| // Licensed to the Apache Software Foundation (ASF) under one |
| // or more contributor license agreements. See the NOTICE file |
| // distributed with this work for additional information |
| // regarding copyright ownership. The ASF licenses this file |
| // to you under the Apache License, Version 2.0 (the |
| // "License"); you may not use this file except in compliance |
| // with the License. You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, |
| // software distributed under the License is distributed on an |
| // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| // KIND, either express or implied. See the License for the |
| // specific language governing permissions and limitations |
| // under the License. |
| |
| #include "kudu/consensus/leader_election.h" |
| |
| #include <algorithm> |
| #include <mutex> |
| #include <ostream> |
| #include <type_traits> |
| #include <vector> |
| |
| #include <boost/bind.hpp> // IWYU pragma: keep |
| #include <glog/logging.h> |
| |
| #include "kudu/common/wire_protocol.h" |
| #include "kudu/consensus/consensus_peers.h" |
| #include "kudu/consensus/metadata.pb.h" |
| #include "kudu/gutil/bind.h" |
| #include "kudu/gutil/callback.h" |
| #include "kudu/gutil/map-util.h" |
| #include "kudu/gutil/port.h" |
| #include "kudu/gutil/stl_util.h" |
| #include "kudu/gutil/strings/join.h" |
| #include "kudu/gutil/strings/substitute.h" |
| #include "kudu/rpc/rpc_controller.h" |
| #include "kudu/tserver/tserver.pb.h" |
| #include "kudu/util/logging.h" |
| #include "kudu/util/pb_util.h" |
| #include "kudu/util/status.h" |
| |
| namespace kudu { |
| namespace consensus { |
| |
| using std::string; |
| using std::vector; |
| using strings::Substitute; |
| |
| /////////////////////////////////////////////////// |
| // VoteCounter |
| /////////////////////////////////////////////////// |
| |
| VoteCounter::VoteCounter(int num_voters, int majority_size) |
| : num_voters_(num_voters), |
| majority_size_(majority_size), |
| yes_votes_(0), |
| no_votes_(0) { |
| CHECK_LE(majority_size, num_voters); |
| CHECK_GT(num_voters_, 0); |
| CHECK_GT(majority_size_, 0); |
| } |
| |
| Status VoteCounter::RegisterVote(const std::string& voter_uuid, ElectionVote vote, |
| bool* is_duplicate) { |
| // Handle repeated votes. |
| if (PREDICT_FALSE(ContainsKey(votes_, voter_uuid))) { |
| // Detect changed votes. |
| ElectionVote prior_vote = votes_[voter_uuid]; |
| if (PREDICT_FALSE(prior_vote != vote)) { |
| string msg = Substitute("Peer $0 voted a different way twice in the same election. " |
| "First vote: $1, second vote: $2.", |
| voter_uuid, prior_vote, vote); |
| return Status::InvalidArgument(msg); |
| } |
| |
| // This was just a duplicate. Allow the caller to log it but don't change |
| // the voting record. |
| *is_duplicate = true; |
| return Status::OK(); |
| } |
| |
| // Sanity check to ensure we did not exceed the allowed number of voters. |
| if (PREDICT_FALSE(yes_votes_ + no_votes_ == num_voters_)) { |
| // More unique voters than allowed! |
| return Status::InvalidArgument(Substitute( |
| "Vote from peer $0 would cause the number of votes to exceed the expected number of " |
| "voters, which is $1. Votes already received from the following peers: {$2}", |
| voter_uuid, |
| num_voters_, |
| JoinKeysIterator(votes_.begin(), votes_.end(), ", "))); |
| } |
| |
| // This is a valid vote, so store it. |
| InsertOrDie(&votes_, voter_uuid, vote); |
| switch (vote) { |
| case VOTE_GRANTED: |
| ++yes_votes_; |
| break; |
| case VOTE_DENIED: |
| ++no_votes_; |
| break; |
| } |
| *is_duplicate = false; |
| return Status::OK(); |
| } |
| |
| bool VoteCounter::IsDecided() const { |
