prometheus.remote_write: notify remote_write of data upon WAL commit

This commit fixes an issue where the remote_write queue only checked for
new WAL data every 15 seconds. remote_write can be notified of new data
immediately by calling `Notify` on the remote storage, but we weren't
doing this, which caused us to fall back to the 15 second interval.

CHANGELOG.md

@@ -47,8 +47,12 @@ Main (unreleased)
 
 - In `mimir.rules.kubernetes`, fix an issue where unrecoverable errors from the Mimir API were retried. (@56quarters)
 
-- Flow: Fix an issue where `faro.receiver`'s `extra_log_labels` with empty value don't
-  map existing value in log line. (@hainenber)
+- Fix an issue where `faro.receiver`'s `extra_log_labels` with empty value
+  don't map existing value in log line. (@hainenber)
+
+- Fix an issue where `prometheus.remote_write` only queued data for sending
+  every 15 seconds instead of as soon as data was written to the WAL.
+  (@rfratto)
 
 ### Other changes
 

internal/component/prometheus/remotewrite/remote_write.go

@@ -84,6 +84,8 @@ func New(o component.Options, c Arguments) (*Component, error) {
 	remoteLogger := log.With(o.Logger, "subcomponent", "rw")
 	remoteStore := remote.NewStorage(remoteLogger, o.Registerer, startTime, o.DataPath, remoteFlushDeadline, nil)
 
+	walStorage.SetNotifier(remoteStore)
+
 	service, err := o.GetServiceData(labelstore.ServiceName)
 	if err != nil {
 		return nil, err

internal/static/metrics/wal/wal.go

@@ -141,6 +141,8 @@ type Storage struct {
 	deleted map[chunks.HeadSeriesRef]int // Deleted series, and what WAL segment they must be kept until.
 
 	metrics *storageMetrics
+
+	notifier wlog.WriteNotified
 }
 
 // NewStorage makes a new Storage.
@@ -457,6 +459,12 @@ func (w *Storage) loadWAL(r *wlog.Reader, multiRef map[chunks.HeadSeriesRef]chun
 	}
 }
 
+// SetNotifier sets the notifier for the WAL storage. SetNotifier must only be
+// called before data is written to the WAL.
+func (w *Storage) SetNotifier(n wlog.WriteNotified) {
+	w.notifier = n
+}
+
 // Directory returns the path where the WAL storage is held.
 func (w *Storage) Directory() string {
 	return w.path
@@ -859,6 +867,10 @@ func (a *appender) Commit() error {
 		return err
 	}
 
+	if a.w.notifier != nil {
+		a.w.notifier.Notify()
+	}
+
 	a.clearData()
 	a.w.appenderPool.Put(a)
 	return nil

internal/static/metrics/wal/wal_test.go

@@ -64,11 +64,15 @@ func TestStorage_InvalidSeries(t *testing.T) {
 func TestStorage(t *testing.T) {
 	walDir := t.TempDir()
 
+	onNotify := util.NewWaitTrigger()
+	notifier := &fakeNotifier{NotitfyFunc: onNotify.Trigger}
+
 	s, err := NewStorage(log.NewNopLogger(), nil, walDir)
 	require.NoError(t, err)
 	defer func() {
 		require.NoError(t, s.Close())
 	}()
+	s.SetNotifier(notifier)
 
 	app := s.Appender(context.Background())
 
@@ -99,6 +103,8 @@ func TestStorage(t *testing.T) {
 	actualExemplars := collector.exemplars
 	sort.Sort(byRefExemplar(actualExemplars))
 	require.Equal(t, expectedExemplars, actualExemplars)
+
+	require.NoError(t, onNotify.Wait(time.Minute), "Expected Notify to be called")
 }
 
 func TestStorage_Rollback(t *testing.T) {
@@ -664,3 +670,13 @@ func (b byRefExemplar) Less(i, j int) bool {
 	}
 	return b[i].Ref < b[j].Ref
 }
+
+type fakeNotifier struct {
+	NotitfyFunc func()
+}
+
+func (fn *fakeNotifier) Notify() {
+	if fn.NotitfyFunc != nil {
+		fn.NotitfyFunc()
+	}
+}