diff --git a/cayley.go b/cayley.go
index 99294dc..2e7522c 100644
--- a/cayley.go
+++ b/cayley.go
@@ -219,6 +219,9 @@ func decompressAndLoad(qw graph.QuadWriter, cfg *config.Config, path, typ string
 	if path == "" {
 		path = cfg.DatabasePath
 	}
+	if path == "" {
+		return nil
+	}
 	u, err := url.Parse(path)
 	if err != nil || u.Scheme == "file" || u.Scheme == "" {
 		// Don't alter relative URL path or non-URL path parameter.
diff --git a/graph/iterator/hasa_iterator.go b/graph/iterator/hasa_iterator.go
index 99dec4f..b88f58b 100644
--- a/graph/iterator/hasa_iterator.go
+++ b/graph/iterator/hasa_iterator.go
@@ -202,8 +202,7 @@ func (it *HasA) Next() bool {
 		return graph.NextLogOut(it, 0, false)
 	}
 	tID := it.primaryIt.Result()
-	name := it.ts.Quad(tID).Get(it.dir)
-	val := it.ts.ValueOf(name)
+	val := it.ts.TripleDirection(tID, it.dir)
 	it.result = val
 	return graph.NextLogOut(it, val, true)
 }
diff --git a/graph/leveldb/iterator.go b/graph/leveldb/iterator.go
index d3c5ea5..bddc75d 100644
--- a/graph/leveldb/iterator.go
+++ b/graph/leveldb/iterator.go
@@ -45,7 +45,7 @@ type Iterator struct {
 
 func NewIterator(prefix string, d quad.Direction, value graph.Value, qs *TripleStore) graph.Iterator {
 	vb := value.(Token)
-	p := make([]byte, 0, 2+qs.hasher.Size())
+	p := make([]byte, 0, 2+qs.hasherSize)
 	p = append(p, []byte(prefix)...)
 	p = append(p, []byte(vb[1:])...)
 
@@ -180,9 +180,9 @@ func PositionOf(prefix []byte, d quad.Direction, qs *TripleStore) int {
 		case quad.Subject:
 			return 2
 		case quad.Predicate:
-			return qs.hasher.Size() + 2
+			return qs.hasherSize + 2
 		case quad.Object:
-			return 2*qs.hasher.Size() + 2
+			return 2*qs.hasherSize + 2
 		case quad.Label:
 			return 3*qs.hasher.Size() + 2
 		}
@@ -190,11 +190,11 @@ func PositionOf(prefix []byte, d quad.Direction, qs *TripleStore) int {
 	if bytes.Equal(prefix, []byte("po")) {
 		switch d {
 		case quad.Subject:
-			return 2*qs.hasher.Size() + 2
+			return 2*qs.hasherSize + 2
 		case quad.Predicate:
 			return 2
 		case quad.Object:
-			return qs.hasher.Size() + 2
+			return qs.hasherSize + 2
 		case quad.Label:
 			return 3*qs.hasher.Size() + 2
 		}
@@ -202,9 +202,9 @@ func PositionOf(prefix []byte, d quad.Direction, qs *TripleStore) int {
 	if bytes.Equal(prefix, []byte("os")) {
 		switch d {
 		case quad.Subject:
-			return qs.hasher.Size() + 2
+			return qs.hasherSize + 2
 		case quad.Predicate:
-			return 2*qs.hasher.Size() + 2
+			return 2*qs.hasherSize + 2
 		case quad.Object:
 			return 2
 		case quad.Label:
@@ -214,11 +214,11 @@ func PositionOf(prefix []byte, d quad.Direction, qs *TripleStore) int {
 	if bytes.Equal(prefix, []byte("cp")) {
 		switch d {
 		case quad.Subject:
-			return 2*qs.hasher.Size() + 2
+			return 2*qs.hasherSize + 2
 		case quad.Predicate:
-			return qs.hasher.Size() + 2
+			return qs.hasherSize + 2
 		case quad.Object:
-			return 3*qs.hasher.Size() + 2
+			return 3*qs.hasherSize + 2
 		case quad.Label:
 			return 2
 		}
diff --git a/graph/leveldb/triplestore.go b/graph/leveldb/triplestore.go
index 9648d1c..06b57bd 100644
--- a/graph/leveldb/triplestore.go
+++ b/graph/leveldb/triplestore.go
@@ -50,15 +50,17 @@ func (t Token) Key() interface{} {
 }
 