| return yes_votes_ >= majority_size_ || |
| no_votes_ > num_voters_ - majority_size_; |
| } |
| |
| Status VoteCounter::GetDecision(ElectionVote* decision) const { |
| if (yes_votes_ >= majority_size_) { |
| *decision = VOTE_GRANTED; |
| return Status::OK(); |
| } |
| if (no_votes_ > num_voters_ - majority_size_) { |
| *decision = VOTE_DENIED; |
| return Status::OK(); |
| } |
| return Status::IllegalState("Vote not yet decided"); |
| } |
| |
| int VoteCounter::GetTotalVotesCounted() const { |
| return yes_votes_ + no_votes_; |
| } |
| |
| bool VoteCounter::AreAllVotesIn() const { |
| return GetTotalVotesCounted() == num_voters_; |
| } |
| |
| /////////////////////////////////////////////////// |
| // ElectionResult |
| /////////////////////////////////////////////////// |
| |
| ElectionResult::ElectionResult(VoteRequestPB vote_request, ElectionVote decision, |
| ConsensusTerm highest_voter_term, const std::string& message) |
| : vote_request(std::move(vote_request)), |
| decision(decision), |
| highest_voter_term(highest_voter_term), |
| message(message) { |
| DCHECK(!message.empty()); |
| } |
| |
| /////////////////////////////////////////////////// |
| // LeaderElection::VoterState |
| /////////////////////////////////////////////////// |
| |
| string LeaderElection::VoterState::PeerInfo() const { |
| std::string info = peer_uuid; |
| if (proxy) { |
| strings::SubstituteAndAppend(&info, " ($0)", proxy->PeerName()); |
| } |
| return info; |
| } |
| |
| /////////////////////////////////////////////////// |
| // LeaderElection |
| /////////////////////////////////////////////////// |
| |
| LeaderElection::LeaderElection(RaftConfigPB config, |
| PeerProxyFactory* proxy_factory, |
| VoteRequestPB request, |
| gscoped_ptr<VoteCounter> vote_counter, |
| MonoDelta timeout, |
| ElectionDecisionCallback decision_callback) |
| : has_responded_(false), |
| config_(std::move(config)), |
| proxy_factory_(proxy_factory), |
| request_(std::move(request)), |
| vote_counter_(std::move(vote_counter)), |
| timeout_(timeout), |
| decision_callback_(std::move(decision_callback)), |
| highest_voter_term_(0) { |
| } |
| |
| LeaderElection::~LeaderElection() { |
| std::lock_guard<Lock> guard(lock_); |
| DCHECK(has_responded_); // We must always call the callback exactly once. |
| STLDeleteValues(&voter_state_); |
| } |
| |
| void LeaderElection::Run() { |
| VLOG_WITH_PREFIX(1) << "Running leader election."; |
| |
| // Initialize voter state tracking. |
| vector<string> other_voter_uuids; |
| voter_state_.clear(); |
| for (const RaftPeerPB& peer : config_.peers()) { |
| if (request_.candidate_uuid() == peer.permanent_uuid()) { |
| DCHECK_EQ(peer.member_type(), RaftPeerPB::VOTER) |
| << Substitute("non-voter member $0 tried to start an election; " |
| "Raft config {$1}", |
| peer.permanent_uuid(), |
| pb_util::SecureShortDebugString(config_)); |
| continue; |
| } |
| if (peer.member_type() != RaftPeerPB::VOTER) { |
| continue; |
| } |
| other_voter_uuids.emplace_back(peer.permanent_uuid()); |
| |
| gscoped_ptr<VoterState> state(new VoterState()); |
| state->peer_uuid = peer.permanent_uuid(); |
| state->proxy_status = proxy_factory_->NewProxy(peer, &state->proxy); |
| InsertOrDie(&voter_state_, peer.permanent_uuid(), state.release()); |
| } |
| |
| // Ensure that the candidate has already voted for itself. |
| CHECK_EQ(1, vote_counter_->GetTotalVotesCounted()) << "Candidate must vote for itself first"; |
| |
| // Ensure that existing votes + future votes add up to the expected total. |
| CHECK_EQ(vote_counter_->GetTotalVotesCounted() + other_voter_uuids.size(), |
| vote_counter_->GetTotalExpectedVotes()) |
| << "Expected different number of voters. Voter UUIDs: [" |
