summaryrefslogtreecommitdiff
path: root/src/couchdb/couch_btree.erl
blob: 0231d83c06a23e96cbb91068cea6e8220182b7f6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License.  You may obtain a copy of
% the License at
%
%   http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
% License for the specific language governing permissions and limitations under
% the License.

-module(couch_btree).

-export([open/2, open/3, query_modify/4, add/2, add_remove/3, foldl/3, foldl/4]).
-export([foldr/3, foldr/4, fold/4, fold/5, full_reduce/1, final_reduce/2]).
-export([fold_reduce/6, fold_reduce/7, lookup/2, get_state/1, set_options/2]).

-define(CHUNK_THRESHOLD, 16#4ff).

-record(btree,
    {fd,
    root,
    extract_kv = fun({Key, Value}) -> {Key, Value} end,
    assemble_kv =  fun(Key, Value) -> {Key, Value} end,
    less = fun(A, B) -> A < B end,
    reduce = nil
    }).

extract(#btree{extract_kv=Extract}, Value) ->
    Extract(Value).

assemble(#btree{assemble_kv=Assemble}, Key, Value) ->
    Assemble(Key, Value).

less(#btree{less=Less}, A, B) ->
    Less(A, B).

% pass in 'nil' for State if a new Btree.
open(State, Fd) ->
    {ok, #btree{root=State, fd=Fd}}.
    
set_options(Bt, []) ->
    Bt;
set_options(Bt, [{split, Extract}|Rest]) ->
    set_options(Bt#btree{extract_kv=Extract}, Rest);
set_options(Bt, [{join, Assemble}|Rest]) ->
    set_options(Bt#btree{assemble_kv=Assemble}, Rest);
set_options(Bt, [{less, Less}|Rest]) ->
    set_options(Bt#btree{less=Less}, Rest);
set_options(Bt, [{reduce, Reduce}|Rest]) ->
    set_options(Bt#btree{reduce=Reduce}, Rest).

open(State, Fd, Options) ->
    {ok, set_options(#btree{root=State, fd=Fd}, Options)}.

get_state(#btree{root=Root}) ->
    Root.

final_reduce(#btree{reduce=Reduce}, Val) ->
    final_reduce(Reduce, Val);
final_reduce(Reduce, {[], []}) ->
    Reduce(reduce, []);
final_reduce(_Bt, {[], [Red]}) ->
    Red;
final_reduce(Reduce, {[], Reductions}) ->
    Reduce(rereduce, Reductions);
final_reduce(Reduce, {KVs, Reductions}) ->
    Red = Reduce(reduce, KVs),
    final_reduce(Reduce, {[], [Red | Reductions]}).
    
fold_reduce(Bt, StartKey, EndKey, KeyGroupFun, Fun, Acc) ->
    fold_reduce(Bt, fwd, StartKey, EndKey, KeyGroupFun, Fun, Acc).

fold_reduce(#btree{root=Root}=Bt, Dir, StartKey, EndKey, KeyGroupFun, Fun, Acc) ->
    {StartKey2, EndKey2} =
    case Dir of
        rev -> {EndKey, StartKey};
        fwd -> {StartKey, EndKey}
    end,
    try
        {ok, Acc2, GroupedRedsAcc2, GroupedKVsAcc2, GroupedKey2} =
            reduce_stream_node(Bt, Dir, Root, StartKey2, EndKey2, nil, [], [],
            KeyGroupFun, Fun, Acc),
        if GroupedKey2 == nil ->
            {ok, Acc2};
        true ->
            case Fun(GroupedKey2, {GroupedKVsAcc2, GroupedRedsAcc2}, Acc2) of
            {ok, Acc3} -> {ok, Acc3};
            {stop, Acc3} -> {ok, Acc3}
            end
        end
    catch
        throw:{stop, AccDone} -> {ok, AccDone}
    end.

full_reduce(#btree{root=nil,reduce=Reduce}) ->
    {ok, Reduce(reduce, [])};
full_reduce(#btree{root={_P, Red}}) ->
    {ok, Red}.

foldl(Bt, Fun, Acc) ->
    fold(Bt, fwd, Fun, Acc).

foldl(Bt, Key, Fun, Acc) ->
    fold(Bt, Key, fwd, Fun, Acc).

foldr(Bt, Fun, Acc) ->
    fold(Bt, rev, Fun, Acc).

foldr(Bt, Key, Fun, Acc) ->
    fold(Bt, Key, rev, Fun, Acc).

