111 lines
3.2 KiB
Go
111 lines
3.2 KiB
Go
package store
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import (
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"time"
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"github.com/lbryio/lbry.go/v2/extras/errors"
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"github.com/lbryio/lbry.go/v2/stream"
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"github.com/lbryio/reflector.go/internal/metrics"
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"golang.org/x/sync/singleflight"
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)
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// CachingStore combines two stores, typically a local and a remote store, to improve performance.
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// Accessed blobs are stored in and retrieved from the cache. If they are not in the cache, they
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// are retrieved from the origin and cached. Puts are cached and also forwarded to the origin.
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type CachingStore struct {
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origin, cache BlobStore
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sf *singleflight.Group
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}
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// NewCachingStore makes a new caching disk store and returns a pointer to it.
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func NewCachingStore(origin, cache BlobStore) *CachingStore {
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return &CachingStore{origin: origin, cache: cache, sf: new(singleflight.Group)}
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}
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const nameCaching = "caching"
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// Name is the cache type name
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func (c *CachingStore) Name() string { return nameCaching }
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// Has checks the cache and then the origin for a hash. It returns true if either store has it.
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func (c *CachingStore) Has(hash string) (bool, error) {
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has, err := c.cache.Has(hash)
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if has || err != nil {
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return has, err
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}
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return c.origin.Has(hash)
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}
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// Get tries to get the blob from the cache first, falling back to the origin. If the blob comes
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// from the origin, it is also stored in the cache.
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func (c *CachingStore) Get(hash string) (stream.Blob, error) {
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start := time.Now()
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blob, err := c.cache.Get(hash)
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if err == nil || !errors.Is(err, ErrBlobNotFound) {
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metrics.CacheHitCount.Inc()
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rate := float64(len(blob)) / 1024 / 1024 / time.Since(start).Seconds()
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metrics.RetrieverSpeed.With(map[string]string{metrics.LabelSource: "cache"}).Set(rate)
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return blob, err
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}
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metrics.CacheMissCount.Inc()
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return c.getFromOrigin(hash)
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}
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// getFromOrigin ensures that only one Get 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 (c *CachingStore) getFromOrigin(hash string) (stream.Blob, error) {
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metrics.CacheWaitingRequestsCount.Inc()
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defer metrics.CacheWaitingRequestsCount.Dec()
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originBlob, err, _ := c.sf.Do(hash, func() (interface{}, error) {
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metrics.CacheOriginRequestsCount.Inc()
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defer metrics.CacheOriginRequestsCount.Dec()
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start := time.Now()
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blob, err := c.origin.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.RetrieverSpeed.With(map[string]string{metrics.LabelSource: "origin"}).Set(rate)
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err = c.cache.Put(hash, blob)
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return blob, err
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})
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if err != nil {
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return nil, err
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}
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return originBlob.(stream.Blob), nil
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}
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// Put stores the blob in the origin and the cache
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func (c *CachingStore) Put(hash string, blob stream.Blob) error {
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err := c.origin.Put(hash, blob)
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if err != nil {
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return err
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}
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return c.cache.Put(hash, blob)
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}
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// PutSD stores the sd blob in the origin and the cache
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func (c *CachingStore) PutSD(hash string, blob stream.Blob) error {
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err := c.origin.PutSD(hash, blob)
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if err != nil {
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return err
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}
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return c.cache.PutSD(hash, blob)
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}
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// Delete deletes the blob from the origin and the cache
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func (c *CachingStore) Delete(hash string) error {
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err := c.origin.Delete(hash)
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if err != nil {
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return err
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}
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return c.cache.Delete(hash)
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}
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