func repairBadIndexVersion(logger log.Logger, dir string) error {
	subdirs, err := fileutil.ReadDir(dir)
	if err != nil {
		return err
	}
	for _, d := range subdirs {
		if _, err := ulid.Parse(d); err != nil {
			continue
		}
		d = path.Join(dir, d)
		meta, err := readBogusMetaFile(d)
		if err != nil {
			return err
		}
		if meta.Version == 1 {
			level.Info(logger).Log(
				"msg", "found healthy block",
				"mint", meta.MinTime,
				"maxt", meta.MaxTime,
				"ulid", meta.ULID,
			)
			continue
		}
		level.Info(logger).Log(
			"msg", "fixing broken block",
			"mint", meta.MinTime,
			"maxt", meta.MaxTime,
			"ulid", meta.ULID,
		)
		repl, err := os.Create(filepath.Join(d, "index.repaired"))
		if err != nil {
			return err
		}
		broken, err := os.Open(filepath.Join(d, "index"))
		if err != nil {
			return err
		}
		if _, err := io.Copy(repl, broken); err != nil {
			return err
		}
		if _, err := repl.WriteAt([]byte{2}, 4); err != nil {
			return err
		}
		if err := fileutil.Fsync(repl); err != nil {
			return err
		}
		if err := repl.Close(); err != nil {
			return err
		}
		if err := broken.Close(); err != nil {
			return err
		}
		if err := renameFile(repl.Name(), broken.Name()); err != nil {
			return err
		}
		meta.Version = 1
		if err := writeMetaFile(d, meta); err != nil {
			return err
		}
	}
	return nil
}
repairBadIndexVersion repairs an issue in index and meta.json persistence introduced in
commit 129773b41a565fde5156301e37f9a87158030443.
package tsdb
import (
	"encoding/json"
	"io"
	"io/ioutil"
	"os"
	"path"
	"path/filepath"
	"github.com/go-kit/kit/log"
	"github.com/go-kit/kit/log/level"
	"github.com/oklog/ulid"
	"github.com/pkg/errors"
	"github.com/prometheus/tsdb/fileutil"
)