% wraps a 2 arity function with the proper 3 arity function
convert_fun_arity(Fun) when is_function(Fun, 2) ->
    fun(KV, _Reds, AccIn) -> Fun(KV, AccIn) end;
convert_fun_arity(Fun) when is_function(Fun, 3) ->
    Fun.    % Already arity 3

fold(Bt, Dir, Fun, Acc) ->
    {_ContinueFlag, Acc2} = stream_node(Bt, [], Bt#btree.root, nil, Dir, convert_fun_arity(Fun), Acc),
    {ok, Acc2}.

fold(Bt, Key, Dir, Fun, Acc) ->
    {_ContinueFlag, Acc2} = stream_node(Bt, [], Bt#btree.root, Key, Dir, convert_fun_arity(Fun), Acc),
    {ok, Acc2}.

add(Bt, InsertKeyValues) ->
    add_remove(Bt, InsertKeyValues, []).

add_remove(Bt, InsertKeyValues, RemoveKeys) ->
    {ok, [], Bt2} = query_modify(Bt, [], InsertKeyValues, RemoveKeys),
    {ok, Bt2}.

query_modify(Bt, LookupKeys, InsertValues, RemoveKeys) ->
    #btree{root=Root} = Bt,
    InsertActions = lists:map(
        fun(KeyValue) ->
            {Key, Value} = extract(Bt, KeyValue),
            {insert, Key, Value}
        end, InsertValues),
    RemoveActions = [{remove, Key, nil} || Key <- RemoveKeys],
    FetchActions = [{fetch, Key, nil} || Key <- LookupKeys],
    SortFun =
        fun({OpA, A, _}, {OpB, B, _}) ->
            case less(Bt, A, B) of
            true -> true;
            false ->
                case less(Bt, B, A) of
                true -> false;
                false ->
                    % A and B are equal, sort by op.
                    op_order(OpA) < op_order(OpB)
                end
            end
        end,
    Actions = lists:sort(SortFun, lists:append([InsertActions, RemoveActions, FetchActions])),
    {ok, KeyPointers, QueryResults, Bt2} = modify_node(Bt, Root, Actions, []),
    {ok, NewRoot, Bt3} = complete_root(Bt2, KeyPointers),
    {ok, QueryResults, Bt3#btree{root=NewRoot}}.

% for ordering different operatations with the same key.
% fetch < remove < insert
op_order(fetch) -> 1;
op_order(remove) -> 2;
op_order(insert) -> 3.

lookup(#btree{root=Root, less=Less}=Bt, Keys) ->
    SortedKeys = lists:sort(Less, Keys),
    {ok, SortedResults} = lookup(Bt, Root, SortedKeys),
    % We want to return the results in the same order as the keys were input
    % but we may have changed the order when we sorted. So we need to put the
    % order back into the results.
    KeyDict = dict:from_list(SortedResults),
    [dict:fetch(Key, KeyDict) || Key <- Keys].

lookup(_Bt, nil, Keys) ->
    {ok, [{Key, not_found} || Key <- Keys]};
lookup(Bt, {Pointer, _Reds}, Keys) ->
    {NodeType, NodeList} = get_node(Bt, Pointer),
    case NodeType of
    kp_node ->
        lookup_kpnode(Bt, list_to_tuple(NodeList), 1, Keys, []);
    kv_node ->
        lookup_kvnode(Bt, list_to_tuple(NodeList), 1, Keys, [])
    end.



