Support Asynchronous Writing Datastores

autobatch/autobatch.go

@@ -64,6 +64,35 @@ func (d *Datastore) Put(k ds.Key, val []byte) error {
 	return nil
 }
 
+// Sync flushes all operations on keys at or under the prefix
+// from the current batch to the underlying datastore
+func (d *Datastore) Sync(prefix ds.Key) error {
+	b, err := d.child.Batch()
+	if err != nil {
+		return err
+	}
+
+	for k, o := range d.buffer {
+		if !(k.Equal(prefix) || k.IsDescendantOf(prefix)) {
+			continue
+		}
+
+		var err error
+		if o.delete {
+			err = b.Delete(k)
+		} else {
+			err = b.Put(k, o.value)
+		}
+		if err != nil {
+			return err
+		}
+
+		delete(d.buffer, k)
+	}
+
+	return b.Commit()
+}
+
 // Flush flushes the current batch to the underlying datastore.
 func (d *Datastore) Flush() error {
 	b, err := d.child.Batch()

autobatch/autobatch_test.go

@@ -103,3 +103,149 @@ func TestFlushing(t *testing.T) {
 		t.Fatal("wrong value")
 	}
 }
+
+func TestSync(t *testing.T) {
+	child := ds.NewMapDatastore()
+	d := NewAutoBatching(child, 100)
+
+	put := func(key ds.Key) {
+		if err := d.Put(key, []byte(key.String())); err != nil {
+			t.Fatal(err)
+		}
+	}
+	del := func(key ds.Key) {
+		if err := d.Delete(key); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	get := func(d ds.Datastore, key ds.Key) {
+		val, err := d.Get(key)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !bytes.Equal(val, []byte(key.String())) {
+			t.Fatal("wrong value")
+		}
+	}
+	invalidGet := func(d ds.Datastore, key ds.Key) {
+		if _, err := d.Get(key); err != ds.ErrNotFound {
+			t.Fatal("should not have found value")
+		}
+	}
+
+	// Test if Syncing Puts works
+	internalSyncTest(t, d, child, put, del, get, invalidGet)
+
+	// Test if Syncing Deletes works
+	internalSyncTest(t, d, child, del, put, invalidGet, get)
+}
+
+// This function can be used to test Sync Puts and Deletes
+// For clarity comments are written as if op = Put and undoOp = Delete
+func internalSyncTest(t *testing.T, d, child ds.Datastore, op, undoOp func(ds.Key),
+	checkOp, checkUndoOp func(ds.Datastore, ds.Key)) {
+	var keys []ds.Key
+	keymap := make(map[ds.Key]int)
+	for i := 0; i < 4; i++ {
+		k := ds.NewKey(fmt.Sprintf("%d", i))
+		keymap[k] = len(keys)
+		keys = append(keys, k)
+		for j := 0; j < 2; j++ {
+			k := ds.NewKey(fmt.Sprintf("%d/%d", i, j))
+			keymap[k] = len(keys)
+			keys = append(keys, k)
+			for k := 0; k < 2; k++ {
+				k := ds.NewKey(fmt.Sprintf("%d/%d/%d", i, j, k))
+				keymap[k] = len(keys)
+				keys = append(keys, k)
+			}
+		}
+	}
+
+	for _, k := range keys {
+		op(k)
+	}
+
+	// Get works normally.
+	for _, k := range keys {
+		checkOp(d, k)
+	}
+
+	// Put not flushed
+	checkUndoOp(child, ds.NewKey("0"))
+
+	// Delete works.
+	deletedKey := ds.NewKey("2/1/1")
+	undoOp(deletedKey)
+	checkUndoOp(d, deletedKey)
+
+	// Put still not flushed
+	checkUndoOp(child, ds.NewKey("0"))
+
+	// Sync the tree "0/*/*"
+	if err := d.Sync(ds.NewKey("0")); err != nil {
+		t.Fatal(err)
+	}
+
+	// Try to get keys "0/*/*" from the child datastore
+	checkKeyRange(t, keymap, keys, d, [][]string{{"0", "0/1/1"}}, checkOp)
+
+	// Verify no other keys were synchronized
+	checkKeyRange(t, keymap, keys, child, [][]string{{"1", "3/1/1"}}, checkUndoOp)
+
+	// Sync the tree "1/1/*"
+	if err := d.Sync(ds.NewKey("1/1")); err != nil {
+		t.Fatal(err)
+	}
+
+	// Try to get keys "0/*/*" and "1/1/*" from the child datastore
+	checkKeyRange(t, keymap, keys, d, [][]string{{"0", "0/1/1"}, {"1/1", "1/1/1"}}, checkOp)
+
+	// Verify no other keys were synchronized
+	checkKeyRange(t, keymap, keys, child, [][]string{{"1", "1/0/1"}, {"2", "3/1/1"}}, checkUndoOp)
+
+	// Sync the tree "3/1/1"
+	if err := d.Sync(ds.NewKey("3/1/1")); err != nil {
+		t.Fatal(err)
+	}
+
+	// Try to get keys "0/*/*", "1/1/*", "3/1/1" from the child datastore
+	checkKeyRange(t, keymap, keys, d, [][]string{{"0", "0/1/1"}, {"1/1", "1/1/1"}, {"3/1/1", "3/1/1"}}, checkOp)
+
+	// Verify no other keys were synchronized
+	checkKeyRange(t, keymap, keys, child, [][]string{{"1", "1/0/1"}, {"2", "3/1/0"}}, checkUndoOp)
+
+	if err := d.Sync(ds.Key{}); err != nil {
+		t.Fatal(err)
+	}
+
+	// Never flushed the deleted key.
+	checkUndoOp(child, deletedKey)
+
+	// Try to get all keys except the deleted key from the child datastore
+	checkKeyRange(t, keymap, keys, d, [][]string{{"0", "2/1/0"}, {"3", "3/1/1"}}, checkOp)
+
+	// Add the deleted key into the datastore
+	op(deletedKey)
+
+	// Sync it
+	if err := d.Sync(deletedKey); err != nil {
+		t.Fatal(err)
+	}
+
+	// Check it
+	checkOp(d, deletedKey)
+}
+
+func checkKeyRange(t *testing.T, keymap map[ds.Key]int, keys []ds.Key,
+	d ds.Datastore, validKeyRanges [][]string, checkFn func(ds.Datastore, ds.Key)) {
+	t.Helper()
+	for _, validKeyBoundaries := range validKeyRanges {
+		start, end := keymap[ds.NewKey(validKeyBoundaries[0])], keymap[ds.NewKey(validKeyBoundaries[1])]
+		for _, k := range keys[start:end] {
+			checkFn(d, k)
+		}
+	}
+}

