~bzr-pqm/bzr/bzr.dev

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
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
# Copyright (C) 2008 Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#

"""B+Tree indices"""

import array
import bisect
from bisect import bisect_right
from copy import deepcopy
import math
import struct
import tempfile
import zlib

from bzrlib import (
    chunk_writer,
    debug,
    errors,
    index,
    lru_cache,
    osutils,
    trace,
    )
from bzrlib.index import _OPTION_NODE_REFS, _OPTION_KEY_ELEMENTS, _OPTION_LEN
from bzrlib.transport import get_transport


_BTSIGNATURE = "B+Tree Graph Index 2\n"
_OPTION_ROW_LENGTHS = "row_lengths="
_LEAF_FLAG = "type=leaf\n"
_INTERNAL_FLAG = "type=internal\n"
_INTERNAL_OFFSET = "offset="

_RESERVED_HEADER_BYTES = 120
_PAGE_SIZE = 4096

# 4K per page: 4MB - 1000 entries
_NODE_CACHE_SIZE = 1000


class _BuilderRow(object):
    """The stored state accumulated while writing out a row in the index.

    :ivar spool: A temporary file used to accumulate nodes for this row
        in the tree.
    :ivar nodes: The count of nodes emitted so far.
    """

    def __init__(self):
        """Create a _BuilderRow."""
        self.nodes = 0
        self.spool = tempfile.TemporaryFile()
        self.writer = None

    def finish_node(self, pad=True):
        byte_lines, _, padding = self.writer.finish()
        if self.nodes == 0:
            # padded note:
            self.spool.write("\x00" * _RESERVED_HEADER_BYTES)
        skipped_bytes = 0
        if not pad and padding:
            del byte_lines[-1]
            skipped_bytes = padding
        self.spool.writelines(byte_lines)
        remainder = (self.spool.tell() + skipped_bytes) % _PAGE_SIZE
        if remainder != 0:
            raise AssertionError("incorrect node length: %d, %d"
                                 % (self.spool.tell(), remainder))
        self.nodes += 1
        self.writer = None


class _InternalBuilderRow(_BuilderRow):
    """The stored state accumulated while writing out internal rows."""

    def finish_node(self, pad=True):
        if not pad:
            raise AssertionError("Must pad internal nodes only.")
        _BuilderRow.finish_node(self)


class _LeafBuilderRow(_BuilderRow):
    """The stored state accumulated while writing out a leaf rows."""


class BTreeBuilder(index.GraphIndexBuilder):
    """A Builder for B+Tree based Graph indices.

    The resulting graph has the structure:

    _SIGNATURE OPTIONS NODES
    _SIGNATURE     := 'B+Tree Graph Index 1' NEWLINE
    OPTIONS        := REF_LISTS KEY_ELEMENTS LENGTH
    REF_LISTS      := 'node_ref_lists=' DIGITS NEWLINE
    KEY_ELEMENTS   := 'key_elements=' DIGITS NEWLINE
    LENGTH         := 'len=' DIGITS NEWLINE
    ROW_LENGTHS    := 'row_lengths' DIGITS (COMMA DIGITS)*
    NODES          := NODE_COMPRESSED*
    NODE_COMPRESSED:= COMPRESSED_BYTES{4096}
    NODE_RAW       := INTERNAL | LEAF
    INTERNAL       := INTERNAL_FLAG POINTERS
    LEAF           := LEAF_FLAG ROWS
    KEY_ELEMENT    := Not-whitespace-utf8
    KEY            := KEY_ELEMENT (NULL KEY_ELEMENT)*
    ROWS           := ROW*
    ROW            := KEY NULL ABSENT? NULL REFERENCES NULL VALUE NEWLINE
    ABSENT         := 'a'
    REFERENCES     := REFERENCE_LIST (TAB REFERENCE_LIST){node_ref_lists - 1}
    REFERENCE_LIST := (REFERENCE (CR REFERENCE)*)?
    REFERENCE      := KEY
    VALUE          := no-newline-no-null-bytes
    """

    def __init__(self, reference_lists=0, key_elements=1, spill_at=100000):
        """See GraphIndexBuilder.__init__.

        :param spill_at: Optional parameter controlling the maximum number
            of nodes that BTreeBuilder will hold in memory.
        """
        index.GraphIndexBuilder.__init__(self, reference_lists=reference_lists,
            key_elements=key_elements)
        self._spill_at = spill_at
        self._backing_indices = []
        # A map of {key: (node_refs, value)}
        self._nodes = {}
        # Indicate it hasn't been built yet
        self._nodes_by_key = None
        self._optimize_for_size = False

    def add_node(self, key, value, references=()):
        """Add a node to the index.

        If adding the node causes the builder to reach its spill_at threshold,
        disk spilling will be triggered.

        :param key: The key. keys are non-empty tuples containing
            as many whitespace-free utf8 bytestrings as the key length
            defined for this index.
        :param references: An iterable of iterables of keys. Each is a
            reference to another key.
        :param value: The value to associate with the key. It may be any
            bytes as long as it does not contain \0 or \n.
        """
        # we don't care about absent_references
        node_refs, _ = self._check_key_ref_value(key, references, value)
        if key in self._nodes:
            raise errors.BadIndexDuplicateKey(key, self)
        self._nodes[key] = (node_refs, value)
        self._keys.add(key)
        if self._nodes_by_key is not None and self._key_length > 1:
            self._update_nodes_by_key(key, value, node_refs)
        if len(self._keys) < self._spill_at:
            return
        self._spill_mem_keys_to_disk()

    def _spill_mem_keys_to_disk(self):
        """Write the in memory keys down to disk to cap memory consumption.

