/Users/deen/code/yugabyte-db/src/yb/consensus/consensus_queue.cc

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// under the License.
//
// The following only applies to changes made to this file as part of YugaByte development.
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// Portions Copyright (c) YugaByte, Inc.
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// in compliance with the License.  You may obtain a copy of the License at
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// Unless required by applicable law or agreed to in writing, software distributed under the License
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#include "yb/consensus/consensus_queue.h"

#include <algorithm>
#include <mutex>
#include <shared_mutex>
#include <string>
#include <utility>

#include <boost/container/small_vector.hpp>
#include <glog/logging.h>

#include "yb/consensus/consensus_context.h"
#include "yb/consensus/log_util.h"
#include "yb/consensus/opid_util.h"
#include "yb/consensus/quorum_util.h"
#include "yb/consensus/raft_consensus.h"
#include "yb/consensus/replicate_msgs_holder.h"

#include "yb/gutil/bind.h"
#include "yb/gutil/dynamic_annotations.h"
#include "yb/gutil/map-util.h"
#include "yb/gutil/stl_util.h"
#include "yb/gutil/strings/substitute.h"

#include "yb/util/enums.h"
#include "yb/util/fault_injection.h"
#include "yb/util/flag_tags.h"
#include "yb/util/locks.h"
#include "yb/util/logging.h"
#include "yb/util/mem_tracker.h"
#include "yb/util/metrics.h"
#include "yb/util/monotime.h"
#include "yb/util/random_util.h"
#include "yb/util/result.h"
#include "yb/util/size_literals.h"
#include "yb/util/status_log.h"
#include "yb/util/threadpool.h"
#include "yb/util/tostring.h"
#include "yb/util/url-coding.h"

using namespace std::literals;
using namespace yb::size_literals;

DECLARE_uint64(rpc_max_message_size);

// We expect that consensus_max_batch_size_bytes + 1_KB would be less than rpc_max_message_size.
// Otherwise such batch would be rejected by RPC layer.
DEFINE_uint64(consensus_max_batch_size_bytes, 4_MB,
              "The maximum per-tablet RPC batch size when updating peers.");
TAG_FLAG(consensus_max_batch_size_bytes, advanced);
TAG_FLAG(consensus_max_batch_size_bytes, runtime);

DEFINE_int32(follower_unavailable_considered_failed_sec, 900,
             "Seconds that a leader is unable to successfully heartbeat to a "
             "follower after which the follower is considered to be failed and "
             "evicted from the config.");
TAG_FLAG(follower_unavailable_considered_failed_sec, advanced);

DEFINE_int32(consensus_inject_latency_ms_in_notifications, 0,
             "Injects a random sleep between 0 and this many milliseconds into "
             "asynchronous notifications from the consensus queue back to the "
             "consensus implementation.");
TAG_FLAG(consensus_inject_latency_ms_in_notifications, hidden);
TAG_FLAG(consensus_inject_latency_ms_in_notifications, unsafe);

DEFINE_int32(cdc_checkpoint_opid_interval_ms, 60 * 1000,
             "Interval up to which CDC consumer's checkpoint is considered for retaining log cache."
             "If we haven't received an updated checkpoint from CDC consumer within the interval "
             "specified by cdc_checkpoint_opid_interval, then log cache does not consider that "
             "consumer while determining which op IDs to evict.");

DEFINE_int64(cdc_intent_retention_ms, 4 * 3600 * 1000,
             "Interval up to which CDC consumer's checkpoint is considered for retaining intents."
             "If we haven't received an updated checkpoint from CDC consumer within the interval "
             "specified by cdc_checkpoint_opid_interval, then CDC does not consider that "
             "consumer while determining which op IDs to delete from the intent.");

DEFINE_bool(enable_consensus_exponential_backoff, true,
            "Whether exponential backoff based on number of retransmissions at tablet leader "
            "for number of entries to replicate to lagging follower is enabled.");
TAG_FLAG(enable_consensus_exponential_backoff, advanced);
TAG_FLAG(enable_consensus_exponential_backoff, runtime);

DEFINE_int32(consensus_lagging_follower_threshold, 10,
             "Number of retransmissions at tablet leader to mark a follower as lagging. "
             "-1 disables the feature.");
TAG_FLAG(consensus_lagging_follower_threshold, advanced);
TAG_FLAG(consensus_lagging_follower_threshold, runtime);

DEFINE_test_flag(bool, disallow_lmp_failures, false,
                 "Whether we disallow PRECEDING_ENTRY_DIDNT_MATCH failures for non new peers.");

namespace {

constexpr const auto kMinRpcThrottleThresholdBytes = 16;

static bool RpcThrottleThresholdBytesValidator(const char* flagname, int64_t value) {
  if (value > 0) {
    if (value < kMinRpcThrottleThresholdBytes) {
      LOG(ERROR) << "Expect " << flagname << " to be at least " << kMinRpcThrottleThresholdBytes;
      return false;
    } else if (implicit_cast<size_t>(value) >= FLAGS_consensus_max_batch_size_bytes) {
      LOG(ERROR) << "Expect " << flagname << " to be less than consensus_max_batch_size_bytes "
                 << "value (" << FLAGS_consensus_max_batch_size_bytes << ")";
      return false;
    }
  }
  return true;
}

} // namespace

DECLARE_int64(rpc_throttle_threshold_bytes);

namespace yb {
namespace consensus {

using log::Log;
using std::unique_ptr;
using rpc::Messenger;
using strings::Substitute;

METRIC_DEFINE_gauge_int64(tablet, majority_done_ops, "Leader Operations Acked by Majority",
                          MetricUnit::kOperations,
                          "Number of operations in the leader queue ack'd by a majority but "
                          "not all peers.");
METRIC_DEFINE_gauge_int64(tablet, in_progress_ops, "Leader Operations in Progress",
                          MetricUnit::kOperations,
                          "Number of operations in the leader queue ack'd by a minority of "
                          "peers.");

const auto kCDCConsumerCheckpointInterval = FLAGS_cdc_checkpoint_opid_interval_ms * 1ms;

const auto kCDCConsumerIntentRetention = FLAGS_cdc_intent_retention_ms * 1ms;

std::string MajorityReplicatedData::ToString() const {
  return Format(
      "{ op_id: $0 leader_lease_expiration: $1 ht_lease_expiration: $2 num_sst_files: $3 }",
      op_id, leader_lease_expiration, ht_lease_expiration, num_sst_files);
}

std::string PeerMessageQueue::TrackedPeer::ToString() const {
  return Format(
      "{ peer: $0 is_new: $1 last_received: $2 next_index: $3 last_known_committed_idx: $4 "
      "is_last_exchange_successful: $5 needs_remote_bootstrap: $6 member_type: $7 "
      "num_sst_files: $8 last_applied: $9 }",
      uuid, is_new, last_received, next_index, last_known_committed_idx,
      is_last_exchange_successful, needs_remote_bootstrap, PeerMemberType_Name(member_type),
      num_sst_files, last_applied);
}

void PeerMessageQueue::TrackedPeer::ResetLeaderLeases() {
  leader_lease_expiration.Reset();
  leader_ht_lease_expiration.Reset();
}

void PeerMessageQueue::TrackedPeer::ResetLastRequest() {
  // Reset so that next transmission is not considered a re-transmission.
  last_num_messages_sent = -1;
  current_retransmissions = -1;
}

#define INSTANTIATE_METRIC(x) \
  x.Instantiate(metric_entity, 0)
PeerMessageQueue::Metrics::Metrics(const scoped_refptr<MetricEntity>& metric_entity)
  : num_majority_done_ops(INSTANTIATE_METRIC(METRIC_majority_done_ops)),
    num_in_progress_ops(INSTANTIATE_METRIC(METRIC_in_progress_ops)) {
}
#undef INSTANTIATE_METRIC

