diff --git a/prototype/tango-prototype/src/tango_oid.erl b/prototype/tango-prototype/src/tango_oid.erl
index 1264e58..a94f06f 100644
--- a/prototype/tango-prototype/src/tango_oid.erl
+++ b/prototype/tango-prototype/src/tango_oid.erl
@@ -24,17 +24,20 @@
 
 %% API
 -export([start_link/4, stop/1,
-         put/3, get/2]).
+         new/2, get/2]).
 
 %% gen_server callbacks
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
          terminate/2, code_change/3]).
 
+%% Tango datatype callbacks (prototype)
+-export([fresh/0,
+         do_pure_op/2, do_dirty_op/6, play_log_mutate_i_state/3]).
+
 -define(SERVER, ?MODULE).
 -define(OID_STREAM_NUMBER, 0).
 
--define(LONG_TIME, 5*1000).
-%% -define(LONG_TIME, 30*1000).
+-define(LONG_TIME, 30*1000).
 
 -define(D(X), io:format(user, "Dbg: ~s =\n  ~p\n", [??X, X])).
 
@@ -58,8 +61,8 @@ start_link(PageSize, SequencerPid, Proj, CallbackMod) ->
 stop(Pid) ->
     gen_server:call(Pid, {stop}, ?LONG_TIME).
 
-put(Pid, Key, Val) ->
-    gen_server:call(Pid, {put, Key, Val}, ?LONG_TIME).
+new(Pid, Key) ->
+    gen_server:call(Pid, {new, Key}, ?LONG_TIME).
 
 get(Pid, Key) ->
     gen_server:call(Pid, {get, Key}, ?LONG_TIME).
@@ -69,7 +72,7 @@ get(Pid, Key) ->
 init([PageSize, SequencerPid, Proj, CallbackMod]) ->
     LastLPN = find_last_lpn(SequencerPid),
     {BackPs, Pages} = fetch_unread_pages(Proj, LastLPN, 0),
-    I_State = play_log_pages(Pages, CallbackMod:fresh(), CallbackMod),
+    I_State = play_log_pages(Pages, CallbackMod:fresh(), CallbackMod, false),
     {ok, #state{page_size=PageSize,
                 seq=SequencerPid,
                 proj=Proj,
@@ -79,28 +82,36 @@ init([PageSize, SequencerPid, Proj, CallbackMod]) ->
                 back_ps=BackPs,
                 i_state=I_State}}.
 
-handle_call({put, _Key, _Val}=Op, _From,
+handle_call({new, Key}, From,
             #state{proj=Proj0, cb_mod=CallbackMod,
                    page_size=PageSize, back_ps=BackPs, i_state=I_State}=State) ->
-    {Res, I_State2, Proj1, LPN, NewBackPs} =
+    Op = {new_oid, Key, From},
+    {_Res, I_State2, Proj1, LPN, NewBackPs} =
         CallbackMod:do_dirty_op(Op, I_State, ?OID_STREAM_NUMBER,
                                 Proj0, PageSize, BackPs),
-    {reply, Res, State#state{i_state=I_State2,
-                             proj=Proj1,
-                             last_write_lpn=LPN,
-                             back_ps=NewBackPs}};
+    %% Let's see how much trouble we can get outselves in here.
+    %% If we're here, then we've written to the log without error.
+    %% So then the cast to roll forward must see that log entry
+    %% (if it also operates without error).  So, the side-effect of
+    %% the op ought to always send a reply to the client.
+    gen_server:cast(self(), {roll_forward}),
+    {noreply, State#state{i_state=I_State2,
+                          proj=Proj1,
+                          last_write_lpn=LPN,
+                          back_ps=NewBackPs}};
 handle_call({get, _Key}=Op, _From, #state{cb_mod=CallbackMod} = State) ->
-    {Pages, State2} = fetch_unread_pages(State),
-    %% ?D(Pages),
-    #state{i_state=I_State} = State3 = play_log_pages(Pages, State2),
+    State2 = #state{i_state=I_State} = roll_log_forward(State),
     Reply = CallbackMod:do_pure_op(Op, I_State),
-    {reply, Reply, State3};
+    {reply, Reply, State2};
 handle_call({stop}, _From, State) ->
     {stop, normal, ok, State};
 handle_call(_Request, _From, State) ->
     Reply = whaaaaaaaaaaaa,
     {reply, Reply, State}.
 
+handle_cast({roll_forward}, State) ->
+    State2 = roll_log_forward(State),
+    {noreply, State2};
 handle_cast(_Msg, State) ->
     {noreply, State}.
 
@@ -142,9 +153,60 @@ fetch_unread_pages(Proj, LastLPN, StopAtLPN) ->
                          [], LPNs),
     {BackPs, Pages}.
 