        If we already have some keys written to disk, we will combine them so
        as to preserve the sorted order.  The algorithm for combining uses
        powers of two.  So on the first spill, write all mem nodes into a
        single index. On the second spill, combine the mem nodes with the nodes
        on disk to create a 2x sized disk index and get rid of the first index.
        On the third spill, create a single new disk index, which will contain
        the mem nodes, and preserve the existing 2x sized index.  On the fourth,
        combine mem with the first and second indexes, creating a new one of
        size 4x. On the fifth create a single new one, etc.
        """
        iterators_to_combine = [self._iter_mem_nodes()]
        pos = -1
        for pos, backing in enumerate(self._backing_indices):
            if backing is None:
                pos -= 1
                break
            iterators_to_combine.append(backing.iter_all_entries())
        backing_pos = pos + 1
        new_backing_file, size = \
            self._write_nodes(self._iter_smallest(iterators_to_combine))
        dir_path, base_name = osutils.split(new_backing_file.name)
        # Note: The transport here isn't strictly needed, because we will use
        #       direct access to the new_backing._file object
        new_backing = BTreeGraphIndex(get_transport(dir_path),
                                      base_name, size)
        # GC will clean up the file
        new_backing._file = new_backing_file
        if len(self._backing_indices) == backing_pos:
            self._backing_indices.append(None)
        self._backing_indices[backing_pos] = new_backing
        for pos in range(backing_pos):
            self._backing_indices[pos] = None
        self._keys = set()
        self._nodes = {}
        self._nodes_by_key = None

    def add_nodes(self, nodes):
        """Add nodes to the index.

        :param nodes: An iterable of (key, node_refs, value) entries to add.
        """
        if self.reference_lists:
            for (key, value, node_refs) in nodes:
                self.add_node(key, value, node_refs)
        else:
            for (key, value) in nodes:
                self.add_node(key, value)

    def _iter_mem_nodes(self):
        """Iterate over the nodes held in memory."""
        nodes = self._nodes
        if self.reference_lists:
            for key in sorted(nodes):
                references, value = nodes[key]
                yield self, key, value, references
        else:
            for key in sorted(nodes):
                references, value = nodes[key]
                yield self, key, value

    def _iter_smallest(self, iterators_to_combine):
        if len(iterators_to_combine) == 1:
            for value in iterators_to_combine[0]:
                yield value
            return
        current_values = []
        for iterator in iterators_to_combine:
            try:
                current_values.append(iterator.next())
            except StopIteration:
                current_values.append(None)
        last = None
        while True:
            # Decorate candidates with the value to allow 2.4's min to be used.
            candidates = [(item[1][1], item) for item
                in enumerate(current_values) if item[1] is not None]
            if not len(candidates):
                return
            selected = min(candidates)
            # undecorate back to (pos, node)
            selected = selected[1]
            if last == selected[1][1]:
                raise errors.BadIndexDuplicateKey(last, self)
            last = selected[1][1]
            # Yield, with self as the index
            yield (self,) + selected[1][1:]
            pos = selected[0]
            try:
                current_values[pos] = iterators_to_combine[pos].next()
            except StopIteration:
                current_values[pos] = None

    def _add_key(self, string_key, line, rows):
        """Add a key to the current chunk.

        :param string_key: The key to add.
        :param line: The fully serialised key and value.
        """
        if rows[-1].writer is None:
            # opening a new leaf chunk;
            for pos, internal_row in enumerate(rows[:-1]):
                # flesh out any internal nodes that are needed to
                # preserve the height of the tree
                if internal_row.writer is None:
                    length = _PAGE_SIZE
                    if internal_row.nodes == 0:
                        length -= _RESERVED_HEADER_BYTES # padded
                    internal_row.writer = chunk_writer.ChunkWriter(length, 0,
                        optimize_for_size=self._optimize_for_size)
                    internal_row.writer.write(_INTERNAL_FLAG)
                    internal_row.writer.write(_INTERNAL_OFFSET +
                        str(rows[pos + 1].nodes) + "\n")
            # add a new leaf
            length = _PAGE_SIZE
            if rows[-1].nodes == 0:
                length -= _RESERVED_HEADER_BYTES # padded
            rows[-1].writer = chunk_writer.ChunkWriter(length,
                optimize_for_size=self._optimize_for_size)
            rows[-1].writer.write(_LEAF_FLAG)
        if rows[-1].writer.write(line):
            # this key did not fit in the node:
            rows[-1].finish_node()
            key_line = string_key + "\n"
            new_row = True
            for row in reversed(rows[:-1]):
                # Mark the start of the next node in the node above. If it
                # doesn't fit then propogate upwards until we find one that
                # it does fit into.
                if row.writer.write(key_line):
                    row.finish_node()
                else:
                    # We've found a node that can handle the pointer.
                    new_row = False
                    break
            # If we reached the current root without being able to mark the
            # division point, then we need a new root:
            if new_row:
                # We need a new row
                if 'index' in debug.debug_flags:
                    trace.mutter('Inserting new global row.')
                new_row = _InternalBuilderRow()
                reserved_bytes = 0
                rows.insert(0, new_row)
                # This will be padded, hence the -100
                new_row.writer = chunk_writer.ChunkWriter(
                    _PAGE_SIZE - _RESERVED_HEADER_BYTES,
                    reserved_bytes,
                    optimize_for_size=self._optimize_for_size)
                new_row.writer.write(_INTERNAL_FLAG)
                new_row.writer.write(_INTERNAL_OFFSET +
                    str(rows[1].nodes - 1) + "\n")
                new_row.writer.write(key_line)
            self._add_key(string_key, line, rows)

    def _write_nodes(self, node_iterator):
        """Write node_iterator out as a B+Tree.

