add metastore, switching sequence to use it

metastore is for storing metadata. This will be used later when moving
to distributed master mode.

go/metastore/backing_test.go

@@ -0,0 +1,30 @@
+package metastore
+
+import (
+	"testing"
+)
+
+func TestMemoryBacking(t *testing.T) {
+	ms := &MetaStore{NewMetaStoreMemoryBacking()}
+	verifySetGet(t, ms)
+}
+
+func TestFileBacking(t *testing.T) {
+	ms := &MetaStore{NewMetaStoreFileBacking()}
+	verifySetGet(t, ms)
+}
+
+func verifySetGet(t *testing.T, ms *MetaStore) {
+	data := uint64(234234)
+	ms.SetUint64(data, "/tmp", "sequence")
+	if !ms.Has("/tmp", "sequence") {
+		t.Errorf("Failed to set data")
+	}
+	if val, err := ms.GetUint64("/tmp", "sequence"); err == nil {
+		if val != data {
+			t.Errorf("Set %d, but read back %d", data, val)
+		}
+	} else {
+		t.Errorf("Failed to get back data:%s", err)
+	}
+}

go/metastore/file_backing.go

@@ -0,0 +1,34 @@
+package metastore
+
+import (
+	"io/ioutil"
+	"os"
+	"path"
+)
+
+// store data on disk, enough for most cases
+
+type MetaStoreFileBacking struct {
+}
+
+func NewMetaStoreFileBacking() MetaStoreFileBacking {
+	mms := MetaStoreFileBacking{}
+	return mms
+}
+
+func (mms MetaStoreFileBacking) Set(val []byte, elem ...string) error {
+	return ioutil.WriteFile(path.Join(elem...), val, 0644)
+}
+
+func (mms MetaStoreFileBacking) Get(elem ...string) (val []byte, err error) {
+	return ioutil.ReadFile(path.Join(elem...))
+}
+
+func (mms MetaStoreFileBacking) Has(elem ...string) (ok bool) {
+	seqFile, se := os.OpenFile(path.Join(elem...), os.O_RDONLY, 0644)
+	if se != nil {
+		return false
+	}
+	defer seqFile.Close()
+	return true
+}

go/metastore/memory_backing.go

@@ -0,0 +1,37 @@
+package metastore
+
+import (
+	"fmt"
+	"path"
+)
+
+//this is for testing only
+
+type MetaStoreMemoryBacking struct {
+	m map[string][]byte
+}
+
+func NewMetaStoreMemoryBacking() MetaStoreMemoryBacking {
+	mms := MetaStoreMemoryBacking{}
+	mms.m = make(map[string][]byte)
+	return mms
+}
+
+func (mms MetaStoreMemoryBacking) Set(val []byte, elem ...string) error {
+	mms.m[path.Join(elem...)] = val
+	return nil
+}
+
+func (mms MetaStoreMemoryBacking) Get(elem ...string) (val []byte, err error) {
+	var ok bool
+	val, ok = mms.m[path.Join(elem...)]
+	if !ok {
+		return nil, fmt.Errorf("Missing value for %s", path.Join(elem...))
+	}
+	return
+}
+
+func (mms MetaStoreMemoryBacking) Has(elem ...string) (ok bool) {
+	_, ok = mms.m[path.Join(elem...)]
+	return
+}

go/metastore/metastore.go

@@ -0,0 +1,35 @@
+package metastore
+
+import (
+	"code.google.com/p/weed-fs/go/util"
+	"errors"
+	"path"
+)
+
+type MetaStoreBacking interface {
+	Get(elem ...string) ([]byte, error)
+	Set(val []byte, elem ...string) error
+  Has(elem ...string) bool
+}
+
+type MetaStore struct {
+	MetaStoreBacking
+}
+
+func (m *MetaStore) SetUint64(val uint64, elem ...string) error {
+	b := make([]byte, 8)
+	util.Uint64toBytes(b, val)
+	return m.Set(b, elem...)
+}
+
+func (m *MetaStore) GetUint64(elem ...string) (val uint64, err error) {
+	if b, e := m.Get(elem...); e == nil && len(b) == 8 {
+		val = util.BytesToUint64(b)
+	} else {
+		if e != nil {
+			return 0, e
+		}
+		err = errors.New("Not found value for " + path.Join(elem...))
+	}
+	return
+}

