docs: add note about retrying UNAVAILABLE (#2774)

jeanbza · web-flow · commit 9d8d97a245af · 2019-04-15T14:59:43.000-06:00
diff --git a/codes/codes.go b/codes/codes.go
@@ -132,7 +132,8 @@ const (
 
 	// Unavailable indicates the service is currently unavailable.
 	// This is a most likely a transient condition and may be corrected
-	// by retrying with a backoff.
+	// by retrying with a backoff. Note that it is not always safe to retry
+	// non-idempotent operations.
 	//
 	// See litmus test above for deciding between FailedPrecondition,
 	// Aborted, and Unavailable.
