Use configurable WAL flush inteval

db.go

@@ -204,7 +204,7 @@ func Open(dir string, l log.Logger, r prometheus.Registerer, opts *Options) (db
 		return nil, errors.Wrap(err, "create leveled compactor")
 	}
 
-	wal, err := OpenSegmentWAL(filepath.Join(dir, "wal"), l, 10*time.Second)
+	wal, err := OpenSegmentWAL(filepath.Join(dir, "wal"), l, opts.WALFlushInterval)
 	if err != nil {
 		return nil, err
 	}