forked from mailgun/groupcache
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathgroupcache.go
More file actions
888 lines (767 loc) · 25.6 KB
/
Copy pathgroupcache.go
File metadata and controls
888 lines (767 loc) · 25.6 KB
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
/*
Copyright 2012 Google Inc.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
// Package groupcache provides a data loading mechanism with caching
// and de-duplication that works across a set of peer processes.
//
// Each data Get first consults its local cache, otherwise delegates
// to the requested key's canonical owner, which then checks its cache
// or finally gets the data. In the common case, many concurrent
// cache misses across a set of peers for the same key result in just
// one cache fill.
package groupcache
import (
"context"
"errors"
"fmt"
"maps"
"slices"
"sync"
"sync/atomic"
"time"
"weak"
pb "github.com/modernprogram/groupcache/v2/groupcachepb"
"github.com/modernprogram/groupcache/v2/lru"
"github.com/modernprogram/groupcache/v2/singleflight"
)
// A Getter loads data for a key.
type Getter interface {
// Get returns the value identified by key, populating dest.
//
// The returned data must be unversioned. That is, key must
// uniquely describe the loaded data, without an implicit
// current time, and without relying on cache expiration
// mechanisms.
Get(ctx context.Context, key string, dest Sink, info *Info) error
}
// A GetterFunc implements Getter with a function.
type GetterFunc func(ctx context.Context, key string, dest Sink, info *Info) error
func (f GetterFunc) Get(ctx context.Context, key string, dest Sink, info *Info) error {
return f(ctx, key, dest, info)
}
// GetGroup returns the named group previously created with NewGroup, or
// nil if there's no such group.
func GetGroup(ws *Workspace, name string) *Group {
ws.mu.RLock()
g := ws.groups[name]
ws.mu.RUnlock()
return g
}
// GetGroupWiths returns all groups previously created with NewGroup, or
// nil if there is no group.
func GetGroups(ws *Workspace) []*Group {
ws.mu.RLock()
list := slices.Collect(maps.Values(ws.groups))
ws.mu.RUnlock()
return list
}
// Options define settings for group.
type Options struct {
Workspace *Workspace
Name string
CacheBytesLimit int64
Getter Getter
// HotCacheWeight and MainCacheWeight compose the ratio between the hot cache and the main cache.
// When the cache memory limit is reached, this ratio is used to limit each cache to its limit.
// One simple way to reason about this ratio is to think of one cache usage against
// the other, and NOT one cache against the total sum.
//
// Consider some examples:
// 1) mainWeigth=8 and hotWeight=1 => the hot cache limit is 1/8 of the main cache limit.
// 2) mainWeight=2 and hotWeight=1 => the hot cache limit is 1/2 of the main cache limit.
// 3) mainWeight=1 and hotWeight=1 => the hot cache limit is equal to the main cache limit.
// 4) mainWeight=1 and hotWeight=2 => the hot cache limit is 2x the main cache limit.
// 5) mainWeight=1 and hotWeight=8 => the hot cache limit is 8x the main cache limit.
//
// If unspecified, HotCacheWeight defaults to 1.
// If unspecified, MainCacheWeight defaults to 1.
HotCacheWeight int64
MainCacheWeight int64
// PurgeExpired enables evicting expired keys on memory full condition.
PurgeExpired bool
// ExpiredKeysEvictionInterval sets interval for periodic eviction of expired keys.
// If unset, defaults to 30-minute period.
// Set to -1 to disable periodic eviction of expired keys.
ExpiredKeysEvictionInterval time.Duration
// PeerLatencyWindow is interval for resetting worst recorded peer latency metric.
// It only affects the recording of peer latency metric.
// If undefined, defaults to 5-minute period.
PeerLatencyWindow time.Duration
// Logger is optional pluggable logger.
// If undefined, groupcache won't log anything.
// If defined, groupcache will log errors retrieving keys from peers.
// slog.Defaut() creates a logger that satifiest this interface.
Logger Logger
}
// Logger is interface for pluggable logger.
// slog.Defaut() creates a logger that satifiest this interface.
type Logger interface {
Info(msg string, args ...any)
Error(msg string, args ...any)
}
// NewGroup creates a coordinated group-aware Getter from a Getter.
//
// The returned Getter tries (but does not guarantee) to run only one
// Get call at once for a given key across an entire set of peer
// processes. Concurrent callers both in the local process and in
// other processes receive copies of the answer once the original Get
// completes.
