receive/expandedpostingscache: fix race (#7937)

Porting cortexproject/cortex#6369 to our code
base. Add test that fails without the fix.

Signed-off-by: Giedrius Statkevičius <[email protected]>

Author: GiedriusS

pkg/receive/expandedpostingscache/cache.go

@@ -43,7 +43,7 @@ type BlocksPostingsForMatchersCache struct {
 	postingsForMatchersFunc func(ctx context.Context, ix tsdb.IndexReader, ms ...*labels.Matcher) (index.Postings, error)
 	timeNow                 func() time.Time
 
-	metrics *ExpandedPostingsCacheMetrics
+	metrics ExpandedPostingsCacheMetrics
 }
 
 var (
@@ -66,8 +66,8 @@ type ExpandedPostingsCacheMetrics struct {
 	NonCacheableQueries *prometheus.CounterVec
 }
 
-func NewPostingCacheMetrics(r prometheus.Registerer) *ExpandedPostingsCacheMetrics {
-	return &ExpandedPostingsCacheMetrics{
+func NewPostingCacheMetrics(r prometheus.Registerer) ExpandedPostingsCacheMetrics {
+	return ExpandedPostingsCacheMetrics{
 		CacheRequests: promauto.With(r).NewCounterVec(prometheus.CounterOpts{
 			Name: "expanded_postings_cache_requests_total",
 			Help: "Total number of requests to the cache.",
@@ -87,11 +87,15 @@ func NewPostingCacheMetrics(r prometheus.Registerer) *ExpandedPostingsCacheMetri
 	}
 }
 
-func NewBlocksPostingsForMatchersCache(metrics *ExpandedPostingsCacheMetrics, headExpandedPostingsCacheSize uint64, blockExpandedPostingsCacheSize uint64) ExpandedPostingsCache {
+func NewBlocksPostingsForMatchersCache(metrics ExpandedPostingsCacheMetrics, headExpandedPostingsCacheSize uint64, blockExpandedPostingsCacheSize uint64, seedSize int64) *BlocksPostingsForMatchersCache {
+	if seedSize <= 0 {
+		seedSize = seedArraySize
+	}
+
 	return &BlocksPostingsForMatchersCache{
 		headCache:               newFifoCache[[]storage.SeriesRef]("head", metrics, time.Now, headExpandedPostingsCacheSize),
 		blocksCache:             newFifoCache[[]storage.SeriesRef]("block", metrics, time.Now, blockExpandedPostingsCacheSize),
-		headSeedByMetricName:    make([]int, seedArraySize),
+		headSeedByMetricName:    make([]int, seedSize),
 		strippedLock:            make([]sync.RWMutex, numOfSeedsStripes),
 		postingsForMatchersFunc: tsdb.PostingsForMatchers,
 		timeNow:                 time.Now,
@@ -129,7 +133,7 @@ func (c *BlocksPostingsForMatchersCache) ExpireSeries(metric labels.Labels) {
 
 	h := MemHashString(metricName)
 	i := h % uint64(len(c.headSeedByMetricName))
-	l := h % uint64(len(c.strippedLock))
+	l := i % uint64(len(c.strippedLock))
 	c.strippedLock[l].Lock()
 	defer c.strippedLock[l].Unlock()
 	c.headSeedByMetricName[i]++
@@ -200,7 +204,7 @@ func (c *BlocksPostingsForMatchersCache) result(ce *cacheEntryPromise[[]storage.
 func (c *BlocksPostingsForMatchersCache) getSeedForMetricName(metricName string) string {
 	h := MemHashString(metricName)
 	i := h % uint64(len(c.headSeedByMetricName))
-	l := h % uint64(len(c.strippedLock))
+	l := i % uint64(len(c.strippedLock))
 	c.strippedLock[l].RLock()
 	defer c.strippedLock[l].RUnlock()
 	return strconv.Itoa(c.headSeedByMetricName[i])
@@ -276,13 +280,13 @@ type fifoCache[V any] struct {
 	cachedBytes int64
 }
 
-func newFifoCache[V any](name string, metrics *ExpandedPostingsCacheMetrics, timeNow func() time.Time, maxBytes uint64) *fifoCache[V] {
+func newFifoCache[V any](name string, metrics ExpandedPostingsCacheMetrics, timeNow func() time.Time, maxBytes uint64) *fifoCache[V] {
 	return &fifoCache[V]{
 		cachedValues: new(sync.Map),
 		cached:       list.New(),
 		timeNow:      timeNow,
 		name:         name,
-		metrics:      *metrics,
+		metrics:      metrics,
 		ttl:          10 * time.Minute,
 		maxBytes:     int64(maxBytes),
 	}

pkg/receive/expandedpostingscache/cache_test.go

@@ -15,9 +15,11 @@ import (
 	"time"
 
 	"go.uber.org/atomic"
+	"golang.org/x/exp/rand"
 
 	"github.com/prometheus/client_golang/prometheus"
 	promtest "github.com/prometheus/client_golang/prometheus/testutil"
+	"github.com/prometheus/prometheus/model/labels"
 	"github.com/stretchr/testify/require"
 )
 
@@ -166,3 +168,43 @@ func repeatStringIfNeeded(seed string, length int) string {
 
 	return strings.Repeat(seed, 1+length/len(seed))[:max(length, len(seed))]
 }
+
+func TestLockRaceExpireSeries(t *testing.T) {
+	for j := 0; j < 10; j++ {
+		wg := &sync.WaitGroup{}
+
+		c := NewBlocksPostingsForMatchersCache(ExpandedPostingsCacheMetrics{}, 1<<7, 1<<7, 3)
+		for i := 0; i < 1000; i++ {
+			wg.Add(2)
+
+			go func() {
+				defer wg.Done()
+				for i := 0; i < 10; i++ {
+					c.ExpireSeries(
+						labels.FromMap(map[string]string{"__name__": randSeq(10)}),
+					)
+				}
+			}()
+
+			go func() {
+				defer wg.Done()
+
+				for i := 0; i < 10; i++ {
+					c.getSeedForMetricName(randSeq(10))
+				}
+			}()
+		}
+		wg.Wait()
+	}
+}
+
+var letters = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
+
+func randSeq(n int) string {
+	b := make([]rune, n)
+	rand.Seed(uint64(time.Now().UnixNano()))
+	for i := range b {
+		b[i] = letters[rand.Intn(len(letters))]
+	}
+	return string(b)
+}

pkg/receive/multitsdb.go

@@ -709,7 +709,7 @@ func (t *MultiTSDB) startTSDB(logger log.Logger, tenantID string, tenant *tenant
 	if t.headExpandedPostingsCacheSize > 0 || t.blockExpandedPostingsCacheSize > 0 {
 		var expandedPostingsCacheMetrics = expandedpostingscache.NewPostingCacheMetrics(extprom.WrapRegistererWithPrefix("thanos_", reg))
 
-		expandedPostingsCache = expandedpostingscache.NewBlocksPostingsForMatchersCache(expandedPostingsCacheMetrics, t.headExpandedPostingsCacheSize, t.blockExpandedPostingsCacheSize)
+		expandedPostingsCache = expandedpostingscache.NewBlocksPostingsForMatchersCache(expandedPostingsCacheMetrics, t.headExpandedPostingsCacheSize, t.blockExpandedPostingsCacheSize, 0)
 	}
 
 	opts := *t.tsdbOpts