CHANGELOG-3.4: update "prevent disruptive rejoining"

Signed-off-by: Gyuho Lee <[email protected]>

CHANGELOG-3.4.md

@@ -13,9 +13,9 @@ See [code changes](https://github.com/coreos/etcd/compare/v3.3.0...v3.4.0) and [
 - Improve [long-running concurrent read transactions under light write workloads](https://github.com/coreos/etcd/pull/9296).
   - Previously, periodic commit on pending writes blocks incoming read transactions, even if there is no pending write.
   - Now, periodic commit operation does not block concurrent read transactions, thus improves long-running read transaction performance.
-- Adjust [election timeout on server restart](https://github.com/coreos/etcd/pull/9364) to reduce [disruptive rejoining servers](https://github.com/coreos/etcd/issues/9333).
+- Adjust [election timeout on server restart](https://github.com/coreos/etcd/pull/9415) to reduce [disruptive rejoining servers](https://github.com/coreos/etcd/issues/9333).
   - Previously, etcd fast-forwards election ticks on server start, with only one tick left for leader election. This is to speed up start phase, without having to wait until all election ticks elapse. Advancing election ticks is useful for cross datacenter deployments with larger election timeouts. However, it was affecting cluster availability if the last tick elapses before leader contacts the restarted node.
-  - Now, when etcd restarts, it does not fast-forward election ticks.
+  - Now, when etcd restarts, it adjusts election ticks with more than one tick left, thus more time for leader to prevent disruptive restart.
 - Add [Raft Pre-Vote feature](https://github.com/coreos/etcd/pull/9352) to reduce [disruptive rejoining servers](https://github.com/coreos/etcd/issues/9333).
   - For instance, a flaky(or rejoining) member may drop in and out, and start campaign. This member will end up with a higher term, and ignore all incoming messages with lower term. In this case, a new leader eventually need to get elected, thus disruptive to cluster availability. Raft implements Pre-Vote phase to prevent this kind of disruptions. If enabled, Raft runs an additional phase of election to check if pre-candidate can get enough votes to win an election.
 - Make [Lease `Lookup` non-blocking with concurrent `Grant`/`Revoke`](https://github.com/coreos/etcd/pull/9229).