//
// The group name must be unique for each getter.
func NewGroup(options Options) *Group {
if options.MainCacheWeight == 0 {
options.MainCacheWeight = 1
}
if options.HotCacheWeight == 0 {
options.HotCacheWeight = 1
}
if options.ExpiredKeysEvictionInterval == 0 {
options.ExpiredKeysEvictionInterval = 30 * time.Minute
}
if options.PeerLatencyWindow == 0 {
options.PeerLatencyWindow = 5 * time.Minute
}
return newGroup(options.Workspace, options.Name, options.PurgeExpired,
options.CacheBytesLimit, options.MainCacheWeight, options.HotCacheWeight,
options.ExpiredKeysEvictionInterval, options.PeerLatencyWindow,
options.Getter, nil, options.Logger)
}
// If peers is nil, the peerPicker is called via a sync.Once to initialize it.
func newGroup(ws *Workspace, name string, purgeExpired bool, cacheBytesLimit,
mainCacheWeight, hotCacheWeight int64,
expiredKeysEvictionInterval, peerLatencyWindow time.Duration,
getter Getter,
peers PeerPicker, logger Logger) *Group {
if getter == nil {
panic("nil Getter")
}
ws.mu.Lock()
defer ws.mu.Unlock()
if _, dup := ws.groups[name]; dup {
panic("duplicate registration of group " + name)
}
g := &Group{
ws: ws,
logger: logger,
name: name,
getter: getter,
peers: peers,
cacheBytesLimit: cacheBytesLimit,
mainCacheWeight: mainCacheWeight,
hotCacheWeight: hotCacheWeight,
purgeExpired: purgeExpired,
loadGroup: &singleflight.Group{},
setGroup: &singleflight.Group{},
removeGroup: &singleflight.Group{},
peerLatencyWindow: peerLatencyWindow,
}
ws.groups[name] = g
if expiredKeysEvictionInterval > 0 {
// launch goroutine to periodically evict expired keys
weakGroup := weak.Make(g)
go evictExpiredKeys(weakGroup, expiredKeysEvictionInterval)
}
return g
}
// evictExpiredKeys periodically evicts all expired keys.
func evictExpiredKeys(weakGroup weak.Pointer[Group],
expiredKeysEvictionInterval time.Duration) {
c := time.Tick(expiredKeysEvictionInterval)
for range c {
strong := weakGroup.Value()
if strong == nil {
// group has been garbage collected,
// exit to release goroutine resources
return
}
strong.removeAllExpired()
strong = nil // make sure we got rid of the strong pointer
}
}
// A Group is a cache namespace and associated data loaded spread over
// a group of 1 or more machines.
type Group struct {
ws *Workspace
logger Logger
name string
getter Getter
peersOnce sync.Once
peers PeerPicker
cacheBytesLimit int64 // limit for sum of mainCache and hotCache size
mainCacheWeight int64
hotCacheWeight int64
purgeExpired bool
// mainCache is a cache of the keys for which this process
// (amongst its peers) is authoritative. That is, this cache
// contains keys which consistent hash on to this process's
// peer number.
mainCache cache
// hotCache contains keys/values for which this peer is not
// authoritative (otherwise they would be in mainCache), but
// are popular enough to warrant mirroring in this process to
// avoid going over the network to fetch from a peer. Having
// a hotCache avoids network hotspotting, where a peer's
// network card could become the bottleneck on a popular key.
// This cache is used sparingly to maximize the total number
// of key/value pairs that can be stored globally.
hotCache cache
// loadGroup ensures that each key is only fetched once
// (either locally or remotely), regardless of the number of
// concurrent callers.
loadGroup flightGroup
// setGroup ensures that each added key is only added
// remotely once regardless of the number of concurrent callers.
setGroup flightGroup
// removeGroup ensures that each removed key is only removed
// remotely once regardless of the number of concurrent callers.
removeGroup flightGroup
// peerLatencyMu protects peer latency window bookkeeping fields.
peerLatencyMu sync.Mutex
// lastPeerLatencyReset records last time peer latency window was reset.
lastPeerLatencyReset time.Time
// peerLatencyWindow defines the interval for resetting window
// for recording worst peer latency.
peerLatencyWindow time.Duration
_ int32 // force Stats to be 8-byte aligned on 32-bit platforms
// Stats are statistics on the group.