lookup_kpnode(_Bt, _NodeTuple, _LowerBound, [], Output) ->
    {ok, lists:reverse(Output)};
    
lookup_kpnode(_Bt, NodeTuple, LowerBound, Keys, Output) when size(NodeTuple) < LowerBound ->
    {ok, lists:reverse(Output, [{Key, not_found} || Key <- Keys])};

lookup_kpnode(Bt, NodeTuple, LowerBound, [FirstLookupKey | _] = LookupKeys, Output) ->
    N = find_first_gteq(Bt, NodeTuple, LowerBound, size(NodeTuple), FirstLookupKey),
    {Key, PointerInfo} = element(N, NodeTuple),
    SplitFun = fun(LookupKey) -> not less(Bt, Key, LookupKey) end,
    case lists:splitwith(SplitFun, LookupKeys) of
    {[], GreaterQueries} ->
        lookup_kpnode(Bt, NodeTuple, N + 1, GreaterQueries, Output);
    {LessEqQueries, GreaterQueries} ->
        {ok, Results} = lookup(Bt, PointerInfo, LessEqQueries),
        lookup_kpnode(Bt, NodeTuple, N + 1, GreaterQueries, lists:reverse(Results, Output))
    end.


lookup_kvnode(_Bt, _NodeTuple, _LowerBound, [], Output) ->
    {ok, lists:reverse(Output)};
lookup_kvnode(_Bt, NodeTuple, LowerBound, Keys, Output) when size(NodeTuple) < LowerBound ->
    % keys not found
    {ok, lists:reverse(Output, [{Key, not_found} || Key <- Keys])};
lookup_kvnode(Bt, NodeTuple, LowerBound, [LookupKey | RestLookupKeys], Output) ->
    N = find_first_gteq(Bt, NodeTuple, LowerBound, size(NodeTuple), LookupKey),
    {Key, Value} = element(N, NodeTuple),
    case less(Bt, LookupKey, Key) of
    true ->
        % LookupKey is less than Key
        lookup_kvnode(Bt, NodeTuple, N, RestLookupKeys, [{LookupKey, not_found} | Output]);
    false ->
        case less(Bt, Key, LookupKey) of
        true ->
            % LookupKey is greater than Key
            lookup_kvnode(Bt, NodeTuple, N+1, RestLookupKeys, [{LookupKey, not_found} | Output]);
        false ->
            % LookupKey is equal to Key
            lookup_kvnode(Bt, NodeTuple, N, RestLookupKeys, [{LookupKey, {ok, assemble(Bt, LookupKey, Value)}} | Output])
        end
    end.


complete_root(Bt, []) ->
    {ok, nil, Bt};
complete_root(Bt, [{_Key, PointerInfo}])->
    {ok, PointerInfo, Bt};
complete_root(Bt, KPs) ->
    {ok, ResultKeyPointers, Bt2} = write_node(Bt, kp_node, KPs),
    complete_root(Bt2, ResultKeyPointers).

%%%%%%%%%%%%% The chunkify function sucks! %%%%%%%%%%%%% 
% It is inaccurate as it does not account for compression when blocks are
% written. Plus with the "case size(term_to_binary(InList)) of" code it's
% probably really inefficient.

chunkify(_Bt, []) ->
    [];
chunkify(Bt, InList) ->
    case size(term_to_binary(InList)) of
    Size when Size > ?CHUNK_THRESHOLD ->
        NumberOfChunksLikely = ((Size div ?CHUNK_THRESHOLD) + 1),
        ChunkThreshold = Size div NumberOfChunksLikely,
        chunkify(Bt, InList, ChunkThreshold, [], 0, []);
    _Else ->
        [InList]
    end.

chunkify(_Bt, [], _ChunkThreshold, [], 0, OutputChunks) ->
    lists:reverse(OutputChunks);
chunkify(_Bt, [], _ChunkThreshold, OutList, _OutListSize, OutputChunks) ->
    lists:reverse([lists:reverse(OutList) | OutputChunks]);
chunkify(Bt, [InElement | RestInList], ChunkThreshold, OutList, OutListSize, OutputChunks) ->
    case size(term_to_binary(InElement)) of
    Size when (Size + OutListSize) > ChunkThreshold andalso OutList /= [] ->
        chunkify(Bt, RestInList, ChunkThreshold, [], 0, [lists:reverse([InElement | OutList]) | OutputChunks]);
    Size ->
        chunkify(Bt, RestInList, ChunkThreshold, [InElement | OutList], OutListSize + Size, OutputChunks)
    end.

