-
Notifications
You must be signed in to change notification settings - Fork 109
/
overlay.go
231 lines (189 loc) · 5.4 KB
/
overlay.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
package mkvs
import (
"context"
"fmt"
"github.com/oasisprotocol/oasis-core/go/storage/mkvs/node"
"github.com/oasisprotocol/oasis-core/go/storage/mkvs/syncer"
)
var _ OverlayTree = (*treeOverlay)(nil)
type treeOverlay struct {
inner Tree
overlay Tree
dirty map[string]bool
}
// NewOverlay creates a new key-value tree overlay that holds all updates in memory and only commits
// them if requested. This can be used to create snapshots that can be discarded.
//
// While updates (inserts, removes) are stored in the overlay, reads are not cached in the overlay
// as the inner tree has its own cache and double caching makes less sense.
//
// The overlay is not safe for concurrent use.
func NewOverlay(inner Tree) OverlayTree {
return &treeOverlay{
inner: inner,
overlay: New(nil, nil, inner.RootType(), WithoutWriteLog()),
dirty: make(map[string]bool),
}
}
// Implements KeyValueTree.
func (o *treeOverlay) Insert(ctx context.Context, key, value []byte) error {
err := o.overlay.Insert(ctx, key, value)
if err != nil {
return err
}
o.dirty[string(key)] = true
return nil
}
// Implements KeyValueTree.
func (o *treeOverlay) Get(ctx context.Context, key []byte) ([]byte, error) {
// For dirty values, check the overlay.
if o.dirty[string(key)] {
return o.overlay.Get(ctx, key)
}
// Otherwise fetch from inner tree.
return o.inner.Get(ctx, key)
}
// Implements KeyValueTree.
func (o *treeOverlay) RemoveExisting(ctx context.Context, key []byte) ([]byte, error) {
// For dirty values, remove from the overlay.
if o.dirty[string(key)] {
return o.overlay.RemoveExisting(ctx, key)
}
value, err := o.inner.Get(ctx, key)
if err != nil {
return nil, err
}
// Do not treat a value as dirty if it was not dirty before and did not exist in the inner tree.
if value != nil {
o.dirty[string(key)] = true
}
return value, nil
}
// Implements KeyValueTree.
func (o *treeOverlay) Remove(ctx context.Context, key []byte) error {
// Since we don't care about the previous value, we can just record an update.
o.dirty[string(key)] = true
return o.overlay.Remove(ctx, key)
}
// Implements KeyValueTree.
func (o *treeOverlay) NewIterator(ctx context.Context, options ...IteratorOption) Iterator {
return &treeOverlayIterator{
tree: o,
inner: o.inner.NewIterator(ctx, options...),
overlay: o.overlay.NewIterator(ctx),
}
}
// Implements OverlayTree.
func (o *treeOverlay) Commit(ctx context.Context) error {
it := o.overlay.NewIterator(ctx)
defer it.Close()
// Insert all items present in the overlay.
for it.Rewind(); it.Valid(); it.Next() {
if err := o.inner.Insert(ctx, it.Key(), it.Value()); err != nil {
return err
}
delete(o.dirty, string(it.Key()))
}
if it.Err() != nil {
return it.Err()
}
// Any remaining dirty items must have been removed.
for key := range o.dirty {
if err := o.inner.Remove(ctx, []byte(key)); err != nil {
return err
}
}
o.dirty = make(map[string]bool)
return nil
}
// Implements ClosableTree.
func (o *treeOverlay) Close() {
if o.inner == nil {
return
}
o.overlay.Close()
o.inner = nil
o.overlay = nil
o.dirty = nil
}
type treeOverlayIterator struct {
tree *treeOverlay
inner Iterator
overlay Iterator
key node.Key
value []byte
}
func (it *treeOverlayIterator) Valid() bool {
// If either iterator is valid, the merged iterator is valid.
return it.inner.Valid() || it.overlay.Valid()
}
func (it *treeOverlayIterator) Err() error {
// If either iterator has an error, the merged iterator has an error.
if err := it.inner.Err(); err != nil {
return err
}
if err := it.overlay.Err(); err != nil {
return err
}
return nil
}
func (it *treeOverlayIterator) Rewind() {
it.inner.Rewind()
it.overlay.Rewind()
it.updateIteratorPosition()
}
func (it *treeOverlayIterator) Seek(key node.Key) {
it.inner.Seek(key)
it.overlay.Seek(key)
it.updateIteratorPosition()
}
func (it *treeOverlayIterator) Next() {
if !it.overlay.Valid() || (it.inner.Valid() && it.inner.Key().Compare(it.overlay.Key()) <= 0) {
// Key of inner iterator is smaller or equal than the key of the overlay iterator.
it.inner.Next()
} else {
// Key of inner iterator is greater than the key of the overlay iterator.
it.overlay.Next()
}
it.updateIteratorPosition()
}
func (it *treeOverlayIterator) updateIteratorPosition() {
// Skip over any dirty entries from the inner iterator.
for it.inner.Valid() && it.tree.dirty[string(it.inner.Key())] {
it.inner.Next()
}
iKey := it.inner.Key()
oKey := it.overlay.Key()
if it.inner.Valid() && (!it.overlay.Valid() || iKey.Compare(oKey) < 0) {
// Key of inner iterator is smaller than the key of the overlay iterator.
it.key = iKey
it.value = it.inner.Value()
} else if it.overlay.Valid() {
// Key of overlay iterator is smaller than or equal to the key of the inner iterator.
it.key = oKey
it.value = it.overlay.Value()
} else {
// Both iterators are invalid.
it.key = nil
it.value = nil
}
}
func (it *treeOverlayIterator) Key() node.Key {
return it.key
}
func (it *treeOverlayIterator) Value() []byte {
return it.value
}
func (it *treeOverlayIterator) GetProof() (*syncer.Proof, error) {
panic(fmt.Errorf("tree overlay: proofs are not supported"))
}
func (it *treeOverlayIterator) GetProofBuilder() *syncer.ProofBuilder {
panic(fmt.Errorf("tree overlay: proofs are not supported"))
}
func (it *treeOverlayIterator) Close() {
it.inner.Close()
it.overlay.Close()
it.key = nil
it.value = nil
it.tree = nil
}