[processor/spanmetrics] Prune histograms (open-telemetry#27083)

Prune histograms when the dimension cache evictions are removed

**Description:**
Prunes histograms when the dimension cache is pruned. This prevents
metric series from growing indefinitely

**Link to tracking Issue:**
 open-telemetry#27080

**Testing:**
I modified the the existing test to check `histograms` length instead of
dimensions cache length. This required simulating ticks to hit the
exportMetrics function

**Documentation:** <Describe the documentation added.>

Co-authored-by: Sean Marciniak <30928402+MovieStoreGuy@users.noreply.github.com>

.chloggen/27083-spanmetrics-prune.yaml

@@ -0,0 +1,29 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: processor/spanmetrics
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Prune histograms when dimension cache is pruned.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [27080]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: |
+  Dimension cache was always pruned but histograms were not being pruned. This caused metric series created
+  by processor/spanmetrics to grow unbounded.
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

processor/spanmetricsprocessor/internal/cache/cache.go

@@ -64,6 +64,10 @@ func (c *Cache[K, V]) Get(key K) (V, bool) {
 	return val, ok
 }
 
+func (c *Cache[K, V]) Contains(key K) bool {
+	return c.lru.Contains(key)
+}
+
 // Len returns the number of items in the cache.
 func (c *Cache[K, V]) Len() int {
 	return c.lru.Len()

processor/spanmetricsprocessor/processor.go

@@ -258,6 +258,11 @@ func (p *processorImp) exportMetrics(ctx context.Context) {
 		p.metricKeyToDimensions.Purge()
 	} else {
 		p.metricKeyToDimensions.RemoveEvictedItems()
+		for key := range p.histograms {
+			if !p.metricKeyToDimensions.Contains(key) {
+				delete(p.histograms, key)
+			}
+		}
 	}
 
 	// This component no longer needs to read the metrics once built, so it is safe to unlock.

processor/spanmetricsprocessor/processor_test.go

@@ -47,7 +47,7 @@ const (
 	notInSpanAttrName0     = "shouldBeInMetric"
 	notInSpanAttrName1     = "shouldNotBeInMetric"
 	regionResourceAttrName = "region"
-	DimensionsCacheSize    = 2
+	DimensionsCacheSize    = 1000
 
 	sampleRegion          = "us-east-1"
 	sampleLatency         = float64(11)
@@ -144,7 +144,7 @@ func TestProcessorConcurrentShutdown(t *testing.T) {
 	ticker := mockClock.NewTicker(time.Nanosecond)
 
 	// Test
-	p := newProcessorImp(mexp, tcon, nil, cumulative, logger, ticker)
+	p := newProcessorImp(mexp, tcon, nil, cumulative, logger, ticker, DimensionsCacheSize)
 	err := p.Start(ctx, mhost)
 	require.NoError(t, err)
 
@@ -230,7 +230,7 @@ func TestProcessorConsumeTracesErrors(t *testing.T) {
 	tcon := &mocks.TracesConsumer{}
 	tcon.On("ConsumeTraces", mock.Anything, mock.Anything).Return(fakeErr)
 
-	p := newProcessorImp(mexp, tcon, nil, cumulative, logger, nil)
+	p := newProcessorImp(mexp, tcon, nil, cumulative, logger, nil, DimensionsCacheSize)
 
 	traces := buildSampleTrace()
 
@@ -262,7 +262,7 @@ func TestProcessorConsumeMetricsErrors(t *testing.T) {
 
 	mockClock := clock.NewMock(time.Now())
 	ticker := mockClock.NewTicker(time.Nanosecond)
-	p := newProcessorImp(mexp, tcon, nil, cumulative, logger, ticker)
+	p := newProcessorImp(mexp, tcon, nil, cumulative, logger, ticker, DimensionsCacheSize)
 
 	exporters := map[component.DataType]map[component.ID]component.Component{}
 	mhost := &mocks.Host{}
@@ -362,7 +362,7 @@ func TestProcessorConsumeTraces(t *testing.T) {
 			mockClock := clock.NewMock(time.Now())
 			ticker := mockClock.NewTicker(time.Nanosecond)
 
-			p := newProcessorImp(mexp, tcon, &defaultNullValue, tc.aggregationTemporality, zaptest.NewLogger(t), ticker)
+			p := newProcessorImp(mexp, tcon, &defaultNullValue, tc.aggregationTemporality, zaptest.NewLogger(t), ticker, DimensionsCacheSize)
 
 			exporters := map[component.DataType]map[component.ID]component.Component{}
 			mhost := &mocks.Host{}
@@ -387,39 +387,61 @@ func TestProcessorConsumeTraces(t *testing.T) {
 	}
 }
 
-func TestMetricKeyCache(t *testing.T) {
+func TestMetricCache(t *testing.T) {
+	var wg sync.WaitGroup
+
 	mexp := &mocks.MetricsConsumer{}
-	tcon := &mocks.TracesConsumer{}
+	mexp.On("ConsumeMetrics", mock.Anything, mock.MatchedBy(func(input pmetric.Metrics) bool {
+		wg.Done()
+		return true
+	})).Return(nil)
 
