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|
/**
* Copyright (C) 2014 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <iosfwd>
#include <string>
#include "mongo/base/disallow_copying.h"
#include "mongo/db/repl/last_vote.h"
#include "mongo/db/repl/repl_set_heartbeat_response.h"
#include "mongo/db/repl/replication_coordinator.h"
#include "mongo/db/repl/update_position_args.h"
#include "mongo/db/server_options.h"
#include "mongo/stdx/functional.h"
#include "mongo/util/net/hostandport.h"
#include "mongo/util/time_support.h"
namespace mongo {
class Timestamp;
namespace repl {
class HeartbeatResponseAction;
class MemberData;
class OpTime;
class ReplSetHeartbeatArgs;
class ReplSetConfig;
class TagSubgroup;
struct MemberState;
// Maximum number of retries for a failed heartbeat.
const int kMaxHeartbeatRetries = 2;
/**
* Replication Topology Coordinator
*
* This object is responsible for managing the topology of the cluster.
* Tasks include consensus and leader election, chaining, and configuration management.
* Methods of this class should be non-blocking.
*/
class TopologyCoordinator {
MONGO_DISALLOW_COPYING(TopologyCoordinator);
public:
/**
* Type that denotes the role of a node in the replication protocol.
*
* The role is distinct from MemberState, in that it only deals with the
* roles a node plays in the basic protocol -- leader, follower and candidate.
* The mapping between MemberState and Role is complex -- several MemberStates
* map to the follower role, and MemberState::RS_SECONDARY maps to either
* follower or candidate roles, e.g.
*/
enum class Role { kLeader = 0, kFollower = 1, kCandidate = 2 };
struct Options {
// A sync source is re-evaluated after it lags behind further than this amount.
Seconds maxSyncSourceLagSecs{0};
// Whether or not this node is running as a config server.
ClusterRole clusterRole{ClusterRole::None};
};
/**
* Constructs a Topology Coordinator object.
**/
TopologyCoordinator(Options options);
~TopologyCoordinator();
/**
* Different modes a node can be in while still reporting itself as in state PRIMARY.
*
* Valid transitions:
*
* kNotLeader <----------------------------------
* | |
* | |
* | |
* v |
* kLeaderElect----- |
* | | |
* | | |
* v | |
* kMaster ------------------------- |
* | ^ | | |
* | | ------------------- | |
* | | | | | |
* v | v v v |
* kAttemptingStepDown----------->kSteppingDown |
* | | |
* | | |
* | | |
* ---------------------------------------------
*
*/
enum class LeaderMode {
kNotLeader, // This node is not currently a leader.
kLeaderElect, // This node has been elected leader, but can't yet accept writes.
kMaster, // This node reports ismaster:true and can accept writes.
kSteppingDown, // This node is in the middle of a (hb) stepdown that must complete.
kAttemptingStepDown, // This node is in the middle of a stepdown (cmd) that might fail.
};
////////////////////////////////////////////////////////////
//
// State inspection methods.
//
////////////////////////////////////////////////////////////
/**
* Gets the role of this member in the replication protocol.
*/
Role getRole() const;
/**
* Gets the MemberState of this member in the replica set.
*/
MemberState getMemberState() const;
/**
* Returns whether this node should be allowed to accept writes.
*/
bool canAcceptWrites() const;
/**
* Returns true if this node is in the process of stepping down. Note that this can be
* due to an unconditional stepdown that must succeed (for instance from learning about a new
* term) or due to a stepdown attempt that could fail (for instance from a stepdown cmd that
* could fail if not enough nodes are caught up).
*/
bool isSteppingDown() const;
/**
* Returns the address of the current sync source, or an empty HostAndPort if there is no
* current sync source.
*/
HostAndPort getSyncSourceAddress() const;
/**
* Retrieves a vector of HostAndPorts containing all nodes that are neither DOWN nor
* ourself.
*/
std::vector<HostAndPort> getMaybeUpHostAndPorts() const;
/**
* Gets the earliest time the current node will stand for election.
*/
Date_t getStepDownTime() const;
/**
* Gets the current value of the maintenance mode counter.
*/
int getMaintenanceCount() const;
/**
* Gets the latest term this member is aware of. If this member is the primary,
* it's the current term of the replica set.