PeerMessageQueue::PeerMessageQueue(const scoped_refptr<MetricEntity>& metric_entity,
                                   const scoped_refptr<log::Log>& log,
                                   const MemTrackerPtr& server_tracker,
                                   const MemTrackerPtr& parent_tracker,
                                   const RaftPeerPB& local_peer_pb,
                                   const string& tablet_id,
                                   const server::ClockPtr& clock,
                                   ConsensusContext* context,
                                   unique_ptr<ThreadPoolToken> raft_pool_token)
    : raft_pool_observers_token_(std::move(raft_pool_token)),
      local_peer_pb_(local_peer_pb),
      local_peer_uuid_(local_peer_pb_.has_permanent_uuid() ? local_peer_pb_.permanent_uuid()
                                                           : string()),
      tablet_id_(tablet_id),
      log_cache_(metric_entity, log, server_tracker, local_peer_pb.permanent_uuid(), tablet_id),
      operations_mem_tracker_(
          MemTracker::FindOrCreateTracker("OperationsFromDisk", parent_tracker)),
      metrics_(metric_entity),
      clock_(clock),
      context_(context) {
  DCHECK(local_peer_pb_.has_permanent_uuid());
  DCHECK(!local_peer_pb_.last_known_private_addr().empty());
}

void PeerMessageQueue::Init(const OpId& last_locally_replicated) {
  LockGuard lock(queue_lock_);
  CHECK_EQ(queue_state_.state, State::kQueueConstructed);
  log_cache_.Init(last_locally_replicated.ToPB<OpIdPB>());
  queue_state_.last_appended = last_locally_replicated;
  queue_state_.state = State::kQueueOpen;
  local_peer_ = TrackPeerUnlocked(local_peer_uuid_);

  if (context_) {
    context_->ListenNumSSTFilesChanged(std::bind(&PeerMessageQueue::NumSSTFilesChanged, this));
    installed_num_sst_files_changed_listener_ = true;
  }
}

void PeerMessageQueue::SetLeaderMode(const OpId& committed_op_id,
                                     int64_t current_term,
                                     const OpId& last_applied_op_id,
                                     const RaftConfigPB& active_config) {
  LockGuard lock(queue_lock_);
  queue_state_.current_term = current_term;
  queue_state_.committed_op_id = committed_op_id;
  queue_state_.last_applied_op_id = last_applied_op_id;
  queue_state_.majority_replicated_op_id = committed_op_id;
  queue_state_.active_config.reset(new RaftConfigPB(active_config));
  CHECK(IsRaftConfigVoter(local_peer_uuid_, *queue_state_.active_config))
      << local_peer_pb_.ShortDebugString() << " not a voter in config: "
      << queue_state_.active_config->ShortDebugString();
  queue_state_.majority_size_ = MajoritySize(CountVoters(*queue_state_.active_config));
  queue_state_.mode = Mode::LEADER;

  LOG_WITH_PREFIX_UNLOCKED(INFO) << "Queue going to LEADER mode. State: "
      << queue_state_.ToString();
  CheckPeersInActiveConfigIfLeaderUnlocked();

  // Reset last communication time with all peers to reset the clock on the
  // failure timeout.
  MonoTime now(MonoTime::Now());
  for (const PeersMap::value_type& entry : peers_map_) {
    entry.second->ResetLeaderLeases();
    entry.second->last_successful_communication_time = now;
  }
}

void PeerMessageQueue::SetNonLeaderMode() {
  LockGuard lock(queue_lock_);
  queue_state_.active_config.reset();
  queue_state_.mode = Mode::NON_LEADER;
  queue_state_.majority_size_ = -1;
  LOG_WITH_PREFIX_UNLOCKED(INFO) << "Queue going to NON_LEADER mode. State: "
      << queue_state_.ToString();
}

void PeerMessageQueue::TrackPeer(const string& uuid) {
  LockGuard lock(queue_lock_);
  TrackPeerUnlocked(uuid);
}

PeerMessageQueue::TrackedPeer* PeerMessageQueue::TrackPeerUnlocked(const string& uuid) {
  CHECK(!uuid.empty()) << "Got request to track peer with empty UUID"49;
  DCHECK_EQ(queue_state_.state, State::kQueueOpen);

  TrackedPeer* tracked_peer = new TrackedPeer(uuid);

  // We don't know the last operation received by the peer so, following the Raft protocol, we set
  // next_index to one past the end of our own log. This way, if calling this method is the result
  // of a successful leader election and the logs between the new leader and remote peer match, the
  // peer->next_index will point to the index of the soon-to-be-written NO_OP entry that is used to
  // assert leadership. If we guessed wrong, and the peer does not have a log that matches ours, the
  // normal queue negotiation process will eventually find the right point to resume from.
  tracked_peer->next_index = queue_state_.last_appended.index + 1;
  InsertOrDie(&peers_map_, uuid, tracked_peer);

  CheckPeersInActiveConfigIfLeaderUnlocked();

  // We don't know how far back this peer is, so set the all replicated watermark to
  // MinimumOpId. We'll advance it when we know how far along the peer is.
  queue_state_.all_replicated_op_id = OpId::Min();
  return tracked_peer;
}

void PeerMessageQueue::UntrackPeer(const string& uuid) {
  LockGuard lock(queue_lock_);
  TrackedPeer* peer = EraseKeyReturnValuePtr(&peers_map_, uuid);
  if (peer != nullptr) {
    delete peer;
  }
}

void PeerMessageQueue::CheckPeersInActiveConfigIfLeaderUnlocked() const {
  if (queue_state_.mode != Mode::LEADER) return150k;
  std::unordered_set<std::string> config_peer_uuids;
  for (const RaftPeerPB& peer_pb : queue_state_.active_config->peers()) {
    InsertOrDie(&config_peer_uuids, peer_pb.permanent_uuid());
  }
  for (const PeersMap::value_type& entry : peers_map_) {
    if (!ContainsKey(config_peer_uuids, entry.first)) {
      LOG_WITH_PREFIX_UNLOCKED(FATAL) << Substitute("Peer $0 is not in the active config. "
                                                    "Queue state: $1",
                                                    entry.first,
                                                    queue_state_.ToString());
    }
  }
}

void PeerMessageQueue::NumSSTFilesChanged() {
  auto num_sst_files = context_->NumSSTFiles();

  uint64_t majority_replicated_num_sst_files;
  {
    LockGuard lock(queue_lock_);
    if (queue_state_.mode != Mode::LEADER) {
      return;
    }
    auto it = peers_map_.find(local_peer_uuid_);
    if (it == peers_map_.end()) {
      return;
    }
    it->second->num_sst_files = num_sst_files;
    majority_replicated_num_sst_files = NumSSTFilesWatermark();
  }

  NotifyObservers(
      "majority replicated num SST files changed",
      [majority_replicated_num_sst_files](PeerMessageQueueObserver* observer) {
    observer->MajorityReplicatedNumSSTFilesChanged(majority_replicated_num_sst_files);
  });
}

void PeerMessageQueue::LocalPeerAppendFinished(const OpId& id, const Status& status) {
  CHECK_OK(status);

  // Fake an RPC response from the local peer.
  // TODO: we should probably refactor the ResponseFromPeer function so that we don't need to
  // construct this fake response, but this seems to work for now.
  ConsensusResponsePB fake_response;
  id.ToPB(fake_response.mutable_status()->mutable_last_received());
  id.ToPB(fake_response.mutable_status()->mutable_last_received_current_leader());
  if (context_) {
    fake_response.set_num_sst_files(context_->NumSSTFiles());
  }
  {
    LockGuard lock(queue_lock_);

    // TODO This ugly fix is required because we unlock queue_lock_ while doing AppendOperations.
    // So LocalPeerAppendFinished could be invoked before rest of AppendOperations.
    if (queue_state_.last_appended.index < id.index) {
      queue_state_.last_appended = id;
    }
    fake_response.mutable_status()->set_last_committed_idx(queue_state_.committed_op_id.index);
    queue_state_.last_applied_op_id.ToPB(fake_response.mutable_status()->mutable_last_applied());

    if (queue_state_.mode != Mode::LEADER) {
      log_cache_.EvictThroughOp(id.index);

      UpdateMetrics();
      return;
    }
  }
  ResponseFromPeer(local_peer_uuid_, fake_response);
}

Status PeerMessageQueue::TEST_AppendOperation(const ReplicateMsgPtr& msg) {
  return AppendOperations(
      { msg }, yb::OpId::FromPB(msg->committed_op_id()), RestartSafeCoarseMonoClock().Now());
}

Status PeerMessageQueue::AppendOperations(const ReplicateMsgs& msgs,
                                          const yb::OpId& committed_op_id,
                                          RestartSafeCoarseTimePoint batch_mono_time) {
  DFAKE_SCOPED_LOCK(append_fake_lock_);
  OpId last_id;
  if (!msgs.empty()) {
    std::unique_lock<simple_spinlock> lock(queue_lock_);

    last_id = OpId::FromPB(msgs.back()->id());

    if (last_id.term > queue_state_.current_term) {
      queue_state_.current_term = last_id.term;
    }
  } else {
    std::unique_lock<simple_spinlock> lock(queue_lock_);
    last_id = queue_state_.last_appended;
  }