Stats Stats
}
// flightGroup is defined as an interface which flightgroup.Group
// satisfies. We define this so that we may test with an alternate
// implementation.
type flightGroup interface {
Do(key string, fn func() (any, error)) (any, error)
Lock(fn func())
}
// Stats are per-group statistics.
type Stats struct {
Gets atomic.Int64 // any Get request, including from peers
CacheHits atomic.Int64 // either cache was good
GetFromPeersLatencyLower atomic.Int64 // slowest duration to request value from peers
PeerLoads atomic.Int64 // either remote load or remote cache hit (not an error)
PeerErrors atomic.Int64 // errors when loading values from peers
Loads atomic.Int64 // (gets - cacheHits)
LoadsDeduped atomic.Int64 // after singleflight
LocalLoads atomic.Int64 // total good local loads
LocalLoadErrs atomic.Int64 // total bad local loads
ServerRequests atomic.Int64 // gets that came over the network from peers
CrosstalkRefusals atomic.Int64 // refusals for additional crosstalks
}
// Name returns the name of the group.
func (g *Group) Name() string {
return g.name
}
func (g *Group) initPeers() {
if g.peers == nil {
g.peers = getPeers(g.ws)
}
}
// Get retrieves key for library caller, thus crosstalk is allowed.
// info holds optional user-supplied per-request context fields that are
// propagated to the peer getter load function.
func (g *Group) Get(ctx context.Context, key string, dest Sink, info *Info) error {
const crosstalkAllowed = true
return g.get(ctx, key, dest, crosstalkAllowed, info)
}
// GetForPeer retrieves key for peer in a crosstalk request, thus further crosstalk won't be allowed.
func (g *Group) GetForPeer(ctx context.Context, key string, dest Sink, info *Info) error {
const crosstalkAllowed = false
return g.get(ctx, key, dest, crosstalkAllowed, info)
}
func (g *Group) get(ctx context.Context, key string, dest Sink,
crosstalkAllowed bool, info *Info) error {
g.peersOnce.Do(g.initPeers)
g.Stats.Gets.Add(1)
if dest == nil {
return errors.New("groupcache: nil dest Sink")
}
value, cacheHit := g.lookupCache(key)
if cacheHit {
g.Stats.CacheHits.Add(1)
return setSinkView(dest, value)
}
// Optimization to avoid double unmarshalling or copying: keep
// track of whether the dest was already populated. One caller
// (if local) will set this; the losers will not. The common
// case will likely be one caller.
value, destPopulated, err := g.load(ctx, key, dest, crosstalkAllowed, info)
if err != nil {
return err
}
if destPopulated {
return nil
}
return setSinkView(dest, value)
}
func (g *Group) Set(ctx context.Context, key string, value []byte, expire time.Time, hotCache bool) error {
g.peersOnce.Do(g.initPeers)
if key == "" {
return errors.New("empty Set() key not allowed")
}
_, err := g.setGroup.Do(key, func() (any, error) {
// If remote peer owns this key
owner, ok := g.peers.PickPeer(key)
if ok {
if err := g.setFromPeer(ctx, owner, key, value, expire); err != nil {
return nil, err
}
// TODO(thrawn01): Not sure if this is useful outside of tests...
// maybe we should ALWAYS update the local cache?
if hotCache {
g.localSet(key, value, expire, &g.hotCache)
}
return nil, nil
}
// We own this key
g.localSet(key, value, expire, &g.mainCache)
return nil, nil
})
return err
}
// Remove clears the key from our cache then forwards the remove
// request to all peers.
func (g *Group) Remove(ctx context.Context, key string) error {
g.peersOnce.Do(g.initPeers)
_, err := g.removeGroup.Do(key, func() (any, error) {
// Remove from key owner first
owner, ok := g.peers.PickPeer(key)
if ok {
if err := g.removeFromPeer(ctx, owner, key); err != nil {
return nil, err
}
}
// Remove from our cache next
g.localRemove(key)
wg := sync.WaitGroup{}
errs := make(chan error)
// Asynchronously clear the key from all hot and main caches of peers
for _, peer := range g.peers.GetAll() {
// avoid deleting from owner a second time
if peer == owner {
continue
}
wg.Add(1)
go func(peer ProtoGetter) {
errs <- g.removeFromPeer(ctx, peer, key)
wg.Done()
}(peer)
}
go func() {
wg.Wait()
close(errs)
}()
// TODO(thrawn01): Should we report all errors? Reporting context
// cancelled error for each peer doesn't make much sense.
