-
Notifications
You must be signed in to change notification settings - Fork 117
/
tuple.h
1099 lines (989 loc) · 29.1 KB
/
tuple.h
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
#ifndef _NDB_TUPLE_H_
#define _NDB_TUPLE_H_
#include <atomic>
#include <vector>
#include <string>
#include <utility>
#include <limits>
#include <unordered_map>
#include <ostream>
#include <thread>
#include "amd64.h"
#include "core.h"
#include "counter.h"
#include "macros.h"
#include "varkey.h"
#include "util.h"
#include "rcu.h"
#include "thread.h"
#include "spinlock.h"
#include "small_unordered_map.h"
#include "prefetch.h"
#include "ownership_checker.h"
// debugging tool
//#define TUPLE_LOCK_OWNERSHIP_CHECKING
template <template <typename> class Protocol, typename Traits>
class transaction; // forward decl
// XXX: hack
extern std::string (*g_proto_version_str)(uint64_t v);
/**
* A dbtuple is the type of value which we stick
* into underlying (non-transactional) data structures- it
* also contains the memory of the value
*/
struct dbtuple {
friend std::ostream &
operator<<(std::ostream &o, const dbtuple &tuple);
public:
// trying to save space by putting constraints
// on node maximums
typedef uint32_t version_t;
typedef uint16_t node_size_type;
typedef uint64_t tid_t;
typedef uint8_t * record_type;
typedef const uint8_t * const_record_type;
typedef size_t size_type;
typedef std::string string_type;
static const tid_t MIN_TID = 0;
static const tid_t MAX_TID = (tid_t) -1;
// lock ownership helpers- works by recording all tuple
// locks obtained in each transaction, and then when the txn
// finishes, calling AssertAllTupleLocksReleased(), which makes
// sure the current thread is no longer the owner of any locks
// acquired during the txn
#ifdef TUPLE_LOCK_OWNERSHIP_CHECKING
static inline void
TupleLockRegionBegin()
{
ownership_checker<dbtuple, dbtuple>::NodeLockRegionBegin();
}
// is used to signal the end of a tuple lock region
static inline void
AssertAllTupleLocksReleased()
{
ownership_checker<dbtuple, dbtuple>::AssertAllNodeLocksReleased();
}
private:
static inline void
AddTupleToLockRegion(const dbtuple *n)
{
ownership_checker<dbtuple, dbtuple>::AddNodeToLockRegion(n);
}
#endif
private:
static const version_t HDR_LOCKED_MASK = 0x1;
static const version_t HDR_DELETING_SHIFT = 1;
static const version_t HDR_DELETING_MASK = 0x1 << HDR_DELETING_SHIFT;
static const version_t HDR_WRITE_INTENT_SHIFT = 2;
static const version_t HDR_WRITE_INTENT_MASK = 0x1 << HDR_WRITE_INTENT_SHIFT;
static const version_t HDR_MODIFYING_SHIFT = 3;
static const version_t HDR_MODIFYING_MASK = 0x1 << HDR_MODIFYING_SHIFT;
static const version_t HDR_LATEST_SHIFT = 4;
static const version_t HDR_LATEST_MASK = 0x1 << HDR_LATEST_SHIFT;
static const version_t HDR_VERSION_SHIFT = 5;
static const version_t HDR_VERSION_MASK = ((version_t)-1) << HDR_VERSION_SHIFT;
public:
#ifdef TUPLE_MAGIC
class magic_failed_exception: public std::exception {};
static const uint8_t TUPLE_MAGIC = 0x29U;
uint8_t magic;
inline ALWAYS_INLINE void CheckMagic() const
{
if (unlikely(magic != TUPLE_MAGIC)) {
print(1);
// so we can catch it later and print out useful debugging output
throw magic_failed_exception();
}
}
#else
inline ALWAYS_INLINE void CheckMagic() const {}
#endif
// NB(stephentu): ABA problem happens after some multiple of
// 2^(NBits(version_t)-6) concurrent modifications- somewhat low probability
// event, so we let it happen
//
// <-- low bits
// [ locked | deleting | write_intent | modifying | latest | version ]