  // Unlock ourselves during Append to prevent a deadlock: it's possible that the log buffer is
  // full, in which case AppendOperations would block. However, for the log buffer to empty, it may
  // need to call LocalPeerAppendFinished() which also needs queue_lock_.
  //
  // Since we are doing AppendOperations only in one thread, no concurrent AppendOperations could
  // be executed and queue_state_.last_appended will be updated correctly.
  RETURN_NOT_OK(log_cache_.AppendOperations(
      msgs, committed_op_id, batch_mono_time,
      Bind(&PeerMessageQueue::LocalPeerAppendFinished, Unretained(this), last_id)));

  if (!msgs.empty()) {
    std::unique_lock<simple_spinlock> lock(queue_lock_);
    queue_state_.last_appended = last_id;
    UpdateMetrics();
  }

  return Status::OK();
}

uint64_t GetNumMessagesToSendWithBackoff(int64_t last_num_messages_sent) {
  return std::max<int64_t>((last_num_messages_sent >> 1) - 1, 0);
}

Status PeerMessageQueue::RequestForPeer(const string& uuid,
                                        ConsensusRequestPB* request,
                                        ReplicateMsgsHolder* msgs_holder,
                                        bool* needs_remote_bootstrap,
                                        PeerMemberType* member_type,
                                        bool* last_exchange_successful) {
  static constexpr uint64_t kSendUnboundedLogOps = std::numeric_limits<uint64_t>::max();
  DCHECK(request->ops().empty()) << request->ShortDebugString()61.4k;

  OpId preceding_id;
  MonoDelta unreachable_time = MonoDelta::kMin;
  bool is_voter = false;
  bool is_new;
  int64_t previously_sent_index;
  uint64_t num_log_ops_to_send;
  HybridTime propagated_safe_time;

  // Should be before now_ht, i.e. not greater than propagated_hybrid_time.
  if (context_) {
    propagated_safe_time = VERIFY_RESULT(context_->PreparePeerRequest());
  }

  {
    LockGuard lock(queue_lock_);
    DCHECK_EQ(queue_state_.state, State::kQueueOpen);
    DCHECK_NE(uuid, local_peer_uuid_);

    auto peer = FindPtrOrNull(peers_map_, uuid);
    if (PREDICT_FALSE(peer == nullptr || queue_state_.mode == Mode::NON_LEADER)) {
      return STATUS(NotFound, "Peer not tracked or queue not in leader mode.");
    }

    HybridTime now_ht;

    is_new = peer->is_new;
    if (!is_new) {
      now_ht = clock_->Now();

      auto ht_lease_expiration_micros = now_ht.GetPhysicalValueMicros() +
                                        FLAGS_ht_lease_duration_ms * 1000;
      auto leader_lease_duration_ms = GetAtomicFlag(&FLAGS_leader_lease_duration_ms);
      request->set_leader_lease_duration_ms(leader_lease_duration_ms);
      request->set_ht_lease_expiration(ht_lease_expiration_micros);

      // As noted here:
      // https://red.ht/2sCSErb
      //
      // The _COARSE variants are faster to read and have a precision (also known as resolution) of
      // one millisecond (ms).
      //
      // Coarse clock precision is 1 millisecond.
      const auto kCoarseClockPrecision = 1ms;

      // Because of coarse clocks we subtract 2ms, to be sure that our local version of lease
      // does not expire after it expires at follower.
      peer->leader_lease_expiration.last_sent =
          CoarseMonoClock::Now() + leader_lease_duration_ms * 1ms - kCoarseClockPrecision * 2;
      peer->leader_ht_lease_expiration.last_sent = ht_lease_expiration_micros;
    } else {
      now_ht = clock_->Now();
      request->clear_leader_lease_duration_ms();
      request->clear_ht_lease_expiration();
      peer->leader_lease_expiration.Reset();
      peer->leader_ht_lease_expiration.Reset();
    }
    // This is initialized to the queue's last appended op but gets set to the id of the
    // log entry preceding the first one in 'messages' if messages are found for the peer.
    //
    // The leader does not know the actual state of a peer but it should always send a value of
    // preceding_id that is present in the leader's own log, so the follower can verify the log
    // matching property.
    //
    // In case we decide not to send any messages to the follower this time due to exponential
    // backoff to an unresponsive follower, we will keep preceding_id equal to last_appended.
    // This is safe because unless the follower already has that operation, it will fail to find
    // it in its pending operations in EnforceLogMatchingPropertyMatchesUnlocked and will return
    // a log matching property violation error without applying any incorrect messages from its log.
    //
    // See this scenario for more context on the issue we are trying to avoid:
    // https://github.com/yugabyte/yugabyte-db/issues/8150#issuecomment-827821784
    preceding_id = queue_state_.last_appended;

    request->set_propagated_hybrid_time(now_ht.ToUint64());

    // NOTE: committed_op_id may be overwritten later.
    // In our system committed_op_id means that this operation was also applied.
    // If we have operation that applied significant time, followers would not know that this
    // operation is committed until it is applied in the leader.
    // To address this issue we use majority_replicated_op_id, that is updated before apply.
    // But we could use it only when its term matches current term, see Fig.8 in Raft paper.
    if (queue_state_.majority_replicated_op_id.index > queue_state_.committed_op_id.index &&
        queue_state_.majority_replicated_op_id.term == queue_state_.current_term720k) {
      queue_state_.majority_replicated_op_id.ToPB(request->mutable_committed_op_id());
    } else {
      queue_state_.committed_op_id.ToPB(request->mutable_committed_op_id());
    }

    request->set_caller_term(queue_state_.current_term);
    unreachable_time =
        MonoTime::Now().GetDeltaSince(peer->last_successful_communication_time);
    if (member_type28.8M) *member_type = peer->member_type;
    if (last_exchange_successful28.8M) *last_exchange_successful = peer->is_last_exchange_successful;
    *needs_remote_bootstrap = peer->needs_remote_bootstrap;

    previously_sent_index = peer->next_index - 1;
    if (FLAGS_enable_consensus_exponential_backoff && peer->last_num_messages_sent >= 028.8M) {
      // Previous request to peer has not been acked. Reduce number of entries to be sent
      // in this attempt using exponential backoff. Note that to_index is inclusive.
      num_log_ops_to_send = GetNumMessagesToSendWithBackoff(peer->last_num_messages_sent);
    } else {
      // Previous request to peer has been acked or a heartbeat response has been received.
      // Transmit as many entries as allowed.
      num_log_ops_to_send = kSendUnboundedLogOps;
    }

    peer->current_retransmissions++;

    if (peer->member_type == PeerMemberType::VOTER) {
      is_voter = true;
    }
  }

  if (unreachable_time.ToSeconds() > FLAGS_follower_unavailable_considered_failed_sec) {
    if (!is_voter || CountVoters(*queue_state_.active_config) > 2217k) {
      // We never drop from 2 voters to 1 voter automatically, at least for now (12/4/18). We may
      // want to revisit this later, we're just being cautious with this.
      // We remove unconditionally any failed non-voter replica (PRE_VOTER, PRE_OBSERVER, OBSERVER).
      string msg = Substitute("Leader has been unable to successfully communicate "
                              "with Peer $0 for more than $1 seconds ($2)",
                              uuid,
                              FLAGS_follower_unavailable_considered_failed_sec,
                              unreachable_time.ToString());
      NotifyObserversOfFailedFollower(uuid, queue_state_.current_term, msg);
    }
  }

  if (PREDICT_FALSE(*needs_remote_bootstrap)) {
      YB_LOG_WITH_PREFIX_UNLOCKED_EVERY_N_SECS486(INFO, 30)
          << "Peer needs remote bootstrap: " << uuid;
    return Status::OK();
  }
  *needs_remote_bootstrap = false;

  request->clear_propagated_safe_time();

  // If we've never communicated with the peer, we don't know what messages to send, so we'll send a
  // status-only request. If the peer has not responded to the point that our to_index == next_index
  // due to exponential backoff of replicated segment size, we also send a status-only request.
  // Otherwise, we grab requests from the log starting at the last_received point.
  if (!is_new && num_log_ops_to_send > 028.6M) {
    // The batch of messages to send to the peer.
    auto max_batch_size = FLAGS_consensus_max_batch_size_bytes - request->ByteSizeLong();
    auto to_index = num_log_ops_to_send == kSendUnboundedLogOps ?
        0 : previously_sent_index + num_log_ops_to_send26.9k;
    auto result = ReadFromLogCache(previously_sent_index, to_index, max_batch_size, uuid);

    if (PREDICT_FALSE(!result.ok())) {
      if (PREDICT_TRUE(result.status().IsNotFound())) {
        std::string msg = Format("The logs necessary to catch up peer $0 have been "
                                 "garbage collected. The follower will never be able "
                                 "to catch up ($1)", uuid, result.status());
        NotifyObserversOfFailedFollower(uuid, queue_state_.current_term, msg);
      }
      return result.status();
    }

    preceding_id = result->preceding_op;
    // We use AddAllocated rather than copy, because we pin the log cache at the "all replicated"
    // point. At some point we may want to allow partially loading (and not pinning) earlier
    // messages. At that point we'll need to do something smarter here, like copy or ref-count.
    for (const auto& msg : result->messages) {
      request->mutable_ops()->AddAllocated(msg.get());
    }

