Replace CombineTraceProtos with new Combiner

CHANGELOG.md

@@ -11,6 +11,7 @@
 * [ENHANCEMENT] Enterprise jsonnet: add config to create tokengen job explicitly [#1256](https://github.com/grafana/tempo/pull/1256) (@kvrhdn)
 * [ENHANCEMENT] Add new scaling alerts to the tempo-mixin [#1292](https://github.com/grafana/tempo/pull/1292) (@mapno)
 * [ENHANCEMENT] Improve serverless handler error messages [#1305](https://github.com/grafana/tempo/pull/1305) (@joe-elliott)
+* [ENHANCEMENT] Make trace combination/compaction more efficient [#1291](https://github.com/grafana/tempo/pull/1291) (@mdisibio)
 * [BUGFIX]: Remove unnecessary PersistentVolumeClaim [#1245](https://github.com/grafana/tempo/issues/1245)
 * [BUGFIX] Fixed issue when query-frontend doesn't log request details when request is cancelled [#1136](https://github.com/grafana/tempo/issues/1136) (@adityapwr)
 * [BUGFIX] Update OTLP port in examples (docker-compose & kubernetes) from legacy ports (55680/55681) to new ports (4317/4318) [#1294](https://github.com/grafana/tempo/pull/1294) (@mapno)

cmd/tempo-cli/cmd-query-blocks.go

@@ -47,13 +47,13 @@ func (cmd *queryBlocksCmd) Run(ctx *globalOptions) error {
 	}
 
 	var (
-		combinedTrace *tempopb.Trace
-		marshaller    = new(jsonpb.Marshaler)
-		jsonBytes     = bytes.Buffer{}
+		combiner   = trace.NewCombiner()
+		marshaller = new(jsonpb.Marshaler)
+		jsonBytes  = bytes.Buffer{}
 	)
 
 	fmt.Println()
-	for _, result := range results {
+	for i, result := range results {
 		fmt.Println(result.blockID, ":")
 
 		err := marshaller.Marshal(&jsonBytes, result.trace)
@@ -64,9 +64,10 @@ func (cmd *queryBlocksCmd) Run(ctx *globalOptions) error {
 
 		fmt.Println(jsonBytes.String())
 		jsonBytes.Reset()
-		combinedTrace, _ = trace.CombineTraceProtos(result.trace, combinedTrace)
+		combiner.ConsumeWithFinal(result.trace, i == len(results)-1)
 	}
 
+	combinedTrace, _ := combiner.Result()
 	fmt.Println("combined:")
 	err = marshaller.Marshal(&jsonBytes, combinedTrace)
 	if err != nil {

modules/frontend/tracebyidsharding.go

@@ -65,7 +65,8 @@ func (s shardQuery) RoundTrip(r *http.Request) (*http.Response, error) {
 
 	var overallError error
 	var totalFailedBlocks uint32
-	overallTrace := &tempopb.Trace{}
+	combiner := trace.NewCombiner()
+	combiner.Consume(&tempopb.Trace{}) // The query path returns a non-nil result even if no inputs (which is different than other paths which return nil for no inputs)
 	statusCode := http.StatusNotFound
 	statusMsg := "trace not found"
 
@@ -139,7 +140,7 @@ func (s shardQuery) RoundTrip(r *http.Request) (*http.Response, error) {
 
 			// happy path
 			statusCode = http.StatusOK
-			overallTrace, _ = trace.CombineTraceProtos(overallTrace, traceResp.Trace)
+			combiner.Consume(traceResp.Trace)
 		}(req)
 	}
 	wg.Wait()
@@ -148,6 +149,7 @@ func (s shardQuery) RoundTrip(r *http.Request) (*http.Response, error) {
 		return nil, overallError
 	}
 
+	overallTrace, _ := combiner.Result()
 	if overallTrace == nil || statusCode != http.StatusOK {
 		// translate non-404s into 500s. if, for instance, we get a 400 back from an internal component
 		// it means that we created a bad request. 400 should not be propagated back to the user b/c

modules/querier/querier.go

@@ -167,7 +167,7 @@ func (q *Querier) FindTraceByID(ctx context.Context, req *tempopb.TraceByIDReque
 	span, ctx := opentracing.StartSpanFromContext(ctx, "Querier.FindTraceByID")
 	defer span.Finish()
 
-	var completeTrace *tempopb.Trace
+	combiner := trace.NewCombiner()
 	var spanCount, spanCountTotal, traceCountTotal int
 	if req.QueryMode == QueryModeIngesters || req.QueryMode == QueryModeAll {
 		replicationSet, err := q.ring.GetReplicationSetForOperation(ring.Read)
@@ -184,16 +184,18 @@ func (q *Querier) FindTraceByID(ctx context.Context, req *tempopb.TraceByIDReque
 			return nil, errors.Wrap(err, "error querying ingesters in Querier.FindTraceByID")
 		}
 