var err error
for e := range errs {
err = e
}
return nil, err
})
return err
}
var errFurtherCrosstalkRefused = errors.New("further crosstalk refused")
// load loads key either by invoking the getter locally or by sending it to another machine.
func (g *Group) load(ctx context.Context, key string, dest Sink,
crosstalkAllowed bool, info *Info) (value ByteView, destPopulated bool, err error) {
g.Stats.Loads.Add(1)
viewi, err := g.loadGroup.Do(key, func() (any, error) {
// Check the cache again because singleflight can only dedup calls
// that overlap concurrently. It's possible for 2 concurrent
// requests to miss the cache, resulting in 2 load() calls. An
// unfortunate goroutine scheduling would result in this callback
// being run twice, serially. If we don't check the cache again,
// cache.nbytes would be incremented below even though there will
// be only one entry for this key.
//
// Consider the following serialized event ordering for two
// goroutines in which this callback gets called twice for hte
// same key:
// 1: Get("key")
// 2: Get("key")
// 1: lookupCache("key")
// 2: lookupCache("key")
// 1: load("key")
// 2: load("key")
// 1: loadGroup.Do("key", fn)
// 1: fn()
// 2: loadGroup.Do("key", fn)
// 2: fn()
if value, cacheHit := g.lookupCache(key); cacheHit {
g.Stats.CacheHits.Add(1)
return value, nil
}
g.Stats.LoadsDeduped.Add(1)
var value ByteView
var err error
if peer, ok := g.peers.PickPeer(key); ok {
// other peer (not me) is the key owner
if !crosstalkAllowed {
// crosstalkAllowed=false: we are responding to a crosstalk request.
// then we refuse further crosstalk.
g.Stats.CrosstalkRefusals.Add(1)
return nil, errFurtherCrosstalkRefused
}
// metrics duration start
start := time.Now()
// get value from peers
value, err = g.getFromPeer(ctx, peer, key, info)
end := time.Now()
// metrics duration compute
duration := int64(end.Sub(start)) / int64(time.Millisecond)
g.recordPeerLoadLatency(duration, end)
if err == nil {
g.Stats.PeerLoads.Add(1)
return value, nil
}
if errors.Is(err, context.Canceled) {
return nil, err
}
if errors.Is(err, &ErrNotFound{}) {
return nil, err
}
if errors.Is(err, &ErrRemoteCall{}) {
return nil, err
}
if g.logger != nil {
g.logger.Error(fmt.Sprintf("error retrieving key from peer '%s'", peer.GetURL()),
"err", err,
"key", key,
"category", "groupcache",
)
}
g.Stats.PeerErrors.Add(1)
if ctx != nil && ctx.Err() != nil {
// Return here without attempting to get locally
// since the context is no longer valid
return nil, err
}
// the crosstalk peer request above failed with an unexpected error
// FIXME TODO XXX: we are currently generating the key by ourselves, but should we?
}
// either
// 1. we are the key owner
// then we will generate the key by ourselves
// or
// 2. the crosstalk peer request above failed with an unexpected error
// FIXME TODO XXX: we are currently generating the key by ourselves, but should we?
value, err = g.getLocally(ctx, key, dest, info)
if err != nil {
g.Stats.LocalLoadErrs.Add(1)
return nil, err
}
g.Stats.LocalLoads.Add(1)
destPopulated = true // only one caller of load gets this return value
g.populateCache(key, value, &g.mainCache)
return value, nil
})
if err == nil {
value = viewi.(ByteView)
}
return
}
func (g *Group) recordPeerLoadLatency(duration int64, now time.Time) {
g.peerLatencyMu.Lock()
defer g.peerLatencyMu.Unlock()
if elapLastPeerLatencyReset := now.Sub(g.lastPeerLatencyReset); elapLastPeerLatencyReset > g.peerLatencyWindow {
// reset worst peer latency every peerLatencyWindow interval
g.Stats.GetFromPeersLatencyLower.Store(duration) // record new worst latency
// reset latency window
g.lastPeerLatencyReset = now
} else if duration > g.Stats.GetFromPeersLatencyLower.Load() {
g.Stats.GetFromPeersLatencyLower.Store(duration) // record new worst latency
}
}
func (g *Group) getLocally(ctx context.Context, key string, dest Sink, info *Info) (ByteView, error) {
err := g.getter.Get(ctx, key, dest, info)
if err != nil {
return ByteView{}, err
}
return dest.view()
}
func (g *Group) getFromPeer(ctx context.Context, peer ProtoGetter,
key string, info *Info) (ByteView, error) {
req := &pb.GetRequest{
Group: &g.name,
Key: &key,
}
if info != nil {
// Propagate optional user-supplied per-request information to peer load function.