    {
      LockGuard lock(queue_lock_);
      auto peer = FindPtrOrNull(peers_map_, uuid);
      if (PREDICT_FALSE(peer == nullptr)) {
        return STATUS(NotFound, "Peer not tracked.");
      }

      peer->last_num_messages_sent = result->messages.size();
    }

    ScopedTrackedConsumption consumption;
    if (result->read_from_disk_size) {
      consumption = ScopedTrackedConsumption(operations_mem_tracker_, result->read_from_disk_size);
    }
    *msgs_holder = ReplicateMsgsHolder(
        request->mutable_ops(), std::move(result->messages), std::move(consumption));

    if (propagated_safe_time &&
        !result->have_more_messages25.4M &&
        num_log_ops_to_send == kSendUnboundedLogOps25.4M) {
      // Get the current local safe time on the leader and propagate it to the follower.
      request->set_propagated_safe_time(propagated_safe_time.ToUint64());
    }
  }

  preceding_id.ToPB(request->mutable_preceding_id());

  // All entries committed at leader may not be available at lagging follower.
  // `commited_op_id` in this request may make a lagging follower aware of the
  // highest committed op index at the leader. We have a sanity check during tablet
  // bootstrap, in TabletBootstrap::PlaySegments(), that this tablet did not lose a
  // committed operation. Hence avoid sending a committed op id that is too large
  // to such a lagging follower.
  // If we send operations to it, then last know operation to this follower will be last sent
  // operation. If we don't send any operation, then last known operation will be preceding
  // operation.
  // We don't have to change committed_op_id when it is less than max_allowed_committed_op_id,
  // because it will have actual committed_op_id value and this operation is known to the
  // follower.
  const auto max_allowed_committed_op_id = !request->ops().empty()
      ? OpId::FromPB(request->ops().rbegin()->id())8.27M : preceding_id20.5M;
  if (max_allowed_committed_op_id.index < request->committed_op_id().index()) {
    max_allowed_committed_op_id.ToPB(request->mutable_committed_op_id());
  }

  if (PREDICT_FALSE(VLOG_IS_ON(2))) {
    if (request->ops_size() > 0) {
      VLOG_WITH_PREFIX_UNLOCKED(2) << "Sending request with operations to Peer: " << uuid
          << ". Size: " << request->ops_size()
          << ". From: " << request->ops(0).id().ShortDebugString() << ". To: "
          << request->ops(request->ops_size() - 1).id().ShortDebugString();
      VLOG_WITH_PREFIX_UNLOCKED(3) << "Operations: " << yb::ToString(request->ops());
    } else {
      VLOG_WITH_PREFIX_UNLOCKED(2)
          << "Sending " << (is_new ? "new " : "") << "status only request to Peer: " << uuid
          << ": " << request->ShortDebugString();
    }
  }

  return Status::OK();
}

Result<ReadOpsResult> PeerMessageQueue::ReadFromLogCache(int64_t after_index,
                                                         int64_t to_index,
                                                         size_t max_batch_size,
                                                         const std::string& peer_uuid,
                                                         const CoarseTimePoint deadline) {
  DCHECK_LT(FLAGS_consensus_max_batch_size_bytes + 1_KB, FLAGS_rpc_max_message_size);

  // We try to get the follower's next_index from our log.
  // Note this is not using "term" and needs to change
  auto result = log_cache_.ReadOps(after_index, to_index, max_batch_size, deadline);
  if (PREDICT_FALSE(!result.ok())) {
    auto s = result.status();
    if (PREDICT_TRUE(s.IsNotFound())) {
      return s;
    } else if (s.IsIncomplete()) {
      // IsIncomplete() means that we tried to read beyond the head of the log (in the future).
      // KUDU-1078 points to a fix of this log spew issue that we've ported. This should not
      // happen under normal circumstances.
      LOG_WITH_PREFIX_UNLOCKED(ERROR) << "Error trying to read ahead of the log "
                                      << "while preparing peer request: "
                                      << s.ToString() << ". Destination peer: "
                                      << peer_uuid;
      return s;
    } else {
      LOG_WITH_PREFIX_UNLOCKED(FATAL) << "Error reading the log while preparing peer request: "
                                      << s.ToString() << ". Destination peer: "
                                      << peer_uuid;
      return s;
    }
  }
  return result;
}

// Read majority replicated messages from cache for CDC.
// CDC producer will use this to get the messages to send in response to cdc::GetChanges RPC.
Result<ReadOpsResult> PeerMessageQueue::ReadReplicatedMessagesForCDC(
  const yb::OpId& last_op_id,
  int64_t* repl_index,
  const CoarseTimePoint deadline) {
  // The batch of messages read from cache.

  int64_t to_index;
  bool pending_messages = false;
  {
    LockGuard lock(queue_lock_);
    // Use committed_op_id because it's already been processed by the Transaction codepath.
    to_index = queue_state_.committed_op_id.index;
    // Determine if there are pending operations in RAFT but not yet LogCache.
    pending_messages = to_index != queue_state_.majority_replicated_op_id.index;
  }
  if (repl_index) {
    *repl_index = to_index;
  }

  if (last_op_id.index >= to_index) {
    // Nothing to read.
    return ReadOpsResult();
  }

  // If an empty OpID is only sent on the first read request, start at the earliest known entry.
  int64_t after_op_index = last_op_id.empty() ?
                             max(log_cache_.earliest_op_index(), last_op_id.index) :
                             last_op_id.index14;

  auto result = ReadFromLogCache(
      after_op_index, to_index, FLAGS_consensus_max_batch_size_bytes, local_peer_uuid_, deadline);
  if (PREDICT_FALSE(!result.ok()) && PREDICT_TRUE0(result.status().IsNotFound())) {
    LOG_WITH_PREFIX_UNLOCKED(INFO) << Format(
        "The logs from index $0 have been garbage collected and cannot be read ($1)",
        after_op_index, result.status());
  }
  if (result.ok()) {
    result->have_more_messages = HaveMoreMessages(result->have_more_messages.get() ||
                                                  pending_messages);
  }
  return result;
}

Status PeerMessageQueue::GetRemoteBootstrapRequestForPeer(const string& uuid,
                                                          StartRemoteBootstrapRequestPB* req) {
  TrackedPeer* peer = nullptr;
  {
    LockGuard lock(queue_lock_);
    DCHECK_EQ(queue_state_.state, State::kQueueOpen);
    DCHECK_NE(uuid, local_peer_uuid_);
    peer = FindPtrOrNull(peers_map_, uuid);
    if (PREDICT_FALSE(peer == nullptr || queue_state_.mode == Mode::NON_LEADER)) {
      return STATUS(NotFound, "Peer not tracked or queue not in leader mode.");
    }
  }

  if (PREDICT_FALSE(!peer->needs_remote_bootstrap)) {
    return STATUS(IllegalState, "Peer does not need to remotely bootstrap", uuid);
  }

  if (peer->member_type == PeerMemberType::VOTER || peer->member_type == PeerMemberType::OBSERVER10.6k) {
    LOG(INFO) << "Remote bootstrapping peer " << uuid << " with type "
              << PeerMemberType_Name(peer->member_type);
  }

  req->Clear();
  req->set_dest_uuid(uuid);
  req->set_tablet_id(tablet_id_);
  req->set_bootstrap_peer_uuid(local_peer_uuid_);
  *req->mutable_source_private_addr() = local_peer_pb_.last_known_private_addr();
  *req->mutable_source_broadcast_addr() = local_peer_pb_.last_known_broadcast_addr();
  *req->mutable_source_cloud_info() = local_peer_pb_.cloud_info();
  req->set_caller_term(queue_state_.current_term);
  peer->needs_remote_bootstrap = false; // Now reset the flag.
  return Status::OK();
}

void PeerMessageQueue::UpdateCDCConsumerOpId(const yb::OpId& op_id) {
  std::lock_guard<rw_spinlock> l(cdc_consumer_lock_);
  cdc_consumer_op_id_ = op_id;
  cdc_consumer_op_id_last_updated_ = CoarseMonoClock::Now();
}