*/
long long getTerm() const;
enum class UpdateTermResult { kAlreadyUpToDate, kTriggerStepDown, kUpdatedTerm };
////////////////////////////////////////////////////////////
//
// Basic state manipulation methods.
//
////////////////////////////////////////////////////////////
/**
* Sets the latest term this member is aware of to the higher of its current value and
* the value passed in as "term".
* Returns the result of setting the term value, or if a stepdown should be triggered.
*/
UpdateTermResult updateTerm(long long term, Date_t now);
/**
* Sets the index into the config used when we next choose a sync source
*/
void setForceSyncSourceIndex(int index);
enum class ChainingPreference { kAllowChaining, kUseConfiguration };
/**
* Chooses and sets a new sync source, based on our current knowledge of the world.
*/
HostAndPort chooseNewSyncSource(Date_t now,
const OpTime& lastOpTimeFetched,
ChainingPreference chainingPreference);
/**
* Suppresses selecting "host" as sync source until "until".
*/
void blacklistSyncSource(const HostAndPort& host, Date_t until);
/**
* Removes a single entry "host" from the list of potential sync sources which we
* have blacklisted, if it is supposed to be unblacklisted by "now".
*/
void unblacklistSyncSource(const HostAndPort& host, Date_t now);
/**
* Clears the list of potential sync sources we have blacklisted.
*/
void clearSyncSourceBlacklist();
/**
* Determines if a new sync source should be chosen, if a better candidate sync source is
* available. If the current sync source's last optime ("syncSourceLastOpTime" under
* protocolVersion 1, but pulled from the MemberData in protocolVersion 0) is more than
* _maxSyncSourceLagSecs behind any syncable source, this function returns true. If we are
* running in ProtocolVersion 1, our current sync source is not primary, has no sync source
* ("syncSourceHasSyncSource" is false), and only has data up to "myLastOpTime", returns true.
*
* "now" is used to skip over currently blacklisted sync sources.
*
* TODO (SERVER-27668): Make OplogQueryMetadata non-optional in mongodb 3.8.
*/
bool shouldChangeSyncSource(const HostAndPort& currentSource,
const rpc::ReplSetMetadata& replMetadata,
boost::optional<rpc::OplogQueryMetadata> oqMetadata,
Date_t now) const;
/**
* Checks whether we are a single node set and we are not in a stepdown period. If so,
* puts us into candidate mode, otherwise does nothing. This is used to ensure that
* nodes in a single node replset become primary again when their stepdown period ends.
*/
bool becomeCandidateIfStepdownPeriodOverAndSingleNodeSet(Date_t now);
/**
* Sets the earliest time the current node will stand for election to "newTime".
*
* Until this time, while the node may report itself as electable, it will not stand
* for election.
*/
void setElectionSleepUntil(Date_t newTime);
/**
* Sets the reported mode of this node to one of RS_SECONDARY, RS_STARTUP2, RS_ROLLBACK or
* RS_RECOVERING, when getRole() == Role::follower. This is the interface by which the
* applier changes the reported member state of the current node, and enables or suppresses
* electability of the current node. All modes but RS_SECONDARY indicate an unelectable
* follower state (one that cannot transition to candidate).
*/
void setFollowerMode(MemberState::MS newMode);
/**
* Scan the memberData and determine the highest last applied or last
* durable optime present on a majority of servers; set _lastCommittedOpTime to this
* new entry.
* Whether the last applied or last durable op time is used depends on whether
* the config getWriteConcernMajorityShouldJournal is set.
* Returns true if the _lastCommittedOpTime was changed.
*/
bool updateLastCommittedOpTime();
/**
* Updates _lastCommittedOpTime to be "committedOpTime" if it is more recent than the
* current last committed OpTime. Returns true if _lastCommittedOpTime is changed.
*/
bool advanceLastCommittedOpTime(const OpTime& committedOpTime);
/**
* Returns the OpTime of the latest majority-committed op known to this server.
*/
OpTime getLastCommittedOpTime() const;
/**
* Returns true if it's safe to transition to LeaderMode::kMaster.
*/
bool canCompleteTransitionToPrimary(long long termWhenDrainCompleted) const;
/**
* Called by the ReplicationCoordinator to signal that we have finished catchup and drain modes
* and are ready to fully become primary and start accepting writes.