// [ 0..1 | 1..2 | 2..3 | 3..4 | 4..5 | 5..32 ]
volatile version_t hdr;
#ifdef TUPLE_LOCK_OWNERSHIP_CHECKING
std::thread::id lock_owner;
#endif
// uninterpreted TID
tid_t version;
// small sizes on purpose
node_size_type size; // actual size of record
// (only meaningful is the deleting bit is not set)
node_size_type alloc_size; // max size record allowed. is the space
// available for the record buf
dbtuple *next; // be very careful about traversing this pointer,
// GC is capable of reaping it at certain (well defined)
// points, and will not bother to set it to null
#ifdef TUPLE_CHECK_KEY
// for debugging
std::string key;
void *tree;
#endif
#ifdef CHECK_INVARIANTS
// for debugging
std::atomic<uint64_t> opaque;
#endif
// must be last field
uint8_t value_start[0];
void print(std::ostream &o, unsigned len) const;
private:
// private ctor/dtor b/c we do some special memory stuff
// ctors start node off as latest node
static inline ALWAYS_INLINE node_size_type
CheckBounds(size_type s)
{
INVARIANT(s <= std::numeric_limits<node_size_type>::max());
return s;
}
dbtuple(const dbtuple &) = delete;
dbtuple(dbtuple &&) = delete;
dbtuple &operator=(const dbtuple &) = delete;
// creates a (new) record with a tentative value at MAX_TID
dbtuple(size_type size, size_type alloc_size, bool acquire_lock)
:
#ifdef TUPLE_MAGIC
magic(TUPLE_MAGIC),
#endif
hdr(HDR_LATEST_MASK |
(acquire_lock ? (HDR_LOCKED_MASK | HDR_WRITE_INTENT_MASK) : 0) |
(!size ? HDR_DELETING_MASK : 0))
#ifdef TUPLE_LOCK_OWNERSHIP_CHECKING
, lock_owner()
#endif
, version(MAX_TID)
, size(CheckBounds(size))
, alloc_size(CheckBounds(alloc_size))
, next(nullptr)
#ifdef TUPLE_CHECK_KEY
, key()
, tree(nullptr)
#endif
#ifdef CHECK_INVARIANTS
, opaque(0)
#endif
{
INVARIANT(((char *)this) + sizeof(*this) == (char *) &value_start[0]);
INVARIANT(is_latest());
INVARIANT(size || is_deleting());
++g_evt_dbtuple_creates;
g_evt_dbtuple_bytes_allocated += alloc_size + sizeof(dbtuple);
#ifdef TUPLE_LOCK_OWNERSHIP_CHECKING
if (acquire_lock) {
lock_owner = std::this_thread::get_id();
AddTupleToLockRegion(this);
INVARIANT(is_lock_owner());
}
#endif
COMPILER_MEMORY_FENCE; // for acquire_lock
}
// creates a record at version derived from base
// (inheriting its value).
dbtuple(tid_t version,
struct dbtuple *base,
size_type alloc_size,
bool set_latest)
:
#ifdef TUPLE_MAGIC
magic(TUPLE_MAGIC),
#endif
hdr(set_latest ? HDR_LATEST_MASK : 0)
#ifdef TUPLE_LOCK_OWNERSHIP_CHECKING
, lock_owner()
#endif
, version(version)
, size(base->size)
, alloc_size(CheckBounds(alloc_size))
, next(base->next)
#ifdef TUPLE_CHECK_KEY
, key()
, tree(nullptr)
#endif
#ifdef CHECK_INVARIANTS
, opaque(0)
#endif
{
INVARIANT(size <= alloc_size);
INVARIANT(set_latest == is_latest());
if (base->is_deleting())
mark_deleting();
NDB_MEMCPY(&value_start[0], base->get_value_start(), size);
++g_evt_dbtuple_creates;
g_evt_dbtuple_bytes_allocated += alloc_size + sizeof(dbtuple);
}
// creates a spill record, copying in the *old* value if necessary, but
// setting the size to the *new* value
dbtuple(tid_t version,
const_record_type r,
size_type old_size,
size_type new_size,
size_type alloc_size,
struct dbtuple *next,
bool set_latest,
bool needs_old_value)
:
#ifdef TUPLE_MAGIC
magic(TUPLE_MAGIC),
#endif
hdr((set_latest ? HDR_LATEST_MASK : 0) | (!new_size ? HDR_DELETING_MASK : 0))
#ifdef TUPLE_LOCK_OWNERSHIP_CHECKING
, lock_owner()
#endif
, version(version)
, size(CheckBounds(new_size))
, alloc_size(CheckBounds(alloc_size))
, next(next)
#ifdef TUPLE_CHECK_KEY
, key()