        :param node_iterator: An iterator of sorted nodes. Each node should
            match the output given by iter_all_entries.
        :return: A file handle for a temporary file containing a B+Tree for
            the nodes.
        """
        # The index rows - rows[0] is the root, rows[1] is the layer under it
        # etc.
        rows = []
        # forward sorted by key. In future we may consider topological sorting,
        # at the cost of table scans for direct lookup, or a second index for
        # direct lookup
        key_count = 0
        # A stack with the number of nodes of each size. 0 is the root node
        # and must always be 1 (if there are any nodes in the tree).
        self.row_lengths = []
        # Loop over all nodes adding them to the bottom row
        # (rows[-1]). When we finish a chunk in a row,
        # propogate the key that didn't fit (comes after the chunk) to the
        # row above, transitively.
        for node in node_iterator:
            if key_count == 0:
                # First key triggers the first row
                rows.append(_LeafBuilderRow())
            key_count += 1
            string_key, line = _btree_serializer._flatten_node(node,
                                    self.reference_lists)
            self._add_key(string_key, line, rows)
        for row in reversed(rows):
            pad = (type(row) != _LeafBuilderRow)
            row.finish_node(pad=pad)
        result = tempfile.NamedTemporaryFile()
        lines = [_BTSIGNATURE]
        lines.append(_OPTION_NODE_REFS + str(self.reference_lists) + '\n')
        lines.append(_OPTION_KEY_ELEMENTS + str(self._key_length) + '\n')
        lines.append(_OPTION_LEN + str(key_count) + '\n')
        row_lengths = [row.nodes for row in rows]
        lines.append(_OPTION_ROW_LENGTHS + ','.join(map(str, row_lengths)) + '\n')
        result.writelines(lines)
        position = sum(map(len, lines))
        root_row = True
        if position > _RESERVED_HEADER_BYTES:
            raise AssertionError("Could not fit the header in the"
                                 " reserved space: %d > %d"
                                 % (position, _RESERVED_HEADER_BYTES))
        # write the rows out:
        for row in rows:
            reserved = _RESERVED_HEADER_BYTES # reserved space for first node
            row.spool.flush()
            row.spool.seek(0)
            # copy nodes to the finalised file.
            # Special case the first node as it may be prefixed
            node = row.spool.read(_PAGE_SIZE)
            result.write(node[reserved:])
            result.write("\x00" * (reserved - position))
            position = 0 # Only the root row actually has an offset
            copied_len = osutils.pumpfile(row.spool, result)
            if copied_len != (row.nodes - 1) * _PAGE_SIZE:
                if type(row) != _LeafBuilderRow:
                    raise AssertionError("Incorrect amount of data copied"
                        " expected: %d, got: %d"
                        % ((row.nodes - 1) * _PAGE_SIZE,
                           copied_len))
        result.flush()
        size = result.tell()
        result.seek(0)
        return result, size

    def finish(self):
        """Finalise the index.

        :return: A file handle for a temporary file containing the nodes added
            to the index.
        """
        return self._write_nodes(self.iter_all_entries())[0]

    def iter_all_entries(self):
        """Iterate over all keys within the index

        :return: An iterable of (index, key, reference_lists, value). There is no
            defined order for the result iteration - it will be in the most
            efficient order for the index (in this case dictionary hash order).
        """
        if 'evil' in debug.debug_flags:
            trace.mutter_callsite(3,
                "iter_all_entries scales with size of history.")
        # Doing serial rather than ordered would be faster; but this shouldn't
        # be getting called routinely anyway.
        iterators = [self._iter_mem_nodes()]
        for backing in self._backing_indices:
            if backing is not None:
                iterators.append(backing.iter_all_entries())
        if len(iterators) == 1:
            return iterators[0]
        return self._iter_smallest(iterators)

    def iter_entries(self, keys):
        """Iterate over keys within the index.

        :param keys: An iterable providing the keys to be retrieved.
        :return: An iterable of (index, key, value, reference_lists). There is no
            defined order for the result iteration - it will be in the most
            efficient order for the index (keys iteration order in this case).
        """
        keys = set(keys)
        local_keys = keys.intersection(self._keys)
        if self.reference_lists:
            for key in local_keys:
                node = self._nodes[key]
                yield self, key, node[1], node[0]
        else:
            for key in local_keys:
                node = self._nodes[key]
                yield self, key, node[1]
        # Find things that are in backing indices that have not been handled
        # yet.
        if not self._backing_indices:
            return # We won't find anything there either
        # Remove all of the keys that we found locally
        keys.difference_update(local_keys)
        for backing in self._backing_indices:
            if backing is None:
                continue
            if not keys:
                return
            for node in backing.iter_entries(keys):
                keys.remove(node[1])
                yield (self,) + node[1:]

    def iter_entries_prefix(self, keys):
        """Iterate over keys within the index using prefix matching.

        Prefix matching is applied within the tuple of a key, not to within
        the bytestring of each key element. e.g. if you have the keys ('foo',
        'bar'), ('foobar', 'gam') and do a prefix search for ('foo', None) then
        only the former key is returned.

        :param keys: An iterable providing the key prefixes to be retrieved.
            Each key prefix takes the form of a tuple the length of a key, but
            with the last N elements 'None' rather than a regular bytestring.
            The first element cannot be 'None'.
        :return: An iterable as per iter_all_entries, but restricted to the
            keys with a matching prefix to those supplied. No additional keys
            will be returned, and every match that is in the index will be
            returned.
        """
        # XXX: To much duplication with the GraphIndex class; consider finding
        # a good place to pull out the actual common logic.
        keys = set(keys)
        if not keys:
            return
        for backing in self._backing_indices:
            if backing is None:
                continue
            for node in backing.iter_entries_prefix(keys):
                yield (self,) + node[1:]
        if self._key_length == 1:
            for key in keys:
                # sanity check
                if key[0] is None:
                    raise errors.BadIndexKey(key)
                if len(key) != self._key_length:
                    raise errors.BadIndexKey(key)
                try:
                    node = self._nodes[key]
                except KeyError:
                    continue
                if self.reference_lists:
                    yield self, key, node[1], node[0]
                else:
                    yield self, key, node[1]
            return
        for key in keys:
            # sanity check
            if key[0] is None:
                raise errors.BadIndexKey(key)
            if len(key) != self._key_length:
                raise errors.BadIndexKey(key)
            # find what it refers to:
            key_dict = self._get_nodes_by_key()
            elements = list(key)
            # find the subdict to return
            try:
                while len(elements) and elements[0] is not None:
                    key_dict = key_dict[elements[0]]
                    elements.pop(0)
            except KeyError:
                # a non-existant lookup.
                continue
            if len(elements):
                dicts = [key_dict]
                while dicts:
                    key_dict = dicts.pop(-1)
                    # can't be empty or would not exist
                    item, value = key_dict.iteritems().next()
                    if type(value) == dict:
                        # push keys
                        dicts.extend(key_dict.itervalues())
                    else:
                        # yield keys
                        for value in key_dict.itervalues():
                            yield (self, ) + value
            else:
                yield (self, ) + key_dict

