Change multiBatcher to use sync.Map, avoid global lock on fast path

.chloggen/sharder.yaml

@@ -0,0 +1,11 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: batchprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Change multiBatcher to use sync.Map, avoid global lock on fast path
+
+# One or more tracking issues or pull requests related to the change
+issues: [7714]

processor/batchprocessor/batch_processor.go

@@ -61,42 +61,28 @@
 
 	telemetry *batchProcessorTelemetry
 
-	//  batcherFinder will be either *singletonBatcher or *multiBatcher
-	batcherFinder
+	//  batcher will be either *singletonBatcher or *multiBatcher
+	batcher batcher
 }
 
-type batcherFinder interface {
-	findBatcher(ctx context.Context) (*batcher, error)
+type batcher interface {
+	consume(ctx context.Context, data any) error
 	currentMetadataCardinality() int
 }
 
-// singleBatcher is used when metadataKeys is empty, to avoid the
-// additional lock and map operations used in multiBatcher.
-type singleBatcher struct {
-	*batcher
-}
-
-// multiBatcher is used when metadataKeys is not empty.
-type multiBatcher struct {
-	*batchProcessor
-
-	lock     sync.Mutex
-	batchers map[attribute.Set]*batcher
-}
-
-// batcher is a single instance of the batcher logic.  When metadata
+// shard is a single instance of the batch logic.  When metadata
 // keys are in use, one of these is created per distinct combination
 // of values.
-type batcher struct {
+type shard struct {
 	// processor refers to this processor, for access to common
 	// configuration.
 	processor *batchProcessor
 
 	// exportCtx is a context with the metadata key-values
-	// corresponding with this batcher set.
+	// corresponding with this shard set.
 	exportCtx context.Context
 
-	// timer informs the batcher send a batch.
+	// timer informs the shard send a batch.
 	timer *time.Timer
 
 	// newItem is used to receive data items from producers.
@@ -143,15 +129,14 @@
 		metadataLimit:    int(cfg.MetadataCardinalityLimit),
 	}
 	if len(bp.metadataKeys) == 0 {
-		bp.batcherFinder = &singleBatcher{bp.newBatcher(nil)}
+		bp.batcher = &singleShardBatcher{batcher: bp.newShard(nil)}
 	} else {
-		bp.batcherFinder = &multiBatcher{
+		bp.batcher = &multiShardBatcher{
 			batchProcessor: bp,
-			batchers:       map[attribute.Set]*batcher{},
 		}
 	}
 
-	bpt, err := newBatchProcessorTelemetry(set, bp.currentMetadataCardinality, useOtel)
+	bpt, err := newBatchProcessorTelemetry(set, bp.batcher.currentMetadataCardinality, useOtel)
 	if err != nil {
 		return nil, fmt.Errorf("error creating batch processor telemetry: %w", err)
 	}
@@ -160,12 +145,12 @@
 	return bp, nil
 }
 
-// newBatcher gets or creates a batcher corresponding with attrs.
-func (bp *batchProcessor) newBatcher(md map[string][]string) *batcher {
+// newShard gets or creates a batcher corresponding with attrs.
+func (bp *batchProcessor) newShard(md map[string][]string) *shard {
 	exportCtx := client.NewContext(context.Background(), client.Info{
 		Metadata: client.NewMetadata(md),
 	})
-	b := &batcher{
+	b := &shard{
 		processor: bp,
 		newItem:   make(chan any, runtime.NumCPU()),
 		exportCtx: exportCtx,
@@ -194,7 +179,7 @@
 	return nil
 }
 
-func (b *batcher) start() {
+func (b *shard) start() {
 	defer b.processor.goroutines.Done()
 
 	// timerCh ensures we only block when there is a
@@ -237,7 +222,7 @@
 	}
 }
 
-func (b *batcher) processItem(item any) {
+func (b *shard) processItem(item any) {
 	b.batch.add(item)
 	sent := false
 	for b.batch.itemCount() > 0 && (!b.hasTimer() || b.batch.itemCount() >= b.processor.sendBatchSize) {
@@ -251,23 +236,23 @@
 	}
 }
 
-func (b *batcher) hasTimer() bool {
+func (b *shard) hasTimer() bool {
 	return b.timer != nil
 }
 
-func (b *batcher) stopTimer() {
+func (b *shard) stopTimer() {
 	if b.hasTimer() && !b.timer.Stop() {
 		<-b.timer.C
 	}
 }
 
-func (b *batcher) resetTimer() {
+func (b *shard) resetTimer() {
 	if b.hasTimer() {
 		b.timer.Reset(b.processor.timeout)
 	}
 }
 
