Add barrier to benchmark writer

This adds a barrier to avoid issues with unfair goroutine scheduling
that causes some fake scrapers to run away from the other ones.

cmd/tsdb/Makefile

@@ -3,7 +3,7 @@ build:
 	
 bench: build 
 	@echo ">> running benchmark"
-	@./tsdb bench write --out=$(OUT) --metrics=$(NUM_METRICS) testdata.100k
+	@./tsdb bench write --metrics=$(NUM_METRICS) testdata.100k
 	@go tool pprof -svg ./tsdb benchout/cpu.prof > benchout/cpuprof.svg
 	@go tool pprof -svg ./tsdb benchout/mem.prof > benchout/memprof.svg
 	@go tool pprof -svg ./tsdb benchout/block.prof > benchout/blockprof.svg

cmd/tsdb/main.go

@@ -138,43 +138,7 @@ func (b *writeBenchmark) ingestScrapes(metrics []model.Metric, scrapeCount int)
 	var mu sync.Mutex
 	var total uint64
 
-	for len(metrics) > 0 {
-		l := 1000
-		if len(metrics) < 1000 {
-			l = len(metrics)
-		}
-		batch := metrics[:l]
-		metrics = metrics[l:]
-
-		wg.Add(1)
-		go func(batch []model.Metric) {
-			n, err := b.ingestScrapesShard(batch, scrapeCount)
-			if err != nil {
-				// exitWithError(err)
-				fmt.Println(" err", err)
-			}
-			mu.Lock()
-			total += n
-			mu.Unlock()
-			wg.Done()
-		}(batch)
-	}
-	wg.Wait()
-
-	fmt.Println("> total samples:", total)
-	return nil
-}
-
-func (b *writeBenchmark) ingestScrapesShard(metrics []model.Metric, scrapeCount int) (uint64, error) {
-	app := b.storage.Appender()
-	ts := int64(model.Now())
-
-	type sample struct {
-		labels labels.Labels
-		value  int64
-	}
-
-	scrape := make(map[uint64]*sample, len(metrics))
+	lbls := make([]labels.Labels, 0, len(metrics))
 
 	for _, m := range metrics {
 		lset := make(labels.Labels, 0, len(m))
@@ -183,10 +147,55 @@ func (b *writeBenchmark) ingestScrapesShard(metrics []model.Metric, scrapeCount
 		}
 		sort.Sort(lset)
 
-		scrape[lset.Hash()] = &sample{
-			labels: lset,
-			value:  123456789,
+		lbls = append(lbls, lset)
+	}
+
+	for i := 0; i < scrapeCount; i += 25 {
+		lbls := lbls
+		for len(lbls) > 0 {
+			l := 1000
+			if len(lbls) < 1000 {
+				l = len(lbls)
+			}
+			batch := lbls[:l]
+			lbls = lbls[l:]
+
+			wg.Add(1)
+			go func() {
+				n, err := b.ingestScrapesShard(batch, 25, int64(30000*i))
+				if err != nil {
+					// exitWithError(err)
+					fmt.Println(" err", err)
+				}
+				mu.Lock()
+				total += n
+				mu.Unlock()
+				wg.Done()
+			}()
 		}
+		wg.Wait()
+	}
+
+	fmt.Println("> total samples:", total)
+	return nil
+}
+
+func (b *writeBenchmark) ingestScrapesShard(metrics []labels.Labels, scrapeCount int, baset int64) (uint64, error) {
+	app := b.storage.Appender()
+	ts := baset
+
+	type sample struct {
+		labels labels.Labels
+		value  int64
+	}
+
+	scrape := make([]*sample, 0, len(metrics))
+
+	for _, m := range metrics {
+		scrape = append(scrape, &sample{
+			labels: m,
+			value:  123456789,
+		})
 	}
 	total := uint64(0)