, tree(nullptr)
#endif
#ifdef CHECK_INVARIANTS
, opaque(0)
#endif
{
INVARIANT(!needs_old_value || old_size <= alloc_size);
INVARIANT(new_size <= alloc_size);
INVARIANT(set_latest == is_latest());
INVARIANT(new_size || is_deleting());
if (needs_old_value)
NDB_MEMCPY(&value_start[0], r, old_size);
++g_evt_dbtuple_creates;
g_evt_dbtuple_bytes_allocated += alloc_size + sizeof(dbtuple);
}
friend class rcu;
~dbtuple();
static event_avg_counter g_evt_avg_dbtuple_stable_version_spins;
static event_avg_counter g_evt_avg_dbtuple_lock_acquire_spins;
static event_avg_counter g_evt_avg_dbtuple_read_retries;
public:
enum ReadStatus {
READ_FAILED,
READ_EMPTY,
READ_RECORD,
};
inline void
prefetch() const
{
#ifdef TUPLE_PREFETCH
prefetch_bytes(this, sizeof(*this) + alloc_size);
#endif
}
// gcs *this* instance, ignoring the chain
void gc_this();
inline bool
is_locked() const
{
return IsLocked(hdr);
}
static inline bool
IsLocked(version_t v)
{
return v & HDR_LOCKED_MASK;
}
#ifdef TUPLE_LOCK_OWNERSHIP_CHECKING
inline bool
is_lock_owner() const
{
return std::this_thread::get_id() == lock_owner;
}
#else
inline bool
is_lock_owner() const
{
return true;
}
#endif
inline version_t
lock(bool write_intent)
{
// XXX: implement SPINLOCK_BACKOFF
CheckMagic();
#ifdef ENABLE_EVENT_COUNTERS
unsigned nspins = 0;
#endif
version_t v = hdr;
const version_t lockmask = write_intent ?
(HDR_LOCKED_MASK | HDR_WRITE_INTENT_MASK) :
(HDR_LOCKED_MASK);
while (IsLocked(v) ||
!__sync_bool_compare_and_swap(&hdr, v, v | lockmask)) {
nop_pause();
v = hdr;
#ifdef ENABLE_EVENT_COUNTERS
++nspins;
#endif
}
#ifdef TUPLE_LOCK_OWNERSHIP_CHECKING
lock_owner = std::this_thread::get_id();
AddTupleToLockRegion(this);
INVARIANT(is_lock_owner());
#endif
COMPILER_MEMORY_FENCE;
INVARIANT(IsLocked(hdr));
INVARIANT(!write_intent || IsWriteIntent(hdr));
INVARIANT(!IsModifying(hdr));
#ifdef ENABLE_EVENT_COUNTERS
g_evt_avg_dbtuple_lock_acquire_spins.offer(nspins);
#endif
return hdr;
}
inline void
unlock()
{
CheckMagic();
version_t v = hdr;
bool newv = false;
INVARIANT(IsLocked(v));
INVARIANT(is_lock_owner());
if (IsModifying(v) || IsWriteIntent(v)) {
newv = true;
const version_t n = Version(v);
v &= ~HDR_VERSION_MASK;
v |= (((n + 1) << HDR_VERSION_SHIFT) & HDR_VERSION_MASK);
}
// clear locked + modifying bits
v &= ~(HDR_LOCKED_MASK | HDR_MODIFYING_MASK | HDR_WRITE_INTENT_MASK);
if (newv) {
INVARIANT(!reader_check_version(v));
INVARIANT(!writer_check_version(v));
}
INVARIANT(!IsLocked(v));
INVARIANT(!IsModifying(v));
INVARIANT(!IsWriteIntent(v));
#ifdef TUPLE_LOCK_OWNERSHIP_CHECKING
lock_owner = std::thread::id();
INVARIANT(!is_lock_owner());
#endif
COMPILER_MEMORY_FENCE;
hdr = v;
}
inline bool
is_deleting() const
{
return IsDeleting(hdr);
}
static inline bool
IsDeleting(version_t v)
{
return v & HDR_DELETING_MASK;
}
inline void
mark_deleting()
{
CheckMagic();
// the lock on the latest version guards non-latest versions
INVARIANT(!is_latest() || is_locked());
INVARIANT(!is_latest() || is_lock_owner());
INVARIANT(!is_deleting());
hdr |= HDR_DELETING_MASK;
}
inline void
clear_deleting()
{
CheckMagic();
INVARIANT(is_locked());
INVARIANT(is_lock_owner());
INVARIANT(is_deleting());
hdr &= ~HDR_DELETING_MASK;
}
inline bool
is_modifying() const
{
return IsModifying(hdr);
}
inline void
mark_modifying()
{
CheckMagic();
version_t v = hdr;
INVARIANT(IsLocked(v));
INVARIANT(is_lock_owner());
//INVARIANT(!IsModifying(v)); // mark_modifying() must be re-entrant
v |= HDR_MODIFYING_MASK;
COMPILER_MEMORY_FENCE; // XXX: is this fence necessary?
