summaryrefslogtreecommitdiff
path: root/vendor/github.com/hashicorp/golang-lru/2q.go
blob: e474cd07581ac908575132b99cf3b118bc9d1059 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
package lru

import (
	"fmt"
	"sync"

	"github.com/hashicorp/golang-lru/simplelru"
)

const (
	// Default2QRecentRatio is the ratio of the 2Q cache dedicated
	// to recently added entries that have only been accessed once.
	Default2QRecentRatio = 0.25

	// Default2QGhostEntries is the default ratio of ghost
	// entries kept to track entries recently evicted
	Default2QGhostEntries = 0.50
)

// TwoQueueCache is a thread-safe fixed size 2Q cache.
// 2Q is an enhancement over the standard LRU cache
// in that it tracks both frequently and recently used
// entries separately. This avoids a burst in access to new
// entries from evicting frequently used entries. It adds some
// additional tracking overhead to the standard LRU cache, and is
// computationally about 2x the cost, and adds some metadata over
// head. The ARCCache is similar, but does not require setting any
// parameters.
type TwoQueueCache struct {
	size       int
	recentSize int

	recent      simplelru.LRUCache
	frequent    simplelru.LRUCache
	recentEvict simplelru.LRUCache
	lock        sync.RWMutex
}

// New2Q creates a new TwoQueueCache using the default
// values for the parameters.
func New2Q(size int) (*TwoQueueCache, error) {
	return New2QParams(size, Default2QRecentRatio, Default2QGhostEntries)
}

// New2QParams creates a new TwoQueueCache using the provided
// parameter values.
func New2QParams(size int, recentRatio float64, ghostRatio float64) (*TwoQueueCache, error) {
	if size <= 0 {
		return nil, fmt.Errorf("invalid size")
	}
	if recentRatio < 0.0 || recentRatio > 1.0 {
		return nil, fmt.Errorf("invalid recent ratio")
	}
	if ghostRatio < 0.0 || ghostRatio > 1.0 {
		return nil, fmt.Errorf("invalid ghost ratio")
	}

	// Determine the sub-sizes
	recentSize := int(float64(size) * recentRatio)
	evictSize := int(float64(size) * ghostRatio)

	// Allocate the LRUs
	recent, err := simplelru.NewLRU(size, nil)
	if err != nil {
		return nil, err
	}
	frequent, err := simplelru.NewLRU(size, nil)
	if err != nil {
		return nil, err
	}
	recentEvict, err := simplelru.NewLRU(evictSize, nil)
	if err != nil {
		return nil, err
	}

	// Initialize the cache
	c := &TwoQueueCache{
		size:        size,
		recentSize:  recentSize,
		recent:      recent,
		frequent:    frequent,
		recentEvict: recentEvict,
	}
	return c, nil
}

// Get looks up a key's value from the cache.
func (c *TwoQueueCache) Get(key interface{}) (value interface{}, ok bool) {
	c.lock.Lock()
	defer c.lock.Unlock()

	// Check if this is a frequent value
	if val, ok := c.frequent.Get(key); ok {
		return val, ok
	}

	// If the value is contained in recent, then we
	// promote it to frequent
	if val, ok := c.recent.Peek(key); ok {
		c.recent.Remove(key)
		c.frequent.Add(key, val)
		return val, ok
	}

	// No hit
	return nil, false
}

// Add adds a value to the cache.
func (c *TwoQueueCache) Add(key, value interface{}) {
	c.lock.Lock()
	defer c.lock.Unlock()

	// Check if the value is frequently used already,
	// and just update the value
	if c.frequent.Contains(key) {
		c.frequent.Add(key, value)
		return
	}

	// Check if the value is recently used, and promote
	// the value into the frequent list
	if c.recent.Contains(key) {
		c.recent.Remove(key)
		c.frequent.Add(key, value)
		return
	}

	// If the value was recently evicted, add it to the
	// frequently used list
	if c.recentEvict.Contains(key) {
		c.ensureSpace(true)
		c.recentEvict.Remove(key)
		c.frequent.Add(key, value)
		return
	}

	// Add to the recently seen list
	c.ensureSpace(false)
	c.recent.Add(key, value)
	return
}

// ensureSpace is used to ensure we have space in the cache
func (c *TwoQueueCache) ensureSpace(recentEvict bool) {
	// If we have space, nothing to do
	recentLen := c.recent.Len()
	freqLen := c.frequent.Len()
	if recentLen+freqLen < c.size {
		return
	}

	// If the recent buffer is larger than
	// the target, evict from there
	if recentLen > 0 && (recentLen > c.recentSize || (recentLen == c.recentSize && !recentEvict)) {
		k, _, _ := c.recent.RemoveOldest()
		c.recentEvict.Add(k, nil)
		return
	}

	// Remove from the frequent list otherwise
	c.frequent.RemoveOldest()
}

// Len returns the number of items in the cache.
func (c *TwoQueueCache) Len() int {
	c.lock.RLock()
	defer c.lock.RUnlock()
	return c.recent.Len() + c.frequent.Len()
}

// Keys returns a slice of the keys in the cache.
// The frequently used keys are first in the returned slice.
func (c *TwoQueueCache) Keys() []interface{} {
	c.lock.RLock()
	defer c.lock.RUnlock()
	k1 := c.frequent.Keys()
	k2 := c.recent.Keys()
	return append(k1, k2...)
}

// Remove removes the provided key from the cache.
func (c *TwoQueueCache) Remove(key interface{}) {
	c.lock.Lock()
	defer c.lock.Unlock()
	if c.frequent.Remove(key) {
		return
	}
	if c.recent.Remove(key) {
		return
	}
	if c.recentEvict.Remove(key) {
		return
	}
}

// Purge is used to completely clear the cache.
func (c *TwoQueueCache) Purge() {
	c.lock.Lock()
	defer c.lock.Unlock()
	c.recent.Purge()
	c.frequent.Purge()
	c.recentEvict.Purge()
}

// Contains is used to check if the cache contains a key
// without updating recency or frequency.
func (c *TwoQueueCache) Contains(key interface{}) bool {
	c.lock.RLock()
	defer c.lock.RUnlock()
	return c.frequent.Contains(key) || c.recent.Contains(key)
}

// Peek is used to inspect the cache value of a key
// without updating recency or frequency.
func (c *TwoQueueCache) Peek(key interface{}) (value interface{}, ok bool) {
	c.lock.RLock()
	defer c.lock.RUnlock()
	if val, ok := c.frequent.Peek(key); ok {
		return val, ok
	}
	return c.recent.Peek(key)
}