[Tarantool-patches] [PATCH 3/6] raft: new candidate should wait for leader death

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

When a raft node was configured to be a candidate via
election_mode, it didn't do anything if there was an active
leader.

But it should have started monitoring its health in order to
initiate a new election round when it dies.

The patch fixes this bug. It does not contain a test, because will
be covered by a test for #5339.

Needed for #5339
---
 src/box/raft.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/box/raft.c b/src/box/raft.c
index f51e87fde..ff28e7f08 100644
--- a/src/box/raft.c
+++ b/src/box/raft.c
@@ -926,12 +926,18 @@ raft_cfg_is_candidate(bool is_candidate)
 
 	if (raft.is_candidate) {
 		assert(raft.state == RAFT_STATE_FOLLOWER);
-		/*
-		 * If there is an on-going WAL write, it means there was some
-		 * node who sent newer data to this node.
-		 */
-		if (raft.leader == 0 && raft_is_fully_on_disk())
+		if (raft.leader != 0) {
+			raft_sm_wait_leader_dead();
+		} else if (raft_is_fully_on_disk()) {
 			raft_sm_wait_leader_found();
+		} else {
+			/*
+			 * If there is an on-going WAL write, it means there was
+			 * some node who sent newer data to this node. So it is
+			 * probably a better candidate. Anyway can't do anything
+			 * until the new state is fully persisted.
+			 */
+		}
 	} else if (raft.state != RAFT_STATE_FOLLOWER) {
 		if (raft.state == RAFT_STATE_LEADER)
 			raft.leader = 0;
-- 
2.21.1 (Apple Git-122.3)