code: func (iter *dbCacheIterator) First() bool {
  	// Seek to the first key in both the database and cache iterators and
  	// choose the iterator that is both valid and has the smaller key.
  	iter.dbIter.First()
  	iter.cacheIter.First()
  	return iter.chooseIterator(true)
  }
docs: // First positions the iterator at the first key/value pair and returns whether
  // or not the pair exists.
  //
  // This is part of the leveldb iterator.Iterator interface implementation.