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|
package cache
import (
"context"
"github.com/docker/distribution"
prometheus "github.com/docker/distribution/metrics"
"github.com/opencontainers/go-digest"
)
// Metrics is used to hold metric counters
// related to the number of times a cache was
// hit or missed.
type Metrics struct {
Requests uint64
Hits uint64
Misses uint64
}
// Logger can be provided on the MetricsTracker to log errors.
//
// Usually, this is just a proxy to dcontext.GetLogger.
type Logger interface {
Errorf(format string, args ...interface{})
}
// MetricsTracker represents a metric tracker
// which simply counts the number of hits and misses.
type MetricsTracker interface {
Hit()
Miss()
Metrics() Metrics
Logger(context.Context) Logger
}
type cachedBlobStatter struct {
cache distribution.BlobDescriptorService
backend distribution.BlobDescriptorService
tracker MetricsTracker
}
var (
// cacheCount is the number of total cache request received/hits/misses
cacheCount = prometheus.StorageNamespace.NewLabeledCounter("cache", "The number of cache request received", "type")
)
// NewCachedBlobStatter creates a new statter which prefers a cache and
// falls back to a backend.
func NewCachedBlobStatter(cache distribution.BlobDescriptorService, backend distribution.BlobDescriptorService) distribution.BlobDescriptorService {
return &cachedBlobStatter{
cache: cache,
backend: backend,
}
}
// NewCachedBlobStatterWithMetrics creates a new statter which prefers a cache and
// falls back to a backend. Hits and misses will send to the tracker.
func NewCachedBlobStatterWithMetrics(cache distribution.BlobDescriptorService, backend distribution.BlobDescriptorService, tracker MetricsTracker) distribution.BlobStatter {
return &cachedBlobStatter{
cache: cache,
backend: backend,
tracker: tracker,
}
}
func (cbds *cachedBlobStatter) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
cacheCount.WithValues("Request").Inc(1)
desc, err := cbds.cache.Stat(ctx, dgst)
if err != nil {
if err != distribution.ErrBlobUnknown {
logErrorf(ctx, cbds.tracker, "error retrieving descriptor from cache: %v", err)
}
goto fallback
}
cacheCount.WithValues("Hit").Inc(1)
if cbds.tracker != nil {
cbds.tracker.Hit()
}
return desc, nil
fallback:
cacheCount.WithValues("Miss").Inc(1)
if cbds.tracker != nil {
cbds.tracker.Miss()
}
desc, err = cbds.backend.Stat(ctx, dgst)
if err != nil {
return desc, err
}
if err := cbds.cache.SetDescriptor(ctx, dgst, desc); err != nil {
logErrorf(ctx, cbds.tracker, "error adding descriptor %v to cache: %v", desc.Digest, err)
}
return desc, err
}
func (cbds *cachedBlobStatter) Clear(ctx context.Context, dgst digest.Digest) error {
err := cbds.cache.Clear(ctx, dgst)
if err != nil {
return err
}
err = cbds.backend.Clear(ctx, dgst)
if err != nil {
return err
}
return nil
}
func (cbds *cachedBlobStatter) SetDescriptor(ctx context.Context, dgst digest.Digest, desc distribution.Descriptor) error {
if err := cbds.cache.SetDescriptor(ctx, dgst, desc); err != nil {
logErrorf(ctx, cbds.tracker, "error adding descriptor %v to cache: %v", desc.Digest, err)
}
return nil
}
func logErrorf(ctx context.Context, tracker MetricsTracker, format string, args ...interface{}) {
if tracker == nil {
return
}
logger := tracker.Logger(ctx)
if logger == nil {
return
}
logger.Errorf(format, args...)
}
|
