Fix: PostingCache promise should fetch data only once

Author: alanprot

pkg/storage/tsdb/expanded_postings_cache_test.go

@@ -1,16 +1,48 @@
 package tsdb
 
 import (
-	"context"
 	"fmt"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/stretchr/testify/require"
+	"go.uber.org/atomic"
 )
 
+func Test_ShouldFetchPromiseOnlyOnce(t *testing.T) {
+	cfg := PostingsCacheConfig{
+		Enabled:  true,
+		Ttl:      time.Hour,
+		MaxBytes: 10 << 20,
+	}
+	m := NewPostingCacheMetrics(prometheus.DefaultRegisterer)
+	cache := newFifoCache[int](cfg, "test", m, time.Now)
+	calls := atomic.Int64{}
+	concurrency := 100
+	wg := sync.WaitGroup{}
+	wg.Add(concurrency)
+
+	fetchFunc := func() (int, int64, error) {
+		calls.Inc()
+		time.Sleep(100 * time.Millisecond)
+		return 0, 0, nil
+	}
+
+	for i := 0; i < 100; i++ {
+		go func() {
+			defer wg.Done()
+			cache.getPromiseForKey("key1", fetchFunc)
+		}()
+	}
+
+	wg.Wait()
+	require.Equal(t, int64(1), calls.Load())
+
+}
+
 func TestFifoCacheDisabled(t *testing.T) {
 	cfg := PostingsCacheConfig{}
 	cfg.Enabled = false
@@ -21,9 +53,7 @@ func TestFifoCacheDisabled(t *testing.T) {
 		return 1, 0, nil
 	})
 	require.False(t, loaded)
-	v, err := old.result(context.Background())
-	require.NoError(t, err)
-	require.Equal(t, 1, v)
+	require.Equal(t, 1, old.v)
 	require.False(t, cache.contains("key1"))
 }
 
@@ -68,17 +98,13 @@ func TestFifoCacheExpire(t *testing.T) {
 					return 1, 8, nil
 				})
 				require.False(t, loaded)
-				v, err := p.result(context.Background())
-				require.NoError(t, err)
-				require.Equal(t, 1, v)
+				require.Equal(t, 1, p.v)
 				require.True(t, cache.contains(key))
 				p, loaded = cache.getPromiseForKey(key, func() (int, int64, error) {
 					return 1, 0, nil
 				})
 				require.True(t, loaded)
-				v, err = p.result(context.Background())
-				require.NoError(t, err)
-				require.Equal(t, 1, v)
+				require.Equal(t, 1, p.v)
 			}
 
 			totalCacheSize := 0
@@ -104,10 +130,8 @@ func TestFifoCacheExpire(t *testing.T) {
 						return 2, 18, nil
 					})
 					require.False(t, loaded)
-					v, err := p.result(context.Background())
-					require.NoError(t, err)
 					// New value
-					require.Equal(t, 2, v)
+					require.Equal(t, 2, p.v)
 					// Total Size Updated
 					require.Equal(t, originalSize+10, cache.cachedBytes)
 				}