This repository has been archived by the owner on May 24, 2018. It is now read-only.
forked from etcd-io/bbolt
-
Notifications
You must be signed in to change notification settings - Fork 0
/
node.go
604 lines (516 loc) · 15.8 KB
/
node.go
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
package bolt
import (
"bytes"
"fmt"
"sort"
"unsafe"
)
// node represents an in-memory, deserialized page.
type node struct {
bucket *Bucket
isLeaf bool
unbalanced bool
spilled bool
key []byte
pgid pgid
parent *node
children nodes
inodes inodes
}
// root returns the top-level node this node is attached to.
func (n *node) root() *node {
if n.parent == nil {
return n
}
return n.parent.root()
}
// minKeys returns the minimum number of inodes this node should have.
func (n *node) minKeys() int {
if n.isLeaf {
return 1
}
return 2
}
// size returns the size of the node after serialization.
func (n *node) size() int {
sz, elsz := pageHeaderSize, n.pageElementSize()
for i := 0; i < len(n.inodes); i++ {
item := &n.inodes[i]
sz += elsz + len(item.key) + len(item.value)
}
return sz
}
// sizeLessThan returns true if the node is less than a given size.
// This is an optimization to avoid calculating a large node when we only need
// to know if it fits inside a certain page size.
func (n *node) sizeLessThan(v int) bool {
sz, elsz := pageHeaderSize, n.pageElementSize()
for i := 0; i < len(n.inodes); i++ {
item := &n.inodes[i]
sz += elsz + len(item.key) + len(item.value)
if sz >= v {
return false
}
}
return true
}
// pageElementSize returns the size of each page element based on the type of node.
func (n *node) pageElementSize() int {
if n.isLeaf {
return leafPageElementSize
}
return branchPageElementSize
}
// childAt returns the child node at a given index.
func (n *node) childAt(index int) *node {
if n.isLeaf {
panic(fmt.Sprintf("invalid childAt(%d) on a leaf node", index))
}
return n.bucket.node(n.inodes[index].pgid, n)
}
// childIndex returns the index of a given child node.
func (n *node) childIndex(child *node) int {
index := sort.Search(len(n.inodes), func(i int) bool { return bytes.Compare(n.inodes[i].key, child.key) != -1 })
return index
}
// numChildren returns the number of children.
func (n *node) numChildren() int {
return len(n.inodes)
}
// nextSibling returns the next node with the same parent.
func (n *node) nextSibling() *node {
if n.parent == nil {
return nil
}
index := n.parent.childIndex(n)
if index >= n.parent.numChildren()-1 {
return nil
}
return n.parent.childAt(index + 1)
}
// prevSibling returns the previous node with the same parent.
func (n *node) prevSibling() *node {
if n.parent == nil {
return nil
}
index := n.parent.childIndex(n)
if index == 0 {
return nil
}
return n.parent.childAt(index - 1)
}
// put inserts a key/value.
func (n *node) put(oldKey, newKey, value []byte, pgid pgid, flags uint32) {
if pgid >= n.bucket.tx.meta.pgid {
panic(fmt.Sprintf("pgid (%d) above high water mark (%d)", pgid, n.bucket.tx.meta.pgid))
} else if len(oldKey) <= 0 {
panic("put: zero-length old key")
} else if len(newKey) <= 0 {
panic("put: zero-length new key")
}
// Find insertion index.
index := sort.Search(len(n.inodes), func(i int) bool { return bytes.Compare(n.inodes[i].key, oldKey) != -1 })
// Add capacity and shift nodes if we don't have an exact match and need to insert.
exact := (len(n.inodes) > 0 && index < len(n.inodes) && bytes.Equal(n.inodes[index].key, oldKey))
if !exact {
n.inodes = append(n.inodes, inode{})
copy(n.inodes[index+1:], n.inodes[index:])
}
inode := &n.inodes[index]
inode.flags = flags
inode.key = newKey
inode.value = value
inode.pgid = pgid
_assert(len(inode.key) > 0, "put: zero-length inode key")
}
// del removes a key from the node.
func (n *node) del(key []byte) {
// Find index of key.
index := sort.Search(len(n.inodes), func(i int) bool { return bytes.Compare(n.inodes[i].key, key) != -1 })
// Exit if the key isn't found.
if index >= len(n.inodes) || !bytes.Equal(n.inodes[index].key, key) {
return
}
// Delete inode from the node.
n.inodes = append(n.inodes[:index], n.inodes[index+1:]...)
