feat(tsdb/agent): notify remote storage when commit happens (#13223)

Signed-off-by: Julien Levesy <jlevesy@gmail.com>
Signed-off-by: Callum Styan <callumstyan@gmail.com>
Co-authored-by: Callum Styan <callumstyan@gmail.com>

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## unreleased
+
+* [BUGFIX] Agent: Participate in notify calls. #13223
+
 ## 2.48.0 / 2023-11-16
 
 * [CHANGE] Remote-write: respect Retry-After header on 5xx errors. #12677

cmd/prometheus/main.go

@@ -1127,6 +1127,7 @@ func main() {
 				)
 
 				localStorage.Set(db, 0)
+				db.SetWriteNotified(remoteStorage)
 				close(dbOpen)
 				<-cancel
 				return nil

tsdb/agent/db.go

@@ -241,6 +241,8 @@ type DB struct {
 	donec chan struct{}
 	stopc chan struct{}
 
+	writeNotified wlog.WriteNotified
+
 	metrics *dbMetrics
 }
 
@@ -311,6 +313,12 @@ func Open(l log.Logger, reg prometheus.Registerer, rs *remote.Storage, dir strin
 	return db, nil
 }
 
+// SetWriteNotified allows to set an instance to notify when a write happens.
+// It must be used during initialization. It is not safe to use it during execution.
+func (db *DB) SetWriteNotified(wn wlog.WriteNotified) {
+	db.writeNotified = wn
+}
+
 func validateOptions(opts *Options) *Options {
 	if opts == nil {
 		opts = DefaultOptions()
@@ -962,6 +970,10 @@ func (a *appender) Commit() error {
 
 	a.clearData()
 	a.appenderPool.Put(a)
+
+	if a.writeNotified != nil {
+		a.writeNotified.Notify()
+	}
 	return nil
 }