results := make(chan ObjectInfo, workerSize)
	if err := api.Walk(ctx, r.Bucket, r.Prefix, results, WalkOptions{
		Marker:       lastObject,
		LatestOnly:   false, // we need to visit all versions of the object to implement purge: retainVersions
		VersionsSort: WalkVersionsSortDesc,
	}); err != nil {
		// Do not need to retry if we can't list objects on source.
		return err
	}