func TestDBBatchWriteSync1(t *testing.T) {
 
 func TestDBBatchWriteSync2(t *testing.T) {
 	mdb := newMockDB()
-	batch := mdb.NewBatch()
+	ddb := NewDebugDB(t.Name(), mdb)
+	batch := ddb.NewBatch()
 
 	batch.Set(bz("1"), bz("1"))
 	batch.Set(bz("2"), bz("2"))
diff --git a/db/debug_db.go b/db/debug_db.go
new file mode 100644
index 000000000..7a15bc294
--- /dev/null
+++ b/db/debug_db.go
@@ -0,0 +1,216 @@
+package db
+
+import (
+	"fmt"
+	"sync"
+)
+
+//----------------------------------------
+// debugDB
+
+type debugDB struct {
+	label string
+	db    DB
+}
+
+// For printing all operationgs to the console for debugging.
+func NewDebugDB(label string, db DB) debugDB {
+	return debugDB{
+		label: label,
+		db:    db,
+	}
+}
+
+// Implements atomicSetDeleter.
+func (ddb debugDB) Mutex() *sync.Mutex { return nil }
+
+// Implements DB.
+func (ddb debugDB) Get(key []byte) (value []byte) {
+	defer fmt.Printf("%v.Get(%X) %X\n", ddb.label, key, value)
+	value = ddb.db.Get(key)
+	return
+}
+
+// Implements DB.
+func (ddb debugDB) Has(key []byte) (has bool) {
+	defer fmt.Printf("%v.Has(%X) %v\n", ddb.label, key, has)
+	return ddb.db.Has(key)
+}
+
+// Implements DB.
+func (ddb debugDB) Set(key []byte, value []byte) {
+	fmt.Printf("%v.Set(%X, %X)\n", ddb.label, key, value)
+	ddb.db.Set(key, value)
+}
+
+// Implements DB.
+func (ddb debugDB) SetSync(key []byte, value []byte) {
+	fmt.Printf("%v.SetSync(%X, %X)\n", ddb.label, key, value)
+	ddb.db.SetSync(key, value)
+}
+
+// Implements atomicSetDeleter.
+func (ddb debugDB) SetNoLock(key []byte, value []byte) {
+	fmt.Printf("%v.SetNoLock(%X, %X)\n", ddb.label, key, value)
+	ddb.db.Set(key, value)
+}
+
+// Implements atomicSetDeleter.
+func (ddb debugDB) SetNoLockSync(key []byte, value []byte) {
+	fmt.Printf("%v.SetNoLockSync(%X, %X)\n", ddb.label, key, value)
+	ddb.db.SetSync(key, value)
+}
+
+// Implements DB.
+func (ddb debugDB) Delete(key []byte) {
+	fmt.Printf("%v.Delete(%X)\n", ddb.label, key)
+	ddb.db.Delete(key)
+}
+
+// Implements DB.
+func (ddb debugDB) DeleteSync(key []byte) {
+	fmt.Printf("%v.DeleteSync(%X)\n", ddb.label, key)
+	ddb.db.DeleteSync(key)
+}
+
+// Implements atomicSetDeleter.
+func (ddb debugDB) DeleteNoLock(key []byte) {
+	fmt.Printf("%v.DeleteNoLock(%X)\n", ddb.label, key)
+	ddb.db.Delete(key)
+}
+
+// Implements atomicSetDeleter.
+func (ddb debugDB) DeleteNoLockSync(key []byte) {
+	fmt.Printf("%v.DeleteNoLockSync(%X)\n", ddb.label, key)
+	ddb.db.DeleteSync(key)
+}
+
+// Implements DB.
+func (ddb debugDB) Iterator(start, end []byte) Iterator {
+	fmt.Printf("%v.Iterator(%X, %X)\n", ddb.label, start, end)
+	return NewDebugIterator(ddb.label, ddb.db.Iterator(start, end))
+}
+
+// Implements DB.
+func (ddb debugDB) ReverseIterator(start, end []byte) Iterator {
+	fmt.Printf("%v.ReverseIterator(%X, %X)\n", ddb.label, start, end)
+	return NewDebugIterator(ddb.label, ddb.db.ReverseIterator(start, end))
+}
+
+// Implements DB.
+func (ddb debugDB) NewBatch() Batch {
+	fmt.Printf("%v.NewBatch()\n", ddb.label)
+	return NewDebugBatch(ddb.label, ddb.db.NewBatch())
+}
+
+// Implements DB.
+func (ddb debugDB) Close() {
+	fmt.Printf("%v.Close()\n", ddb.label)
+	ddb.db.Close()
+}
+
+// Implements DB.
+func (ddb debugDB) Print() {
+	ddb.db.Print()
+}
+
+// Implements DB.
+func (ddb debugDB) Stats() map[string]string {
+	return ddb.db.Stats()
+}
+
+//----------------------------------------
+// debugIterator
+
+type debugIterator struct {
+	label string
+	itr   Iterator
+}
+
+// For printing all operationgs to the console for debugging.
+func NewDebugIterator(label string, itr Iterator) debugIterator {
+	return debugIterator{
+		label: label,
+		itr:   itr,
+	}
+}
+
+// Implements Iterator.
+func (ditr debugIterator) Domain() (start []byte, end []byte) {
+	defer fmt.Printf("%v.itr.Domain() (%X,%X)\n", ditr.label, start, end)
+	start, end = ditr.itr.Domain()
+	return
+}
+
+// Implements Iterator.
+func (ditr debugIterator) Valid() (ok bool) {
+	defer fmt.Printf("%v.itr.Valid() %v\n", ditr.label, ok)
+	ok = ditr.itr.Valid()
+	return
+}
+
+// Implements Iterator.
+func (ditr debugIterator) Next() {
+	fmt.Printf("%v.itr.Next()\n", ditr.label)
+	ditr.itr.Next()
+}
+
+// Implements Iterator.
+func (ditr debugIterator) Key() (key []byte) {
+	fmt.Printf("%v.itr.Key() %X\n", ditr.label, key)
+	key = ditr.itr.Key()
+	return
+}
+
+// Implements Iterator.
+func (ditr debugIterator) Value() (value []byte) {
+	fmt.Printf("%v.itr.Value() %X\n", ditr.label, value)
+	value = ditr.itr.Value()
+	return
+}
+
+// Implements Iterator.
+func (ditr debugIterator) Close() {
+	fmt.Printf("%v.itr.Close()\n", ditr.label)
+	ditr.itr.Close()
+}
+
+//----------------------------------------
+// debugBatch
+
+type debugBatch struct {
+	label string
+	bch   Batch
+}
+
+// For printing all operationgs to the console for debugging.
+func NewDebugBatch(label string, bch Batch) debugBatch {
+	return debugBatch{
+		label: label,
+		bch:   bch,
+	}
+}
+
+// Implements Batch.
+func (dbch debugBatch) Set(key, value []byte) {
+	fmt.Printf("%v.batch.Set(%X, %X)\n", dbch.label, key, value)
+	dbch.bch.Set(key, value)
+}
+
+// Implements Batch.
+func (dbch debugBatch) Delete(key []byte) {
+	fmt.Printf("%v.batch.Delete(%X)\n", dbch.label, key)
+	dbch.bch.Delete(key)
+}
+
+// Implements Batch.
+func (dbch debugBatch) Write() {
+	fmt.Printf("%v.batch.Write()\n", dbch.label)
+	dbch.bch.Write()
+}
+
+// Implements Batch.
+func (dbch debugBatch) WriteSync() {
+	fmt.Printf("%v.batch.WriteSync()\n", dbch.label)
+	dbch.bch.WriteSync()
+}
diff --git a/db/mem_batch.go b/db/mem_batch.go
index 756798ded..81a63d62b 100644
--- a/db/mem_batch.go
+++ b/db/mem_batch.go
@@ -45,9 +45,10 @@ func (mBatch *memBatch) WriteSync() {
 }
 
