Add concurrency limit for remote write (#46)

Prior to this commit, unbounded number of write would have been trigged from avalanche based on number of samples and batch size. Adding a new flag to limit the concurrency will be useful to simulate prometheus remote write sharding.

Signed-off-by: Arunprasad Rajkumar <[email protected]>

cmd/avalanche/avalanche.go

@@ -71,6 +71,7 @@ func main() {
 	// TODO(bwplotka): Kill pprof feature, you can install OSS continuous profiling easily instead.
 	remotePprofURLs := kingpin.Flag("remote-pprof-urls", "a list of urls to download pprofs during the remote write: --remote-pprof-urls=http://127.0.0.1:10902/debug/pprof/heap --remote-pprof-urls=http://127.0.0.1:10902/debug/pprof/profile").URLList()
 	remotePprofInterval := kingpin.Flag("remote-pprof-interval", "how often to download pprof profiles. When not provided it will download a profile once before the end of the test.").Duration()
+	remoteConcurrencyLimit := kingpin.Flag("remote-concurrency-limit", "how many concurrent writes can happen at any given time").Default("20").Int()
 	remoteBatchSize := kingpin.Flag("remote-batch-size", "how many samples to send with each remote_write API request.").Default("2000").Int()
 	remoteRequestCount := kingpin.Flag("remote-requests-count", "How many requests to send in total to the remote_write API. Set to -1 to run indefinitely.").Default("100").Int()
 	remoteReqsInterval := kingpin.Flag("remote-write-interval", "delay between each remote write request.").Default("100ms").Duration()
@@ -109,6 +110,7 @@ func main() {
 			BatchSize:       *remoteBatchSize,
 			RequestCount:    *remoteRequestCount,
 			UpdateNotify:    collector.UpdateNotifyCh(),
+			Concurrency:     *remoteConcurrencyLimit,
 			Tenant:          *remoteTenant,
 			TLSClientConfig: tls.Config{
 				InsecureSkipVerify: *tlsClientInsecure,

metrics/write.go

@@ -54,6 +54,7 @@ type ConfigWrite struct {
 	TLSClientConfig tls.Config
 	TenantHeader    string
 	OutOfOrder      bool
+	Concurrency     int
 }
 
 // Client for the remote write requests.
@@ -144,6 +145,8 @@ func (c *Client) write(ctx context.Context) error {
 	ticker := time.NewTicker(c.config.RequestInterval)
 	defer ticker.Stop()
 
+	concurrencyLimitCh := make(chan struct{}, c.config.Concurrency)
+
 	for i := 0; ; {
 		if ctx.Err() != nil {
 			return ctx.Err()
@@ -180,7 +183,11 @@ func (c *Client) write(ctx context.Context) error {
 		start := time.Now()
 		for i := 0; i < len(tss); i += c.config.BatchSize {
 			wgMetrics.Add(1)
+			concurrencyLimitCh <- struct{}{}
 			go func(i int) {
+				defer func() {
+					<-concurrencyLimitCh
+				}()
 				defer wgMetrics.Done()
 				end := i + c.config.BatchSize
 				if end > len(tss) {