req.Ctx1 = &info.Ctx1
req.Ctx2 = &info.Ctx2
}
res := &pb.GetResponse{}
err := peer.Get(ctx, req, res)
if err != nil {
return ByteView{}, err
}
var expire time.Time
if res.Expire != nil && *res.Expire != 0 {
expire = time.Unix(*res.Expire/int64(time.Second), *res.Expire%int64(time.Second))
if time.Now().After(expire) {
return ByteView{}, errors.New("peer returned expired value")
}
}
value := ByteView{b: res.Value, e: expire}
// Always populate the hot cache
g.populateCache(key, value, &g.hotCache)
return value, nil
}
func (g *Group) setFromPeer(ctx context.Context, peer ProtoGetter, k string, v []byte, e time.Time) error {
var expire int64
if !e.IsZero() {
expire = e.UnixNano()
}
req := &pb.SetRequest{
Expire: &expire,
Group: &g.name,
Key: &k,
Value: v,
}
return peer.Set(ctx, req)
}
func (g *Group) removeFromPeer(ctx context.Context, peer ProtoGetter, key string) error {
req := &pb.GetRequest{
Group: &g.name,
Key: &key,
}
return peer.Remove(ctx, req)
}
func (g *Group) lookupCache(key string) (value ByteView, ok bool) {
if g.cacheBytesLimit <= 0 {
return
}
value, ok = g.mainCache.get(key)
if ok {
return
}
value, ok = g.hotCache.get(key)
return
}
func (g *Group) localSet(key string, value []byte, expire time.Time, cache *cache) {
if g.cacheBytesLimit <= 0 {
return
}
bv := ByteView{
b: value,
e: expire,
}
// Ensure no requests are in flight
g.loadGroup.Lock(func() {
g.populateCache(key, bv, cache)
})
}
func (g *Group) localRemove(key string) {
// Clear key from our local cache
if g.cacheBytesLimit <= 0 {
return
}
// Ensure no requests are in flight
g.loadGroup.Lock(func() {
g.hotCache.remove(key)
g.mainCache.remove(key)
})
}
func (g *Group) removeAllExpired() int64 {
mainBytes := g.mainCache.removeAllExpired()
hotBytes := g.hotCache.removeAllExpired()
return mainBytes + hotBytes
}
func (g *Group) populateCache(key string, value ByteView, c *cache) {
if g.cacheBytesLimit <= 0 {
return
}
c.add(key, value)
if g.purgeExpired {
{
mainBytes := g.mainCache.bytes()
hotBytes := g.hotCache.bytes()
if mainBytes+hotBytes <= g.cacheBytesLimit {
return // mem is not full
}
}
// first, attempt to evict only expired keys in order to prevent
// evicting non-expired keys.
if mainAndHotBytes := g.removeAllExpired(); mainAndHotBytes <= g.cacheBytesLimit {
return // mem no longer full
}
}
// mem is still full.
// now we will evict oldest non-expired keys.
// Evict items from cache(s) if necessary.
for {
mainBytes := g.mainCache.bytes()
hotBytes := g.hotCache.bytes()
if mainBytes+hotBytes <= g.cacheBytesLimit {
return // mem no longer full
}
// here we are on mem full condition.
// TODO(bradfitz): this is good-enough-for-now logic.
// It should be something based on measurements and/or
// respecting the costs of different resources.
var victim *cache
// default weights: if hotBytes > mainBytes/8 { ... }
if isHotUsageExcessive(mainBytes, hotBytes, g.mainCacheWeight, g.hotCacheWeight) {
victim = &g.hotCache
} else {
victim = &g.mainCache
}
victim.removeOldest() // removeOldest is used on mem full condition.
}
}
// isHotUsageExcessive reports if hot cache exceeded its limit in comparison to main cache.
// Conversely, it also reports if main cache did NOT exceed its limit in comparison to hot cache.
// For the special case when both caches are using their exact limits, we report the hot cache
// is not exceeding its limit, thus slightly favouring hot cache over main cache.
// One simple way to reason about this function behavior is to think of one cache usage against
// the other, and NOT one cache against the total sum.