yb::OpId PeerMessageQueue::GetCDCConsumerOpIdToEvict() {
  std::shared_lock<rw_spinlock> l(cdc_consumer_lock_);
  // For log cache eviction, we only want to include CDC consumers that are actively polling.
  // If CDC consumer checkpoint has not been updated recently, we exclude it.
  if (CoarseMonoClock::Now() - cdc_consumer_op_id_last_updated_ <= kCDCConsumerCheckpointInterval) {
    return cdc_consumer_op_id_;
  } else {
    return yb::OpId::Max();
  }
}

yb::OpId PeerMessageQueue::GetCDCConsumerOpIdForIntentRemoval() {
  std::shared_lock<rw_spinlock> l(cdc_consumer_lock_);
  if (CoarseMonoClock::Now() - cdc_consumer_op_id_last_updated_ <= kCDCConsumerIntentRetention) {
    return cdc_consumer_op_id_;
  } else {
    return yb::OpId::Max();
  }
}

void PeerMessageQueue::UpdateAllReplicatedOpId(OpId* result) {
  OpId new_op_id = OpId::Max();

  for (const auto& peer : peers_map_) {
    if (!peer.second->is_last_exchange_successful) {
      return;
    }
    if (peer.second->last_received.index < new_op_id.index) {
      new_op_id = peer.second->last_received;
    }
  }

  CHECK_NE(OpId::Max(), new_op_id);
  *result = new_op_id;
}

void PeerMessageQueue::UpdateAllAppliedOpId(OpId* result) {
  OpId all_applied_op_id = OpId::Max();
  for (const auto& peer : peers_map_) {
    if (!peer.second->is_last_exchange_successful) {
      return;
    }
    all_applied_op_id = std::min(all_applied_op_id, peer.second->last_applied);
  }

  CHECK_NE(OpId::Max(), all_applied_op_id);
  *result = all_applied_op_id;
}

void PeerMessageQueue::UpdateAllNonLaggingReplicatedOpId(int32_t threshold) {
  OpId new_op_id = OpId::Max();

  for (const auto& peer : peers_map_) {
    // Ignore lagging follower.
    if (peer.second->current_retransmissions >= threshold) {
      continue;
    }
    if (peer.second->last_received.index < new_op_id.index) {
      new_op_id = peer.second->last_received;
    }
  }

  if (new_op_id == OpId::Max()) {
    LOG_WITH_PREFIX_UNLOCKED(INFO) << "Non lagging peer(s) not found.";
    new_op_id = queue_state_.all_replicated_op_id;
  }

  if (queue_state_.all_nonlagging_replicated_op_id.index < new_op_id.index) {
    queue_state_.all_nonlagging_replicated_op_id = new_op_id;
  }
}

HAS_MEMBER_FUNCTION(InfiniteWatermarkForLocalPeer);

template <class Policy, bool HasMemberFunction_InfiniteWatermarkForLocalPeer>
struct GetInfiniteWatermarkForLocalPeer;

template <class Policy>
struct GetInfiniteWatermarkForLocalPeer<Policy, true> {
  static auto Apply() {
    return Policy::InfiniteWatermarkForLocalPeer();
  }
};

template <class Policy>
struct GetInfiniteWatermarkForLocalPeer<Policy, false> {
  // Should not be invoked, but have to define to make compiler happy.
  static typename Policy::result_type Apply() {
    LOG(DFATAL) << "Invoked Apply when InfiniteWatermarkForLocalPeer is not defined";
    return typename Policy::result_type();
  }
};

template <class Policy>
typename Policy::result_type PeerMessageQueue::GetWatermark() {
  DCHECK(queue_lock_.is_locked());
  const auto num_peers_required = queue_state_.majority_size_;
  if (num_peers_required == kUninitializedMajoritySize) {
    // We don't even know the quorum majority size yet.
    return Policy::NotEnoughPeersValue();
  }
  CHECK_GE(num_peers_required, 0);

  const ssize_t num_peers = peers_map_.size();
  if (num_peers < num_peers_required) {
    return Policy::NotEnoughPeersValue();
  }

  // This flag indicates whether to implicitly assume that the local peer has an "infinite"
  // replicated value of the dimension that we are computing a watermark for. There is a difference
  // in logic between handling of OpIds vs. leader leases:
  // - For OpIds, the local peer might actually be less up-to-date than followers.
  // - For leader leases, we always assume that we've replicated an "infinite" lease to ourselves.
  const bool local_peer_infinite_watermark =
      HasMemberFunction_InfiniteWatermarkForLocalPeer<Policy>::value;

  if (num_peers_required == 1 && local_peer_infinite_watermark3.37M) {
    // We give "infinite lease" to ourselves.
    return GetInfiniteWatermarkForLocalPeer<
        Policy, HasMemberFunction_InfiniteWatermarkForLocalPeer<Policy>::value>::Apply();
  }

  constexpr size_t kMaxPracticalReplicationFactor = 5;
  boost::container::small_vector<
      typename Policy::result_type, kMaxPracticalReplicationFactor> watermarks;
  watermarks.reserve(num_peers - 1 + !local_peer_infinite_watermark);

  for (const PeersMap::value_type &peer_map_entry : peers_map_) {
    const TrackedPeer &peer = *peer_map_entry.second;
    if (local_peer_infinite_watermark && peer.uuid == local_peer_uuid_205M) {
      // Don't even include the local peer in the watermarks array. Assume it has an "infinite"
      // value of the watermark.
      continue;
    }
    if (!IsRaftConfigVoter(peer.uuid, *queue_state_.active_config)) {
      // Only votes from VOTERs in the active config should be taken into consideration
      continue;
    }
    if (peer.is_last_exchange_successful) {
      watermarks.push_back(Policy::ExtractValue(peer));
    }
  }

  // We always assume that local peer has most recent information.
  const ssize_t num_responsive_peers = watermarks.size() + local_peer_infinite_watermark;

  if (num_responsive_peers < num_peers_required) {
    VLOG_WITH_PREFIX_UNLOCKED(2)
        << Policy::Name() << " watermarks by peer: " << ::yb::ToString(watermarks)
        << ", num_peers_required=" << num_peers_required
        << ", num_responsive_peers=" << num_responsive_peers
        << ", not enough responsive peers";
    // There are not enough peers with which the last message exchange was successful.
    return Policy::NotEnoughPeersValue();
  }

  // If there are 5 peers (and num_peers_required is 3), and we have successfully replicated
  // something to 3 of them and 4th is our local peer, there are two possibilities:
  // - If local_peer_infinite_watermark is false (for OpId): watermarks.size() is 4,
  //   and we want an OpId value such that 3 or more peers have replicated that or greater value.
  //   Then index_of_interest = 1, computed as watermarks.size() - num_peers_required, or
  //   num_responsive_peers - num_peers_required.
  //
  // - If local_peer_infinite_watermark is true (for leader leases): watermarks.size() is 3, and we
  //   are assuming that the local peer (leader) has replicated an infinitely high watermark to
  //   itself. Then watermark.size() is 3 (because we skip the local peer when populating
  //   watermarks), but num_responsive_peers is still 4, and the expression stays the same.

  const size_t index_of_interest = num_responsive_peers - num_peers_required;
  DCHECK_LT(index_of_interest, watermarks.size());

  auto nth = watermarks.begin() + index_of_interest;
  std::nth_element(watermarks.begin(), nth, watermarks.end(), typename Policy::Comparator());
  VLOG_WITH_PREFIX_UNLOCKED14.0k(2)
      << Policy::Name() << " watermarks by peer: " << ::yb::ToString(watermarks)
      << ", num_peers_required=" << num_peers_required
      << ", local_peer_infinite_watermark=" << local_peer_infinite_watermark
      << ", watermark: " << yb::ToString(*nth);

  return *nth;
}

CoarseTimePoint PeerMessageQueue::LeaderLeaseExpirationWatermark() {
  struct Policy {
    typedef CoarseTimePoint result_type;
    // Workaround for a gcc bug. That does not understand that Comparator is actually being used.
    __attribute__((unused)) typedef std::less<result_type> Comparator;

    static result_type NotEnoughPeersValue() {
      return result_type::min();
    }

    static result_type InfiniteWatermarkForLocalPeer() {
      return result_type::max();
    }

    static result_type ExtractValue(const TrackedPeer& peer) {
      auto lease_exp = peer.leader_lease_expiration.last_received;
      return lease_exp != CoarseTimePoint() ? lease_exp67.4M : CoarseTimePoint::min()38.3k;
    }

    static const char* Name() {
      return "Leader lease expiration";
    }
  };