+		found := false
 		for _, r := range responses {
 			t := r.response.(*tempopb.TraceByIDResponse).Trace
 			if t != nil {
-				completeTrace, spanCount = trace.CombineTraceProtos(completeTrace, t)
+				spanCount = combiner.Consume(t)
 				spanCountTotal += spanCount
 				traceCountTotal++
+				found = true
 			}
 		}
 		span.LogFields(ot_log.String("msg", "done searching ingesters"),
-			ot_log.Bool("found", completeTrace != nil),
+			ot_log.Bool("found", found),
 			ot_log.Int("combinedSpans", spanCountTotal),
 			ot_log.Int("combinedTraces", traceCountTotal))
 	}
@@ -225,17 +227,19 @@ func (q *Querier) FindTraceByID(ctx context.Context, req *tempopb.TraceByIDReque
 				}
 			}
 
-			completeTrace, spanCount = trace.CombineTraceProtos(completeTrace, storeTrace)
+			spanCount = combiner.Consume(storeTrace)
 			spanCountTotal += spanCount
 			traceCountTotal++
 
 			span.LogFields(ot_log.String("msg", "combined trace protos from store"),
-				ot_log.Bool("found", completeTrace != nil),
+				ot_log.Bool("found", len(partialTraces) > 0),
 				ot_log.Int("combinedSpans", spanCountTotal),
 				ot_log.Int("combinedTraces", traceCountTotal))
 		}
 	}
 
+	completeTrace, _ := combiner.Result()
+
 	return &tempopb.TraceByIDResponse{
 		Trace: completeTrace,
 		Metrics: &tempopb.TraceByIDMetrics{

pkg/model/combine.go

@@ -63,7 +63,10 @@ func CombineForRead(obj []byte, dataEncoding string, t *tempopb.Trace) (*tempopb
 		return nil, fmt.Errorf("error unmarshalling obj (%s): %w", dataEncoding, err)
 	}
 
-	combined, _ := trace.CombineTraceProtos(objTrace, t)
+	c := trace.NewCombiner()
+	c.Consume(objTrace)
+	c.ConsumeWithFinal(t, true)
+	combined, _ := c.Result()
 
 	return combined, nil
 }

pkg/model/combine_test.go

@@ -1,7 +1,6 @@
 package model
 
 import (
-	"fmt"
 	"math/rand"
 	"testing"
 
@@ -102,22 +101,6 @@ func TestCombine(t *testing.T) {
 	}
 }
 
-func BenchmarkCombineTraceProtos(b *testing.B) {
-	sizes := []int{1, 10, 1000, 10000, 100000}
-
-	for _, size := range sizes {
-		b.Run(fmt.Sprint(size), func(b *testing.B) {
-			t1 := test.MakeTraceWithSpanCount(1, size, []byte{0x01, 0x02})
-			t2 := test.MakeTraceWithSpanCount(1, size, []byte{0x01, 0x03})
-
-			b.ResetTimer()
-			for i := 0; i < b.N; i++ {
-				trace.CombineTraceProtos(t1, t2)
-			}
-		})
-	}
-}
-
 func mustMarshalToObject(trace *tempopb.Trace, encoding string) []byte {
 	return mustMarshalToObjectWithRange(trace, encoding, 0, 0)
 }

pkg/model/trace/combine.go

@@ -8,77 +8,132 @@ import (
 	"github.com/grafana/tempo/pkg/tempopb"
 )
 
-// CombineTraceProtos combines two trace protos into one.  Note that it is destructive.
-//  All spans are combined into traceA.  spanCountA, B, and Total are returned for
-//  logging purposes.
-func CombineTraceProtos(traceA, traceB *tempopb.Trace) (*tempopb.Trace, int) {
-	// if one or the other is nil just return 0 for the one that's nil and -1 for the other.  this will be a clear indication this
-	// code path was taken without unnecessarily counting spans
-	if traceA == nil {
-		return traceB, -1
-	}
+// token is uint64 to reduce hash collision rates.  Experimentally, it was observed
+// that fnv32 could approach a collision rate of 1 in 10,000. fnv64 avoids collisions
+// when tested against traces with up to 1M spans (see matching test). A collision
+// results in a dropped span during combine.
+type token uint64
 
-	if traceB == nil {
-		return traceA, -1
-	}
+func newHash() hash.Hash64 {
+	return fnv.New64()
+}
 
-	spanCountTotal := 0
+// tokenForID returns a token for use in a hash map given a span id and span kind
+//  buffer must be a 4 byte slice and is reused for writing the span kind to the hashing function
+//  kind is used along with the actual id b/c in zipkin traces span id is not guaranteed to be unique
+//  as it is shared between client and server spans.
+func tokenForID(h hash.Hash64, buffer []byte, kind int32, b []byte) token {
+	binary.LittleEndian.PutUint32(buffer, uint32(kind))
 
