[MM-52973] Avoid thundering herd problem in IsFirstUserAccount (#23549)

server/channels/app/platform/config.go

@@ -323,21 +323,31 @@ func (ps *PlatformService) LimitedClientConfig() map[string]string {
 }
 
 func (ps *PlatformService) IsFirstUserAccount() bool {
-	if ps.fetchUserCountForFirstUserAccountCheck.Load() {
-		ps.logger.Debug("Fetching user count for first user account check")
-		count, err := ps.Store.User().Count(model.UserCountOptions{IncludeDeleted: true})
-		if err != nil {
-			return false
-		}
-		// Avoid calling the user count query in future if we get a count > 0
-		if count > 0 {
-			ps.fetchUserCountForFirstUserAccountCheck.Store(false)
-			return false
-		}
-		return true
+	if !ps.isFirstUserAccount.Load() {
+		return false
 	}
 
-	return false
+	ps.isFirstUserAccountLock.Lock()
+	defer ps.isFirstUserAccountLock.Unlock()
+	// Retry under lock as another call might have already succeeded.
+	if !ps.isFirstUserAccount.Load() {
+		return false
+	}
+
+	ps.logger.Debug("Fetching user count for first user account check")
+	count, err := ps.Store.User().Count(model.UserCountOptions{IncludeDeleted: true})
+	if err != nil {
+		return false
+	}
+
+	// Avoid calling the user count query in future if we get a count > 0
+	if count > 0 {
+		ps.isFirstUserAccount.Store(false)
+		return false
+	}
+
+	return true
+
 }
 
 func (ps *PlatformService) MaxPostSize() int {