func applyCompaction(kv dstorage.KV, compaction *pb.CompactionRequest) (*pb.CompactionResponse, error) {
resp := &pb.CompactionResponse{}
resp.Header = &pb.ResponseHeader{}
err := kv.Compact(compaction.Revision)
if err != nil {
return nil, err
}
// get the current revision. which key to get is not important.
_, resp.Header.Revision, _ = kv.Range([]byte("compaction"), nil, 1, 0)
return resp, err
}