| << JoinStringsIterator(other_voter_uuids.begin(), other_voter_uuids.end(), ", ") |
| << "]; RaftConfig: {" << pb_util::SecureShortDebugString(config_) << "}"; |
| |
| // Check if we have already won the election (relevant if this is a |
| // single-node configuration, since we always pre-vote for ourselves). |
| CheckForDecision(); |
| |
| // The rest of the code below is for a typical multi-node configuration. |
| for (const auto& voter_uuid : other_voter_uuids) { |
| VoterState* state = nullptr; |
| { |
| std::lock_guard<Lock> guard(lock_); |
| state = FindOrDie(voter_state_, voter_uuid); |
| // Safe to drop the lock because voter_state_ is not mutated outside of |
| // the constructor / destructor. We do this to avoid deadlocks below. |
| } |
| |
| // If we failed to construct the proxy, just record a 'NO' vote with the status |
| // that indicates why it failed. |
| if (!state->proxy_status.ok()) { |
| LOG_WITH_PREFIX(WARNING) << "Was unable to construct an RPC proxy to peer " |
| << state->PeerInfo() << ": " << state->proxy_status.ToString() |
| << ". Counting it as a 'NO' vote."; |
| { |
| std::lock_guard<Lock> guard(lock_); |
| RecordVoteUnlocked(*state, VOTE_DENIED); |
| } |
| CheckForDecision(); |
| continue; |
| } |
| |
| // Send the RPC request. |
| LOG_WITH_PREFIX(INFO) << "Requesting " |
| << (request_.is_pre_election() ? "pre-" : "") |
| << "vote from peer " << state->PeerInfo(); |
| state->rpc.set_timeout(timeout_); |
| |
| state->request = request_; |
| state->request.set_dest_uuid(voter_uuid); |
| |
| state->proxy->RequestConsensusVoteAsync( |
| &state->request, |
| &state->response, |
| &state->rpc, |
| // We use gutil Bind() for the refcounting and boost::bind to adapt the |
| // gutil Callback to a thunk. |
| boost::bind(&Closure::Run, |
| Bind(&LeaderElection::VoteResponseRpcCallback, this, voter_uuid))); |
| } |
| } |
| |
| void LeaderElection::CheckForDecision() { |
| bool to_respond = false; |
| { |
| std::lock_guard<Lock> guard(lock_); |
| // Check if the vote has been newly decided. |
| if (!result_ && vote_counter_->IsDecided()) { |
| ElectionVote decision; |
| CHECK_OK(vote_counter_->GetDecision(&decision)); |
| LOG_WITH_PREFIX(INFO) << "Election decided. Result: candidate " |
| << ((decision == VOTE_GRANTED) ? "won." : "lost."); |
| string msg = (decision == VOTE_GRANTED) ? |
| "achieved majority votes" : "could not achieve majority"; |
| result_.reset(new ElectionResult(request_, decision, highest_voter_term_, msg)); |
| } |
| // Check whether to respond. This can happen as a result of either getting |
| // a majority vote or of something invalidating the election, like |
| // observing a higher term. |
| if (result_ && !has_responded_) { |
| has_responded_ = true; |
| to_respond = true; |
| } |
| } |
| |
| // Respond outside of the lock. |
| if (to_respond) { |
| // This is thread-safe since result_ is write-once. |
| decision_callback_(*result_); |
| } |
| } |
| |
| void LeaderElection::VoteResponseRpcCallback(const std::string& voter_uuid) { |
| { |
| std::lock_guard<Lock> guard(lock_); |
| VoterState* state = FindOrDie(voter_state_, voter_uuid); |
| |
| // Check for RPC errors. |
| if (!state->rpc.status().ok()) { |
| LOG_WITH_PREFIX(WARNING) << "RPC error from VoteRequest() call to peer " |
| << state->PeerInfo() << ": " |
| << state->rpc.status().ToString(); |
| RecordVoteUnlocked(*state, VOTE_DENIED); |
| |
| // Check for tablet errors. |
| } else if (state->response.has_error()) { |
| LOG_WITH_PREFIX(WARNING) << "Tablet error from VoteRequest() call to peer " |
| << state->PeerInfo() << ": " |
| << StatusFromPB(state->response.error().status()).ToString(); |