// Mark the node as needing rebalancing.
n.unbalanced = true
}
// read initializes the node from a page.
func (n *node) read(p *page) {
n.pgid = p.id
n.isLeaf = ((p.flags & leafPageFlag) != 0)
n.inodes = make(inodes, int(p.count))
for i := 0; i < int(p.count); i++ {
inode := &n.inodes[i]
if n.isLeaf {
elem := p.leafPageElement(uint16(i))
inode.flags = elem.flags
inode.key = elem.key()
inode.value = elem.value()
} else {
elem := p.branchPageElement(uint16(i))
inode.pgid = elem.pgid
inode.key = elem.key()
}
_assert(len(inode.key) > 0, "read: zero-length inode key")
}
// Save first key so we can find the node in the parent when we spill.
if len(n.inodes) > 0 {
n.key = n.inodes[0].key
_assert(len(n.key) > 0, "read: zero-length node key")
} else {
n.key = nil
}
}
// write writes the items onto one or more pages.
func (n *node) write(p *page) {
// Initialize page.
if n.isLeaf {
p.flags |= leafPageFlag
} else {
p.flags |= branchPageFlag
}
if len(n.inodes) >= 0xFFFF {
panic(fmt.Sprintf("inode overflow: %d (pgid=%d)", len(n.inodes), p.id))
}
p.count = uint16(len(n.inodes))
// Stop here if there are no items to write.
if p.count == 0 {
return
}
// Loop over each item and write it to the page.
b := (*[maxAllocSize]byte)(unsafe.Pointer(&p.ptr))[n.pageElementSize()*len(n.inodes):]
for i, item := range n.inodes {
_assert(len(item.key) > 0, "write: zero-length inode key")
// Write the page element.
if n.isLeaf {
elem := p.leafPageElement(uint16(i))
elem.pos = uint32(uintptr(unsafe.Pointer(&b[0])) - uintptr(unsafe.Pointer(elem)))
elem.flags = item.flags
elem.ksize = uint32(len(item.key))
elem.vsize = uint32(len(item.value))
} else {
elem := p.branchPageElement(uint16(i))
elem.pos = uint32(uintptr(unsafe.Pointer(&b[0])) - uintptr(unsafe.Pointer(elem)))
elem.ksize = uint32(len(item.key))
elem.pgid = item.pgid
_assert(elem.pgid != p.id, "write: circular dependency occurred")
}
// If the length of key+value is larger than the max allocation size
// then we need to reallocate the byte array pointer.
//
// See: https://github.com/boltdb/bolt/pull/335
klen, vlen := len(item.key), len(item.value)
if len(b) < klen+vlen {
b = (*[maxAllocSize]byte)(unsafe.Pointer(&b[0]))[:]
}
// Write data for the element to the end of the page.
copy(b[0:], item.key)
b = b[klen:]
copy(b[0:], item.value)
b = b[vlen:]
}
// DEBUG ONLY: n.dump()
}
// split breaks up a node into multiple smaller nodes, if appropriate.
// This should only be called from the spill() function.
func (n *node) split(pageSize int) []*node {
var nodes []*node
node := n
for {
// Split node into two.
a, b := node.splitTwo(pageSize)
nodes = append(nodes, a)
// If we can't split then exit the loop.
if b == nil {
break
}
// Set node to b so it gets split on the next iteration.
node = b
}
return nodes
}
// splitTwo breaks up a node into two smaller nodes, if appropriate.
// This should only be called from the split() function.
func (n *node) splitTwo(pageSize int) (*node, *node) {
// Ignore the split if the page doesn't have at least enough nodes for
// two pages or if the nodes can fit in a single page.
if len(n.inodes) <= (minKeysPerPage*2) || n.sizeLessThan(pageSize) {
return n, nil
}
// Determine the threshold before starting a new node.
var fillPercent = n.bucket.FillPercent
if fillPercent < minFillPercent {
fillPercent = minFillPercent
} else if fillPercent > maxFillPercent {
fillPercent = maxFillPercent
}
threshold := int(float64(pageSize) * fillPercent)
// Determine split position and sizes of the two pages.
splitIndex, _ := n.splitIndex(threshold)
// Split node into two separate nodes.
