func openDBBench(b *testing.B, noCompress bool) *dbBench {
	_, err := os.Stat(benchDB)
	if err == nil {
		err = os.RemoveAll(benchDB)
		if err != nil {
			b.Fatal("cannot remove old db: ", err)
		}
	}

	p := &dbBench{
		b:  b,
		o:  &opt.Options{},
		ro: &opt.ReadOptions{},
		wo: &opt.WriteOptions{},
	}
	p.stor, err = storage.OpenFile(benchDB)
	if err != nil {
		b.Fatal("cannot open stor: ", err)
	}
	if noCompress {
		p.o.Compression = opt.NoCompression
	}

	p.db, err = Open(p.stor, p.o)
	if err != nil {
		b.Fatal("cannot open db: ", err)
	}

	runtime.GOMAXPROCS(runtime.NumCPU())
	return p
}
// RecoverFile recovers and opens a DB with missing or corrupted manifest files
// for the given path. It will ignore any manifest files, valid or not.
// The DB must already exist or it will returns an error.
// Also, Recover will ignore ErrorIfMissing and ErrorIfExist options.
//
// RecoverFile uses standard file-system backed storage implementation as desribed
// in the leveldb/storage package.
//
// The returned DB instance is goroutine-safe.
// The DB must be closed after use, by calling Close method.
func RecoverFile(path string, o *opt.Options) (db *DB, err error) {
	stor, err := storage.OpenFile(path)
	if err != nil {
		return
	}
	db, err = Recover(stor, o)
	if err != nil {
		stor.Close()
	} else {
		db.closer = stor
	}
	return
}
func newTestStorage(t *testing.T) *testStorage {
	var stor storage.Storage
	var closeFn func() error
	if tsFS {
		for {
			tsMU.Lock()
			num := tsNum
			tsNum++
			tsMU.Unlock()
			tempdir := tsTempdir
			if tempdir == "" {
				tempdir = os.TempDir()
			}
			path := filepath.Join(tempdir, fmt.Sprintf("goleveldb-test%d0%d0%d", os.Getuid(), os.Getpid(), num))
			if _, err := os.Stat(path); err != nil {
				stor, err = storage.OpenFile(path)
				if err != nil {
					t.Fatalf("F: cannot create storage: %v", err)
				}
				t.Logf("I: storage created: %s", path)
				closeFn = func() error {
					for _, name := range []string{"LOG.old", "LOG"} {
						f, err := os.Open(filepath.Join(path, name))
						if err != nil {
							continue
						}
						if log, err := ioutil.ReadAll(f); err != nil {
							t.Logf("---------------------- %s ----------------------", name)
							t.Logf("cannot read log: %v", err)
							t.Logf("---------------------- %s ----------------------", name)
						} else if len(log) > 0 {
							t.Logf("---------------------- %s ----------------------\n%s", name, string(log))
							t.Logf("---------------------- %s ----------------------", name)
						}
						f.Close()
					}
					if t.Failed() {
						t.Logf("testing failed, test DB preserved at %s", path)
						return nil
					}
					if tsKeepFS {
						return nil
					}
					return os.RemoveAll(path)
				}

				break
			}
		}
	} else {
		stor = storage.NewMemStorage()
	}
	ts := &testStorage{
		t:              t,
		Storage:        stor,
		closeFn:        closeFn,
		opens:          make(map[uint64]bool),
		emuErrOnceMap:  make(map[uint64]uint),
		emuRandErrProb: 0x999,
		emuRandRand:    rand.New(rand.NewSource(0xfacedead)),
	}
	ts.cond.L = &ts.mu
	return ts
}