From 8da46f78fe9ddb8fc53b3e6229d55caefd998c04 Mon Sep 17 00:00:00 2001
From: Scott Lystig Fritchie <slfritchie@snookles.com>
Date: Sun, 21 Sep 2014 15:48:20 +0900
Subject: [PATCH] BAH! Checkpoint is quite broken, see new README.tango.md

---
 prototype/tango-prototype/README.tango.md     | 18 ++++++++++++++++++
 prototype/tango-prototype/src/tango_dt.erl    |  3 +++
 prototype/tango-prototype/test/tango_test.erl |  5 +++++
 3 files changed, 26 insertions(+)
 create mode 100644 prototype/tango-prototype/README.tango.md

diff --git a/prototype/tango-prototype/README.tango.md b/prototype/tango-prototype/README.tango.md
new file mode 100644
index 0000000..eb7ef1a
--- /dev/null
+++ b/prototype/tango-prototype/README.tango.md
@@ -0,0 +1,18 @@
+
+Tango prototype TODO list
+=========================
+
+__ The current checkpoint implementation is fundamentally broken and
+   needs a rewrite, or else.
+   option 1: fix checkpoint to be 100% correct
+   option 2: checkpointing is for the weak and the memory-constrained, so
+             don't bother.  Instead, rip out the current checkpoint code,
+             period. 
+
+__ Checkpoint fix option #1: history splicing within the same OID?
+
+__ Checkpoint fix option #2: checkpoint to a new OID, history writes to both
+                             OIDs during the CP, then a marker in the old OID
+                             to switch over to the new OID?
+
+
diff --git a/prototype/tango-prototype/src/tango_dt.erl b/prototype/tango-prototype/src/tango_dt.erl
index ad2863f..7a60ffe 100644
--- a/prototype/tango-prototype/src/tango_dt.erl
+++ b/prototype/tango-prototype/src/tango_dt.erl
@@ -75,6 +75,7 @@ checkpoint(Pid) ->
 init([PageSize, SequencerPid, Proj, CallbackMod, StreamNum]) ->
     LastLPN = find_last_lpn(SequencerPid, StreamNum),
     {LPNs, Pages} = fetch_unread_pages(Proj, LastLPN, 0, StreamNum),
+?D({self(), LPNs}),
     BackPs = tango:append_lpns(LPNs, []),
     LastFetchLPN = tango:back_ps2last_lpn(BackPs),
     I_State = play_log_pages(Pages, CallbackMod:fresh(), CallbackMod, false),
@@ -113,6 +114,7 @@ handle_call({sync_checkpoint}, From,
     {_OpT, I_State2, Proj1, _LPN} =
         CallbackMod:do_dirty_op(CheckpointOps, From, I_State, StreamNum,
                                 Proj0, PageSize),
+?D({sync_checkpoint, _LPN}),
     %% TODO: Use this LPN so that we can tell the corfurl log GC
     %%       that we have created some dead bytes in the log.
     {reply, ok, State#state{i_state=I_State2,
@@ -161,6 +163,7 @@ roll_log_forward(#state{seq=SequencerPid, proj=Proj, all_back_ps=BackPs,
                         last_fetch_lpn=StopAtLPN} = State) ->
     LastLPN = find_last_lpn(SequencerPid, StreamNum),
     {LPNs, Pages} = fetch_unread_pages(Proj, LastLPN, StopAtLPN, StreamNum),
+?D({self(), LPNs}),
     NewBackPs = tango:append_lpns(LPNs, BackPs),
     LastFetchLPN = tango:back_ps2last_lpn(NewBackPs),
     play_log_pages(Pages, true,
diff --git a/prototype/tango-prototype/test/tango_test.erl b/prototype/tango-prototype/test/tango_test.erl
index eea5e05..0ddf1e0 100644
--- a/prototype/tango-prototype/test/tango_test.erl
+++ b/prototype/tango-prototype/test/tango_test.erl
@@ -294,12 +294,17 @@ tango_dt_queue_int(PageSize, Seq, Proj) ->
     ok = C1(Q2, Num1),
     ok = C1(Q1, Num1),
 
+?D(before_CPs_start),
     [ok = MOD:checkpoint(Q1) || _ <- lists:seq(1, 4)],
+?D(after_CPs_end),
     [ok = C1(X, Num1) || X <- [Q1, Q2]],
     {ok, Q3} = MOD:start_link(PageSize, Seq, Proj, Q1Num),
     [ok = C1(X, Num1) || X <- [Q1, Q2, Q3]],
+?D(before_Q4_start),
     {ok, Q4} = MOD:start_link(PageSize, Seq, Proj, Q1Num),
+?D({after_Q4_start, Q4}),
     ok = MOD:in(Q4, 89),
+?D(after_Q4_in),
     Num1Plus1 = Num1 + 1,
     [ok = C1(X, Num1Plus1) || X <- [Q1, Q2, Q3, Q4]],