 type TripleStore struct {
-	dbOpts    *opt.Options
-	db        *leveldb.DB
-	path      string
-	open      bool
-	size      int64
-	horizon   int64
-	hasher    hash.Hash
-	writeopts *opt.WriteOptions
-	readopts  *opt.ReadOptions
+	dbOpts     *opt.Options
+	db         *leveldb.DB
+	path       string
+	open       bool
+	size       int64
+	horizon    int64
+	hasher     hash.Hash
+	hasherSize int
+	makeHasher func() hash.Hash
+	writeopts  *opt.WriteOptions
+	readopts   *opt.ReadOptions
 }
 
 func createNewLevelDB(path string, _ graph.Options) error {
@@ -96,7 +98,8 @@ func newTripleStore(path string, options graph.Options) (graph.TripleStore, erro
 		write_buffer_mb = val
 	}
 	qs.dbOpts.WriteBuffer = write_buffer_mb * opt.MiB
-	qs.hasher = sha1.New()
+	qs.hasherSize = sha1.Size
+	qs.makeHasher = sha1.New
 	qs.writeopts = &opt.WriteOptions{
 		Sync: false,
 	}
@@ -141,20 +144,22 @@ func (qa *TripleStore) createDeltaKeyFor(d *graph.Delta) []byte {
 }
 
 func (qs *TripleStore) createKeyFor(d [4]quad.Direction, triple quad.Quad) []byte {
-	key := make([]byte, 0, 2+(qs.hasher.Size()*4))
+	hasher := qs.makeHasher()
+	key := make([]byte, 0, 2+(qs.hasherSize*3))
 	// TODO(kortschak) Remove dependence on String() method.
 	key = append(key, []byte{d[0].Prefix(), d[1].Prefix()}...)
-	key = append(key, qs.convertStringToByteHash(triple.Get(d[0]))...)
-	key = append(key, qs.convertStringToByteHash(triple.Get(d[1]))...)
-	key = append(key, qs.convertStringToByteHash(triple.Get(d[2]))...)
-	key = append(key, qs.convertStringToByteHash(triple.Get(d[3]))...)
+	key = append(key, qs.convertStringToByteHash(triple.Get(d[0]), hasher)...)
+	key = append(key, qs.convertStringToByteHash(triple.Get(d[1]), hasher)...)
+	key = append(key, qs.convertStringToByteHash(triple.Get(d[2]), hasher)...)
+	key = append(key, qs.convertStringToByteHash(triple.Get(d[3]), hasher)...)
 	return key
 }
 
 func (qs *TripleStore) createValueKeyFor(s string) []byte {
-	key := make([]byte, 0, 1+qs.hasher.Size())
+	hasher := qs.makeHasher()
+	key := make([]byte, 0, 1+qs.hasherSize)
 	key = append(key, []byte("z")...)
-	key = append(key, qs.convertStringToByteHash(s)...)
+	key = append(key, qs.convertStringToByteHash(s, hasher)...)
 	return key
 }
 
@@ -341,11 +346,11 @@ func (qs *TripleStore) Quad(k graph.Value) quad.Quad {
 	return triple
 }
 
-func (qs *TripleStore) convertStringToByteHash(s string) []byte {
-	qs.hasher.Reset()
-	key := make([]byte, 0, qs.hasher.Size())
-	qs.hasher.Write([]byte(s))
-	key = qs.hasher.Sum(key)
+func (qs *TripleStore) convertStringToByteHash(s string, hasher hash.Hash) []byte {
+	hasher.Reset()
+	key := make([]byte, 0, qs.hasherSize)
+	hasher.Write([]byte(s))
+	key = hasher.Sum(key)
 	return key
 }
 
