reflector.go/store/singleflight.go

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