basic_ds.go

@@ -28,6 +28,11 @@ func (d *MapDatastore) Put(key Key, value []byte) (err error) {
 	return nil
 }
 
+// Sync implements Datastore.Sync
+func (d *MapDatastore) Sync(prefix Key) error {
+	return nil
+}
+
 // Get implements Datastore.Get
 func (d *MapDatastore) Get(key Key) (value []byte, err error) {
 	val, found := d.values[key]
@@ -95,6 +100,11 @@ func (d *NullDatastore) Put(key Key, value []byte) (err error) {
 	return nil
 }
 
+// Sync implements Datastore.Sync
+func (d *NullDatastore) Sync(prefix Key) error {
+	return nil
+}
+
 // Get implements Datastore.Get
 func (d *NullDatastore) Get(key Key) (value []byte, err error) {
 	return nil, ErrNotFound

datastore.go

@@ -34,6 +34,13 @@ should be checked by callers.
 type Datastore interface {
 	Read
 	Write
+	// Sync guarantees that any Put or Delete calls under prefix that returned
+	// before Sync(prefix) was called will be observed after Sync(prefix)
+	// returns, even if the program crashes. If Put/Delete operations already
+	// satisfy these requirements then Sync may be a no-op.
+	//
+	// If the prefix fails to Sync this method returns an error.
+	Sync(prefix Key) error
 	io.Closer
 }
 

delayed/delayed.go

@@ -30,6 +30,12 @@ func (dds *Delayed) Put(key ds.Key, value []byte) (err error) {
 	return dds.ds.Put(key, value)
 }
 