 func (mBatch *memBatch) write(doSync bool) {
-	mtx := mBatch.db.Mutex()
-	mtx.Lock()
-	defer mtx.Unlock()
+	if mtx := mBatch.db.Mutex(); mtx != nil {
+		mtx.Lock()
+		defer mtx.Unlock()
+	}
 
 	for i, op := range mBatch.ops {
 		if doSync && i == (len(mBatch.ops)-1) {
diff --git a/db/prefix_db.go b/db/prefix_db.go
index 5947e7fce..4381ce070 100644
--- a/db/prefix_db.go
+++ b/db/prefix_db.go
@@ -123,10 +123,10 @@ func (pdb *prefixDB) Iterator(start, end []byte) Iterator {
 	pdb.mtx.Lock()
 	defer pdb.mtx.Unlock()
 
-	pstart := append([]byte(pdb.prefix), start...)
+	pstart := append(pdb.prefix, start...)
 	pend := []byte(nil)
 	if end != nil {
-		pend = append([]byte(pdb.prefix), end...)
+		pend = append(pdb.prefix, end...)
 	}
 	return newUnprefixIterator(
 		pdb.prefix,
@@ -144,11 +144,11 @@ func (pdb *prefixDB) ReverseIterator(start, end []byte) Iterator {
 
 	pstart := []byte(nil)
 	if start != nil {
-		pstart = append([]byte(pdb.prefix), start...)
+		pstart = append(pdb.prefix, start...)
 	}
 	pend := []byte(nil)
 	if end != nil {
-		pend = append([]byte(pdb.prefix), end...)
+		pend = append(pdb.prefix, end...)
 	}
 	return newUnprefixIterator(
 		pdb.prefix,
@@ -201,7 +201,7 @@ func (pdb *prefixDB) Stats() map[string]string {
 }
 
 func (pdb *prefixDB) prefixed(key []byte) []byte {
-	return append([]byte(pdb.prefix), key...)
+	return append(pdb.prefix, key...)
 }
 
 //----------------------------------------
diff --git a/merkle/simple_tree.go b/merkle/simple_tree.go
index a363ea8e8..9bdf52cb2 100644
--- a/merkle/simple_tree.go
+++ b/merkle/simple_tree.go
@@ -31,6 +31,9 @@ import (
 func SimpleHashFromTwoHashes(left []byte, right []byte) []byte {
 	var hasher = ripemd160.New()
 	err := encodeByteSlice(hasher, left)
+	if err != nil {
+		panic(err)
+	}
 	err = encodeByteSlice(hasher, right)
 	if err != nil {
 		panic(err)