hdr = v;
COMPILER_MEMORY_FENCE;
}
static inline bool
IsModifying(version_t v)
{
return v & HDR_MODIFYING_MASK;
}
inline bool
is_write_intent() const
{
return IsWriteIntent(hdr);
}
static inline bool
IsWriteIntent(version_t v)
{
return v & HDR_WRITE_INTENT_MASK;
}
inline bool
is_latest() const
{
return IsLatest(hdr);
}
static inline bool
IsLatest(version_t v)
{
return v & HDR_LATEST_MASK;
}
inline void
clear_latest()
{
CheckMagic();
INVARIANT(is_locked());
INVARIANT(is_lock_owner());
INVARIANT(is_latest());
hdr &= ~HDR_LATEST_MASK;
}
static inline version_t
Version(version_t v)
{
return (v & HDR_VERSION_MASK) >> HDR_VERSION_SHIFT;
}
inline version_t
reader_stable_version(bool allow_write_intent) const
{
version_t v = hdr;
#ifdef ENABLE_EVENT_COUNTERS
unsigned long nspins = 0;
#endif
while (IsModifying(v) ||
(!allow_write_intent && IsWriteIntent(v))) {
nop_pause();
v = hdr;
#ifdef ENABLE_EVENT_COUNTERS
++nspins;
#endif
}
COMPILER_MEMORY_FENCE;
#ifdef ENABLE_EVENT_COUNTERS
g_evt_avg_dbtuple_stable_version_spins.offer(nspins);
#endif
return v;
}
/**
* returns true if succeeded, false otherwise
*/
inline bool
try_writer_stable_version(version_t &v, unsigned int spins) const
{
v = hdr;
while (IsWriteIntent(v) && spins--) {
INVARIANT(IsLocked(v));
nop_pause();
v = hdr;
}
const bool ret = !IsWriteIntent(v);
COMPILER_MEMORY_FENCE;
INVARIANT(ret || IsLocked(v));
INVARIANT(!ret || !IsModifying(v));
return ret;
}
inline version_t
unstable_version() const
{
return hdr;
}
inline bool
reader_check_version(version_t version) const
{
COMPILER_MEMORY_FENCE;
// are the versions the same, modulo the
// {locked, write_intent, latest} bits?
const version_t MODULO_BITS =
(HDR_LOCKED_MASK | HDR_WRITE_INTENT_MASK | HDR_LATEST_MASK);
return (hdr & ~MODULO_BITS) == (version & ~MODULO_BITS);
}
inline bool
writer_check_version(version_t version) const
{
COMPILER_MEMORY_FENCE;
return hdr == version;
}
inline ALWAYS_INLINE struct dbtuple *
get_next()
{
return next;
}
inline const struct dbtuple *
get_next() const
{
return next;
}
inline ALWAYS_INLINE void
set_next(struct dbtuple *next)
{
CheckMagic();
this->next = next;
}
inline void
clear_next()
{
CheckMagic();
this->next = nullptr;
}
inline ALWAYS_INLINE uint8_t *
get_value_start()
{
CheckMagic();
return &value_start[0];
}
inline ALWAYS_INLINE const uint8_t *
get_value_start() const
{
return &value_start[0];
}
// worst name ever...