+// Sync implements Datastore.Sync
+func (dds *Delayed) Sync(prefix ds.Key) error {
+	dds.delay.Wait()
+	return dds.ds.Sync(prefix)
+}
+
 // Get implements the ds.Datastore interface.
 func (dds *Delayed) Get(key ds.Key) (value []byte, err error) {
 	dds.delay.Wait()

examples/fs.go

@@ -63,6 +63,12 @@ func (d *Datastore) Put(key ds.Key, value []byte) (err error) {
 	return ioutil.WriteFile(fn, value, 0666)
 }
 
+// Sync would ensure that any previous Puts under the prefix are written to disk.
+// However, they already are.
+func (d *Datastore) Sync(prefix ds.Key) error {
+	return nil
+}
+
 // Get returns the value for given key
 func (d *Datastore) Get(key ds.Key) (value []byte, err error) {
 	fn := d.KeyFilename(key)
@@ -103,8 +109,9 @@ func (d *Datastore) Query(q query.Query) (query.Results, error) {
 
 	walkFn := func(path string, info os.FileInfo, err error) error {
 		// remove ds path prefix
-		if strings.HasPrefix(path, d.path) {
-			path = path[len(d.path):]
+		relPath, err := filepath.Rel(d.path, path)
+		if err == nil {
+			path = filepath.ToSlash(relPath)
 		}
 
 		if !info.IsDir() {
@@ -167,7 +174,7 @@ func (d *Datastore) DiskUsage() (uint64, error) {
 			log.Println(err)
 			return err
 		}
-		if f != nil {
+		if f != nil && f.Mode().IsRegular() {
 			du += uint64(f.Size())
 		}
 		return nil

examples/fs_test.go

@@ -96,13 +96,16 @@ func (ks *DSSuite) TestDiskUsage(c *C) {
 		"foo/bar/baz/barb",
 	})
 
+	totalBytes := 0
 	for _, k := range keys {
-		err := ks.ds.Put(k, []byte(k.String()))
+		value := []byte(k.String())
+		totalBytes += len(value)
+		err := ks.ds.Put(k, value)
 		c.Check(err, Equals, nil)
 	}
 
 	if ps, ok := ks.ds.(ds.PersistentDatastore); ok {
-		if s, err := ps.DiskUsage(); s <= 100 || err != nil {
+		if s, err := ps.DiskUsage(); s != uint64(totalBytes) || err != nil {
 			c.Error("unexpected size is: ", s)
 		}
 	} else {

failstore/failstore.go

@@ -36,6 +36,16 @@ func (d *Failstore) Put(k ds.Key, val []byte) error {
 	return d.child.Put(k, val)
 }
 
+// Sync implements Datastore.Sync
+func (d *Failstore) Sync(prefix ds.Key) error {
+	err := d.errfunc("sync")
+	if err != nil {
+		return err
+	}
+
+	return d.child.Sync(prefix)
+}
+
 // Get retrieves a value from the datastore.
 func (d *Failstore) Get(k ds.Key) ([]byte, error) {
 	err := d.errfunc("get")

keytransform/keytransform.go

@@ -37,6 +37,11 @@ func (d *Datastore) Put(key ds.Key, value []byte) (err error) {
 	return d.child.Put(d.ConvertKey(key), value)
 }
 
+// Sync implements Datastore.Sync
+func (d *Datastore) Sync(prefix ds.Key) error {
+	return d.child.Sync(d.ConvertKey(prefix))
+}
+
 // Get returns the value for given key, transforming the key first.
 func (d *Datastore) Get(key ds.Key) (value []byte, err error) {
 	return d.child.Get(d.ConvertKey(key))

mount/mount.go

@@ -189,6 +189,24 @@ func (d *Datastore) Put(key ds.Key, value []byte) error {
 	return cds.Put(k, value)
 }
 
+// Sync implements Datastore.Sync
+func (d *Datastore) Sync(prefix ds.Key) error {
+	// Sync all mount points below the prefix
+	// Sync the mount point right at (or above) the prefix
+	dstores, mountPts, rest := d.lookupAll(prefix)
+	for i, suffix := range rest {
+		if err := dstores[i].Sync(suffix); err != nil {
+			return err
+		}
+
+		if mountPts[i].Equal(prefix) || suffix.String() != "/" {
+			return nil
+		}
+	}
+
+	return nil
+}
+
 func (d *Datastore) Get(key ds.Key) (value []byte, err error) {
 	cds, _, k := d.lookup(key)
 	if cds == nil {