@@ -462,7 +467,7 @@ func (qs *TripleStore) TripleDirection(val graph.Value, d quad.Direction) graph.
 	v := val.(Token)
 	offset := PositionOf(v[0:2], d, qs)
 	if offset != -1 {
-		return Token(append([]byte("z"), v[offset:offset+qs.hasher.Size()]...))
+		return Token(append([]byte("z"), v[offset:offset+qs.hasherSize]...))
 	} else {
 		return Token(qs.Quad(val).Get(d))
 	}
diff --git a/graph/mongo/iterator.go b/graph/mongo/iterator.go
index 1495eca..ed65e3a 100644
--- a/graph/mongo/iterator.go
+++ b/graph/mongo/iterator.go
@@ -187,13 +187,13 @@ func (it *Iterator) Contains(v graph.Value) bool {
 	case quad.Subject:
 		offset = 0
 	case quad.Predicate:
-		offset = (it.qs.hasher.Size() * 2)
+		offset = (it.qs.hasherSize * 2)
 	case quad.Object:
-		offset = (it.qs.hasher.Size() * 2) * 2
+		offset = (it.qs.hasherSize * 2) * 2
 	case quad.Label:
-		offset = (it.qs.hasher.Size() * 2) * 3
+		offset = (it.qs.hasherSize * 2) * 3
 	}
-	val := v.(string)[offset : it.qs.hasher.Size()*2+offset]
+	val := v.(string)[offset : it.qs.hasherSize*2+offset]
 	if val == it.hash {
 		it.result = v
 		return graph.ContainsLogOut(it, v, true)
diff --git a/graph/mongo/triplestore.go b/graph/mongo/triplestore.go
index 7165900..7e54aee 100644
--- a/graph/mongo/triplestore.go
+++ b/graph/mongo/triplestore.go
@@ -35,10 +35,11 @@ func init() {
 const DefaultDBName = "cayley"
 
 type TripleStore struct {
-	session *mgo.Session
-	db      *mgo.Database
-	hasher  hash.Hash
-	idCache *IDLru
+	session    *mgo.Session
+	db         *mgo.Database
+	hasherSize int
+	makeHasher func() hash.Hash
+	idCache    *IDLru
 }
 
 func createNewMongoGraph(addr string, options graph.Options) error {
@@ -90,24 +91,26 @@ func newTripleStore(addr string, options graph.Options) (graph.TripleStore, erro
 	}
 	qs.db = conn.DB(dbName)
 	qs.session = conn
-	qs.hasher = sha1.New()
+	qs.hasherSize = sha1.Size
+	qs.makeHasher = sha1.New
 	qs.idCache = NewIDLru(1 << 16)
 	return &qs, nil
 }
 
 func (qs *TripleStore) getIdForTriple(t quad.Quad) string {
-	id := qs.ConvertStringToByteHash(t.Subject)
-	id += qs.ConvertStringToByteHash(t.Predicate)
-	id += qs.ConvertStringToByteHash(t.Object)
-	id += qs.ConvertStringToByteHash(t.Label)
+	hasher := qs.makeHasher()
+	id := qs.convertStringToByteHash(t.Subject, hasher)
+	id += qs.convertStringToByteHash(t.Predicate, hasher)
+	id += qs.convertStringToByteHash(t.Object, hasher)
+	id += qs.convertStringToByteHash(t.Label, hasher)
 	return id
 }
 
-func (qs *TripleStore) ConvertStringToByteHash(s string) string {
-	qs.hasher.Reset()
-	key := make([]byte, 0, qs.hasher.Size())
-	qs.hasher.Write([]byte(s))
-	key = qs.hasher.Sum(key)
+func (qs *TripleStore) convertStringToByteHash(s string, hasher hash.Hash) string {
+	hasher.Reset()
+	key := make([]byte, 0, qs.hasherSize)
+	hasher.Write([]byte(s))
+	key = hasher.Sum(key)
 	return hex.EncodeToString(key)
 }
 
@@ -290,7 +293,8 @@ func (qs *TripleStore) TriplesAllIterator() graph.Iterator {
 }
 
 func (qs *TripleStore) ValueOf(s string) graph.Value {
-	return qs.ConvertStringToByteHash(s)
+	h := qs.makeHasher()
+	return qs.convertStringToByteHash(s, h)
 }
 
 func (qs *TripleStore) NameOf(v graph.Value) string {
@@ -348,13 +352,13 @@ func (qs *TripleStore) TripleDirection(in graph.Value, d quad.Direction) graph.V
 	case quad.Subject:
 		offset = 0
 	case quad.Predicate:
-		offset = (qs.hasher.Size() * 2)
+		offset = (qs.hasherSize * 2)
 	case quad.Object:
-		offset = (qs.hasher.Size() * 2) * 2
+		offset = (qs.hasherSize * 2) * 2
 	case quad.Label:
-		offset = (qs.hasher.Size() * 2) * 3
+		offset = (qs.hasherSize * 2) * 3
 	}
-	val := in.(string)[offset : qs.hasher.Size()*2+offset]
+	val := in.(string)[offset : qs.hasherSize*2+offset]
 	return val
 }