// Consider some examples:
// 1) mainWeigth=8 and hotWeight=1 => the hot cache limit is 1/8 of the main cache limit.
// 2) mainWeight=2 and hotWeight=1 => the hot cache limit is 1/2 of the main cache limit.
// 3) mainWeight=1 and hotWeight=1 => the hot cache limit is equal to the main cache limit.
// 4) mainWeight=1 and hotWeight=2 => the hot cache limit is 2x the main cache limit.
// 5) mainWeight=1 and hotWeight=8 => the hot cache limit is 8x the main cache limit.
func isHotUsageExcessive(mainBytes, hotBytes, mainWeight, hotWeight int64) bool {
return hotBytes*mainWeight > mainBytes*hotWeight
}
// CacheType represents a type of cache.
type CacheType int
const (
// MainCache is the cache for items that this peer is the
// owner for.
MainCache CacheType = iota + 1
// HotCache is the cache for items that seem popular
// enough to replicate to this node, even though it's not the
// owner.
HotCache
)
// CacheStats returns stats about the provided cache within the group.
func (g *Group) CacheStats(which CacheType) CacheStats {
switch which {
case MainCache:
return g.mainCache.stats()
case HotCache:
return g.hotCache.stats()
default:
return CacheStats{}
}
}
// NowFunc returns the current time which is used by the LRU to
// determine if the value has expired. This can be overridden by
// tests to ensure items are evicted when expired.
var NowFunc lru.NowFunc = time.Now
// cache is a wrapper around an *lru.Cache that adds synchronization,
// makes values always be ByteView, and counts the size of all keys and
// values.
type cache struct {
mu sync.RWMutex
nbytes int64 // of all keys and values
lru *lru.Cache
nhit, nget int64
nevict int64 // number of evictions
nevictNonExpiredOnMemFull int64 // number of evictions for non-expired items on mem full condition
}
func (c *cache) stats() CacheStats {
c.mu.RLock()
defer c.mu.RUnlock()
return CacheStats{
Bytes: c.nbytes,
Items: c.itemsLocked(),
Gets: c.nget,
Hits: c.nhit,
Evictions: c.nevict,
EvictionsNonExpiredOnMemFull: c.nevictNonExpiredOnMemFull,
}
}
func (c *cache) add(key string, value ByteView) {
c.mu.Lock()
defer c.mu.Unlock()
if c.lru == nil {
c.lru = &lru.Cache{
Now: NowFunc,
OnEvicted: func(key lru.Key, value any, nonExpiredAndMemFull bool) {
val := value.(ByteView)
c.nbytes -= int64(len(key.(string))) + int64(val.Len())
c.nevict++
if nonExpiredAndMemFull {
c.nevictNonExpiredOnMemFull++
}
},
}
}
c.lru.Add(key, value, value.Expire())
c.nbytes += int64(len(key)) + int64(value.Len())
}
func (c *cache) get(key string) (value ByteView, ok bool) {
c.mu.Lock()
defer c.mu.Unlock()
c.nget++
if c.lru == nil {
return
}
vi, ok := c.lru.Get(key)
if !ok {
return
}
c.nhit++
return vi.(ByteView), true
}
func (c *cache) remove(key string) {
c.mu.Lock()
defer c.mu.Unlock()
if c.lru == nil {
return
}
c.lru.Remove(key)
}
// removeOldest is used on mem full condition.
func (c *cache) removeOldest() {
c.mu.Lock()
defer c.mu.Unlock()
if c.lru != nil {
c.lru.RemoveOldest()
}
}
// removeAllExpired is used on mem full condition.
func (c *cache) removeAllExpired() int64 {
c.mu.Lock()
defer c.mu.Unlock()
if c.lru != nil {
c.lru.RemoveAllExpired()
}
return c.nbytes
}
func (c *cache) bytes() int64 {
c.mu.RLock()
defer c.mu.RUnlock()
return c.nbytes
}
func (c *cache) items() int64 {
c.mu.RLock()
defer c.mu.RUnlock()
return c.itemsLocked()
}
func (c *cache) itemsLocked() int64 {
if c.lru == nil {
return 0
}
return int64(c.lru.Len())
}
// CacheStats are returned by stats accessors on Group.
type CacheStats struct {
Bytes int64
Items int64
Gets int64
Hits int64
Evictions int64
EvictionsNonExpiredOnMemFull int64 // number of evictions for non-expired items on mem full condition
}