modify_node(Bt, RootPointerInfo, Actions, QueryOutput) ->
    case RootPointerInfo of
    nil ->
        NodeType = kv_node,
        NodeList = [];
    {Pointer, _Reds} ->
        {NodeType, NodeList} = get_node(Bt, Pointer)
    end,
    NodeTuple = list_to_tuple(NodeList),
    
    {ok, NewNodeList, QueryOutput2, Bt2} =
    case NodeType of
    kp_node -> modify_kpnode(Bt, NodeTuple, 1, Actions, [], QueryOutput);
    kv_node -> modify_kvnode(Bt, NodeTuple, 1, Actions, [], QueryOutput)
    end,
    case NewNodeList of
    [] ->  % no nodes remain
        {ok, [], QueryOutput2, Bt2};
    NodeList ->  % nothing changed
        {LastKey, _LastValue} = element(size(NodeTuple), NodeTuple),
        {ok, [{LastKey, RootPointerInfo}], QueryOutput2, Bt2};
    _Else2 ->
        {ok, ResultList, Bt3} = write_node(Bt2, NodeType, NewNodeList),
        {ok, ResultList, QueryOutput2, Bt3}
    end.

reduce_node(#btree{reduce=nil}, _NodeType, _NodeList) ->
    [];
reduce_node(#btree{reduce=R}, kp_node, NodeList) ->
    R(rereduce, [Red || {_K, {_P, Red}} <- NodeList]);
reduce_node(#btree{reduce=R}=Bt, kv_node, NodeList) ->
    R(reduce, [assemble(Bt, K, V) || {K, V} <- NodeList]).


get_node(#btree{fd = Fd}, NodePos) ->
    {ok, {NodeType, NodeList}} = couch_file:pread_term(Fd, NodePos),
    {NodeType, NodeList}.

write_node(Bt, NodeType, NodeList) ->
    % split up nodes into smaller sizes
    NodeListList = chunkify(Bt, NodeList),
    % now write out each chunk and return the KeyPointer pairs for those nodes
    ResultList = [
        begin
            {ok, Pointer} = couch_file:append_term(Bt#btree.fd, {NodeType, ANodeList}),
            {LastKey, _} = lists:last(ANodeList),
            {LastKey, {Pointer, reduce_node(Bt, NodeType, ANodeList)}}
        end
    ||
        ANodeList <- NodeListList
    ],
    {ok, ResultList, Bt}.
    
modify_kpnode(Bt, {}, _LowerBound, Actions, [], QueryOutput) ->
    modify_node(Bt, nil, Actions, QueryOutput);
modify_kpnode(Bt, NodeTuple, LowerBound, [], ResultNode, QueryOutput) ->
    {ok, lists:reverse(ResultNode, bounded_tuple_to_list(NodeTuple, LowerBound,
            size(NodeTuple),  [])), QueryOutput, Bt};
modify_kpnode(Bt, NodeTuple, LowerBound,
        [{_, FirstActionKey, _}|_]=Actions, ResultNode, QueryOutput) ->
    N = find_first_gteq(Bt, NodeTuple, LowerBound, size(NodeTuple), FirstActionKey),
    case N == size(NodeTuple) of
    true  ->
        % perform remaining actions on last node
        {_, PointerInfo} = element(size(NodeTuple), NodeTuple),
        {ok, ChildKPs, QueryOutput2, Bt2} =
            modify_node(Bt, PointerInfo, Actions, QueryOutput),
        NodeList = lists:reverse(ResultNode, bounded_tuple_to_list(NodeTuple, LowerBound,
            size(NodeTuple) - 1, ChildKPs)),
        {ok, NodeList, QueryOutput2, Bt2};
    false ->
        {NodeKey, PointerInfo} = element(N, NodeTuple),
        SplitFun = fun({_ActionType, ActionKey, _ActionValue}) ->
                not less(Bt, NodeKey, ActionKey)
            end,
        {LessEqQueries, GreaterQueries} = lists:splitwith(SplitFun, Actions),
        {ok, ChildKPs, QueryOutput2, Bt2} =
                modify_node(Bt, PointerInfo, LessEqQueries, QueryOutput),
        ResultNode2 = lists:reverse(ChildKPs, bounded_tuple_to_revlist(NodeTuple,
                LowerBound, N - 1, ResultNode)),
        modify_kpnode(Bt2, NodeTuple, N+1, GreaterQueries, ResultNode2, QueryOutput2)
    end.
    