    def _get_nodes_by_key(self):
        if self._nodes_by_key is None:
            nodes_by_key = {}
            if self.reference_lists:
                for key, (references, value) in self._nodes.iteritems():
                    key_dict = nodes_by_key
                    for subkey in key[:-1]:
                        key_dict = key_dict.setdefault(subkey, {})
                    key_dict[key[-1]] = key, value, references
            else:
                for key, (references, value) in self._nodes.iteritems():
                    key_dict = nodes_by_key
                    for subkey in key[:-1]:
                        key_dict = key_dict.setdefault(subkey, {})
                    key_dict[key[-1]] = key, value
            self._nodes_by_key = nodes_by_key
        return self._nodes_by_key

    def key_count(self):
        """Return an estimate of the number of keys in this index.

        For InMemoryGraphIndex the estimate is exact.
        """
        return len(self._keys) + sum(backing.key_count() for backing in
            self._backing_indices if backing is not None)

    def validate(self):
        """In memory index's have no known corruption at the moment."""


class _LeafNode(object):
    """A leaf node for a serialised B+Tree index."""

    def __init__(self, bytes, key_length, ref_list_length):
        """Parse bytes to create a leaf node object."""
        # splitlines mangles the \r delimiters.. don't use it.
        self.keys = dict(_btree_serializer._parse_leaf_lines(bytes,
            key_length, ref_list_length))


class _InternalNode(object):
    """An internal node for a serialised B+Tree index."""

    def __init__(self, bytes):
        """Parse bytes to create an internal node object."""
        # splitlines mangles the \r delimiters.. don't use it.
        self.keys = self._parse_lines(bytes.split('\n'))

    def _parse_lines(self, lines):
        nodes = []
        self.offset = int(lines[1][7:])
        for line in lines[2:]:
            if line == '':
                break
            nodes.append(tuple(line.split('\0')))
        return nodes


class BTreeGraphIndex(object):
    """Access to nodes via the standard GraphIndex interface for B+Tree's.

    Individual nodes are held in a LRU cache. This holds the root node in
    memory except when very large walks are done.
    """

    def __init__(self, transport, name, size):
        """Create a B+Tree index object on the index name.

        :param transport: The transport to read data for the index from.
        :param name: The file name of the index on transport.
        :param size: Optional size of the index in bytes. This allows
            compatibility with the GraphIndex API, as well as ensuring that
            the initial read (to read the root node header) can be done
            without over-reading even on empty indices, and on small indices
            allows single-IO to read the entire index.
        """
        self._transport = transport
        self._name = name
        self._size = size
        self._file = None
        self._recommended_pages = self._compute_recommended_pages()
        self._root_node = None
        # Default max size is 100,000 leave values
        self._leaf_value_cache = None # lru_cache.LRUCache(100*1000)
        self._leaf_node_cache = lru_cache.LRUCache(_NODE_CACHE_SIZE)
        self._internal_node_cache = lru_cache.LRUCache()
        self._key_count = None
        self._row_lengths = None
        self._row_offsets = None # Start of each row, [-1] is the end

    def __eq__(self, other):
        """Equal when self and other were created with the same parameters."""
        return (
            type(self) == type(other) and
            self._transport == other._transport and
            self._name == other._name and
            self._size == other._size)

    def __ne__(self, other):
        return not self.__eq__(other)

    def _get_and_cache_nodes(self, nodes):
        """Read nodes and cache them in the lru.

        The nodes list supplied is sorted and then read from disk, each node
        being inserted it into the _node_cache.

        Note: Asking for more nodes than the _node_cache can contain will
        result in some of the results being immediately discarded, to prevent
        this an assertion is raised if more nodes are asked for than are
        cachable.

        :return: A dict of {node_pos: node}
        """
        found = {}
        start_of_leaves = None
        for node_pos, node in self._read_nodes(sorted(nodes)):
            if node_pos == 0: # Special case
                self._root_node = node
            else:
                if start_of_leaves is None:
                    start_of_leaves = self._row_offsets[-2]
                if node_pos < start_of_leaves:
                    self._internal_node_cache.add(node_pos, node)
                else:
                    self._leaf_node_cache.add(node_pos, node)
            found[node_pos] = node
        return found

    def _compute_recommended_pages(self):
        """Convert transport's recommended_page_size into btree pages.

        recommended_page_size is in bytes, we want to know how many _PAGE_SIZE
        pages fit in that length.
        """
        recommended_read = self._transport.recommended_page_size()
        recommended_pages = int(math.ceil(recommended_read /
                                          float(_PAGE_SIZE)))
        return recommended_pages

    def _compute_total_pages_in_index(self):
        """How many pages are in the index.

        If we have read the header we will use the value stored there.
        Otherwise it will be computed based on the length of the index.
        """
        if self._size is None:
            raise AssertionError('_compute_total_pages_in_index should not be'
                                 ' called when self._size is None')
        if self._root_node is not None:
            # This is the number of pages as defined by the header
            return self._row_offsets[-1]
        # This is the number of pages as defined by the size of the index. They
        # should be indentical.
        total_pages = int(math.ceil(self._size / float(_PAGE_SIZE)))
        return total_pages

    def _expand_offsets(self, offsets):
        """Find extra pages to download.

