From e65536f81d7fc5c31cea1593a4e6f9691d18799e Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Sat, 16 Jan 2021 07:47:02 -0700
Subject: [PATCH] Stop waiting for replica if generation changes

---
 replica.go | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/replica.go b/replica.go
index d6e53f4..39bb207 100644
--- a/replica.go
+++ b/replica.go
@@ -1072,10 +1072,14 @@ func waitForReplica(ctx context.Context, r Replica, pos Pos) error {
 			continue
 		}
 
-		ready := true
+		// Exit if the generation has changed while waiting as there will be
+		// no further progress on the old generation.
 		if curr.Generation != pos.Generation {
-			ready = false
-		} else if curr.Index < pos.Index {
+			return fmt.Errorf("generation changed")
+		}
+
+		ready := true
+		if curr.Index < pos.Index {
 			ready = false
 		} else if curr.Index == pos.Index && curr.Offset < pos.Offset {
 			ready = false