73 lines
1.9 KiB
Go
73 lines
1.9 KiB
Go
package store
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import (
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"time"
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"github.com/lbryio/reflector.go/internal/metrics"
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"github.com/lbryio/lbry.go/v2/stream"
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"golang.org/x/sync/singleflight"
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)
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func WithSingleFlight(component string, origin BlobStore) BlobStore {
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return &singleflightStore{
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BlobStore: origin,
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component: component,
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sf: new(singleflight.Group),
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}
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}
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type singleflightStore struct {
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BlobStore
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component string
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sf *singleflight.Group
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}
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func (s *singleflightStore) Name() string {
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return "sf_" + s.BlobStore.Name()
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}
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// Get ensures that only one request per hash is sent to the origin at a time,
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// thereby protecting against https://en.wikipedia.org/wiki/Thundering_herd_problem
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func (s *singleflightStore) Get(hash string) (stream.Blob, error) {
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metrics.CacheWaitingRequestsCount.With(metrics.CacheLabels(s.Name(), s.component)).Inc()
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defer metrics.CacheWaitingRequestsCount.With(metrics.CacheLabels(s.Name(), s.component)).Dec()
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blob, err, _ := s.sf.Do(hash, s.getter(hash))
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if err != nil {
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return nil, err
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}
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return blob.(stream.Blob), nil
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}
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// getter returns a function that gets a blob from the origin
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// only one getter per hash will be executing at a time
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func (s *singleflightStore) getter(hash string) func() (interface{}, error) {
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return func() (interface{}, error) {
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metrics.CacheOriginRequestsCount.With(metrics.CacheLabels(s.Name(), s.component)).Inc()
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defer metrics.CacheOriginRequestsCount.With(metrics.CacheLabels(s.Name(), s.component)).Dec()
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start := time.Now()
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blob, err := s.BlobStore.Get(hash)
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if err != nil {
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return nil, err
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}
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rate := float64(len(blob)) / 1024 / 1024 / time.Since(start).Seconds()
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metrics.CacheRetrievalSpeed.With(map[string]string{
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metrics.LabelCacheType: s.Name(),
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metrics.LabelComponent: s.component,
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metrics.LabelSource: "origin",
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}).Set(rate)
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return blob, nil
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}
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}
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// Shutdown shuts down the store gracefully
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func (s *singleflightStore) Shutdown() {
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s.BlobStore.Shutdown()
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return
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}
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