bounded_tuple_to_revlist(_Tuple, Start, End, Tail) when Start > End ->
    Tail;
bounded_tuple_to_revlist(Tuple, Start, End, Tail) ->
    bounded_tuple_to_revlist(Tuple, Start+1, End, [element(Start, Tuple)|Tail]).
        
bounded_tuple_to_list(Tuple, Start, End, Tail) ->
    bounded_tuple_to_list2(Tuple, Start, End, [], Tail).
    
bounded_tuple_to_list2(_Tuple, Start, End, Acc, Tail) when Start > End ->
    lists:reverse(Acc, Tail);
bounded_tuple_to_list2(Tuple, Start, End, Acc, Tail) ->
    bounded_tuple_to_list2(Tuple, Start + 1, End, [element(Start, Tuple) | Acc], Tail).

find_first_gteq(_Bt, _Tuple, Start, End, _Key) when Start == End ->
    End;
find_first_gteq(Bt, Tuple, Start, End, Key) ->
    Mid = Start + ((End - Start) div 2),
    {TupleKey, _} = element(Mid, Tuple),
    case less(Bt, TupleKey, Key) of
    true ->
        find_first_gteq(Bt, Tuple, Mid+1, End, Key);
    false ->
        find_first_gteq(Bt, Tuple, Start, Mid, Key)
    end.

modify_kvnode(Bt, NodeTuple, LowerBound, [], ResultNode, QueryOutput) ->
    {ok, lists:reverse(ResultNode, bounded_tuple_to_list(NodeTuple, LowerBound, size(NodeTuple), [])), QueryOutput, Bt};
modify_kvnode(Bt, NodeTuple, LowerBound, [{ActionType, ActionKey, ActionValue} | RestActions], ResultNode, QueryOutput) when LowerBound > size(NodeTuple) ->
    case ActionType of
    insert ->
        modify_kvnode(Bt, NodeTuple, LowerBound, RestActions, [{ActionKey, ActionValue} | ResultNode], QueryOutput);
    remove ->
        % just drop the action
        modify_kvnode(Bt, NodeTuple, LowerBound, RestActions, ResultNode, QueryOutput);
    fetch ->
        % the key/value must not exist in the tree
        modify_kvnode(Bt, NodeTuple, LowerBound, RestActions, ResultNode, [{not_found, {ActionKey, nil}} | QueryOutput])
    end;
modify_kvnode(Bt, NodeTuple, LowerBound, [{ActionType, ActionKey, ActionValue} | RestActions], AccNode, QueryOutput) ->
    N = find_first_gteq(Bt, NodeTuple, LowerBound, size(NodeTuple), ActionKey),
    {Key, Value} = element(N, NodeTuple),
    ResultNode =  bounded_tuple_to_revlist(NodeTuple, LowerBound, N - 1, AccNode),
    case less(Bt, ActionKey, Key) of
    true ->
        case ActionType of
        insert ->
            % ActionKey is less than the Key, so insert
            modify_kvnode(Bt, NodeTuple, N, RestActions, [{ActionKey, ActionValue} | ResultNode], QueryOutput);
        remove ->
            % ActionKey is less than the Key, just drop the action
            modify_kvnode(Bt, NodeTuple, N, RestActions, ResultNode, QueryOutput);
        fetch ->
            % ActionKey is less than the Key, the key/value must not exist in the tree
            modify_kvnode(Bt, NodeTuple, N, RestActions, ResultNode, [{not_found, {ActionKey, nil}} | QueryOutput])
        end;
    false ->
        % ActionKey and Key are maybe equal.
        case less(Bt, Key, ActionKey) of
        false ->
            case ActionType of
            insert ->
                modify_kvnode(Bt, NodeTuple, N+1, RestActions, [{ActionKey, ActionValue} | ResultNode], QueryOutput);
            remove ->
                modify_kvnode(Bt, NodeTuple, N+1, RestActions, ResultNode, QueryOutput);
            fetch ->
                % ActionKey is equal to the Key, insert into the QueryOuput, but re-process the node
                % since an identical action key can follow it.
                modify_kvnode(Bt, NodeTuple, N, RestActions, ResultNode, [{ok, assemble(Bt, Key, Value)} | QueryOutput])
            end;
        true ->
            modify_kvnode(Bt, NodeTuple, N + 1, [{ActionType, ActionKey, ActionValue} | RestActions], [{Key, Value} | ResultNode], QueryOutput)
        end
    end.


