diff --git a/pkg/cacheutil/async_op.go b/pkg/cacheutil/async_op.go
index 524d2fdba2..f03f1d0827 100644
--- a/pkg/cacheutil/async_op.go
+++ b/pkg/cacheutil/async_op.go
@@ -5,9 +5,15 @@ package cacheutil
 
 import (
 	"sync"
+
+	"github.com/pkg/errors"
+)
+
+var (
+	ErrAsyncBufferFull = errors.New("the async buffer is full")
 )
 
-type asyncOperationProcessor struct {
+type AsyncOperationProcessor struct {
 	// Channel used to notify internal goroutines when they should quit.
 	stop chan struct{}
 
@@ -18,8 +24,9 @@ type asyncOperationProcessor struct {
 	workers sync.WaitGroup
 }
 
-func newAsyncOperationProcessor(bufferSize, concurrency int) *asyncOperationProcessor {
-	p := &asyncOperationProcessor{
+// NewAsyncOperationProcessor creates an async processor with given bufferSize and concurrency.
+func NewAsyncOperationProcessor(bufferSize, concurrency int) *AsyncOperationProcessor {
+	p := &AsyncOperationProcessor{
 		stop:       make(chan struct{}, 1),
 		asyncQueue: make(chan func(), bufferSize),
 	}
@@ -32,14 +39,14 @@ func newAsyncOperationProcessor(bufferSize, concurrency int) *asyncOperationProc
 	return p
 }
 
-func (p *asyncOperationProcessor) Stop() {
+func (p *AsyncOperationProcessor) Stop() {
 	close(p.stop)
 
 	// Wait until all workers have terminated.
 	p.workers.Wait()
 }
 
-func (p *asyncOperationProcessor) asyncQueueProcessLoop() {
+func (p *AsyncOperationProcessor) asyncQueueProcessLoop() {
 	defer p.workers.Done()
 
 	for {
@@ -52,11 +59,12 @@ func (p *asyncOperationProcessor) asyncQueueProcessLoop() {
 	}
 }
 
-func (p *asyncOperationProcessor) enqueueAsync(op func()) error {
+// EnqueueAsync enqueues op to async queue. If enqueue failed, ErrAsyncBufferFull is returned.
+func (p *AsyncOperationProcessor) EnqueueAsync(op func()) error {
 	select {
 	case p.asyncQueue <- op:
 		return nil
 	default:
-		return errMemcachedAsyncBufferFull
+		return ErrAsyncBufferFull
 	}
 }
diff --git a/pkg/cacheutil/memcached_client.go b/pkg/cacheutil/memcached_client.go
index 55d07d9d5a..29caaed02b 100644
--- a/pkg/cacheutil/memcached_client.go
+++ b/pkg/cacheutil/memcached_client.go
@@ -40,7 +40,6 @@ const (
 )
 
 var (
-	errMemcachedAsyncBufferFull                = errors.New("the async buffer is full")
 	errMemcachedConfigNoAddrs                  = errors.New("no memcached addresses provided")
 	errMemcachedDNSUpdateIntervalNotPositive   = errors.New("DNS provider update interval must be positive")
 	errMemcachedMaxAsyncConcurrencyNotPositive = errors.New("max async concurrency must be positive")
@@ -195,7 +194,7 @@ type memcachedClient struct {
 	duration   *prometheus.HistogramVec
 	dataSize   *prometheus.HistogramVec
 
-	p *asyncOperationProcessor
+	p *AsyncOperationProcessor
 }
 
 // AddressProvider performs node address resolution given a list of clusters.
@@ -278,7 +277,7 @@ func newMemcachedClient(
 			config.MaxGetMultiConcurrency,
 			gate.Gets,
 		),
-		p: newAsyncOperationProcessor(config.MaxAsyncBufferSize, config.MaxAsyncConcurrency),
+		p: NewAsyncOperationProcessor(config.MaxAsyncBufferSize, config.MaxAsyncConcurrency),
 	}
 
 	c.clientInfo = promauto.With(reg).NewGaugeFunc(prometheus.GaugeOpts{
@@ -372,7 +371,7 @@ func (c *memcachedClient) SetAsync(key string, value []byte, ttl time.Duration)
 		return nil
 	}
 
-	err := c.p.enqueueAsync(func() {
+	err := c.p.EnqueueAsync(func() {
 		start := time.Now()
 		c.operations.WithLabelValues(opSet).Inc()
 
@@ -400,7 +399,7 @@ func (c *memcachedClient) SetAsync(key string, value []byte, ttl time.Duration)
 		c.duration.WithLabelValues(opSet).Observe(time.Since(start).Seconds())
 	})
 
-	if errors.Is(err, errMemcachedAsyncBufferFull) {
+	if errors.Is(err, ErrAsyncBufferFull) {
 		c.skipped.WithLabelValues(opSet, reasonAsyncBufferFull).Inc()
 		level.Debug(c.logger).Log("msg", "failed to store item to memcached because the async buffer is full", "err", err, "size", len(c.p.asyncQueue))
 		return nil
diff --git a/pkg/cacheutil/redis_client.go b/pkg/cacheutil/redis_client.go
index 1ef3755ca7..032ed2942d 100644
--- a/pkg/cacheutil/redis_client.go
+++ b/pkg/cacheutil/redis_client.go
@@ -149,7 +149,7 @@ type RedisClient struct {
 	durationSetMulti prometheus.Observer
 	durationGetMulti prometheus.Observer
 
-	p *asyncOperationProcessor
+	p *AsyncOperationProcessor
 }
 
 // NewRedisClient makes a new RedisClient.
@@ -221,7 +221,7 @@ func NewRedisClientWithConfig(logger log.Logger, name string, config RedisClient
 		client: client,
 		config: config,
 		logger: logger,
-		p:      newAsyncOperationProcessor(config.MaxAsyncBufferSize, config.MaxAsyncConcurrency),
+		p:      NewAsyncOperationProcessor(config.MaxAsyncBufferSize, config.MaxAsyncConcurrency),
 		getMultiGate: gate.New(
 			extprom.WrapRegistererWithPrefix("thanos_redis_getmulti_", reg),
 			config.MaxGetMultiConcurrency,
@@ -247,7 +247,7 @@ func NewRedisClientWithConfig(logger log.Logger, name string, config RedisClient
 
 // SetAsync implement RemoteCacheClient.
 func (c *RedisClient) SetAsync(key string, value []byte, ttl time.Duration) error {
-	return c.p.enqueueAsync(func() {
+	return c.p.EnqueueAsync(func() {
 		start := time.Now()
 		if err := c.client.Do(context.Background(), c.client.B().Set().Key(key).Value(rueidis.BinaryString(value)).ExSeconds(int64(ttl.Seconds())).Build()).Error(); err != nil {
 			level.Warn(c.logger).Log("msg", "failed to set item into redis", "err", err, "key", key, "value_size", len(value))