* "firstOpTimeOfTerm" is a floor on the OpTimes this node will be allowed to consider committed
* for this tenure as primary. This prevents entries from before our election from counting as
* committed in our view, until our election (the "firstOpTimeOfTerm" op) has been committed.
* Returns PrimarySteppedDown if this node is no longer eligible to begin accepting writes.
*/
Status completeTransitionToPrimary(const OpTime& firstOpTimeOfTerm);
/**
* Adjusts the maintenance mode count by "inc".
*
* It is an error to call this method if getRole() does not return Role::follower.
* It is an error to allow the maintenance count to go negative.
*/
void adjustMaintenanceCountBy(int inc);
////////////////////////////////////////////////////////////
//
// Methods that prepare responses to command requests.
//
////////////////////////////////////////////////////////////
// produces a reply to a replSetSyncFrom command
void prepareSyncFromResponse(const HostAndPort& target,
BSONObjBuilder* response,
Status* result);
// produce a reply to a replSetFresh command
void prepareFreshResponse(const ReplicationCoordinator::ReplSetFreshArgs& args,
Date_t now,
BSONObjBuilder* response,
Status* result);
// produce a reply to a received electCmd
void prepareElectResponse(const ReplicationCoordinator::ReplSetElectArgs& args,
Date_t now,
BSONObjBuilder* response,
Status* result);
// produce a reply to a heartbeat
Status prepareHeartbeatResponse(Date_t now,
const ReplSetHeartbeatArgs& args,
const std::string& ourSetName,
ReplSetHeartbeatResponse* response);
// produce a reply to a V1 heartbeat
Status prepareHeartbeatResponseV1(Date_t now,
const ReplSetHeartbeatArgsV1& args,
const std::string& ourSetName,
ReplSetHeartbeatResponse* response);
struct ReplSetStatusArgs {
Date_t now;
unsigned selfUptime;
const OpTime& readConcernMajorityOpTime;
const BSONObj& initialSyncStatus;
};
// produce a reply to a status request
void prepareStatusResponse(const ReplSetStatusArgs& rsStatusArgs,
BSONObjBuilder* response,
Status* result);
// Produce a replSetUpdatePosition command to be sent to the node's sync source.
StatusWith<BSONObj> prepareReplSetUpdatePositionCommand(
OpTime currentCommittedSnapshotOpTime) const;
// produce a reply to an ismaster request. It is only valid to call this if we are a
// replset.
void fillIsMasterForReplSet(IsMasterResponse* response);
// Produce member data for the serverStatus command and diagnostic logging.
void fillMemberData(BSONObjBuilder* result);
enum class PrepareFreezeResponseResult { kNoAction, kElectSelf };
/**
* Produce a reply to a freeze request. Returns a PostMemberStateUpdateAction on success that
* may trigger state changes in the caller.
*/
StatusWith<PrepareFreezeResponseResult> prepareFreezeResponse(Date_t now,
int secs,
BSONObjBuilder* response);
////////////////////////////////////////////////////////////
//
// Methods for sending and receiving heartbeats,
// reconfiguring and handling the results of standing for
// election.
//
////////////////////////////////////////////////////////////
/**
* Updates the topology coordinator's notion of the replica set configuration.
*
* "newConfig" is the new configuration, and "selfIndex" is the index of this
* node's configuration information in "newConfig", or "selfIndex" is -1 to
* indicate that this node is not a member of "newConfig".
*
* newConfig.isInitialized() should be true, though implementations may accept
* configurations where this is not true, for testing purposes.
*/
void updateConfig(const ReplSetConfig& newConfig, int selfIndex, Date_t now);
/**
* Prepares a heartbeat request appropriate for sending to "target", assuming the
* current time is "now". "ourSetName" is used as the name for our replica set if
* the topology coordinator does not have a valid configuration installed.
*
* The returned pair contains proper arguments for a replSetHeartbeat command, and
* an amount of time to wait for the response.
*
* This call should be paired (with intervening network communication) with a call to
* processHeartbeatResponse for the same "target".
*/
std::pair<ReplSetHeartbeatArgs, Milliseconds> prepareHeartbeatRequest(
Date_t now, const std::string& ourSetName, const HostAndPort& target);
std::pair<ReplSetHeartbeatArgsV1, Milliseconds> prepareHeartbeatRequestV1(
Date_t now, const std::string& ourSetName, const HostAndPort& target);
/**
* Processes a heartbeat response from "target" that arrived around "now", having
* spent "networkRoundTripTime" millis on the network.
