[TESTS] Remote-Write: Fix BenchmarkStartup

It was crashing due to uninitialized metrics, and not terminating due to
incorrectly reading segment names.

We need to export `SetMetrics` to avoid the first problem.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

storage/remote/queue_manager_test.go

@@ -20,6 +20,7 @@ import (
 	"math"
 	"math/rand"
 	"os"
+	"path"
 	"runtime/pprof"
 	"sort"
 	"strconv"
@@ -48,6 +49,7 @@ import (
 	"github.com/prometheus/prometheus/scrape"
 	"github.com/prometheus/prometheus/tsdb/chunks"
 	"github.com/prometheus/prometheus/tsdb/record"
+	"github.com/prometheus/prometheus/tsdb/wlog"
 	"github.com/prometheus/prometheus/util/runutil"
 	"github.com/prometheus/prometheus/util/testutil"
 )
@@ -1407,12 +1409,12 @@ func BenchmarkStartup(b *testing.B) {
 
 	// Find the second largest segment; we will replay up to this.
 	// (Second largest as WALWatcher will start tailing the largest).
-	dirents, err := os.ReadDir(dir)
+	dirents, err := os.ReadDir(path.Join(dir, "wal"))
 	require.NoError(b, err)
 
 	var segments []int
 	for _, dirent := range dirents {
-		if i, err := strconv.Atoi(dirent.Name()); err != nil {
+		if i, err := strconv.Atoi(dirent.Name()); err == nil {
 			segments = append(segments, i)
 		}
 	}
@@ -1424,13 +1426,15 @@ func BenchmarkStartup(b *testing.B) {
 	mcfg := config.DefaultMetadataConfig
 	for n := 0; n < b.N; n++ {
 		metrics := newQueueManagerMetrics(nil, "", "")
+		watcherMetrics := wlog.NewWatcherMetrics(nil)
 		c := NewTestBlockedWriteClient()
 		// todo: test with new proto type(s)
-		m := NewQueueManager(metrics, nil, nil, logger, dir,
+		m := NewQueueManager(metrics, watcherMetrics, nil, logger, dir,
 			newEWMARate(ewmaWeight, shardUpdateDuration),
 			cfg, mcfg, labels.EmptyLabels(), nil, c, 1*time.Minute, newPool(), newHighestTimestampMetric(), nil, false, false, config.RemoteWriteProtoMsgV1)
 		m.watcher.SetStartTime(timestamp.Time(math.MaxInt64))
 		m.watcher.MaxSegment = segments[len(segments)-2]
+		m.watcher.SetMetrics()
 		err := m.watcher.Run()
 		require.NoError(b, err)
 	}

tsdb/wlog/watcher.go

@@ -206,7 +206,7 @@ func (w *Watcher) Notify() {
 	}
 }
 
-func (w *Watcher) setMetrics() {
+func (w *Watcher) SetMetrics() {
 	// Setup the WAL Watchers metrics. We do this here rather than in the
 	// constructor because of the ordering of creating Queue Managers's,
 	// stopping them, and then starting new ones in storage/remote/storage.go ApplyConfig.
@@ -221,7 +221,7 @@ func (w *Watcher) setMetrics() {
 
 // Start the Watcher.
 func (w *Watcher) Start() {
-	w.setMetrics()
+	w.SetMetrics()
 	w.logger.Info("Starting WAL watcher", "queue", w.name)
 
 	go w.loop()

tsdb/wlog/watcher_test.go

@@ -234,7 +234,7 @@ func TestTailSamples(t *testing.T) {
 			watcher.SetStartTime(now)
 
 			// Set the Watcher's metrics so they're not nil pointers.
-			watcher.setMetrics()
+			watcher.SetMetrics()
 			for i := first; i <= last; i++ {
 				segment, err := OpenReadSegment(SegmentName(watcher.walDir, i))
 				require.NoError(t, err)
@@ -548,7 +548,7 @@ func TestReadCheckpointMultipleSegments(t *testing.T) {
 			watcher.MaxSegment = -1
 
 			// Set the Watcher's metrics so they're not nil pointers.
-			watcher.setMetrics()
+			watcher.SetMetrics()
 
 			lastCheckpoint, _, err := LastCheckpoint(watcher.walDir)
 			require.NoError(t, err)
@@ -699,7 +699,7 @@ func TestRun_StartupTime(t *testing.T) {
 			watcher := NewWatcher(wMetrics, nil, nil, "", wt, dir, false, false, false)
 			watcher.MaxSegment = segments
 
-			watcher.setMetrics()
+			watcher.SetMetrics()
 			startTime := time.Now()
 
 			err = watcher.Run()
@@ -768,7 +768,7 @@ func TestRun_AvoidNotifyWhenBehind(t *testing.T) {
 			// Set up the watcher and run it in the background.
 			wt := newWriteToMock(time.Millisecond)
 			watcher := NewWatcher(wMetrics, nil, nil, "", wt, dir, false, false, false)
-			watcher.setMetrics()
+			watcher.SetMetrics()
 			watcher.MaxSegment = segmentsToRead
 
 			var g errgroup.Group