  return GetWatermark<Policy>();
}

MicrosTime PeerMessageQueue::HybridTimeLeaseExpirationWatermark() {
  struct Policy {
    typedef MicrosTime result_type;
    // Workaround for a gcc bug. That does not understand that Comparator is actually being used.
    __attribute__((unused)) typedef std::less<result_type> Comparator;

    static result_type NotEnoughPeersValue() {
      return HybridTime::kMin.GetPhysicalValueMicros();
    }

    static result_type InfiniteWatermarkForLocalPeer() {
      return HybridTime::kMax.GetPhysicalValueMicros();
    }

    static result_type ExtractValue(const TrackedPeer& peer) {
      return peer.leader_ht_lease_expiration.last_received;
    }

    static const char* Name() {
      return "Hybrid time leader lease expiration";
    }
  };

  return GetWatermark<Policy>();
}

uint64_t PeerMessageQueue::NumSSTFilesWatermark() {
  struct Policy {
    typedef uint64_t result_type;
    // Workaround for a gcc bug. That does not understand that Comparator is actually being used.
    __attribute__((unused)) typedef std::greater<result_type> Comparator;

    static result_type NotEnoughPeersValue() {
      return 0;
    }

    static result_type ExtractValue(const TrackedPeer& peer) {
      return peer.num_sst_files;
    }

    static const char* Name() {
      return "Num SST files";
    }
  };

  auto watermark = GetWatermark<Policy>();
  return std::max(watermark, local_peer_->num_sst_files);
}

OpId PeerMessageQueue::OpIdWatermark() {
  struct Policy {
    typedef OpId result_type;

    static result_type NotEnoughPeersValue() {
      return OpId::Min();
    }

    static result_type ExtractValue(const TrackedPeer& peer) {
      return peer.last_received;
    }

    struct Comparator {
      bool operator()(const OpId& lhs, const OpId& rhs) {
        return lhs.index < rhs.index;
      }
    };

    static const char* Name() {
      return "OpId";
    }
  };

  return GetWatermark<Policy>();
}

void PeerMessageQueue::NotifyPeerIsResponsiveDespiteError(const std::string& peer_uuid) {
  LockGuard l(queue_lock_);
  TrackedPeer* peer = FindPtrOrNull(peers_map_, peer_uuid);
  if (!peer) return0;
  peer->last_successful_communication_time = MonoTime::Now();
}

void PeerMessageQueue::RequestWasNotSent(const std::string& peer_uuid) {
  LockGuard scoped_lock(queue_lock_);
  DCHECK_NE(State::kQueueConstructed, queue_state_.state);

  TrackedPeer* peer = FindPtrOrNull(peers_map_, peer_uuid);
  if (PREDICT_FALSE(queue_state_.state != State::kQueueOpen || peer == nullptr)) {
    LOG_WITH_PREFIX_UNLOCKED(WARNING) << "Queue is closed or peer was untracked.";
    return;
  }

  peer->ResetLastRequest();
}


bool PeerMessageQueue::ResponseFromPeer(const std::string& peer_uuid,
                                        const ConsensusResponsePB& response) {
  DCHECK(response.IsInitialized()) << "Error: Uninitialized: "
      << response.InitializationErrorString() << ". Response: " << response.ShortDebugString();

  MajorityReplicatedData majority_replicated;
  Mode mode_copy;
  bool result = false;
  {
    LockGuard scoped_lock(queue_lock_);
    DCHECK_NE(State::kQueueConstructed, queue_state_.state);

    TrackedPeer* peer = FindPtrOrNull(peers_map_, peer_uuid);
    if (PREDICT_FALSE(queue_state_.state != State::kQueueOpen || peer == nullptr)) {
      LOG_WITH_PREFIX_UNLOCKED(WARNING) << "Queue is closed or peer was untracked, disregarding "
          "peer response. Response: " << response.ShortDebugString();
      return false;
    }

    // Remotely bootstrap the peer if the tablet is not found or deleted.
    if (response.has_error()) {
      // We only let special types of errors through to this point from the peer.
      CHECK_EQ(tserver::TabletServerErrorPB::TABLET_NOT_FOUND, response.error().code())
          << response.ShortDebugString();

      peer->needs_remote_bootstrap = true;
      // Since we received a response from the peer, we know it is alive. So we need to update
      // peer->last_successful_communication_time, otherwise, we will remove this peer from the
      // configuration if the remote bootstrap is not completed within
      // FLAGS_follower_unavailable_considered_failed_sec seconds.
      peer->last_successful_communication_time = MonoTime::Now();
      YB_LOG_WITH_PREFIX_UNLOCKED_EVERY_N_SECS485(INFO, 30)
          << "Marked peer as needing remote bootstrap: " << peer->ToString();
      return true;
    }

    if (34.8Mqueue_state_.active_config34.8M) {
      RaftPeerPB peer_pb;
      if (!GetRaftConfigMember(*queue_state_.active_config, peer_uuid, &peer_pb).ok()) {
        LOG(FATAL) << "Peer " << peer_uuid << " not in active config";
      }
      peer->member_type = peer_pb.member_type();
    } else {
      peer->member_type = PeerMemberType::UNKNOWN_MEMBER_TYPE;
    }

    // Application level errors should be handled elsewhere
    DCHECK(!response.has_error());

    // Take a snapshot of the current peer status.
    TrackedPeer previous = *peer;

    // Update the peer status based on the response.
    peer->is_new = false;
    peer->last_successful_communication_time = MonoTime::Now();

    peer->ResetLastRequest();

    if (response.has_status()) {
      const auto& status = response.status();
      // Sanity checks.  Some of these can be eventually removed, but they are handy for now.
      DCHECK(status.IsInitialized()) << "Error: Uninitialized: "
                                                << response.InitializationErrorString()
                                                << ". Response: " << response.ShortDebugString();
      // The status must always have a last received op id and a last committed index.
      DCHECK(status.has_last_received());
      DCHECK(status.has_last_received_current_leader());
      DCHECK(status.has_last_committed_idx());

      peer->last_known_committed_idx = status.last_committed_idx();
      peer->last_applied = OpId::FromPB(status.last_applied());

      // If the reported last-received op for the replica is in our local log, then resume sending
      // entries from that point onward. Otherwise, resume after the last op they received from us.
      // If we've never successfully sent them anything, start after the last-committed op in their
      // log, which is guaranteed by the Raft protocol to be a valid op.

      bool peer_has_prefix_of_log = IsOpInLog(yb::OpId::FromPB(status.last_received()));
      if (peer_has_prefix_of_log34.8M) {
        // If the latest thing in their log is in our log, we are in sync.
        peer->last_received = OpId::FromPB(status.last_received());
        peer->next_index = peer->last_received.index + 1;

      } else if (!OpIdEquals(status.last_received_current_leader(), MinimumOpId())) {
        // Their log may have diverged from ours, however we are in the process of replicating our
        // ops to them, so continue doing so. Eventually, we will cause the divergent entry in their
        // log to be overwritten.
        peer->last_received = OpId::FromPB(status.last_received_current_leader());
        peer->next_index = peer->last_received.index + 1;
      } else {
        // The peer is divergent and they have not (successfully) received anything from us yet.
        // Start sending from their last committed index.  This logic differs from the Raft spec
        // slightly because instead of stepping back one-by-one from the end until we no longer have
        // an LMP error, we jump back to the last committed op indicated by the peer with the hope
        // that doing so will result in a faster catch-up process.
        DCHECK_GE(peer->last_known_committed_idx, 0);
        peer->next_index = peer->last_known_committed_idx + 1;
      }

      if (PREDICT_FALSE(status.has_error())) {
        peer->is_last_exchange_successful = false;
        switch (status.error().code()) {
          case ConsensusErrorPB::PRECEDING_ENTRY_DIDNT_MATCH: {
            DCHECK(status.has_last_received());
            if (previous.is_new) {
              // That's currently how we can detect that we able to connect to a peer.
              LOG_WITH_PREFIX_UNLOCKED(INFO) << "Connected to new peer: " << peer->ToString();
            } else {
              LOG_WITH_PREFIX_UNLOCKED(INFO) << "Got LMP mismatch error from peer: "
                                             << peer->ToString();
              CHECK(!FLAGS_TEST_disallow_lmp_failures);
            }
            return true;
          }
          case ConsensusErrorPB::INVALID_TERM: {
            CHECK(response.has_responder_term());
            LOG_WITH_PREFIX_UNLOCKED(INFO) << "Peer responded invalid term: " << peer->ToString()
                                           << ". Peer's new term: " << response.responder_term();
            NotifyObserversOfTermChange(response.responder_term());
            return false;
          }
          default: {
            LOG_WITH_PREFIX_UNLOCKED(FATAL) << "Unexpected consensus error. Code: "
                << ConsensusErrorPB::Code_Name(status.error().code()) << ". Response: "
                << response.ShortDebugString();
          }
        }
      }
    }

    peer->is_last_exchange_successful = true;
    peer->num_sst_files = response.num_sst_files();

    if (response.has_responder_term()) {
      // The peer must have responded with a term that is greater than or equal to the last known
      // term for that peer.
      peer->CheckMonotonicTerms(response.responder_term());