-func (b *batcher) sendItems(trigger trigger) {
+func (b *shard) sendItems(trigger trigger) {
 	sent, bytes, err := b.batch.export(b.exportCtx, b.processor.sendBatchMaxSize, b.processor.telemetry.detailed)
 	if err != nil {
 		b.processor.logger.Warn("Sender failed", zap.Error(err))
@@ -276,11 +261,33 @@
 	}
 }
 
-func (sb *singleBatcher) findBatcher(_ context.Context) (*batcher, error) {
-	return sb.batcher, nil
+// singleShardBatcher is used when metadataKeys is empty, to avoid the
+// additional lock and map operations used in multiBatcher.
+type singleShardBatcher struct {
+	batcher *shard
+}
+
+func (sb *singleShardBatcher) consume(_ context.Context, data any) error {
+	sb.batcher.newItem <- data
+	return nil
+}
+
+func (sb *singleShardBatcher) currentMetadataCardinality() int {
+	return 1
+}
+
+// multiBatcher is used when metadataKeys is not empty.
+type multiShardBatcher struct {
+	*batchProcessor
+	batchers sync.Map
+
+	// Guards the size and the storing logic to ensure no more than limit items are stored.
+	// If we are willing to allow "some" extra items than the limit this can be removed and size can be made atomic.
+	lock sync.Mutex
+	size int
 }
 
-func (mb *multiBatcher) findBatcher(ctx context.Context) (*batcher, error) {
+func (mb *multiShardBatcher) consume(ctx context.Context, data any) error {
 	// Get each metadata key value, form the corresponding
 	// attribute set for use as a map lookup key.
 	info := client.FromContext(ctx)
@@ -300,63 +307,46 @@
 	}
 	aset := attribute.NewSet(attrs...)
 
-	mb.lock.Lock()
-	defer mb.lock.Unlock()
-
-	b, ok := mb.batchers[aset]
-	if ok {
-		return b, nil
-	}
+	b, ok := mb.batchers.Load(aset)
+	if !ok {
+		mb.lock.Lock()
+		if mb.metadataLimit != 0 && mb.size >= mb.metadataLimit {
+			mb.lock.Unlock()
+			return errTooManyBatchers
+		}
 
-	if limit := mb.metadataLimit; limit != 0 && len(mb.batchers) >= limit {
-		return nil, errTooManyBatchers
+		// aset.ToSlice() returns the sorted, deduplicated,
+		// and name-downcased list of attributes.
+		var loaded bool
+		b, loaded = mb.batchers.LoadOrStore(aset, mb.newShard(md))
+		if !loaded {
+			mb.size++
+		}
+		mb.lock.Unlock()
 	}
-
-	// aset.ToSlice() returns the sorted, deduplicated,
-	// and name-downcased list of attributes.
-	b = mb.newBatcher(md)
-	mb.batchers[aset] = b
-	return b, nil
-}
-
-func (sb *singleBatcher) currentMetadataCardinality() int {
-	return 1
+	b.(*shard).newItem <- data
+	return nil
 }
 
-func (mb *multiBatcher) currentMetadataCardinality() int {
+func (mb *multiShardBatcher) currentMetadataCardinality() int {
 	mb.lock.Lock()
 	defer mb.lock.Unlock()
-	return len(mb.batchers)
+	return mb.size
 }
 
 // ConsumeTraces implements TracesProcessor
 func (bp *batchProcessor) ConsumeTraces(ctx context.Context, td ptrace.Traces) error {
-	b, err := bp.findBatcher(ctx)
-	if err != nil {
-		return err
-	}
-	b.newItem <- td
-	return nil
+	return bp.batcher.consume(ctx, td)
 }
 
 // ConsumeMetrics implements MetricsProcessor
 func (bp *batchProcessor) ConsumeMetrics(ctx context.Context, md pmetric.Metrics) error {
-	b, err := bp.findBatcher(ctx)
-	if err != nil {
-		return err
-	}
-	b.newItem <- md
-	return nil
+	return bp.batcher.consume(ctx, md)
 }
 
 // ConsumeLogs implements LogsProcessor
 func (bp *batchProcessor) ConsumeLogs(ctx context.Context, ld plog.Logs) error {
-	b, err := bp.findBatcher(ctx)
-	if err != nil {
-		return err
-	}
-	b.newItem <- ld
-	return nil
+	return bp.batcher.consume(ctx, ld)
 }
 
 // newBatchTracesProcessor creates a new batch processor that batches traces by size or with timeout