        The idea is that we always want to make big-enough requests (like 64kB
        for http), so that we don't waste round trips. So given the entries
        that we already have cached and the new pages being downloaded figure
        out what other pages we might want to read.

        See also doc/developers/btree_index_prefetch.txt for more details.

        :param offsets: The offsets to be read
        :return: A list of offsets to download
        """
        if 'index' in debug.debug_flags:
            trace.mutter('expanding: %s\toffsets: %s', self._name, offsets)

        if len(offsets) >= self._recommended_pages:
            # Don't add more, we are already requesting more than enough
            if 'index' in debug.debug_flags:
                trace.mutter('  not expanding large request (%s >= %s)',
                             len(offsets), self._recommended_pages)
            return offsets
        if self._size is None:
            # Don't try anything, because we don't know where the file ends
            if 'index' in debug.debug_flags:
                trace.mutter('  not expanding without knowing index size')
            return offsets
        total_pages = self._compute_total_pages_in_index()
        cached_offsets = self._get_offsets_to_cached_pages()
        # If reading recommended_pages would read the rest of the index, just
        # do so.
        if total_pages - len(cached_offsets) <= self._recommended_pages:
            # Read whatever is left
            if cached_offsets:
                expanded = [x for x in xrange(total_pages)
                               if x not in cached_offsets]
            else:
                expanded = range(total_pages)
            if 'index' in debug.debug_flags:
                trace.mutter('  reading all unread pages: %s', expanded)
            return expanded

        if self._root_node is None:
            # ATM on the first read of the root node of a large index, we don't
            # bother pre-reading any other pages. This is because the
            # likelyhood of actually reading interesting pages is very low.
            # See doc/developers/btree_index_prefetch.txt for a discussion, and
            # a possible implementation when we are guessing that the second
            # layer index is small
            final_offsets = offsets
        else:
            tree_depth = len(self._row_lengths)
            if len(cached_offsets) < tree_depth and len(offsets) == 1:
                # We haven't read enough to justify expansion
                # If we are only going to read the root node, and 1 leaf node,
                # then it isn't worth expanding our request. Once we've read at
                # least 2 nodes, then we are probably doing a search, and we
                # start expanding our requests.
                if 'index' in debug.debug_flags:
                    trace.mutter('  not expanding on first reads')
                return offsets
            final_offsets = self._expand_to_neighbors(offsets, cached_offsets,
                                                      total_pages)

        final_offsets = sorted(final_offsets)
        if 'index' in debug.debug_flags:
            trace.mutter('expanded:  %s', final_offsets)
        return final_offsets

    def _expand_to_neighbors(self, offsets, cached_offsets, total_pages):
        """Expand requests to neighbors until we have enough pages.

        This is called from _expand_offsets after policy has determined that we
        want to expand.
        We only want to expand requests within a given layer. We cheat a little
        bit and assume all requests will be in the same layer. This is true
        given the current design, but if it changes this algorithm may perform
        oddly.

        :param offsets: requested offsets
        :param cached_offsets: offsets for pages we currently have cached
        :return: A set() of offsets after expansion
        """
        final_offsets = set(offsets)
        first = end = None
        new_tips = set(final_offsets)
        while len(final_offsets) < self._recommended_pages and new_tips:
            next_tips = set()
            for pos in new_tips:
                if first is None:
                    first, end = self._find_layer_first_and_end(pos)
                previous = pos - 1
                if (previous > 0
                    and previous not in cached_offsets
                    and previous not in final_offsets
                    and previous >= first):
                    next_tips.add(previous)
                after = pos + 1
                if (after < total_pages
                    and after not in cached_offsets
                    and after not in final_offsets
                    and after < end):
                    next_tips.add(after)
                # This would keep us from going bigger than
                # recommended_pages by only expanding the first offsets.
                # However, if we are making a 'wide' request, it is
                # reasonable to expand all points equally.
                # if len(final_offsets) > recommended_pages:
                #     break
            final_offsets.update(next_tips)
            new_tips = next_tips
        return final_offsets

    def external_references(self, ref_list_num):
        if self._root_node is None:
            self._get_root_node()
        if ref_list_num + 1 > self.node_ref_lists:
            raise ValueError('No ref list %d, index has %d ref lists'
                % (ref_list_num, self.node_ref_lists))
        keys = set()
        refs = set()
        for node in self.iter_all_entries():
            keys.add(node[1])
            refs.update(node[3][ref_list_num])
        return refs - keys

    def _find_layer_first_and_end(self, offset):
        """Find the start/stop nodes for the layer corresponding to offset.

        :return: (first, end)
            first is the first node in this layer
            end is the first node of the next layer
        """
        first = end = 0
        for roffset in self._row_offsets:
            first = end
            end = roffset
            if offset < roffset:
                break
        return first, end

    def _get_offsets_to_cached_pages(self):
        """Determine what nodes we already have cached."""
        cached_offsets = set(self._internal_node_cache.keys())
        cached_offsets.update(self._leaf_node_cache.keys())
        if self._root_node is not None:
            cached_offsets.add(0)
        return cached_offsets

    def _get_root_node(self):
        if self._root_node is None:
            # We may not have a root node yet
            self._get_internal_nodes([0])
        return self._root_node

    def _get_nodes(self, cache, node_indexes):
        found = {}
        needed = []
        for idx in node_indexes:
            if idx == 0 and self._root_node is not None:
                found[0] = self._root_node
                continue
            try:
                found[idx] = cache[idx]
            except KeyError:
                needed.append(idx)
        if not needed:
            return found
        needed = self._expand_offsets(needed)
        found.update(self._get_and_cache_nodes(needed))
        return found

    def _get_internal_nodes(self, node_indexes):
        """Get a node, from cache or disk.