-	mexp.On("ConsumeMetrics", mock.Anything, mock.Anything).Return(nil)
+	tcon := &mocks.TracesConsumer{}
 	tcon.On("ConsumeTraces", mock.Anything, mock.Anything).Return(nil)
 
 	defaultNullValue := pcommon.NewValueStr("defaultNullValue")
-	p := newProcessorImp(mexp, tcon, &defaultNullValue, cumulative, zaptest.NewLogger(t), nil)
-	traces := buildSampleTrace()
+	mockClock := clock.NewMock(time.Now())
+	ticker := mockClock.NewTicker(time.Nanosecond)
+	dimensionsCacheSize := 2
+
+	p := newProcessorImp(mexp, tcon, &defaultNullValue, cumulative, zaptest.NewLogger(t), ticker, dimensionsCacheSize)
+
+	exporters := map[component.DataType]map[component.ID]component.Component{}
+	mhost := &mocks.Host{}
+	mhost.On("GetExporters").Return(exporters)
 
 	// Test
 	ctx := metadata.NewIncomingContext(context.Background(), nil)
+	err := p.Start(ctx, mhost)
+	require.NoError(t, err)
 
 	// 0 key was cached at beginning
-	assert.Zero(t, p.metricKeyToDimensions.Len())
+	assert.Zero(t, len(p.histograms))
+
+	traces := buildSampleTrace()
+	require.Condition(t, func() bool {
+		return traces.SpanCount() >= dimensionsCacheSize
+	})
+
+	err = p.ConsumeTraces(ctx, traces)
+	wg.Add(1)
+	mockClock.Add(time.Nanosecond)
+	wg.Wait()
 
-	err := p.ConsumeTraces(ctx, traces)
 	// Validate
 	require.NoError(t, err)
 	// 2 key was cached, 1 key was evicted and cleaned after the processing
-	assert.Eventually(t, func() bool {
-		return p.metricKeyToDimensions.Len() == DimensionsCacheSize
-	}, 10*time.Second, time.Millisecond*100)
+	assert.Equal(t, len(p.histograms), dimensionsCacheSize)
 
 	// consume another batch of traces
 	err = p.ConsumeTraces(ctx, traces)
 	require.NoError(t, err)
+	wg.Add(1)
+	mockClock.Add(time.Nanosecond)
+	wg.Wait()
 
 	// 2 key was cached, other keys were evicted and cleaned after the processing
-	assert.Eventually(t, func() bool {
-		return p.metricKeyToDimensions.Len() == DimensionsCacheSize
-	}, 10*time.Second, time.Millisecond*100)
+	assert.Equal(t, len(p.histograms), dimensionsCacheSize)
 }
 
 func BenchmarkProcessorConsumeTraces(b *testing.B) {
@@ -431,7 +453,7 @@ func BenchmarkProcessorConsumeTraces(b *testing.B) {
 	tcon.On("ConsumeTraces", mock.Anything, mock.Anything).Return(nil)
 
 	defaultNullValue := pcommon.NewValueStr("defaultNullValue")
-	p := newProcessorImp(mexp, tcon, &defaultNullValue, cumulative, zaptest.NewLogger(b), nil)
+	p := newProcessorImp(mexp, tcon, &defaultNullValue, cumulative, zaptest.NewLogger(b), nil, DimensionsCacheSize)
 
 	traces := buildSampleTrace()
 
@@ -442,10 +464,10 @@ func BenchmarkProcessorConsumeTraces(b *testing.B) {
 	}
 }
 
-func newProcessorImp(mexp *mocks.MetricsConsumer, tcon *mocks.TracesConsumer, defaultNullValue *pcommon.Value, temporality string, logger *zap.Logger, ticker *clock.Ticker) *processorImp {
+func newProcessorImp(mexp *mocks.MetricsConsumer, tcon *mocks.TracesConsumer, defaultNullValue *pcommon.Value, temporality string, logger *zap.Logger, ticker *clock.Ticker, cacheSize int) *processorImp {
 	defaultNotInSpanAttrVal := pcommon.NewValueStr("defaultNotInSpanAttrVal")
 	// use size 2 for LRU cache for testing purpose
-	metricKeyToDimensions, err := cache.NewCache[metricKey, pcommon.Map](DimensionsCacheSize)
+	metricKeyToDimensions, err := cache.NewCache[metricKey, pcommon.Map](cacheSize)
 	if err != nil {
 		panic(err)
 	}
@@ -979,8 +1001,7 @@ func TestConsumeTracesEvictedCacheKey(t *testing.T) {
 	mockClock := clock.NewMock(time.Now())
 	ticker := mockClock.NewTicker(time.Nanosecond)
 
-	// Note: default dimension key cache size is 2.
-	p := newProcessorImp(mexp, tcon, &defaultNullValue, cumulative, zaptest.NewLogger(t), ticker)
+	p := newProcessorImp(mexp, tcon, &defaultNullValue, cumulative, zaptest.NewLogger(t), ticker, DimensionsCacheSize)
 
 	exporters := map[component.DataType]map[component.ID]component.Component{}