cloudflare/pint
Publicmirrored from https://github.com/cloudflare/pintAvailable
internal/promapi/cache.go
251lines · modecode
| 1 | package promapi |
| 2 | |
| 3 | import ( |
| 4 | "sort" |
| 5 | "sync" |
| 6 | "time" |
| 7 | |
| 8 | "github.com/prometheus/client_golang/prometheus" |
| 9 | ) |
| 10 | |
| 11 | type cacheEntry struct { |
| 12 | data queryResult |
| 13 | expiresAt time.Time |
| 14 | cost int |
| 15 | gets int |
| 16 | } |
| 17 | |
| 18 | type cacheLine struct { |
| 19 | key uint64 |
| 20 | val *cacheEntry |
| 21 | ttl time.Duration |
| 22 | isExpired bool |
| 23 | } |
| 24 | |
| 25 | type cacheLines []cacheLine |
| 26 | |
| 27 | func (cl cacheLines) Len() int { |
| 28 | return len(cl) |
| 29 | } |
| 30 | |
| 31 | func (cl cacheLines) Swap(i, j int) { |
| 32 | cl[i], cl[j] = cl[j], cl[i] |
| 33 | } |
| 34 | |
| 35 | // [expired, costly, cheap, high ttl] |
| 36 | func (cl cacheLines) Less(i, j int) bool { |
| 37 | if cl[i].isExpired != cl[j].isExpired { |
| 38 | return cl[i].isExpired |
| 39 | } |
| 40 | |
| 41 | if cl[i].val.gets == 0 { |
| 42 | return true |
| 43 | } |
| 44 | if cl[j].val.gets == 0 { |
| 45 | return false |
| 46 | } |
| 47 | |
| 48 | if cl[i].val.cost != cl[j].val.cost { |
| 49 | ca := float64(cl[i].val.cost) / float64(cl[i].val.gets) |
| 50 | cb := float64(cl[j].val.cost) / float64(cl[j].val.gets) |
| 51 | if ca != cb { |
| 52 | return ca >= cb |
| 53 | } |
| 54 | } |
| 55 | |
| 56 | if cl[i].val.gets != cl[j].val.gets { |
| 57 | return cl[i].val.gets < cl[j].val.gets |
| 58 | } |
| 59 | |
| 60 | return cl[i].ttl < cl[j].ttl |
| 61 | } |
| 62 | |
| 63 | type endpointStats struct { |
| 64 | hits int |
| 65 | misses int |
| 66 | } |
| 67 | |
| 68 | func (e *endpointStats) hit() { e.hits++ } |
| 69 | func (e *endpointStats) miss() { e.misses++ } |
| 70 | |
| 71 | func newQueryCache(maxSize int) *queryCache { |
| 72 | return &queryCache{ |
| 73 | entries: map[uint64]*cacheEntry{}, |
| 74 | stats: map[string]*endpointStats{}, |
| 75 | maxCost: maxSize, |
| 76 | } |
| 77 | } |
| 78 | |
| 79 | type queryCache struct { |
| 80 | mu sync.Mutex |
| 81 | entries map[uint64]*cacheEntry |
| 82 | stats map[string]*endpointStats |
| 83 | cost int |
| 84 | maxCost int |
| 85 | evictions int |
| 86 | } |
| 87 | |
| 88 | func (c *queryCache) endpointStats(endpoint string) *endpointStats { |
| 89 | e, ok := c.stats[endpoint] |
| 90 | if ok { |
| 91 | return e |
| 92 | } |
| 93 | |
| 94 | e = &endpointStats{} |
| 95 | c.stats[endpoint] = e |
| 96 | return e |
| 97 | } |
| 98 | |
| 99 | func (c *queryCache) get(key uint64, endpoint string) (v queryResult, ok bool) { |
| 100 | c.mu.Lock() |
| 101 | defer c.mu.Unlock() |
| 102 | |
| 103 | var ce *cacheEntry |
| 104 | ce, ok = c.entries[key] |
| 105 | if !ok { |
| 106 | c.endpointStats(endpoint).miss() |
| 107 | return v, ok |
| 108 | } |
| 109 | |
| 110 | ce.gets++ |
| 111 | c.endpointStats(endpoint).hit() |
| 112 | |
| 113 | return ce.data, true |
| 114 | } |
| 115 | |
| 116 | // Cache results if it was requested at least twice EVER - which means it's either |
| 117 | // popular and requested multiple times within a loop OR this cache key survives between loops. |
| 118 | func (c *queryCache) set(key uint64, val queryResult, ttl time.Duration, cost int, endpoint string) { |
| 119 | c.mu.Lock() |
| 120 | defer c.mu.Unlock() |
| 121 | |
| 122 | oe, ok := c.entries[key] |
| 123 | if ok { |
| 124 | c.cost -= oe.cost |
| 125 | } |
| 126 | |
| 127 | // If we're not updating in-place then we need to make room for this entry |
| 128 | if !ok && c.cost+cost > c.maxCost { |
| 129 | c.makeRoom(cost) |
| 130 | } |
| 131 | |
| 132 | c.cost += cost |
| 133 | c.entries[key] = &cacheEntry{ |
| 134 | data: val, |
| 135 | cost: cost, |
| 136 | } |
| 137 | if ttl > 0 { |