go/sequence/sequence.go

@@ -1,9 +1,10 @@
 package sequence
 
 import (
+	"bytes"
 	"code.google.com/p/weed-fs/go/glog"
+	"code.google.com/p/weed-fs/go/metastore"
 	"encoding/gob"
-	"os"
 	"path"
 	"sync"
 )
@@ -24,25 +25,28 @@ type SequencerImpl struct {
 
 	FileIdSequence uint64
 	fileIdCounter  uint64
+
+	metaStore *metastore.MetaStore
 }
 
 func NewSequencer(dirname string, filename string) (m *SequencerImpl) {
 	m = &SequencerImpl{dir: dirname, fileName: filename}
+	m.metaStore = &metastore.MetaStore{metastore.NewMetaStoreFileBacking()}
 
-	seqFile, se := os.OpenFile(path.Join(m.dir, m.fileName+".seq"), os.O_RDONLY, 0644)
-	if se != nil {
+	if !m.metaStore.Has(m.dir, m.fileName+".seq") {
 		m.FileIdSequence = FileIdSaveInterval
 		glog.V(0).Infoln("Setting file id sequence", m.FileIdSequence)
 	} else {
-		decoder := gob.NewDecoder(seqFile)
-		defer seqFile.Close()
-		if se = decoder.Decode(&m.FileIdSequence); se != nil {
-			glog.V(0).Infof("error decoding FileIdSequence: %s", se)
-			m.FileIdSequence = FileIdSaveInterval
-			glog.V(0).Infoln("Setting file id sequence", m.FileIdSequence)
+		var err error
+		if m.FileIdSequence, err = m.metaStore.GetUint64(m.dir, m.fileName+".seq"); err != nil {
+			if data, err := m.metaStore.Get(m.dir, m.fileName+".seq"); err == nil {
+				m.FileIdSequence = decode(data)
+        glog.V(0).Infoln("Decoding old version of FileIdSequence", m.FileIdSequence)
 			} else {
-			glog.V(0).Infoln("Loading file id sequence", m.FileIdSequence, "=>", m.FileIdSequence+FileIdSaveInterval)
-			m.FileIdSequence += FileIdSaveInterval
+				glog.V(0).Infof("No existing FileIdSequence: %s", err)
+			}
+		} else {
+			glog.V(0).Infoln("Loading file id sequence", m.FileIdSequence)
 		}
 		//in case the server stops between intervals
 	}
@@ -66,13 +70,18 @@ func (m *SequencerImpl) NextFileId(count int) (uint64, int) {
 }
 func (m *SequencerImpl) saveSequence() {
 	glog.V(0).Infoln("Saving file id sequence", m.FileIdSequence, "to", path.Join(m.dir, m.fileName+".seq"))
-	seqFile, e := os.OpenFile(path.Join(m.dir, m.fileName+".seq"), os.O_CREATE|os.O_WRONLY, 0644)
-	if e != nil {
-		glog.Fatalf("Sequence File Save [ERROR] %s", e)
+	if e := m.metaStore.SetUint64(m.FileIdSequence, m.dir, m.fileName+".seq"); e != nil {
+		glog.Fatalf("Sequence id Save [ERROR] %s", e)
 	}
-	defer seqFile.Close()
-	encoder := gob.NewEncoder(seqFile)
-	if e = encoder.Encode(m.FileIdSequence); e != nil {
-		glog.Fatalf("Sequence File Save [ERROR] %s", e)
 }
+
+//decode are for backward compatible purpose
+func decode(input []byte) uint64 {
+	var x uint64
+	b := bytes.NewReader(input)
+	decoder := gob.NewDecoder(b)
+	if e := decoder.Decode(&x); e == nil {
+		return x
+	}
+	return 0
 }