        After getting it, the node will be cached.
        """
        return self._get_nodes(self._internal_node_cache, node_indexes)

    def _cache_leaf_values(self, nodes):
        """Cache directly from key => value, skipping the btree."""
        if self._leaf_value_cache is not None:
            for node in nodes.itervalues():
                for key, value in node.keys.iteritems():
                    if key in self._leaf_value_cache:
                        # Don't add the rest of the keys, we've seen this node
                        # before.
                        break
                    self._leaf_value_cache[key] = value

    def _get_leaf_nodes(self, node_indexes):
        """Get a bunch of nodes, from cache or disk."""
        found = self._get_nodes(self._leaf_node_cache, node_indexes)
        self._cache_leaf_values(found)
        return found

    def iter_all_entries(self):
        """Iterate over all keys within the index.

        :return: An iterable of (index, key, value) or (index, key, value, reference_lists).
            The former tuple is used when there are no reference lists in the
            index, making the API compatible with simple key:value index types.
            There is no defined order for the result iteration - it will be in
            the most efficient order for the index.
        """
        if 'evil' in debug.debug_flags:
            trace.mutter_callsite(3,
                "iter_all_entries scales with size of history.")
        if not self.key_count():
            return
        if self._row_offsets[-1] == 1:
            # There is only the root node, and we read that via key_count()
            if self.node_ref_lists:
                for key, (value, refs) in sorted(self._root_node.keys.items()):
                    yield (self, key, value, refs)
            else:
                for key, (value, refs) in sorted(self._root_node.keys.items()):
                    yield (self, key, value)
            return
        start_of_leaves = self._row_offsets[-2]
        end_of_leaves = self._row_offsets[-1]
        needed_offsets = range(start_of_leaves, end_of_leaves)
        if needed_offsets == [0]:
            # Special case when we only have a root node, as we have already
            # read everything
            nodes = [(0, self._root_node)]
        else:
            nodes = self._read_nodes(needed_offsets)
        # We iterate strictly in-order so that we can use this function
        # for spilling index builds to disk.
        if self.node_ref_lists:
            for _, node in nodes:
                for key, (value, refs) in sorted(node.keys.items()):
                    yield (self, key, value, refs)
        else:
            for _, node in nodes:
                for key, (value, refs) in sorted(node.keys.items()):
                    yield (self, key, value)

    @staticmethod
    def _multi_bisect_right(in_keys, fixed_keys):
        """Find the positions where each 'in_key' would fit in fixed_keys.

        This is equivalent to doing "bisect_right" on each in_key into
        fixed_keys

        :param in_keys: A sorted list of keys to match with fixed_keys
        :param fixed_keys: A sorted list of keys to match against
        :return: A list of (integer position, [key list]) tuples.
        """
        if not in_keys:
            return []
        if not fixed_keys:
            # no pointers in the fixed_keys list, which means everything must
            # fall to the left.
            return [(0, in_keys)]

        # TODO: Iterating both lists will generally take M + N steps
        #       Bisecting each key will generally take M * log2 N steps.
        #       If we had an efficient way to compare, we could pick the method
        #       based on which has the fewer number of steps.
        #       There is also the argument that bisect_right is a compiled
        #       function, so there is even more to be gained.
        # iter_steps = len(in_keys) + len(fixed_keys)
        # bisect_steps = len(in_keys) * math.log(len(fixed_keys), 2)
        if len(in_keys) == 1: # Bisect will always be faster for M = 1
            return [(bisect_right(fixed_keys, in_keys[0]), in_keys)]
        # elif bisect_steps < iter_steps:
        #     offsets = {}
        #     for key in in_keys:
        #         offsets.setdefault(bisect_right(fixed_keys, key),
        #                            []).append(key)
        #     return [(o, offsets[o]) for o in sorted(offsets)]
        in_keys_iter = iter(in_keys)
        fixed_keys_iter = enumerate(fixed_keys)
        cur_in_key = in_keys_iter.next()
        cur_fixed_offset, cur_fixed_key = fixed_keys_iter.next()

        class InputDone(Exception): pass
        class FixedDone(Exception): pass

        output = []
        cur_out = []

        # TODO: Another possibility is that rather than iterating on each side,
        #       we could use a combination of bisecting and iterating. For
        #       example, while cur_in_key < fixed_key, bisect to find its
        #       point, then iterate all matching keys, then bisect (restricted
        #       to only the remainder) for the next one, etc.
        try:
            while True:
                if cur_in_key < cur_fixed_key:
                    cur_keys = []
                    cur_out = (cur_fixed_offset, cur_keys)
                    output.append(cur_out)
                    while cur_in_key < cur_fixed_key:
                        cur_keys.append(cur_in_key)
                        try:
                            cur_in_key = in_keys_iter.next()
                        except StopIteration:
                            raise InputDone
                    # At this point cur_in_key must be >= cur_fixed_key
                # step the cur_fixed_key until we pass the cur key, or walk off
                # the end
                while cur_in_key >= cur_fixed_key:
                    try:
                        cur_fixed_offset, cur_fixed_key = fixed_keys_iter.next()
                    except StopIteration:
                        raise FixedDone
        except InputDone:
            # We consumed all of the input, nothing more to do
            pass
        except FixedDone:
            # There was some input left, but we consumed all of fixed, so we
            # have to add one more for the tail
            cur_keys = [cur_in_key]
            cur_keys.extend(in_keys_iter)
            cur_out = (len(fixed_keys), cur_keys)
            output.append(cur_out)
        return output

    def iter_entries(self, keys):
        """Iterate over keys within the index.