*
* Updates internal topology coordinator state, and returns instructions about what action
* to take next.
*
* If the next action indicates StartElection, the topology coordinator has transitioned to
* the "candidate" role, and will remain there until processWinElection or
* processLoseElection are called.
*
* If the next action indicates "StepDownSelf", the topology coordinator has transitioned
* to the "follower" role from "leader", and the caller should take any necessary actions
* to become a follower.
*
* If the next action indicates "StepDownRemotePrimary", the caller should take steps to
* cause the specified remote host to step down from primary to secondary.
*
* If the next action indicates "Reconfig", the caller should verify the configuration in
* hbResponse is acceptable, perform any other reconfiguration actions it must, and call
* updateConfig with the new configuration and the appropriate value for "selfIndex". It
* must also wrap up any outstanding elections (by calling processLoseElection or
* processWinElection) before calling updateConfig.
*
* This call should be paired (with intervening network communication) with a call to
* prepareHeartbeatRequest for the same "target".
*/
HeartbeatResponseAction processHeartbeatResponse(
Date_t now,
Milliseconds networkRoundTripTime,
const HostAndPort& target,
const StatusWith<ReplSetHeartbeatResponse>& hbResponse);
/**
* Returns whether or not at least 'numNodes' have reached the given opTime.
* "durablyWritten" indicates whether the operation has to be durably applied.
*/
bool haveNumNodesReachedOpTime(const OpTime& opTime, int numNodes, bool durablyWritten);
/**
* Returns whether or not at least one node matching the tagPattern has reached
* the given opTime.
* "durablyWritten" indicates whether the operation has to be durably applied.
*/
bool haveTaggedNodesReachedOpTime(const OpTime& opTime,
const ReplSetTagPattern& tagPattern,
bool durablyWritten);
/**
* Returns a vector of members that have applied the operation with OpTime 'op'.
* "durablyWritten" indicates whether the operation has to be durably applied.
* "skipSelf" means to exclude this node whether or not the op has been applied.
*/
std::vector<HostAndPort> getHostsWrittenTo(const OpTime& op,
bool durablyWritten,
bool skipSelf);
/**
* Marks a member as down from our perspective and returns a bool which indicates if we can no
* longer see a majority of the nodes and thus should step down.
*/
bool setMemberAsDown(Date_t now, const int memberIndex);
/**
* Goes through the memberData and determines which member that is currently live
* has the stalest (earliest) last update time. Returns (-1, Date_t::max()) if there are
* no other members.
*/
std::pair<int, Date_t> getStalestLiveMember() const;
/**
* Go through the memberData, and mark nodes which haven't been updated
* recently (within an election timeout) as "down". Returns a HeartbeatResponseAction, which
* will be StepDownSelf if we can no longer see a majority of the nodes, otherwise NoAction.
*/
HeartbeatResponseAction checkMemberTimeouts(Date_t now);
/**
* Set all nodes in memberData to not stale with a lastUpdate of "now".
*/
void resetAllMemberTimeouts(Date_t now);
/**
* Set all nodes in memberData that are present in member_set
* to not stale with a lastUpdate of "now".
*/
void resetMemberTimeouts(Date_t now, const stdx::unordered_set<HostAndPort>& member_set);
/*
* Returns the last optime that this node has applied, whether or not it has been journaled.
*/
OpTime getMyLastAppliedOpTime() const;
/*
* Sets the last optime that this node has applied, whether or not it has been journaled. Fails
* with an invariant if 'isRollbackAllowed' is false and we're attempting to set the optime
* backwards. The Date_t 'now' is used to track liveness; setting a node's applied optime
* updates its liveness information.
*/
void setMyLastAppliedOpTime(OpTime opTime, Date_t now, bool isRollbackAllowed);
/*
* Returns the last optime that this node has applied and journaled.
*/
OpTime getMyLastDurableOpTime() const;
/*
* Sets the last optime that this node has applied and journaled. Fails with an invariant if
* 'isRollbackAllowed' is false and we're attempting to set the optime backwards. The Date_t
* 'now' is used to track liveness; setting a node's durable optime updates its liveness
* information.
*/
void setMyLastDurableOpTime(OpTime opTime, Date_t now, bool isRollbackAllowed);
/*
* Sets the last optimes for a node, other than this node, based on the data from a
* replSetUpdatePosition command.
