anchor.diff:      State
       end.
   
  -commit_to_both(Source, Target) ->
  +commit_to_both(Source, Target, RequiredSeq) ->
       % commit the src async
       ParentPid = self(),
       SrcCommitPid = spawn_link(fun() ->
  -            ParentPid ! {self(), ensure_full_commit(Source)} end),
  +            ParentPid ! {self(), ensure_full_commit(Source, RequiredSeq)} end),
   
       % commit tgt sync
       TargetStartTime = ensure_full_commit(Target),
  
positive.code:     end,
      {SourceStartTime, TargetStartTime}.
      
  ensure_full_commit(#http_db{} = Db) ->
      Req = Db#http_db{
          resource = "_ensure_full_commit",
          method = post,
          body = true
  
negative.code:         stats = Stats
      } = State,
      ?LOG_INFO("recording a checkpoint at source update_seq ~p", [NewSeqNum]),
      RecordSeqNum = case commit_to_both(Source, Target, NewSeqNum) of
      {SrcInstanceStartTime, TgtInstanceStartTime} ->
          NewSeqNum;
      _Else ->
  