reduce_stream_node(_Bt, _Dir, nil, _KeyStart, _KeyEnd, GroupedKey, GroupedKVsAcc, 
        GroupedRedsAcc, _KeyGroupFun, _Fun, Acc) ->
    {ok, Acc, GroupedRedsAcc, GroupedKVsAcc, GroupedKey}; 
reduce_stream_node(Bt, Dir, {P, _R}, KeyStart, KeyEnd, GroupedKey, GroupedKVsAcc, 
        GroupedRedsAcc, KeyGroupFun, Fun, Acc) ->
    case get_node(Bt, P) of
    {kp_node, NodeList} ->
        reduce_stream_kp_node(Bt, Dir, NodeList, KeyStart, KeyEnd, GroupedKey,
                GroupedKVsAcc, GroupedRedsAcc, KeyGroupFun, Fun, Acc);
    {kv_node, KVs} ->
        reduce_stream_kv_node(Bt, Dir, KVs, KeyStart, KeyEnd, GroupedKey,
                GroupedKVsAcc, GroupedRedsAcc, KeyGroupFun, Fun, Acc)
    end.

reduce_stream_kv_node(Bt, Dir, KVs, KeyStart, KeyEnd,
                        GroupedKey, GroupedKVsAcc, GroupedRedsAcc,
                        KeyGroupFun, Fun, Acc) ->

    GTEKeyStartKVs =
    case KeyStart of
    nil ->
        KVs;
    _ ->
        lists:dropwhile(fun({Key,_}) -> less(Bt, Key, KeyStart) end, KVs)
    end,
    KVs2 =
    case KeyEnd of
    nil ->
        GTEKeyStartKVs;
    _ ->
        lists:takewhile(
            fun({Key,_}) ->
                not less(Bt, KeyEnd, Key)
            end, GTEKeyStartKVs)
    end,
    reduce_stream_kv_node2(Bt, adjust_dir(Dir, KVs2), GroupedKey, GroupedKVsAcc, GroupedRedsAcc,
                        KeyGroupFun, Fun, Acc).


reduce_stream_kv_node2(_Bt, [], GroupedKey, GroupedKVsAcc, GroupedRedsAcc,
        _KeyGroupFun, _Fun, Acc) ->
    {ok, Acc, GroupedRedsAcc, GroupedKVsAcc, GroupedKey};
reduce_stream_kv_node2(Bt, [{Key, Value}| RestKVs], GroupedKey, GroupedKVsAcc,
        GroupedRedsAcc, KeyGroupFun, Fun, Acc) ->
    case GroupedKey of
    nil ->
        reduce_stream_kv_node2(Bt, RestKVs, Key,
                [assemble(Bt,Key,Value)], [], KeyGroupFun, Fun, Acc);
    _ ->
    
        case KeyGroupFun(GroupedKey, Key) of
        true ->
            reduce_stream_kv_node2(Bt, RestKVs, GroupedKey,
                [assemble(Bt,Key,Value)|GroupedKVsAcc], GroupedRedsAcc, KeyGroupFun,
                Fun, Acc);
        false ->
            case Fun(GroupedKey, {GroupedKVsAcc, GroupedRedsAcc}, Acc) of
            {ok, Acc2} ->
                reduce_stream_kv_node2(Bt, RestKVs, Key, [assemble(Bt,Key,Value)],
                    [], KeyGroupFun, Fun, Acc2);
            {stop, Acc2} ->
                throw({stop, Acc2})
            end
        end
    end.