*
* Returns a Status if the position could not be set, false if the last optimes for the node
* did not change, or true if either the last applied or last durable optime did change.
*/
StatusWith<bool> setLastOptime(const UpdatePositionArgs::UpdateInfo& args,
Date_t now,
long long* configVersion);
/*
* Sets the last optimes for a slave node.
*
* Used only in master/slave replication.
*/
void setLastOptimeForSlave(const OID& rid, const OpTime& opTime, Date_t now);
/*
* Set the RID for this node.
*
* Used only in master/slave replication.
*/
void setMyRid(const OID& rid);
/**
* Process a handshake command, adding the slave to the member list if it isn't already there.
* Used only in master/slave mode
*/
Status processHandshake(const OID& rid, const HostAndPort& hostAndPort);
/**
* If getRole() == Role::candidate and this node has not voted too recently, updates the
* lastVote tracker and returns true. Otherwise, returns false.
*/
bool voteForMyself(Date_t now);
/**
* Sets lastVote to be for ourself in this term.
*/
void voteForMyselfV1();
/**
* Sets election id and election optime.
*/
void setElectionInfo(OID electionId, Timestamp electionOpTime);
/**
* Performs state updates associated with winning an election.
*
* It is an error to call this if the topology coordinator is not in candidate mode.
*
* Exactly one of either processWinElection or processLoseElection must be called if
* processHeartbeatResponse returns StartElection, to exit candidate mode.
*/
void processWinElection(OID electionId, Timestamp electionOpTime);
/**
* Performs state updates associated with losing an election.
*
* It is an error to call this if the topology coordinator is not in candidate mode.
*
* Exactly one of either processWinElection or processLoseElection must be called if
* processHeartbeatResponse returns StartElection, to exit candidate mode.
*/
void processLoseElection();
/**
* Readies the TopologyCoordinator for an attempt to stepdown that may fail. This is used
* when we receive a stepdown command (which can fail if not enough secondaries are caught up)
* to ensure that we never process more than one stepdown request at a time.
* Returns OK if it is safe to continue with the stepdown attempt, or returns:
* - NotMaster if this node is not a leader.
* - ConflictingOperationInProgess if this node is already processing a stepdown request of any
* kind.
*/
Status prepareForStepDownAttempt();
/**
* If this node is still attempting to process a stepdown attempt, aborts the attempt and
* returns this node to normal primary/master state. If this node has already completed
* stepping down or is now in the process of handling an unconditional stepdown, then this
* method does nothing.
*/
void abortAttemptedStepDownIfNeeded();
/**
* Tries to transition the coordinator from the leader role to the follower role.
*
* A step down succeeds based on the following conditions:
*
* C1. 'force' is true and now > waitUntil
*
* C2. A majority set of nodes, M, in the replica set have optimes greater than or
* equal to the last applied optime of the primary.
*
* C3. There exists at least one electable secondary node in the majority set M.
*
*
* If C1 is true, or if both C2 and C3 are true, then the stepdown occurs and this method
* returns true. If the conditions for successful stepdown aren't met yet, but waiting for more
* time to pass could make it succeed, returns false. If the whole stepdown attempt should be
* abandoned (for example because the time limit expired or because we've already stepped down),
* throws an exception.
* TODO(spencer): Unify with the finishUnconditionalStepDown() method.
*/
bool attemptStepDown(
long long termAtStart, Date_t now, Date_t waitUntil, Date_t stepDownUntil, bool force);
/**
* Returns whether it is safe for a stepdown attempt to complete, ignoring the 'force' argument.
* This is essentially checking conditions C2 and C3 as described in the comment to
* attemptStepDown().
*/
bool isSafeToStepDown();
/**
* Readies the TopologyCoordinator for stepdown. Returns false if we're already in the process
* of an unconditional step down. If we are in the middle of a stepdown command attempt when
* this is called then this unconditional stepdown will supersede the stepdown attempt, which
* will cause the stepdown to fail. When this returns true it must be followed by a call to
* finishUnconditionalStepDown() that is called when holding the global X lock.
