From e147dd9d1e206658be01e13749ab1d62310428b1 Mon Sep 17 00:00:00 2001
From: Kresten Krab Thorup <krab@trifork.com>
Date: Thu, 26 Apr 2012 01:00:01 +0200
Subject: [PATCH] Improve merge work computation

---
 src/hanoi_level.erl | 47 ++++++++++++++++++++++++++-------------------
 1 file changed, 27 insertions(+), 20 deletions(-)

diff --git a/src/hanoi_level.erl b/src/hanoi_level.erl
index 180b057..5e5ab9c 100644
--- a/src/hanoi_level.erl
+++ b/src/hanoi_level.erl
@@ -31,14 +31,14 @@
 -include("src/hanoi.hrl").
 
 %%
-%% Manages a "pair" of hanoi index (or rathern, 0, 1 or 2), and governs
-%% the process of injecting/merging parent trees into this pair.
+%% Manages 0..2 of hanoi index file, and governs all aspects of
+%% merging, lookup, folding, etc. for these files
 %%
 
 %%
-%% For now, we use plain_fsm, because we *want* selective receive to postpone
-%% pending injects while we're merging.  That's a lot simpler than maintaining
-%% to corresponding merge queue.
+%% DESIGN: uses plain_fsm, because we *want* selective receive to
+%% postpone pending injects while we're merging.  That's a lot simpler
+%% than maintaining to corresponding merge queue.
 %%
 
 -behavior(plain_fsm).
@@ -52,7 +52,7 @@
 -record(state, {
           a, b, c, next, dir, level, inject_done_ref, merge_pid, folding = [],
           step_next_ref, step_caller, step_merge_ref,
-          opts = [], owner, work_done=0
+          opts = [], owner, work_in_progress=0, work_done=0
           }).
 
 
@@ -279,7 +279,11 @@ main_loop(State = #state{ next=Next }) ->
                State#state.step_next_ref  == undefined
                ->
 
-            WorkLeftHere = max(0,total_unmerged(State) - State#state.work_done),
+            if State#state.b =/= undefined ->
+                    WorkLeftHere = max(0, (2 * ?BTREE_SIZE(State#state.level)) - State#state.work_done);
+               true ->
+                    WorkLeftHere = 0
+            end,
             WorkToDoHere = min(WorkLeftHere, HowMuch),
             DelegateWork = max(0,HowMuch - WorkToDoHere),
 
@@ -294,35 +298,37 @@ main_loop(State = #state{ next=Next }) ->
 
             if (State#state.merge_pid == undefined)
                orelse (WorkToDoHere =< 0) ->
-                    MergeRef = undefined,
-                    NewWorkDone = State#state.work_done;
+                    MergeRef = undefined;
                true ->
                     MergePID = State#state.merge_pid,
                     MergeRef = monitor(process, MergePID),
-                    MergePID ! {step, {self(), MergeRef}, WorkToDoHere},
-                    NewWorkDone = State#state.work_done + WorkToDoHere
+                    MergePID ! {step, {self(), MergeRef}, WorkToDoHere}
             end,
 
             if (Next =:= undefined) andalso (MergeRef =:= undefined) ->
                     %% nothing to do ... just return OK
+
                     State2 = reply_step_ok(State#state { step_caller = StepFrom }),
-                    main_loop(State2#state { work_done = NewWorkDone });
+                    main_loop(State2);
                true ->
                     main_loop(State#state{ step_next_ref=DelegateRef,
                                            step_caller=StepFrom,
                                            step_merge_ref=MergeRef,
-                                           work_done = NewWorkDone
+                                           work_in_progress = WorkToDoHere
                                          })
             end;
 
         {MRef, step_done} when MRef == State#state.step_merge_ref ->
             demonitor(MRef, [flush]),
 
-            case State#state.step_next_ref of
+            State1 = State#state{ work_done = State#state.work_done + State#state.work_in_progress,
+                                  work_in_progress = 0 },
+
+            case State1#state.step_next_ref of
                 undefined ->
-                    State2 = reply_step_ok(State);
+                    State2 = reply_step_ok(State1);
                 _ ->
-                    State2 = State
+                    State2 = State1
             end,
 
             main_loop(State2#state{ step_merge_ref=undefined });
@@ -338,7 +344,7 @@ main_loop(State = #state{ next=Next }) ->
                     State2 = State
             end,
 
-            main_loop(State2#state{ step_merge_ref=undefined });
+            main_loop(State2#state{ step_merge_ref=undefined, work_in_progress=0 });
 
 
         ?REPLY(MRef, ok)
@@ -573,10 +579,11 @@ reply_step_ok(State) ->
 
 total_unmerged(State) ->
     Files =
-          (if State#state.b == undefined -> 0; true -> 1 end)
-        + (if State#state.c == undefined -> 0; true -> 1 end),
+          (if State#state.b == undefined -> 0; true -> 2 end)
+%        + (if State#state.c == undefined -> 0; true -> 1 end)
+,
 
-    Files * ?BTREE_SIZE( State#state.level ).
+    Files * 1 * ?BTREE_SIZE( State#state.level ).