// If there's no parent then we'll need to create one.
if n.parent == nil {
n.parent = &node{bucket: n.bucket, children: []*node{n}}
}
// Create a new node and add it to the parent.
next := &node{bucket: n.bucket, isLeaf: n.isLeaf, parent: n.parent}
n.parent.children = append(n.parent.children, next)
// Split inodes across two nodes.
next.inodes = n.inodes[splitIndex:]
n.inodes = n.inodes[:splitIndex]
// Update the statistics.
n.bucket.tx.stats.Split++
return n, next
}
// splitIndex finds the position where a page will fill a given threshold.
// It returns the index as well as the size of the first page.
// This is only be called from split().
func (n *node) splitIndex(threshold int) (index, sz int) {
sz = pageHeaderSize
// Loop until we only have the minimum number of keys required for the second page.
for i := 0; i < len(n.inodes)-minKeysPerPage; i++ {
index = i
inode := n.inodes[i]
elsize := n.pageElementSize() + len(inode.key) + len(inode.value)
// If we have at least the minimum number of keys and adding another
// node would put us over the threshold then exit and return.
if i >= minKeysPerPage && sz+elsize > threshold {
break
}
// Add the element size to the total size.
sz += elsize
}
return
}
// spill writes the nodes to dirty pages and splits nodes as it goes.
// Returns an error if dirty pages cannot be allocated.
func (n *node) spill() error {
var tx = n.bucket.tx
if n.spilled {
return nil
}
// Spill child nodes first. Child nodes can materialize sibling nodes in
// the case of split-merge so we cannot use a range loop. We have to check
// the children size on every loop iteration.
sort.Sort(n.children)
for i := 0; i < len(n.children); i++ {
if err := n.children[i].spill(); err != nil {
return err
}
}
// We no longer need the child list because it's only used for spill tracking.
n.children = nil
// Split nodes into appropriate sizes. The first node will always be n.
var nodes = n.split(tx.db.pageSize)
for _, node := range nodes {
// Add node's page to the freelist if it's not new.
if node.pgid > 0 {
tx.db.freelist.free(tx.meta.txid, tx.page(node.pgid))
node.pgid = 0
}
// Allocate contiguous space for the node.
p, err := tx.allocate((node.size() + tx.db.pageSize - 1) / tx.db.pageSize)
if err != nil {
return err
}
// Write the node.
if p.id >= tx.meta.pgid {
panic(fmt.Sprintf("pgid (%d) above high water mark (%d)", p.id, tx.meta.pgid))
}
node.pgid = p.id
node.write(p)
node.spilled = true
// Insert into parent inodes.
if node.parent != nil {
var key = node.key
if key == nil {
key = node.inodes[0].key
}
node.parent.put(key, node.inodes[0].key, nil, node.pgid, 0)
node.key = node.inodes[0].key
_assert(len(node.key) > 0, "spill: zero-length node key")
}
// Update the statistics.
tx.stats.Spill++
}
// If the root node split and created a new root then we need to spill that
// as well. We'll clear out the children to make sure it doesn't try to respill.
if n.parent != nil && n.parent.pgid == 0 {
n.children = nil
return n.parent.spill()
}
return nil
}
// rebalance attempts to combine the node with sibling nodes if the node fill
// size is below a threshold or if there are not enough keys.
func (n *node) rebalance() {
if !n.unbalanced {
return
}
n.unbalanced = false
// Update statistics.
n.bucket.tx.stats.Rebalance++
// Ignore if node is above threshold (25%) and has enough keys.
var threshold = n.bucket.tx.db.pageSize / 4
if n.size() > threshold && len(n.inodes) > n.minKeys() {
return
}
// Root node has special handling.
if n.parent == nil {
// If root node is a branch and only has one node then collapse it.
if !n.isLeaf && len(n.inodes) == 1 {
// Move root's child up.
child := n.bucket.node(n.inodes[0].pgid, n)
n.isLeaf = child.isLeaf
n.inodes = child.inodes[:]
n.children = child.children
// Reparent all child nodes being moved.
for _, inode := range n.inodes {
if child, ok := n.bucket.nodes[inode.pgid]; ok {
child.parent = n
}
}
// Remove old child.
child.parent = nil
delete(n.bucket.nodes, child.pgid)
child.free()
}
return
}
// If node has no keys then just remove it.