inline bool
is_not_behind(tid_t t) const
{
return version <= t;
}
private:
#ifdef ENABLE_EVENT_COUNTERS
struct scoped_recorder {
scoped_recorder(unsigned long &n) : n(&n) {}
~scoped_recorder()
{
g_evt_avg_dbtuple_read_retries.offer(*n);
}
private:
unsigned long *n;
};
#endif
// written to be non-recursive
template <typename Reader, typename StringAllocator>
static ReadStatus
record_at_chain(
const dbtuple *starting, tid_t t, tid_t &start_t,
Reader &reader, StringAllocator &sa, bool allow_write_intent)
{
#ifdef ENABLE_EVENT_COUNTERS
unsigned long nretries = 0;
scoped_recorder rec(nretries);
#endif
const dbtuple *current = starting;
loop:
INVARIANT(current->version != MAX_TID);
const version_t v = current->reader_stable_version(allow_write_intent);
const struct dbtuple *p;
const bool found = current->is_not_behind(t);
if (found) {
start_t = current->version;
const size_t read_sz = IsDeleting(v) ? 0 : current->size;
if (unlikely(read_sz && !reader(current->get_value_start(), read_sz, sa)))
goto retry;
if (unlikely(!current->reader_check_version(v)))
goto retry;
return read_sz ? READ_RECORD : READ_EMPTY;
} else {
p = current->get_next();
}
if (unlikely(!current->reader_check_version(v)))
goto retry;
if (p) {
current = p;
goto loop;
}
// see note in record_at()
start_t = MIN_TID;
return READ_EMPTY;
retry:
#ifdef ENABLE_EVENT_COUNTERS
++nretries;
#endif
goto loop;
}
// we force one level of inlining, but don't force record_at_chain()
// to be inlined
template <typename Reader, typename StringAllocator>
inline ALWAYS_INLINE ReadStatus
record_at(
tid_t t, tid_t &start_t,
Reader &reader, StringAllocator &sa, bool allow_write_intent) const
{
#ifdef ENABLE_EVENT_COUNTERS
unsigned long nretries = 0;
scoped_recorder rec(nretries);
#endif
if (unlikely(version == MAX_TID)) {
// XXX(stephentu): HACK! we use MAX_TID to indicate a tentative
// "insert"- the actual latest value is empty.
//
// since our system is screwed anyways if we ever reach MAX_TID, this
// is OK for now, but a real solution should exist at some point
start_t = MIN_TID;
return READ_EMPTY;
}
loop:
const version_t v = reader_stable_version(allow_write_intent);
const struct dbtuple *p;
const bool found = is_not_behind(t);
if (found) {
//if (unlikely(!IsLatest(v)))
// return READ_FAILED;
start_t = version;
const size_t read_sz = IsDeleting(v) ? 0 : size;
if (unlikely(read_sz && !reader(get_value_start(), read_sz, sa)))
goto retry;
if (unlikely(!reader_check_version(v)))
goto retry;
return read_sz ? READ_RECORD : READ_EMPTY;
} else {
p = get_next();
}
if (unlikely(!reader_check_version(v)))
goto retry;
if (p)
return record_at_chain(p, t, start_t, reader, sa, allow_write_intent);
// NB(stephentu): if we reach the end of a chain then we assume that
// the record exists as a deleted record.
//
// This is safe because we have been very careful to not garbage collect
// elements along the chain until it is guaranteed that the record
// is superceded by later record in any consistent read. Therefore,
// if we reach the end of the chain, then it *must* be the case that
// the record does not actually exist.