reduce_stream_kp_node(Bt, Dir, NodeList, KeyStart, KeyEnd,
                        GroupedKey, GroupedKVsAcc, GroupedRedsAcc,
                        KeyGroupFun, Fun, Acc) ->
    Nodes =
    case KeyStart of
    nil ->
        NodeList;
    _ ->
        lists:dropwhile(
            fun({Key,_}) ->
                less(Bt, Key, KeyStart)
            end, NodeList)
    end,
    NodesInRange =
    case KeyEnd of
    nil ->
        Nodes;
    _ ->
        {InRange, MaybeInRange} = lists:splitwith(
            fun({Key,_}) ->
                less(Bt, Key, KeyEnd)
            end, Nodes),
        InRange ++ case MaybeInRange of [] -> []; [FirstMaybe|_] -> [FirstMaybe] end
    end,
    reduce_stream_kp_node2(Bt, Dir, adjust_dir(Dir, NodesInRange), KeyStart, KeyEnd,
        GroupedKey, GroupedKVsAcc, GroupedRedsAcc, KeyGroupFun, Fun, Acc).


reduce_stream_kp_node2(Bt, Dir, [{_Key, NodeInfo} | RestNodeList], KeyStart, KeyEnd,
                        nil, [], [], KeyGroupFun, Fun, Acc) ->
    {ok, Acc2, GroupedRedsAcc2, GroupedKVsAcc2, GroupedKey2} =
            reduce_stream_node(Bt, Dir, NodeInfo, KeyStart, KeyEnd, nil,
                [], [], KeyGroupFun, Fun, Acc),
    reduce_stream_kp_node2(Bt, Dir, RestNodeList, KeyStart, KeyEnd, GroupedKey2,
            GroupedKVsAcc2, GroupedRedsAcc2, KeyGroupFun, Fun, Acc2);
reduce_stream_kp_node2(Bt, Dir, NodeList, KeyStart, KeyEnd,
        GroupedKey, GroupedKVsAcc, GroupedRedsAcc, KeyGroupFun, Fun, Acc) ->
    {Grouped0, Ungrouped0} = lists:splitwith(fun({Key,_}) ->
        KeyGroupFun(GroupedKey, Key) end, NodeList),
    {GroupedNodes, UngroupedNodes} = 
    case Grouped0 of
    [] ->
        {Grouped0, Ungrouped0};
    _ ->
        [FirstGrouped | RestGrouped] = lists:reverse(Grouped0),
        {RestGrouped, [FirstGrouped | Ungrouped0]}
    end,
    GroupedReds = [R || {_, {_,R}} <- GroupedNodes],
    case UngroupedNodes of
    [{_Key, NodeInfo}|RestNodes] ->
        {ok, Acc2, GroupedRedsAcc2, GroupedKVsAcc2, GroupedKey2} = 
            reduce_stream_node(Bt, Dir, NodeInfo, KeyStart, KeyEnd, GroupedKey,
                GroupedKVsAcc, GroupedReds ++ GroupedRedsAcc, KeyGroupFun, Fun, Acc),
        reduce_stream_kp_node2(Bt, Dir, RestNodes, KeyStart, KeyEnd, GroupedKey2,
                GroupedKVsAcc2, GroupedRedsAcc2, KeyGroupFun, Fun, Acc2);
    [] ->
        {ok, Acc, GroupedReds ++ GroupedRedsAcc, GroupedKVsAcc, GroupedKey}
    end.

adjust_dir(fwd, List) ->
    List;
adjust_dir(rev, List) ->
    lists:reverse(List).

stream_node(Bt, Reds, PointerInfo, nil, Dir, Fun, Acc) ->
    stream_node(Bt, Reds, PointerInfo, Dir, Fun, Acc);
stream_node(Bt, Reds, PointerInfo, {}, rev, Fun, Acc) ->
    stream_node(Bt, Reds, PointerInfo, rev, Fun, Acc);
stream_node(_Bt, _Reds, nil, _StartKey, _Dir, _Fun, Acc) ->
    {ok, Acc};
stream_node(Bt, Reds, {Pointer, _Reds}, StartKey, Dir, Fun, Acc) ->
    {NodeType, NodeList} = get_node(Bt, Pointer),
    case NodeType of
    kp_node ->
        stream_kp_node(Bt, Reds, adjust_dir(Dir, NodeList), StartKey, Dir, Fun, Acc);
    kv_node ->
        stream_kv_node(Bt, Reds, adjust_dir(Dir, NodeList), StartKey, Dir, Fun, Acc)
    end.