*/
bool prepareForUnconditionalStepDown();
/**
* Sometimes a request to step down comes in (like via a heartbeat), but we don't have the
* global exclusive lock so we can't actually stepdown at that moment. When that happens
* we record that a stepdown request is pending (by calling prepareForUnconditionalStepDown())
* and schedule work to stepdown in the global X lock. This method is called after holding the
* global lock to perform the actual stepdown.
* TODO(spencer): Unify with the finishAttemptedStepDown() method.
*/
void finishUnconditionalStepDown();
/**
* Considers whether or not this node should stand for election, and returns true
* if the node has transitioned to candidate role as a result of the call.
*/
Status checkShouldStandForElection(Date_t now) const;
/**
* Set the outgoing heartbeat message from self
*/
void setMyHeartbeatMessage(const Date_t now, const std::string& s);
/**
* Prepares a ReplSetMetadata object describing the current term, primary, and lastOp
* information.
*/
rpc::ReplSetMetadata prepareReplSetMetadata(const OpTime& lastVisibleOpTime) const;
/**
* Prepares an OplogQueryMetadata object describing the current sync source, rbid, primary,
* lastOpApplied, and lastOpCommitted.
*/
rpc::OplogQueryMetadata prepareOplogQueryMetadata(int rbid) const;
/**
* Writes into 'output' all the information needed to generate a summary of the current
* replication state for use by the web interface.
*/
void summarizeAsHtml(ReplSetHtmlSummary* output);
/**
* Prepares a ReplSetRequestVotesResponse.
*/
void processReplSetRequestVotes(const ReplSetRequestVotesArgs& args,
ReplSetRequestVotesResponse* response);
/**
* Loads an initial LastVote document, which was read from local storage.
*
* Called only during replication startup. All other updates are done internally.
*/
void loadLastVote(const LastVote& lastVote);
/**
* Updates the current primary index.
*/
void setPrimaryIndex(long long primaryIndex);
/**
* Returns the current primary index.
*/
int getCurrentPrimaryIndex() const;
enum StartElectionReason {
kElectionTimeout,
kPriorityTakeover,
kStepUpRequest,
kCatchupTakeover
};
/**
* Transitions to the candidate role if the node is electable.
*/
Status becomeCandidateIfElectable(const Date_t now, StartElectionReason reason);
/**
* Updates the storage engine read committed support in the TopologyCoordinator options after
* creation.
*/
void setStorageEngineSupportsReadCommitted(bool supported);
/**
* Reset the booleans to record the last heartbeat restart.
*/
void restartHeartbeats();
/**
* Scans through all members that are 'up' and return the latest known optime, if we have
* received (successful or failed) heartbeats from all nodes since heartbeat restart.
*
* Returns boost::none if any node hasn't responded to a heartbeat since we last restarted
* heartbeats.
* Returns OpTime(Timestamp(0, 0), 0), the smallest OpTime in PV1, if other nodes are all down.
*/
boost::optional<OpTime> latestKnownOpTimeSinceHeartbeatRestart() const;
////////////////////////////////////////////////////////////
//
// Test support methods
//
////////////////////////////////////////////////////////////
// Changes _memberState to newMemberState. Only for testing.
void changeMemberState_forTest(const MemberState& newMemberState,
const Timestamp& electionTime = Timestamp(0, 0));
// Sets "_electionTime" to "newElectionTime". Only for testing.
void _setElectionTime(const Timestamp& newElectionTime);
// Sets _currentPrimaryIndex to the given index. Should only be used in unit tests!
// TODO(spencer): Remove this once we can easily call for an election in unit tests to
// set the current primary.
void _setCurrentPrimaryForTest(int primaryIndex);
// Returns _electionTime. Only used in unittests.
Timestamp getElectionTime() const;
// Returns _electionId. Only used in unittests.
OID getElectionId() const;
// Returns the name for a role. Only used in unittests.
static std::string roleToString(TopologyCoordinator::Role role);
private:
typedef int UnelectableReasonMask;
class PingStats;
enum UnelectableReason {
None = 0,
CannotSeeMajority = 1 << 0,
NotCloseEnoughToLatestOptime = 1 << 1,
ArbiterIAm = 1 << 2,
NotSecondary = 1 << 3,
NoPriority = 1 << 4,
StepDownPeriodActive = 1 << 5,
NoData = 1 << 6,
NotInitialized = 1 << 7,
VotedTooRecently = 1 << 8,
RefusesToStand = 1 << 9,
NotCloseEnoughToLatestForPriorityTakeover = 1 << 10,
NotFreshEnoughForCatchupTakeover = 1 << 11,
};
// Set what type of PRIMARY this node currently is.
void _setLeaderMode(LeaderMode mode);
// Returns the number of heartbeat pings which have occurred.
int _getTotalPings();
// Returns the current "ping" value for the given member by their address
Milliseconds _getPing(const HostAndPort& host);
// Determines if we will veto the member specified by "args.id".
