diff --git a/db/db.go b/db/db.go
index aa8ff48a..8156c1e9 100644
--- a/db/db.go
+++ b/db/db.go
@@ -10,10 +10,11 @@ type DB interface {
 	DeleteSync([]byte)
 	Close()
 	NewBatch() Batch
+	Iterator() Iterator
+	IteratorPrefix([]byte) Iterator
 
 	// For debugging
 	Print()
-	Iterator() Iterator
 	Stats() map[string]string
 }
 
@@ -28,6 +29,9 @@ type Iterator interface {
 
 	Key() []byte
 	Value() []byte
+
+	Release()
+	Error() error
 }
 
 //-----------------------------------------------------------------------------
diff --git a/db/go_level_db.go b/db/go_level_db.go
index 54ae1149..f3ed79e3 100644
--- a/db/go_level_db.go
+++ b/db/go_level_db.go
@@ -6,7 +6,9 @@ import (
 
 	"github.com/syndtr/goleveldb/leveldb"
 	"github.com/syndtr/goleveldb/leveldb/errors"
+	"github.com/syndtr/goleveldb/leveldb/iterator"
 	"github.com/syndtr/goleveldb/leveldb/opt"
+	"github.com/syndtr/goleveldb/leveldb/util"
 
 	. "github.com/tendermint/tmlibs/common"
 )
@@ -115,8 +117,34 @@ func (db *GoLevelDB) Stats() map[string]string {
 	return stats
 }
 
+type goLevelDBIterator struct {
+	iterator.Iterator
+}
+
+// Key returns a copy of the current key.
+func (it *goLevelDBIterator) Key() []byte {
+	key := it.Key()
+	k := make([]byte, len(key))
+	copy(k, key)
+
+	return k
+}
+
+// Value returns a copy of the current value.
+func (it *goLevelDBIterator) Value() []byte {
+	val := it.Value()
+	v := make([]byte, len(val))
+	copy(v, val)
+
+	return v
+}
+
 func (db *GoLevelDB) Iterator() Iterator {
-	return db.db.NewIterator(nil, nil)
+	return &goLevelDBIterator{db.db.NewIterator(nil, nil)}
+}
+
+func (db *GoLevelDB) IteratorPrefix(prefix []byte) Iterator {
+	return &goLevelDBIterator{db.db.NewIterator(util.BytesPrefix(prefix), nil)}
 }
 
 func (db *GoLevelDB) NewBatch() Batch {
diff --git a/db/mem_db.go b/db/mem_db.go
index 58e74895..55d594fa 100644
--- a/db/mem_db.go
+++ b/db/mem_db.go
@@ -2,6 +2,7 @@ package db
 
 import (
 	"fmt"
+	"strings"
 	"sync"
 )
 
@@ -99,7 +100,21 @@ func (it *memDBIterator) Value() []byte {
 	return it.db.Get(it.Key())
 }
 
+func (it *memDBIterator) Release() {
+	it.db = nil
+	it.keys = nil
+	return
+}
+
+func (it *memDBIterator) Error() error {
+	return nil
+}
+
 func (db *MemDB) Iterator() Iterator {
+	return db.IteratorPrefix([]byte{})
+}
+
+func (db *MemDB) IteratorPrefix(prefix []byte) Iterator {
 	it := newMemDBIterator()
 	it.db = db
 	it.last = -1
@@ -109,7 +124,9 @@ func (db *MemDB) Iterator() Iterator {
 
 	// unfortunately we need a copy of all of the keys
 	for key, _ := range db.db {
-		it.keys = append(it.keys, key)
+		if strings.HasPrefix(key, string(prefix)) {
+			it.keys = append(it.keys, key)
+		}
 	}
 	return it
 }