      // If the responder didn't send an error back that must mean that it has a term that is the
      // same or lower than ours.
      CHECK_LE(response.responder_term(), queue_state_.current_term);
    }

    if (PREDICT_FALSE(VLOG_IS_ON(2))) {
      VLOG_WITH_PREFIX_UNLOCKED0(2) << "Received Response from Peer (" << peer->ToString() << "). "
          << "Response: " << response.ShortDebugString();
    }

    // If our log has the next request for the peer or if the peer's committed index is lower than
    // our own, set 'more_pending' to true.
    result = log_cache_.HasOpBeenWritten(peer->next_index) ||
        (peer->last_known_committed_idx < queue_state_.committed_op_id.index)32.4M;

    mode_copy = queue_state_.mode;
    if (mode_copy == Mode::LEADER34.7M) {
      auto new_majority_replicated_opid = OpIdWatermark();
      if (new_majority_replicated_opid != OpId::Min()) {
        if (new_majority_replicated_opid.index == MaximumOpId().index()) {
          queue_state_.majority_replicated_op_id = local_peer_->last_received;
        } else {
          queue_state_.majority_replicated_op_id = new_majority_replicated_opid;
        }
      }

      peer->leader_lease_expiration.OnReplyFromFollower();
      peer->leader_ht_lease_expiration.OnReplyFromFollower();

      majority_replicated.op_id = queue_state_.majority_replicated_op_id;
      majority_replicated.leader_lease_expiration = LeaderLeaseExpirationWatermark();
      majority_replicated.ht_lease_expiration = HybridTimeLeaseExpirationWatermark();
      majority_replicated.num_sst_files = NumSSTFilesWatermark();
      if (peer->last_received == queue_state_.last_applied_op_id) {
        majority_replicated.peer_got_all_ops = peer->uuid;
      }
    }

    UpdateAllReplicatedOpId(&queue_state_.all_replicated_op_id);
    UpdateAllAppliedOpId(&queue_state_.all_applied_op_id);

    auto evict_index = GetCDCConsumerOpIdToEvict().index;

    int32_t lagging_follower_threshold = FLAGS_consensus_lagging_follower_threshold;
    if (lagging_follower_threshold > 0) {
      UpdateAllNonLaggingReplicatedOpId(lagging_follower_threshold);
      evict_index = std::min(evict_index, queue_state_.all_nonlagging_replicated_op_id.index);
    } else {
      evict_index = std::min(evict_index, queue_state_.all_replicated_op_id.index);
    }

    log_cache_.EvictThroughOp(evict_index);

    UpdateMetrics();
  }

  if (mode_copy == Mode::LEADER34.7M) {
    NotifyObserversOfMajorityReplOpChange(majority_replicated);
  }

  return result;
}

PeerMessageQueue::TrackedPeer PeerMessageQueue::GetTrackedPeerForTests(string uuid) {
  LockGuard scoped_lock(queue_lock_);
  TrackedPeer* tracked = FindOrDie(peers_map_, uuid);
  return *tracked;
}

OpId PeerMessageQueue::TEST_GetAllReplicatedIndex() const {
  LockGuard lock(queue_lock_);
  return queue_state_.all_replicated_op_id;
}

OpId PeerMessageQueue::GetAllAppliedOpId() const {
  LockGuard lock(queue_lock_);
  return queue_state_.all_applied_op_id;
}

OpId PeerMessageQueue::TEST_GetCommittedIndex() const {
  LockGuard lock(queue_lock_);
  return queue_state_.committed_op_id;
}

OpId PeerMessageQueue::TEST_GetMajorityReplicatedOpId() const {
  LockGuard lock(queue_lock_);
  return queue_state_.majority_replicated_op_id;
}

OpId PeerMessageQueue::TEST_GetLastAppended() const {
  LockGuard lock(queue_lock_);
  return queue_state_.last_appended;
}

OpId PeerMessageQueue::TEST_GetLastAppliedOpId() const {
  LockGuard lock(queue_lock_);
  return queue_state_.last_applied_op_id;
}

void PeerMessageQueue::UpdateMetrics() {
  // Since operations have consecutive indices we can update the metrics based on simple index math.
  metrics_.num_majority_done_ops->set_value(
      queue_state_.committed_op_id.index - queue_state_.all_replicated_op_id.index);
  metrics_.num_in_progress_ops->set_value(
      queue_state_.last_appended.index - queue_state_.committed_op_id.index);
}

void PeerMessageQueue::DumpToHtml(std::ostream& out) const {
  using std::endl;

  LockGuard lock(queue_lock_);
  out << "<h3>Watermarks</h3>" << endl;
  out << "<table>" << endl;;
  out << "  <tr><th>Peer</th><th>Watermark</th></tr>" << endl;
  for (const PeersMap::value_type& entry : peers_map_) {
    out << Substitute("  <tr><td>$0</td><td>$1</td></tr>",
                      EscapeForHtmlToString(entry.first),
                      EscapeForHtmlToString(entry.second->ToString())) << endl;
  }
  out << "</table>" << endl;

  log_cache_.DumpToHtml(out);
}

void PeerMessageQueue::ClearUnlocked() {
  STLDeleteValues(&peers_map_);
  queue_state_.state = State::kQueueClosed;
}

void PeerMessageQueue::Close() {
  if (installed_num_sst_files_changed_listener_) {
    context_->ListenNumSSTFilesChanged(std::function<void()>());
    installed_num_sst_files_changed_listener_ = false;
  }
  raft_pool_observers_token_->Shutdown();
  LockGuard lock(queue_lock_);
  ClearUnlocked();
}

string PeerMessageQueue::ToString() const {
  // Even though metrics are thread-safe obtain the lock so that we get a "consistent" snapshot of
  // the metrics.
  LockGuard lock(queue_lock_);
  return ToStringUnlocked();
}

string PeerMessageQueue::ToStringUnlocked() const {
  return Substitute("Consensus queue metrics:"
                    "Only Majority Done Ops: $0, In Progress Ops: $1, Cache: $2",
                    metrics_.num_majority_done_ops->value(), metrics_.num_in_progress_ops->value(),
                    log_cache_.StatsString());
}

void PeerMessageQueue::RegisterObserver(PeerMessageQueueObserver* observer) {
  LockGuard lock(queue_lock_);
  auto iter = std::find(observers_.begin(), observers_.end(), observer);
  if (iter == observers_.end()) {
    observers_.push_back(observer);
  }
}

Status PeerMessageQueue::UnRegisterObserver(PeerMessageQueueObserver* observer) {
  LockGuard lock(queue_lock_);
  auto iter = std::find(observers_.begin(), observers_.end(), observer);
  if (iter == observers_.end()) {
    return STATUS(NotFound, "Can't find observer.");
  }
  observers_.erase(iter);
  return Status::OK();
}

const char* PeerMessageQueue::ModeToStr(Mode mode) {
  switch (mode) {
    case Mode::LEADER: return "LEADER";
    case Mode::NON_LEADER: return "NON_LEADER";
  }
  FATAL_INVALID_ENUM_VALUE(PeerMessageQueue::Mode, mode);
}

const char* PeerMessageQueue::StateToStr(State state) {
  switch (state) {
    case State::kQueueConstructed:
      return "QUEUE_CONSTRUCTED";
    case State::kQueueOpen:
      return "QUEUE_OPEN";
    case State::kQueueClosed:
      return "QUEUE_CLOSED";