        :param keys: An iterable providing the keys to be retrieved.
        :return: An iterable as per iter_all_entries, but restricted to the
            keys supplied. No additional keys will be returned, and every
            key supplied that is in the index will be returned.
        """
        # 6 seconds spent in miss_torture using the sorted() line.
        # Even with out of order disk IO it seems faster not to sort it when
        # large queries are being made.
        # However, now that we are doing multi-way bisecting, we need the keys
        # in sorted order anyway. We could change the multi-way code to not
        # require sorted order. (For example, it bisects for the first node,
        # does an in-order search until a key comes before the current point,
        # which it then bisects for, etc.)
        keys = frozenset(keys)
        if not keys:
            return

        if not self.key_count():
            return

        needed_keys = []
        if self._leaf_value_cache is None:
            needed_keys = keys
        else:
            for key in keys:
                value = self._leaf_value_cache.get(key, None)
                if value is not None:
                    # This key is known not to be here, skip it
                    value, refs = value
                    if self.node_ref_lists:
                        yield (self, key, value, refs)
                    else:
                        yield (self, key, value)
                else:
                    needed_keys.append(key)

        last_key = None
        needed_keys = keys
        if not needed_keys:
            return
        # 6 seconds spent in miss_torture using the sorted() line.
        # Even with out of order disk IO it seems faster not to sort it when
        # large queries are being made.
        needed_keys = sorted(needed_keys)

        nodes_and_keys = [(0, needed_keys)]

        for row_pos, next_row_start in enumerate(self._row_offsets[1:-1]):
            node_indexes = [idx for idx, s_keys in nodes_and_keys]
            nodes = self._get_internal_nodes(node_indexes)

            next_nodes_and_keys = []
            for node_index, sub_keys in nodes_and_keys:
                node = nodes[node_index]
                positions = self._multi_bisect_right(sub_keys, node.keys)
                node_offset = next_row_start + node.offset
                next_nodes_and_keys.extend([(node_offset + pos, s_keys)
                                           for pos, s_keys in positions])
            nodes_and_keys = next_nodes_and_keys
        # We should now be at the _LeafNodes
        node_indexes = [idx for idx, s_keys in nodes_and_keys]

        # TODO: We may *not* want to always read all the nodes in one
        #       big go. Consider setting a max size on this.

        nodes = self._get_leaf_nodes(node_indexes)
        for node_index, sub_keys in nodes_and_keys:
            if not sub_keys:
                continue
            node = nodes[node_index]
            for next_sub_key in sub_keys:
                if next_sub_key in node.keys:
                    value, refs = node.keys[next_sub_key]
                    if self.node_ref_lists:
                        yield (self, next_sub_key, value, refs)
                    else:
                        yield (self, next_sub_key, value)

    def iter_entries_prefix(self, keys):
        """Iterate over keys within the index using prefix matching.

        Prefix matching is applied within the tuple of a key, not to within
        the bytestring of each key element. e.g. if you have the keys ('foo',
        'bar'), ('foobar', 'gam') and do a prefix search for ('foo', None) then
        only the former key is returned.

        WARNING: Note that this method currently causes a full index parse
        unconditionally (which is reasonably appropriate as it is a means for
        thunking many small indices into one larger one and still supplies
        iter_all_entries at the thunk layer).

        :param keys: An iterable providing the key prefixes to be retrieved.
            Each key prefix takes the form of a tuple the length of a key, but
            with the last N elements 'None' rather than a regular bytestring.
            The first element cannot be 'None'.
        :return: An iterable as per iter_all_entries, but restricted to the
            keys with a matching prefix to those supplied. No additional keys
            will be returned, and every match that is in the index will be
            returned.
        """
        keys = sorted(set(keys))
        if not keys:
            return
        # Load if needed to check key lengths
        if self._key_count is None:
            self._get_root_node()
        # TODO: only access nodes that can satisfy the prefixes we are looking
        # for. For now, to meet API usage (as this function is not used by
        # current bzrlib) just suck the entire index and iterate in memory.
        nodes = {}
        if self.node_ref_lists:
            if self._key_length == 1:
                for _1, key, value, refs in self.iter_all_entries():
                    nodes[key] = value, refs
            else:
                nodes_by_key = {}
                for _1, key, value, refs in self.iter_all_entries():
                    key_value = key, value, refs
                    # For a key of (foo, bar, baz) create
                    # _nodes_by_key[foo][bar][baz] = key_value
                    key_dict = nodes_by_key
                    for subkey in key[:-1]:
                        key_dict = key_dict.setdefault(subkey, {})
                    key_dict[key[-1]] = key_value
        else:
            if self._key_length == 1:
                for _1, key, value in self.iter_all_entries():
                    nodes[key] = value
            else:
                nodes_by_key = {}
                for _1, key, value in self.iter_all_entries():
                    key_value = key, value
                    # For a key of (foo, bar, baz) create
                    # _nodes_by_key[foo][bar][baz] = key_value
                    key_dict = nodes_by_key
                    for subkey in key[:-1]:
                        key_dict = key_dict.setdefault(subkey, {})
                    key_dict[key[-1]] = key_value
        if self._key_length == 1:
            for key in keys:
                # sanity check
                if key[0] is None:
                    raise errors.BadIndexKey(key)
                if len(key) != self._key_length:
                    raise errors.BadIndexKey(key)
                try:
                    if self.node_ref_lists:
                        value, node_refs = nodes[key]
                        yield self, key, value, node_refs
                    else:
                        yield self, key, nodes[key]
                except KeyError:
                    pass
            return
        for key in keys:
            # sanity check
            if key[0] is None:
                raise errors.BadIndexKey(key)
            if len(key) != self._key_length:
                raise errors.BadIndexKey(key)
            # find what it refers to:
            key_dict = nodes_by_key
            elements = list(key)
            # find the subdict whose contents should be returned.
            try:
                while len(elements) and elements[0] is not None:
                    key_dict = key_dict[elements[0]]
                    elements.pop(0)
            except KeyError:
                # a non-existant lookup.
                continue
            if len(elements):
                dicts = [key_dict]
                while dicts:
                    key_dict = dicts.pop(-1)
                    # can't be empty or would not exist
                    item, value = key_dict.iteritems().next()
                    if type(value) == dict:
                        # push keys
                        dicts.extend(key_dict.itervalues())
                    else:
                        # yield keys
                        for value in key_dict.itervalues():
                            # each value is the key:value:node refs tuple
                            # ready to yield.
                            yield (self, ) + value
            else:
                # the last thing looked up was a terminal element
                yield (self, ) + key_dict

    def key_count(self):
        """Return an estimate of the number of keys in this index.