//
// Note that MIN_TID is the *wrong* tid to use here given wrap-around- we
// really should be setting this value to the tid which represents the
// oldest TID possible in the system. But we currently don't implement
// wrap around
start_t = MIN_TID;
return READ_EMPTY;
retry:
#ifdef ENABLE_EVENT_COUNTERS
++nretries;
#endif
goto loop;
}
static event_counter g_evt_dbtuple_creates;
static event_counter g_evt_dbtuple_logical_deletes;
static event_counter g_evt_dbtuple_physical_deletes;
static event_counter g_evt_dbtuple_bytes_allocated;
static event_counter g_evt_dbtuple_bytes_freed;
static event_counter g_evt_dbtuple_spills;
static event_counter g_evt_dbtuple_inplace_buf_insufficient;
static event_counter g_evt_dbtuple_inplace_buf_insufficient_on_spill;
static event_avg_counter g_evt_avg_record_spill_len;
public:
/**
* Read the record at tid t. Returns true if such a record exists, false
* otherwise (ie the record was GC-ed, or other reasons). On a successful
* read, the value @ start_t will be stored in r
*
* NB(stephentu): calling stable_read() while holding the lock
* is an error- this will cause deadlock
*/
template <typename Reader, typename StringAllocator>
inline ALWAYS_INLINE ReadStatus
stable_read(
tid_t t, tid_t &start_t,
Reader &reader, StringAllocator &sa,
bool allow_write_intent) const
{
return record_at(t, start_t, reader, sa, allow_write_intent);
}
inline bool
is_latest_version(tid_t t) const
{
return is_latest() && is_not_behind(t);
}
bool
stable_is_latest_version(tid_t t) const
{
version_t v = 0;
if (!try_writer_stable_version(v, 16))
return false;
// now v is a stable version
INVARIANT(!IsWriteIntent(v));
INVARIANT(!IsModifying(v));
const bool ret = IsLatest(v) && is_not_behind(t);
// only check_version() if the answer would be true- otherwise,
// no point in doing a version check
if (ret && writer_check_version(v))
return true;
else
// no point in retrying, since we know it will fail (since we had a
// version change)
return false;
}
inline bool
latest_value_is_nil() const
{
return is_latest() && size == 0;
}
inline bool
stable_latest_value_is_nil() const
{
version_t v = 0;
if (!try_writer_stable_version(v, 16))
return false;
INVARIANT(!IsWriteIntent(v));
INVARIANT(!IsModifying(v));
const bool ret = IsLatest(v) && size == 0;
if (ret && writer_check_version(v))
return true;
else
return false;
}
struct write_record_ret {
write_record_ret() : head_(), rest_(), forced_spill_() {}
write_record_ret(dbtuple *head, dbtuple* rest, bool forced_spill)
: head_(head), rest_(rest), forced_spill_(forced_spill)
{
INVARIANT(head);
INVARIANT(head != rest);
INVARIANT(!forced_spill || rest);
}
dbtuple *head_;
dbtuple *rest_;
bool forced_spill_;
};
// XXX: kind of hacky, but we do this to avoid virtual
// functions / passing multiple function pointers around
enum TupleWriterMode {
TUPLE_WRITER_NEEDS_OLD_VALUE, // all three args ignored
TUPLE_WRITER_COMPUTE_NEEDED,
TUPLE_WRITER_COMPUTE_DELTA_NEEDED, // last two args ignored
TUPLE_WRITER_DO_WRITE,
TUPLE_WRITER_DO_DELTA_WRITE,
};
typedef size_t (*tuple_writer_t)(TupleWriterMode, const void *, uint8_t *, size_t);
/**
* Always writes the record in the latest (newest) version slot,
* not asserting whether or not inserting r @ t would violate the
* sorted order invariant
*
* ret.first = latest tuple after the write (guaranteed to not be nullptr)
* ret.second = old version of tuple, iff no overwrite (can be nullptr)
*
* Note: if this != ret.first, then we need a tree replacement
*/
template <typename Transaction>
write_record_ret
write_record_at(const Transaction *txn, tid_t t,
const void *v, tuple_writer_t writer)
{
#ifndef DISABLE_OVERWRITE_IN_PLACE
CheckMagic();
INVARIANT(is_locked());
INVARIANT(is_lock_owner());
INVARIANT(is_latest());
INVARIANT(is_write_intent());
const size_t new_sz =
v ? writer(TUPLE_WRITER_COMPUTE_NEEDED, v, get_value_start(), size) : 0;
INVARIANT(!v || new_sz);
INVARIANT(is_deleting() || size);