-play_log_pages(Pages, #state{cb_mod=CallbackMod, i_state=I_State} = State) ->
-    I_State2 = play_log_pages(Pages, I_State, CallbackMod),
+play_log_pages(Pages, SideEffectsP,
+               #state{cb_mod=CallbackMod, i_state=I_State} = State) ->
+    I_State2 = play_log_pages(Pages, I_State, CallbackMod, SideEffectsP),
     State#state{i_state=I_State2}.
 
-play_log_pages(Pages, I_State, CallbackMod) ->
-    CallbackMod:play_log_mutate_i_state(Pages, I_State).
+play_log_pages(Pages, I_State, CallbackMod, SideEffectsP) ->
+    CallbackMod:play_log_mutate_i_state(Pages, SideEffectsP, I_State).
+
+roll_log_forward(State) ->
+    {Pages, State2} = fetch_unread_pages(State),
+    play_log_pages(Pages, true, State2).
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+-record(oid_map, {
+          next :: non_neg_integer(),
+          map :: dict()
+         }).
+
+-define(DICTMOD, dict).
+
+fresh() ->
+    #oid_map{next=1,
+             map=?DICTMOD:new()}.
+
+do_pure_op({get, Key}, #oid_map{map=Dict}) ->
+    ?DICTMOD:find(Key, Dict).
+
+do_dirty_op({new_oid, _Key, _From}=Op,
+            I_State, StreamNum, Proj0, PageSize, BackPs) ->
+    Page = term_to_binary(Op),
+    FullPage = tango:pack_v1([{StreamNum, BackPs}], Page, PageSize),
+    {{ok, LPN}, Proj1} = corfurl_client:append_page(Proj0, FullPage),
+    NewBackPs = tango:add_back_pointer(BackPs, LPN),
+    {ok, I_State, Proj1, LPN, NewBackPs}.
+
+play_log_mutate_i_state(Pages, SideEffectsP, I_State) ->
+    lists:foldl(fun({new_oid, Key, From}=_Op, #oid_map{map=Dict, next=Next}=O) ->
+                        {Res, O2} = 
+                            case ?DICTMOD:find(Key, Dict) of
+                                error ->
+                                    Dict2 = ?DICTMOD:store(Key, Next, Dict),
+                                    {{ok, Next},O#oid_map{map=Dict2,
+                                                          next=Next + 1}};
+                                {ok, _} ->
+                                    {already_exists, O}
+                            end,
+                        if SideEffectsP ->
+                                gen_server:reply(From, Res);
+                           true ->
+                                ok
+                        end,
+                        O2
+                end,
+                I_State,
+                [binary_to_term(Page) || Page <- Pages]).
+    
diff --git a/prototype/tango-prototype/test/tango_oid_test.erl b/prototype/tango-prototype/test/tango_oid_test.erl
index b19270d..3b1e878 100644
--- a/prototype/tango-prototype/test/tango_oid_test.erl
+++ b/prototype/tango-prototype/test/tango_oid_test.erl
@@ -36,7 +36,7 @@ tango_oid_smoke_test() ->
                              fun tango_oid_smoke_test_int/3).
 
 tango_oid_smoke_test_int(PageSize, Seq, Proj) ->
-    {ok, OID_Map} = tango_oid:start_link(PageSize, Seq, Proj, tango_dt_map),
+    {ok, OID_Map} = tango_oid:start_link(PageSize, Seq, Proj, tango_oid),
 
     ok = tango_oid:stop(OID_Map),
     ok.
@@ -46,18 +46,22 @@ tango_oid_one_test() ->
                              fun tango_oid_one_test_int/3).
 
 tango_oid_one_test_int(PageSize, Seq, Proj) ->
-    {ok, OID_Map} = tango_oid:start_link(PageSize, Seq, Proj, tango_dt_map),
+    {ok, OID_Map} = tango_oid:start_link(PageSize, Seq, Proj, tango_oid),
 
     try
         K1 = foo,
-        V1 = bar1,
-        V2 = bar2,
-        ok = tango_oid:put(OID_Map, K1, V1),
-        {ok, V1} = tango_oid:get(OID_Map, K1),
-        ok = tango_oid:put(OID_Map, K1, V2),
-        {ok, V2} = tango_oid:get(OID_Map, K1),
+        K2 = bar,
+        OID_Num1 = 1,
+        {ok, OID_Num1} = tango_oid:new(OID_Map, K1),
+        {ok, OID_Num1} = tango_oid:get(OID_Map, K1),
+        already_exists = tango_oid:new(OID_Map, K1),
+        %% The V2 put should *not* have clobbered the previous value
+        {ok, OID_Num1} = tango_oid:get(OID_Map, K1),
         error = tango_oid:get(OID_Map, "does not exist"),
 
+        {ok, OID_Num2} = tango_oid:new(OID_Map, K2),
+        {ok, OID_Num2} = tango_oid:get(OID_Map, K2),
+
         ok
     after
         tango_oid:stop(OID_Map)