-	h := fnv.New32()
+	h.Reset()
+	_, _ = h.Write(b)
+	_, _ = h.Write(buffer)
+	return token(h.Sum64())
+}
+
+// Combiner combines multiple partial traces into one, deduping spans based on
+// ID and kind.  Note that it is destructive. There are design decisions for
+// efficiency:
+// * Only scan/hash the spans for each input once, which is reused across calls.
+// * Only sort the final result once and if needed.
+// * Don't scan/hash the spans for the last input (final=true).
+type Combiner struct {
+	result   *tempopb.Trace
+	spans    map[token]struct{}
+	combined bool
+}
+
+func NewCombiner() *Combiner {
+	return &Combiner{}
+}
+
+// Consume the given trace and destructively combines its contents.
+func (c *Combiner) Consume(tr *tempopb.Trace) (spanCount int) {
+	return c.ConsumeWithFinal(tr, false)
+}
+
+// ConsumeWithFinal consumes the trace, but allows for performance savings when
+// it is known that this is the last expected input trace.
+func (c *Combiner) ConsumeWithFinal(tr *tempopb.Trace, final bool) (spanCount int) {
+	if tr == nil {
+		return
+	}
+
+	h := newHash()
 	buffer := make([]byte, 4)
 
-	spansInA := make(map[uint32]struct{})
-	for _, batchA := range traceA.Batches {
-		for _, ilsA := range batchA.InstrumentationLibrarySpans {
-			for _, spanA := range ilsA.Spans {
-				spansInA[tokenForID(h, buffer, int32(spanA.Kind), spanA.SpanId)] = struct{}{}
+	// First call?
+	if c.result == nil {
+		c.result = tr
+
+		// Pre-alloc map with input size. This saves having to grow the
+		// map from the small starting size.
+		n := 0
+		for _, b := range c.result.Batches {
+			for _, ils := range b.InstrumentationLibrarySpans {
+				n += len(ils.Spans)
 			}
-			spanCountTotal += len(ilsA.Spans)
 		}
+		c.spans = make(map[token]struct{}, n)
+
+		for _, b := range c.result.Batches {
+			for _, ils := range b.InstrumentationLibrarySpans {
+				for _, s := range ils.Spans {
+					c.spans[tokenForID(h, buffer, int32(s.Kind), s.SpanId)] = struct{}{}
+				}
+			}
+		}
+		return
 	}
 
 	// loop through every span and copy spans in B that don't exist to A
-	for _, batchB := range traceB.Batches {
-		notFoundILS := batchB.InstrumentationLibrarySpans[:0]
-
-		for _, ilsB := range batchB.InstrumentationLibrarySpans {
-			notFoundSpans := ilsB.Spans[:0]
-			for _, spanB := range ilsB.Spans {
-				// if found in A, remove from the batch
-				_, ok := spansInA[tokenForID(h, buffer, int32(spanB.Kind), spanB.SpanId)]
+	for _, b := range tr.Batches {
+		notFoundILS := b.InstrumentationLibrarySpans[:0]
+
+		for _, ils := range b.InstrumentationLibrarySpans {
+			notFoundSpans := ils.Spans[:0]
+			for _, s := range ils.Spans {
+				// if not already encountered, then keep
+				token := tokenForID(h, buffer, int32(s.Kind), s.SpanId)
+				_, ok := c.spans[token]
 				if !ok {
-					notFoundSpans = append(notFoundSpans, spanB)
+					notFoundSpans = append(notFoundSpans, s)
+
+					// If last expected input, then we don't need to record
+					// the visited spans. Optimization has significant savings.
+					if !final {
+						c.spans[token] = struct{}{}
+					}
 				}
 			}
 
 			if len(notFoundSpans) > 0 {
-				spanCountTotal += len(notFoundSpans)
-				ilsB.Spans = notFoundSpans
-				notFoundILS = append(notFoundILS, ilsB)
+				ils.Spans = notFoundSpans
+				spanCount += len(notFoundSpans)
+				notFoundILS = append(notFoundILS, ils)
 			}
 		}
 
 		// if there were some spans not found in A, add everything left in the batch
 		if len(notFoundILS) > 0 {
-			batchB.InstrumentationLibrarySpans = notFoundILS
-			traceA.Batches = append(traceA.Batches, batchB)
+			b.InstrumentationLibrarySpans = notFoundILS
+			c.result.Batches = append(c.result.Batches, b)
 		}
 	}
 
-	SortTrace(traceA)
-
-	return traceA, spanCountTotal
+	c.combined = true
+	return
 }
 
-// tokenForID returns a uint32 token for use in a hash map given a span id and span kind
-//  buffer must be a 4 byte slice and is reused for writing the span kind to the hashing function
-//  kind is used along with the actual id b/c in zipkin traces span id is not guaranteed to be unique
-//  as it is shared between client and server spans.
-func tokenForID(h hash.Hash32, buffer []byte, kind int32, b []byte) uint32 {
-	binary.LittleEndian.PutUint32(buffer, uint32(kind))
+// Result returns the final trace and span count.
+func (c *Combiner) Result() (*tempopb.Trace, int) {
+	spanCount := -1
 
-	h.Reset()
-	_, _ = h.Write(b)
-	_, _ = h.Write(buffer)
-	return h.Sum32()
+	if c.result != nil && c.combined {
+		// Only if anything combined
+		SortTrace(c.result)
+		spanCount = len(c.spans)
+	}
+
+	return c.result, spanCount
 }