  }
  FATAL_INVALID_ENUM_VALUE(PeerMessageQueue::State, state);
}

bool PeerMessageQueue::IsOpInLog(const yb::OpId& desired_op) const {
  auto result = log_cache_.LookupOpId(desired_op.index);
  if (PREDICT_TRUE34.8M(result.ok())) {
    return desired_op == *result;
  }
  if (PREDICT_TRUE(result.status().IsNotFound() || result.status().IsIncomplete())) {
    return false;
  }
  LOG_WITH_PREFIX_UNLOCKED(FATAL) << "Error while reading the log: " << result.status();
  return false; // Unreachable; here to squelch GCC warning.
}

void PeerMessageQueue::NotifyObserversOfMajorityReplOpChange(
    const MajorityReplicatedData& majority_replicated_data) {
  WARN_NOT_OK(raft_pool_observers_token_->SubmitClosure(
      Bind(&PeerMessageQueue::NotifyObserversOfMajorityReplOpChangeTask,
           Unretained(this),
           majority_replicated_data)),
      LogPrefixUnlocked() + "Unable to notify RaftConsensus of "
                           "majority replicated op change.");
}

template <class Func>
void PeerMessageQueue::NotifyObservers(const char* title, Func&& func) {
  WARN_NOT_OK(
      raft_pool_observers_token_->SubmitFunc(
          [this, func = std::move(func)] {
        MAYBE_INJECT_RANDOM_LATENCY(FLAGS_consensus_inject_latency_ms_in_notifications);
        std::vector<PeerMessageQueueObserver*> copy;
        {
          LockGuard lock(queue_lock_);
          copy = observers_;
        }

        for (PeerMessageQueueObserver* observer : copy) {
          func(observer);
        }
      }),
      Format("$0Unable to notify observers for $1.", LogPrefixUnlocked(), title));
}

void PeerMessageQueue::NotifyObserversOfTermChange(int64_t term) {
  NotifyObservers("term change", [term](PeerMessageQueueObserver* observer) {
    observer->NotifyTermChange(term);
  });
}

void PeerMessageQueue::NotifyObserversOfMajorityReplOpChangeTask(
    const MajorityReplicatedData& majority_replicated_data) {
  std::vector<PeerMessageQueueObserver*> copy;
  {
    LockGuard lock(queue_lock_);
    copy = observers_;
  }

  // TODO move commit index advancement here so that the queue is not dependent on consensus at all,
  // but that requires a bit more work.
  OpId new_committed_op_id;
  OpId last_applied_op_id;
  for (PeerMessageQueueObserver* observer : copy) {
    observer->UpdateMajorityReplicated(
        majority_replicated_data, &new_committed_op_id, &last_applied_op_id);
  }

  {
    LockGuard lock(queue_lock_);
    if (!new_committed_op_id.empty() &&
        new_committed_op_id.index > queue_state_.committed_op_id.index34.6M) {
      queue_state_.committed_op_id = new_committed_op_id;
    }
    queue_state_.last_applied_op_id.MakeAtLeast(last_applied_op_id);
    local_peer_->last_applied = queue_state_.last_applied_op_id;
    UpdateAllAppliedOpId(&queue_state_.all_applied_op_id);
  }
}

void PeerMessageQueue::NotifyObserversOfFailedFollower(const string& uuid,
                                                       const string& reason) {
  int64_t current_term;
  {
    LockGuard lock(queue_lock_);
    current_term = queue_state_.current_term;
  }
  NotifyObserversOfFailedFollower(uuid, current_term, reason);
}

void PeerMessageQueue::NotifyObserversOfFailedFollower(const string& uuid,
                                                       int64_t term,
                                                       const string& reason) {
  NotifyObservers("failed follower", [uuid, term, reason](PeerMessageQueueObserver* observer) {
    observer->NotifyFailedFollower(uuid, term, reason);
  });
}

bool PeerMessageQueue::PeerAcceptedOurLease(const std::string& uuid) const {
  std::lock_guard<simple_spinlock> lock(queue_lock_);
  TrackedPeer* peer = FindPtrOrNull(peers_map_, uuid);
  if (peer == nullptr) {
    return false;
  }

  return peer->leader_lease_expiration.last_received != CoarseTimePoint();
}

bool PeerMessageQueue::CanPeerBecomeLeader(const std::string& peer_uuid) const {
  std::lock_guard<simple_spinlock> lock(queue_lock_);
  TrackedPeer* peer = FindPtrOrNull(peers_map_, peer_uuid);
  if (peer == nullptr) {
    LOG(ERROR) << "Invalid peer UUID: " << peer_uuid;
    return false;
  }
  const bool peer_can_be_leader = peer->last_received >= queue_state_.majority_replicated_op_id;
  if (!peer_can_be_leader) {
    LOG(INFO) << Format(
        "Peer $0 cannot become Leader as it is not caught up: Majority OpId $1, Peer OpId $2",
        peer_uuid, queue_state_.majority_replicated_op_id, peer->last_received);
  }
  return peer_can_be_leader;
}

OpId PeerMessageQueue::PeerLastReceivedOpId(const TabletServerId& uuid) const {
  std::lock_guard<simple_spinlock> lock(queue_lock_);
  TrackedPeer* peer = FindPtrOrNull(peers_map_, uuid);
  if (peer == nullptr) {
    LOG(ERROR) << "Invalid peer UUID: " << uuid;
    return OpId::Min();
  }
  return peer->last_received;
}

string PeerMessageQueue::GetUpToDatePeer() const {
  OpId highest_op_id = OpId::Min();
  std::vector<std::string> candidates;

  {
    std::lock_guard<simple_spinlock> lock(queue_lock_);
    for (const PeersMap::value_type& entry : peers_map_) {
      if (local_peer_uuid_ == entry.first) {
        continue;
      }
      if (highest_op_id > entry.second->last_received) {
        continue;
      } else if (highest_op_id == entry.second->last_received) {
        candidates.push_back(entry.first);
      } else {
        candidates = {entry.first};
        highest_op_id = entry.second->last_received;
      }
    }
  }

  if (candidates.empty()) {
    return string();
  }
  size_t index = 0;
  if (candidates.size() > 1) {
    // choose randomly among candidates at the same opid
    index = RandomUniformInt<size_t>(0, candidates.size() - 1);
  }
  return candidates[index];
}

PeerMessageQueue::~PeerMessageQueue() {
  Close();
}

string PeerMessageQueue::LogPrefixUnlocked() const {
  // TODO: we should probably use an atomic here. We'll just annotate away the TSAN error for now,
  // since the worst case is a slightly out-of-date log message, and not very likely.
  Mode mode = ANNOTATE_UNPROTECTED_READ(queue_state_.mode);
  return Substitute("T $0 P $1 [$2]: ",
                    tablet_id_,
                    local_peer_uuid_,
                    ModeToStr(mode));
}

string PeerMessageQueue::QueueState::ToString() const {
  return Format(
      "All replicated op: $0, Majority replicated op: $1, Committed index: $2, Last applied: $3, "
      "Last appended: $4, Current term: $5, Majority size: $6, State: $7, Mode: $8$9",
      /* 0 */ all_replicated_op_id,
      /* 1 */ majority_replicated_op_id,
      /* 2 */ committed_op_id,
      /* 3 */ last_applied_op_id,
      /* 4 */ last_appended,
      /* 5 */ current_term,
      /* 6 */ majority_size_,
      /* 7 */ StateToStr(state),
      /* 8 */ ModeToStr(mode),
      /* 9 */ active_config ? ", active raft config: " + active_config->ShortDebugString()67.8k : ""161k);
}

size_t PeerMessageQueue::LogCacheSize() {
  return log_cache_.BytesUsed();
}

size_t PeerMessageQueue::EvictLogCache(size_t bytes_to_evict) {
  return log_cache_.EvictThroughOp(std::numeric_limits<int64_t>::max(), bytes_to_evict);
}

Status PeerMessageQueue::FlushLogIndex() {
  return log_cache_.FlushIndex();
}

void PeerMessageQueue::TrackOperationsMemory(const OpIds& op_ids) {
  log_cache_.TrackOperationsMemory(op_ids);
}

Result<OpId> PeerMessageQueue::TEST_GetLastOpIdWithType(
    int64_t max_allowed_index, OperationType op_type) {
  return log_cache_.TEST_GetLastOpIdWithType(max_allowed_index, op_type);
}

Status ValidateFlags() {
  // Normally we would have used
  //   DEFINE_validator(rpc_throttle_threshold_bytes, &RpcThrottleThresholdBytesValidator);
  // right after defining the rpc_throttle_threshold_bytes flag. However, this leads to a segfault
  // in the LTO-enabled build, presumably due to indeterminate order of static initialization.
  // Instead, we invoke this function from master/tserver main() functions when static
  // initialization is already finished.
  if (!RpcThrottleThresholdBytesValidator(
      "rpc_throttle_threshold_bytes", FLAGS_rpc_throttle_threshold_bytes)) {
    return STATUS(InvalidArgument, "Flag validation failed");
  }

  return Status::OK();
}

}  // namespace consensus
}  // namespace yb

YugabyteDB (2.13.1.0-b60, 21121d69985fbf76aa6958d8f04a9bfa936293b5)

Coverage Report

Created: 2022-03-22 16:43