| 138 | c.entries[key].expiresAt = time.Now().Add(ttl) |
| 139 | } |
| 140 | } |
| 141 | |
| 142 | func (c *queryCache) makeRoom(needed int) { |
| 143 | now := time.Now() |
| 144 | for key, ce := range c.entries { |
| 145 | if !ce.expiresAt.IsZero() && ce.expiresAt.Before(now) { |
| 146 | c.cost -= ce.cost |
| 147 | needed -= ce.cost |
| 148 | delete(c.entries, key) |
| 149 | c.evictions++ |
| 150 | } |
| 151 | } |
| 152 | if needed <= 0 { |
| 153 | return |
| 154 | } |
| 155 | |
| 156 | entries := make(cacheLines, 0, len(c.entries)) |
| 157 | for key, ce := range c.entries { |
| 158 | entries = append(entries, cacheLine{ |
| 159 | key: key, |
| 160 | val: ce, |
| 161 | ttl: ce.expiresAt.Sub(now).Round(time.Second), |
| 162 | isExpired: ce.expiresAt.Before(now), |
| 163 | }) |
| 164 | } |
| 165 | sort.Stable(entries) |
| 166 | |
| 167 | for i := len(entries) - 1; i >= 0; i-- { |
| 168 | c.cost -= entries[i].val.cost |
| 169 | needed -= entries[i].val.cost |
| 170 | delete(c.entries, entries[i].key) |
| 171 | c.evictions++ |
| 172 | if needed <= 0 { |
| 173 | return |
| 174 | } |
| 175 | } |
| 176 | } |
| 177 | |
| 178 | func (c *queryCache) gc() { |
| 179 | c.mu.Lock() |
| 180 | defer c.mu.Unlock() |
| 181 | |
| 182 | entries := map[uint64]*cacheEntry{} |
| 183 | |
| 184 | now := time.Now() |
| 185 | for key, ce := range c.entries { |
| 186 | if !ce.expiresAt.IsZero() && ce.expiresAt.Before(now) { |
| 187 | c.cost -= ce.cost |
| 188 | c.evictions++ |
| 189 | continue |
| 190 | } |
| 191 | entries[key] = ce |
| 192 | } |
| 193 | c.entries = entries |
| 194 | } |
| 195 | |
| 196 | type cacheCollector struct { |
| 197 | cache *queryCache |
| 198 | entries *prometheus.Desc |
| 199 | hits *prometheus.Desc |
| 200 | misses *prometheus.Desc |
| 201 | evictions *prometheus.Desc |
| 202 | } |
| 203 | |
| 204 | func newCacheCollector(cache *queryCache, name string) *cacheCollector { |
| 205 | return &cacheCollector{ |
| 206 | cache: cache, |
| 207 | entries: prometheus.NewDesc( |
| 208 | "pint_prometheus_cache_size", |
| 209 | "Total number of entries currently stored in Prometheus query cache", |
| 210 | nil, |
| 211 | prometheus.Labels{"name": name}, |
| 212 | ), |
| 213 | hits: prometheus.NewDesc( |
| 214 | "pint_prometheus_cache_hits_total", |
| 215 | "Total number of query cache hits", |
| 216 | []string{"endpoint"}, |
| 217 | prometheus.Labels{"name": name}, |
| 218 | ), |
| 219 | misses: prometheus.NewDesc( |
| 220 | "pint_prometheus_cache_miss_total", |
| 221 | "Total number of query cache misses", |
| 222 | []string{"endpoint"}, |
| 223 | prometheus.Labels{"name": name}, |
| 224 | ), |
| 225 | evictions: prometheus.NewDesc( |
| 226 | "pint_prometheus_cache_evictions_total", |
| 227 | "Total number of times an entry was evicted from query cache due to size limit or TTL", |
| 228 | nil, |
| 229 | prometheus.Labels{"name": name}, |
| 230 | ), |
| 231 | } |
| 232 | } |
| 233 | |
| 234 | func (c *cacheCollector) Describe(ch chan<- *prometheus.Desc) { |
| 235 | ch <- c.entries |
| 236 | ch <- c.hits |
| 237 | ch <- c.misses |
| 238 | ch <- c.evictions |
| 239 | } |
| 240 | |
| 241 | func (c *cacheCollector) Collect(ch chan<- prometheus.Metric) { |
| 242 | c.cache.mu.Lock() |
| 243 | defer c.cache.mu.Unlock() |
| 244 | ch <- prometheus.MustNewConstMetric(c.entries, prometheus.GaugeValue, float64(c.cache.cost)) |
| 245 | |
| 246 | for endpoint, stats := range c.cache.stats { |
| 247 | ch <- prometheus.MustNewConstMetric(c.hits, prometheus.CounterValue, float64(stats.hits), endpoint) |
| 248 | ch <- prometheus.MustNewConstMetric(c.misses, prometheus.CounterValue, float64(stats.misses), endpoint) |
| 249 | } |
| 250 | ch <- prometheus.MustNewConstMetric(c.evictions, prometheus.CounterValue, float64(c.cache.evictions)) |
| 251 | } |
| 252 | |