new: add support for memcached metadata store

weed/filer/memcached_store/memcached_store.go

@@ -0,0 +1,56 @@
+package memcached_store
+
+import (
+	memcache "github.com/bradfitz/gomemcache/memcache"
+	"github.com/chrislusf/seaweedfs/weed/filer"
+	"github.com/chrislusf/seaweedfs/weed/glog"
+)
+
+type MemcacheStore struct {
+	Client *memcache.Client
+}
+
+func NewMemcacheStore(hostPort ...string) *MemcacheStore {
+	client := memcache.New(hostPort...)
+	return &MemcacheStore{Client: client}
+}
+
+func (s *MemcacheStore) Get(fullFileName string) (fid string, err error) {
+	item, err := s.Client.Get(fullFileName)
+	if err == memcache.ErrCacheMiss {
+		err = filer.ErrNotFound
+	}
+	if err != nil {
+		return "", err
+	}
+	fid = string(item.Value)
+	return fid, err
+}
+
+func (s *MemcacheStore) Put(fullFileName string, fid string) (err error) {
+	item := memcache.Item{
+		Key:   fullFileName,
+		Value: []byte(fid),
+	}
+	err = s.Client.Set(&item)
+	return err
+}
+
+func (s *MemcacheStore) Delete(fullFileName string) (err error) {
+	err = s.Client.Delete(fullFileName)
+	// ErrCacheMiss means key is not cached in memcache
+	// which is the same as deleted
+	// so it should not be consider as an error
+	if err == memcache.ErrCacheMiss {
+		glog.V(0).Infof("Full file name %s not exists in memcache", fullFileName)
+		err = nil
+	}
+	return err
+}
+
+func (s *MemcacheStore) Close() {
+	// For now the memcache client do not provide a way to close client
+	// and all cleanup job depends on GC
+	// related issue: https://github.com/bradfitz/gomemcache/issues/51
+	s.Client = nil
+}