const size_t old_sz = is_deleting() ? 0 : size;
if (!new_sz)
++g_evt_dbtuple_logical_deletes;
// try to overwrite this record
if (likely(txn->can_overwrite_record_tid(version, t) && old_sz)) {
INVARIANT(!is_deleting());
// see if we have enough space
if (likely(new_sz <= alloc_size)) {
// directly update in place
mark_modifying();
if (v)
writer(TUPLE_WRITER_DO_WRITE, v, get_value_start(), old_sz);
version = t;
size = new_sz;
if (!new_sz)
mark_deleting();
return write_record_ret(this, nullptr, false);
}
//std::cerr
// << "existing: " << g_proto_version_str(version) << std::endl
// << "new : " << g_proto_version_str(t) << std::endl
// << "alloc_size : " << alloc_size << std::endl
// << "new_sz : " << new_sz << std::endl;
// keep this tuple in the chain (it's wasteful, but not incorrect)
// so that cleanup is easier
//
// XXX(stephentu): alloc_spill() should acquire the lock on
// the returned tuple in the ctor, as an optimization
const bool needs_old_value =
writer(TUPLE_WRITER_NEEDS_OLD_VALUE, nullptr, nullptr, 0);
INVARIANT(new_sz);
INVARIANT(v);
dbtuple * const rep =
alloc_spill(t, get_value_start(), old_sz, new_sz,
this, true, needs_old_value);
writer(TUPLE_WRITER_DO_WRITE, v, rep->get_value_start(), old_sz);
INVARIANT(rep->is_latest());
INVARIANT(rep->size == new_sz);
clear_latest();
++g_evt_dbtuple_inplace_buf_insufficient;
// [did not spill because of epochs, need to replace this with rep]
return write_record_ret(rep, this, false);
}
//std::cerr
// << "existing: " << g_proto_version_str(version) << std::endl
// << "new : " << g_proto_version_str(t) << std::endl
// << "alloc_size : " << alloc_size << std::endl
// << "new_sz : " << new_sz << std::endl;
// need to spill
++g_evt_dbtuple_spills;
g_evt_avg_record_spill_len.offer(size);
if (new_sz <= alloc_size && old_sz) {
INVARIANT(!is_deleting());
dbtuple * const spill = alloc(version, this, false);
INVARIANT(!spill->is_latest());
mark_modifying();
set_next(spill);
if (v)
writer(TUPLE_WRITER_DO_WRITE, v, get_value_start(), size);
version = t;
size = new_sz;
if (!new_sz)
mark_deleting();
return write_record_ret(this, spill, true);
}
const bool needs_old_value =
writer(TUPLE_WRITER_NEEDS_OLD_VALUE, nullptr, nullptr, 0);
dbtuple * const rep =
alloc_spill(t, get_value_start(), old_sz, new_sz,
this, true, needs_old_value);
if (v)
writer(TUPLE_WRITER_DO_WRITE, v, rep->get_value_start(), size);
INVARIANT(rep->is_latest());
INVARIANT(rep->size == new_sz);
INVARIANT(new_sz || rep->is_deleting()); // set by alloc_spill()
clear_latest();
++g_evt_dbtuple_inplace_buf_insufficient_on_spill;
return write_record_ret(rep, this, true);
#else
CheckMagic();
INVARIANT(is_locked());
INVARIANT(is_lock_owner());
INVARIANT(is_latest());
INVARIANT(is_write_intent());
const size_t new_sz =
v ? writer(TUPLE_WRITER_COMPUTE_NEEDED, v, get_value_start(), size) : 0;
INVARIANT(!v || new_sz);
INVARIANT(is_deleting() || size);
const size_t old_sz = is_deleting() ? 0 : size;
if (!new_sz)
++g_evt_dbtuple_logical_deletes;
const bool needs_old_value =
writer(TUPLE_WRITER_NEEDS_OLD_VALUE, nullptr, nullptr, 0);
dbtuple * const rep =
alloc_spill(t, get_value_start(), old_sz, new_sz,
this, true, needs_old_value);
if (v)
writer(TUPLE_WRITER_DO_WRITE, v, rep->get_value_start(), size);
INVARIANT(rep->is_latest());
INVARIANT(rep->size == new_sz);
INVARIANT(new_sz || rep->is_deleting()); // set by alloc_spill()
clear_latest();
++g_evt_dbtuple_inplace_buf_insufficient_on_spill;
return write_record_ret(rep, this, true);
#endif
}
// NB: we round up allocation sizes because jemalloc will do this
// internally anyways, so we might as well grab more usable space (really
// just internal vs external fragmentation)
static inline dbtuple *
alloc_first(size_type sz, bool acquire_lock)
{
INVARIANT(sz <= std::numeric_limits<node_size_type>::max());
const size_t max_alloc_sz =
std::numeric_limits<node_size_type>::max() + sizeof(dbtuple);
const size_t alloc_sz =
std::min(