| RecordVoteUnlocked(*state, VOTE_DENIED); |
| |
| // If the peer changed their IP address, we shouldn't count this vote since |
| // our knowledge of the configuration is in an inconsistent state. |
| } else if (PREDICT_FALSE(voter_uuid != state->response.responder_uuid())) { |
| LOG_WITH_PREFIX(DFATAL) << "Received vote response from peer " |
| << state->PeerInfo() << ": " |
| << "we thought peer had UUID " << voter_uuid |
| << " but its actual UUID is " |
| << state->response.responder_uuid(); |
| RecordVoteUnlocked(*state, VOTE_DENIED); |
| |
| } else { |
| // No error: count actual votes. |
| |
| highest_voter_term_ = std::max(highest_voter_term_, state->response.responder_term()); |
| if (state->response.vote_granted()) { |
| HandleVoteGrantedUnlocked(*state); |
| } else { |
| HandleVoteDeniedUnlocked(*state); |
| } |
| } |
| } |
| |
| // Check for a decision outside the lock. |
| CheckForDecision(); |
| } |
| |
| void LeaderElection::RecordVoteUnlocked(const VoterState& state, ElectionVote vote) { |
| DCHECK(lock_.is_locked()); |
| |
| // Record the vote. |
| bool duplicate; |
| Status s = vote_counter_->RegisterVote(state.peer_uuid, vote, &duplicate); |
| if (!s.ok()) { |
| LOG_WITH_PREFIX(WARNING) << "Error registering vote for peer " |
| << state.PeerInfo() << ": " << s.ToString(); |
| return; |
| } |
| if (duplicate) { |
| // Note: This is DFATAL because at the time of writing we do not support |
| // retrying vote requests, so this should be impossible. It may be valid to |
| // receive duplicate votes in the future if we implement retry. |
| LOG_WITH_PREFIX(DFATAL) << "Duplicate vote received from peer " << state.PeerInfo(); |
| } |
| } |
| |
| void LeaderElection::HandleHigherTermUnlocked(const VoterState& state) { |
| DCHECK(lock_.is_locked()); |
| DCHECK_GT(state.response.responder_term(), election_term()); |
| |
| string msg = Substitute("Vote denied by peer $0 with higher term. Message: $1", |
| state.PeerInfo(), |
| StatusFromPB(state.response.consensus_error().status()).ToString()); |
| LOG_WITH_PREFIX(WARNING) << msg; |
| |
| if (!result_) { |
| LOG_WITH_PREFIX(INFO) << "Cancelling election due to peer responding with higher term"; |
| result_.reset(new ElectionResult(request_, VOTE_DENIED, |
| state.response.responder_term(), msg)); |
| } |
| } |
| |
| void LeaderElection::HandleVoteGrantedUnlocked(const VoterState& state) { |
| DCHECK(lock_.is_locked()); |
| if (!request_.is_pre_election()) { |
| DCHECK_EQ(state.response.responder_term(), election_term()); |
| } |
| DCHECK(state.response.vote_granted()); |
| |
| LOG_WITH_PREFIX(INFO) << "Vote granted by peer " << state.PeerInfo(); |
| RecordVoteUnlocked(state, VOTE_GRANTED); |
| } |
| |
| void LeaderElection::HandleVoteDeniedUnlocked(const VoterState& state) { |
| DCHECK(lock_.is_locked()); |
| DCHECK(!state.response.vote_granted()); |
| |
| // If one of the voters responds with a greater term than our own, and we |
| // have not yet triggered the decision callback, it cancels the election. |
| if (state.response.responder_term() > election_term()) { |
| return HandleHigherTermUnlocked(state); |
| } |
| |
| LOG_WITH_PREFIX(INFO) << "Vote denied by peer " << state.PeerInfo() << ". Message: " |
| << StatusFromPB(state.response.consensus_error().status()).ToString(); |
| RecordVoteUnlocked(state, VOTE_DENIED); |
| } |
| |
| std::string LeaderElection::LogPrefix() const { |
| return Substitute("T $0 P $1 [CANDIDATE]: Term $2 $3election: ", |
| request_.tablet_id(), |
| request_.candidate_uuid(), |
| request_.candidate_term(), |
| request_.is_pre_election() ? "pre-" : ""); |
| } |
| |
| } // namespace consensus |
| } // namespace kudu |