stream_node(_Bt, _Reds, nil, _Dir, _Fun, Acc) ->
    {ok, Acc};
stream_node(Bt, Reds, {Pointer, _Reds}, Dir, Fun, Acc) ->
    {NodeType, NodeList} = get_node(Bt, Pointer),
    case NodeType of
    kp_node ->
        stream_kp_node(Bt, Reds, adjust_dir(Dir, NodeList), Dir, Fun, Acc);
    kv_node ->
        stream_kv_node2(Bt, Reds, [], adjust_dir(Dir, NodeList), Dir, Fun, Acc)
    end.

stream_kp_node(_Bt, _Reds, [], _Dir, _Fun, Acc) ->
    {ok, Acc};
stream_kp_node(Bt, Reds, [{_Key, {Pointer, Red}} | Rest], Dir, Fun, Acc) ->
    case stream_node(Bt, Reds, {Pointer, Red}, Dir, Fun, Acc) of
    {ok, Acc2} ->
        stream_kp_node(Bt, [Red | Reds], Rest, Dir, Fun, Acc2);
    {stop, Acc2} ->
        {stop, Acc2}
    end.

drop_nodes(_Bt, Reds, _StartKey, []) ->
    {Reds, []};
drop_nodes(Bt, Reds, StartKey, [{NodeKey, {Pointer, Red}} | RestKPs]) ->
    case less(Bt, NodeKey, StartKey) of
    true -> drop_nodes(Bt, [Red | Reds], StartKey, RestKPs);
    false -> {Reds, [{NodeKey, {Pointer, Red}} | RestKPs]}
    end.

stream_kp_node(Bt, Reds, KPs, StartKey, Dir, Fun, Acc) ->
    {NewReds, NodesToStream} =
    case Dir of
    fwd ->
        % drop all nodes sorting before the key
        drop_nodes(Bt, Reds, StartKey, KPs);
    rev ->
        % keep all nodes sorting before the key, AND the first node to sort after
        RevKPs = lists:reverse(KPs),
        case lists:splitwith(fun({Key, _Pointer}) -> less(Bt, Key, StartKey) end, RevKPs) of
        {_RevBefore, []} ->
            % everything sorts before it
            {Reds, KPs};
        {RevBefore, [FirstAfter | Drop]} ->
            {[Red || {_K,{_P,Red}} <- Drop] ++ Reds,
                [FirstAfter | lists:reverse(RevBefore)]}
        end
    end,
    case NodesToStream of
    [] ->
        {ok, Acc};
    [{_Key, {Pointer, Red}} | Rest] ->
        case stream_node(Bt, NewReds, {Pointer, Red}, StartKey, Dir, Fun, Acc) of
        {ok, Acc2} ->
            stream_kp_node(Bt, [Red | NewReds], Rest, Dir, Fun, Acc2);
        {stop, Acc2} ->
            {stop, Acc2}
        end
    end.

stream_kv_node(Bt, Reds, KVs, StartKey, Dir, Fun, Acc) ->
    DropFun =
    case Dir of
    fwd ->
        fun({Key, _}) -> less(Bt, Key, StartKey) end;
    rev ->
        fun({Key, _}) -> less(Bt, StartKey, Key) end
    end,
    {LTKVs, GTEKVs} = lists:splitwith(DropFun, KVs),
    AssembleLTKVs = [assemble(Bt,K,V) || {K,V} <- LTKVs],
    stream_kv_node2(Bt, Reds, AssembleLTKVs, GTEKVs, Dir, Fun, Acc).

stream_kv_node2(_Bt, _Reds, _PrevKVs, [], _Dir, _Fun, Acc) ->
    {ok, Acc};
stream_kv_node2(Bt, Reds, PrevKVs, [{K,V} | RestKVs], Dir, Fun, Acc) ->
    AssembledKV = assemble(Bt, K, V),
    case Fun(AssembledKV, {PrevKVs, Reds}, Acc) of
    {ok, Acc2} ->
        stream_kv_node2(Bt, Reds, [AssembledKV | PrevKVs], RestKVs, Dir, Fun, Acc2);
    {stop, Acc2} ->
        {stop, Acc2}
    end.