Revert "raft: fully activate pre-voting"

This reverts commit de92a78a.

src/raft/RaftDirector.cc

@@ -127,27 +127,20 @@ void RaftDirector::runForLeader() {
   // it could have changed in-between
   RaftStateSnapshotPtr snapshot = state.getSnapshot();
 
+  // advance the term by one, become a candidate.
+  if(!state.observed(snapshot->term+1, {})) return;
+  if(!state.becomeCandidate(snapshot->term+1)) return;
+
   // prepare vote request
   RaftVoteRequest votereq;
   votereq.term = snapshot->term+1;
   votereq.lastIndex = journal.getLogSize()-1;
   if(!journal.fetch(votereq.lastIndex, votereq.lastTerm).ok()) {
     qdb_critical("Unable to fetch journal entry " << votereq.lastIndex << " when running for leader");
+    state.dropOut(snapshot->term+1);
     return;
   }
 
-  ElectionOutcome prevoteOutcome = RaftElection::performPreVote(votereq, state, contactDetails);
-  if(prevoteOutcome == ElectionOutcome::kVetoed) {
-    lastHeartbeatBeforeVeto = lastHeartbeat;
-    qdb_info("Pre-vote round for term " << snapshot->term + 1 << " resulted in a veto. This means, the next leader of this cluster cannot be me. Stopping election attempts until I receive a heartbeat.");
-  }
-
-  if(prevoteOutcome != ElectionOutcome::kElected) return;
-
-  // pre-vote succeeded, advance the term by one, become a candidate.
-  if(!state.observed(snapshot->term+1, {})) return;
-  if(!state.becomeCandidate(snapshot->term+1)) return;
-
   ElectionOutcome electionOutcome = RaftElection::perform(votereq, state, lease, contactDetails);
 
   if(electionOutcome != ElectionOutcome::kElected) {

src/raft/RaftTalker.cc

@@ -203,15 +203,10 @@ std::future<redisReplyPtr> RaftTalker::appendEntries(
   return qcl->execute(payload);
 }
 
-std::future<redisReplyPtr> RaftTalker::requestVote(const RaftVoteRequest &req, bool preVote) {
+std::future<redisReplyPtr> RaftTalker::requestVote(const RaftVoteRequest &req) {
   RedisRequest payload;
 
-  if(preVote) {
-    payload.emplace_back("RAFT_REQUEST_PRE_VOTE");
-  }
-  else {
-    payload.emplace_back("RAFT_REQUEST_VOTE");
-  }
+  payload.emplace_back("RAFT_REQUEST_VOTE");
   payload.emplace_back(std::to_string(req.term));
   payload.emplace_back(req.candidate.toString());
   payload.emplace_back(std::to_string(req.lastIndex));

src/raft/RaftTalker.hh

@@ -47,7 +47,7 @@ public:
                                            RaftTerm prevTerm, LogIndex commit,
                                            const std::vector<RaftSerializedEntry> &entries);
 
-  std::future<redisReplyPtr> requestVote(const RaftVoteRequest &req, bool preVote = false);
+  std::future<redisReplyPtr> requestVote(const RaftVoteRequest &req);
   std::future<redisReplyPtr> fetch(LogIndex index);
 
   std::future<redisReplyPtr> resilveringStart(const ResilveringEventID &id);

src/raft/RaftUtils.cc

@@ -33,41 +33,6 @@
 
 namespace quarkdb {
 
-ElectionOutcome RaftElection::performPreVote(RaftVoteRequest votereq, RaftState &state, const RaftContactDetails &contactDetails) {
-  if(!votereq.candidate.empty()) {
-    qdb_throw("candidate member of votereq must be empty, it is filled out by this function");
-  }
-
-  votereq.candidate = state.getMyself();
-
-  qdb_info("Starting pre-vote round for term " << votereq.term);
-
-  std::chrono::steady_clock::time_point broadcastTimepoint = std::chrono::steady_clock::now();
-  std::vector<std::unique_ptr<RaftTalker>> talkers;
-  std::map<RaftServer, std::future<redisReplyPtr>> futures;
-
-  for(const RaftServer &node : state.getNodes()) {
-    if(node != votereq.candidate) {
-      talkers.emplace_back(new RaftTalker(node, contactDetails, "internal-vote-request"));
-      futures[node] = talkers.back()->requestVote(votereq, true);
-    }
-  }
-
-  std::chrono::steady_clock::time_point deadline = broadcastTimepoint + contactDetails.getRaftTimeouts().getHeartbeatInterval()*2;
-
-  qdb_info("Pre-vote requests have been sent off, will allow a window of "
-    << contactDetails.getRaftTimeouts().getLow().count() << "ms to receive replies.");
-
-  RaftVoteRegistry registry(votereq.term, true);
-
-  for(auto it = futures.begin(); it != futures.end(); it++) {
-    registry.registerVote(it->first, it->second, deadline);
-  }
-
-  qdb_info(registry.describeOutcome());
-  return registry.determineOutcome();
-}
-
 ElectionOutcome RaftElection::perform(RaftVoteRequest votereq, RaftState &state, RaftLease &lease, const RaftContactDetails &contactDetails) {
   if(!votereq.candidate.empty()) {
     qdb_throw("candidate member of votereq must be empty, it is filled out by this function");

src/raft/RaftUtils.hh

@@ -48,9 +48,16 @@ public:
   static bool fetchLastResponse(const qclient::redisReplyPtr &source, std::vector<RaftEntry> &entries);
 };
 
+struct ElectionSingleTally {
+  bool timeout;
+  bool error;
+  RaftVoteResponse resp;
+};
+
+using ElectionTally = std::map<RaftServer, ElectionSingleTally>;
+
 class RaftElection {
 public:
-  static ElectionOutcome performPreVote(RaftVoteRequest votereq, RaftState &state, const RaftContactDetails &contactDetails);
   static ElectionOutcome perform(RaftVoteRequest votereq, RaftState &state, RaftLease &lease, const RaftContactDetails &contactDetails);
 };
 

test/raft.cc

@@ -811,6 +811,7 @@ TEST_F(Raft_Director, late_consensus) {
 
   // verify the node tried to ascend, and failed
   RaftStateSnapshotPtr snapshot = state(0)->getSnapshot();
+  ASSERT_GE(snapshot->term, 1);
   ASSERT_TRUE(snapshot->leader.empty());
   ASSERT_TRUE( (snapshot->status == RaftStatus::FOLLOWER) || (snapshot->status == RaftStatus::CANDIDATE) );