        For BTreeGraphIndex the estimate is exact as it is contained in the
        header.
        """
        if self._key_count is None:
            self._get_root_node()
        return self._key_count

    def _compute_row_offsets(self):
        """Fill out the _row_offsets attribute based on _row_lengths."""
        offsets = []
        row_offset = 0
        for row in self._row_lengths:
            offsets.append(row_offset)
            row_offset += row
        offsets.append(row_offset)
        self._row_offsets = offsets

    def _parse_header_from_bytes(self, bytes):
        """Parse the header from a region of bytes.

        :param bytes: The data to parse.
        :return: An offset, data tuple such as readv yields, for the unparsed
            data. (which may be of length 0).
        """
        signature = bytes[0:len(self._signature())]
        if not signature == self._signature():
            raise errors.BadIndexFormatSignature(self._name, BTreeGraphIndex)
        lines = bytes[len(self._signature()):].splitlines()
        options_line = lines[0]
        if not options_line.startswith(_OPTION_NODE_REFS):
            raise errors.BadIndexOptions(self)
        try:
            self.node_ref_lists = int(options_line[len(_OPTION_NODE_REFS):])
        except ValueError:
            raise errors.BadIndexOptions(self)
        options_line = lines[1]
        if not options_line.startswith(_OPTION_KEY_ELEMENTS):
            raise errors.BadIndexOptions(self)
        try:
            self._key_length = int(options_line[len(_OPTION_KEY_ELEMENTS):])
        except ValueError:
            raise errors.BadIndexOptions(self)
        options_line = lines[2]
        if not options_line.startswith(_OPTION_LEN):
            raise errors.BadIndexOptions(self)
        try:
            self._key_count = int(options_line[len(_OPTION_LEN):])
        except ValueError:
            raise errors.BadIndexOptions(self)
        options_line = lines[3]
        if not options_line.startswith(_OPTION_ROW_LENGTHS):
            raise errors.BadIndexOptions(self)
        try:
            self._row_lengths = map(int, [length for length in
                options_line[len(_OPTION_ROW_LENGTHS):].split(',')
                if len(length)])
        except ValueError:
            raise errors.BadIndexOptions(self)
        self._compute_row_offsets()

        # calculate the bytes we have processed
        header_end = (len(signature) + sum(map(len, lines[0:4])) + 4)
        return header_end, bytes[header_end:]

    def _read_nodes(self, nodes):
        """Read some nodes from disk into the LRU cache.

        This performs a readv to get the node data into memory, and parses each
        node, then yields it to the caller. The nodes are requested in the
        supplied order. If possible doing sort() on the list before requesting
        a read may improve performance.

        :param nodes: The nodes to read. 0 - first node, 1 - second node etc.
        :return: None
        """
        # may be the byte string of the whole file
        bytes = None
        # list of (offset, length) regions of the file that should, evenually
        # be read in to data_ranges, either from 'bytes' or from the transport
        ranges = []
        for index in nodes:
            offset = index * _PAGE_SIZE
            size = _PAGE_SIZE
            if index == 0:
                # Root node - special case
                if self._size:
                    size = min(_PAGE_SIZE, self._size)
                else:
                    # The only case where we don't know the size, is for very
                    # small indexes. So we read the whole thing
                    bytes = self._transport.get_bytes(self._name)
                    self._size = len(bytes)
                    # the whole thing should be parsed out of 'bytes'
                    ranges.append((0, len(bytes)))
                    break
            else:
                if offset > self._size:
                    raise AssertionError('tried to read past the end'
                                         ' of the file %s > %s'
                                         % (offset, self._size))
                size = min(size, self._size - offset)
            ranges.append((offset, size))
        if not ranges:
            return
        elif bytes is not None:
            # already have the whole file
            data_ranges = [(start, bytes[start:start+_PAGE_SIZE])
                           for start in xrange(0, len(bytes), _PAGE_SIZE)]
        elif self._file is None:
            data_ranges = self._transport.readv(self._name, ranges)
        else:
            data_ranges = []
            for offset, size in ranges:
                self._file.seek(offset)
                data_ranges.append((offset, self._file.read(size)))
        for offset, data in data_ranges:
            if offset == 0:
                # extract the header
                offset, data = self._parse_header_from_bytes(data)
                if len(data) == 0:
                    continue
            bytes = zlib.decompress(data)
            if bytes.startswith(_LEAF_FLAG):
                node = _LeafNode(bytes, self._key_length, self.node_ref_lists)
            elif bytes.startswith(_INTERNAL_FLAG):
                node = _InternalNode(bytes)
            else:
                raise AssertionError("Unknown node type for %r" % bytes)
            yield offset / _PAGE_SIZE, node

    def _signature(self):
        """The file signature for this index type."""
        return _BTSIGNATURE

    def validate(self):
        """Validate that everything in the index can be accessed."""
        # just read and parse every node.
        self._get_root_node()
        if len(self._row_lengths) > 1:
            start_node = self._row_offsets[1]
        else:
            # We shouldn't be reading anything anyway
            start_node = 1
        node_end = self._row_offsets[-1]
        for node in self._read_nodes(range(start_node, node_end)):
            pass


try:
    from bzrlib import _btree_serializer_c as _btree_serializer
except ImportError:
    from bzrlib import _btree_serializer_py as _btree_serializer