if n.numChildren() == 0 {
n.parent.del(n.key)
n.parent.removeChild(n)
delete(n.bucket.nodes, n.pgid)
n.free()
n.parent.rebalance()
return
}
_assert(n.parent.numChildren() > 1, "parent must have at least 2 children")
// Destination node is right sibling if idx == 0, otherwise left sibling.
var target *node
var useNextSibling = (n.parent.childIndex(n) == 0)
if useNextSibling {
target = n.nextSibling()
} else {
target = n.prevSibling()
}
// If both this node and the target node are too small then merge them.
if useNextSibling {
// Reparent all child nodes being moved.
for _, inode := range target.inodes {
if child, ok := n.bucket.nodes[inode.pgid]; ok {
child.parent.removeChild(child)
child.parent = n
child.parent.children = append(child.parent.children, child)
}
}
// Copy over inodes from target and remove target.
n.inodes = append(n.inodes, target.inodes...)
n.parent.del(target.key)
n.parent.removeChild(target)
delete(n.bucket.nodes, target.pgid)
target.free()
} else {
// Reparent all child nodes being moved.
for _, inode := range n.inodes {
if child, ok := n.bucket.nodes[inode.pgid]; ok {
child.parent.removeChild(child)
child.parent = target
child.parent.children = append(child.parent.children, child)
}
}
// Copy over inodes to target and remove node.
target.inodes = append(target.inodes, n.inodes...)
n.parent.del(n.key)
n.parent.removeChild(n)
delete(n.bucket.nodes, n.pgid)
n.free()
}
// Either this node or the target node was deleted from the parent so rebalance it.
n.parent.rebalance()
}
// removes a node from the list of in-memory children.
// This does not affect the inodes.
func (n *node) removeChild(target *node) {
for i, child := range n.children {
if child == target {
n.children = append(n.children[:i], n.children[i+1:]...)
return
}
}
}
// dereference causes the node to copy all its inode key/value references to heap memory.
// This is required when the mmap is reallocated so inodes are not pointing to stale data.
func (n *node) dereference() {
if n.key != nil {
key := make([]byte, len(n.key))
copy(key, n.key)
n.key = key
_assert(n.pgid == 0 || len(n.key) > 0, "dereference: zero-length node key on existing node")
}
for i := range n.inodes {
inode := &n.inodes[i]
key := make([]byte, len(inode.key))
copy(key, inode.key)
inode.key = key
_assert(len(inode.key) > 0, "dereference: zero-length inode key")
value := make([]byte, len(inode.value))
copy(value, inode.value)
inode.value = value
}
// Recursively dereference children.
for _, child := range n.children {
child.dereference()
}
// Update statistics.
n.bucket.tx.stats.NodeDeref++
}
// free adds the node's underlying page to the freelist.
func (n *node) free() {
if n.pgid != 0 {
n.bucket.tx.db.freelist.free(n.bucket.tx.meta.txid, n.bucket.tx.page(n.pgid))
n.pgid = 0
}
}
// dump writes the contents of the node to STDERR for debugging purposes.
/*
func (n *node) dump() {
// Write node header.
var typ = "branch"
if n.isLeaf {
typ = "leaf"
}
warnf("[NODE %d {type=%s count=%d}]", n.pgid, typ, len(n.inodes))
// Write out abbreviated version of each item.
for _, item := range n.inodes {
if n.isLeaf {
if item.flags&bucketLeafFlag != 0 {
bucket := (*bucket)(unsafe.Pointer(&item.value[0]))
warnf("+L %08x -> (bucket root=%d)", trunc(item.key, 4), bucket.root)
} else {
warnf("+L %08x -> %08x", trunc(item.key, 4), trunc(item.value, 4))
}
} else {
warnf("+B %08x -> pgid=%d", trunc(item.key, 4), item.pgid)
}
}
warn("")
}
*/
type nodes []*node
func (s nodes) Len() int { return len(s) }
func (s nodes) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
func (s nodes) Less(i, j int) bool { return bytes.Compare(s[i].inodes[0].key, s[j].inodes[0].key) == -1 }
// inode represents an internal node inside of a node.
// It can be used to point to elements in a page or point
// to an element which hasn't been added to a page yet.
type inode struct {
flags uint32
pgid pgid
key []byte
value []byte
}
type inodes []inode