code: func (cmd *CompactCommand) walk(db *bolt.DB, walkFn walkFunc) error {
  	return db.View(func(tx *bolt.Tx) error {
  		return tx.ForEach(func(name []byte, b *bolt.Bucket) error {
  			return cmd.walkBucket(b, nil, name, nil, b.Sequence(), walkFn)
  		})
  	})
  }
docs: // walk walks recursively the bolt database db, calling walkFn for each key it finds.