db: Add comment: Appender not goroutine safe
@@ -73,6 +73,8 @@ type Options struct {
// Appender allows appending a batch of data. It must be completed with a
// call to Commit or Rollback and must not be reused afterwards.
+//
+// Operations on the Appender interface are not goroutine-safe.
type Appender interface {
// Add adds a sample pair for the given series. A reference number is
// returned which can be used to add further samples in the same or later