// If we veto, the errmsg will be filled in with a reason
bool _shouldVetoMember(const ReplicationCoordinator::ReplSetFreshArgs& args,
const Date_t& now,
std::string* errmsg) const;
// Returns the index of the member with the matching id, or -1 if none match.
int _getMemberIndex(int id) const;
// Sees if a majority number of votes are held by members who are currently "up"
bool _aMajoritySeemsToBeUp() const;
// Checks if the node can see a healthy primary of equal or greater priority to the
// candidate. If so, returns the index of that node. Otherwise returns -1.
int _findHealthyPrimaryOfEqualOrGreaterPriority(const int candidateIndex) const;
// Is otherOpTime close enough (within 10 seconds) to the latest known optime to qualify
// for an election
bool _isOpTimeCloseEnoughToLatestToElect(const OpTime& otherOpTime) const;
// Is our optime close enough to the latest known optime to call for a priority takeover.
bool _amIFreshEnoughForPriorityTakeover() const;
// Is the primary node still in catchup mode and is our optime the latest
// known optime of all the up nodes.
bool _amIFreshEnoughForCatchupTakeover() const;
// Returns reason why "self" member is unelectable
UnelectableReasonMask _getMyUnelectableReason(const Date_t now,
StartElectionReason reason) const;
// Returns reason why memberIndex is unelectable
UnelectableReasonMask _getUnelectableReason(int memberIndex) const;
// Returns the nice text of why the node is unelectable
std::string _getUnelectableReasonString(UnelectableReasonMask ur) const;
// Return true if we are currently primary
bool _iAmPrimary() const;
// Scans through all members that are 'up' and return the latest known optime.
OpTime _latestKnownOpTime() const;
// Scans the electable set and returns the highest priority member index
int _getHighestPriorityElectableIndex(Date_t now) const;
// Returns true if "one" member is higher priority than "two" member
bool _isMemberHigherPriority(int memberOneIndex, int memberTwoIndex) const;
// Helper shortcut to self config
const MemberConfig& _selfConfig() const;
// Helper shortcut to self member data for const members.
const MemberData& _selfMemberData() const;
// Helper shortcut to self member data for non-const members.
MemberData& _selfMemberData();
// Index of self member in member data.
const int _selfMemberDataIndex() const;
/*
* Returns information we have on the state of the node identified by memberId. Returns
* nullptr if memberId is not found in the configuration.
*/
MemberData* _findMemberDataByMemberId(const int memberId);
/*
* Returns information we have on the state of the node identified by rid. Returns
* nullptr if rid is not found in the heartbeat data. This method is used only for
* master/slave replication.
*/
MemberData* _findMemberDataByRid(const OID rid);
// Returns NULL if there is no primary, or the MemberConfig* for the current primary
const MemberConfig* _currentPrimaryMember() const;
/**
* Performs updating "_currentPrimaryIndex" for processHeartbeatResponse(), and determines if an
* election or stepdown should commence.
* _updatePrimaryFromHBDataV1() is a simplified version of _updatePrimaryFromHBData() to be used
* when in ProtocolVersion1.
*/
HeartbeatResponseAction _updatePrimaryFromHBData(int updatedConfigIndex,
const MemberState& originalState,
Date_t now);
HeartbeatResponseAction _updatePrimaryFromHBDataV1(int updatedConfigIndex,
const MemberState& originalState,
Date_t now);
/**
* Updates _memberData based on the newConfig, ensuring that every member in the newConfig
* has an entry in _memberData. If any nodes in the newConfig are also present in
* _currentConfig, copies their heartbeat info into the corresponding entry in the updated
* _memberData vector.
*/
void _updateHeartbeatDataForReconfig(const ReplSetConfig& newConfig, int selfIndex, Date_t now);
/**
* Returns whether a stepdown attempt should be allowed to proceed. See the comment for
* attemptStepDown() for more details on the rules of when stepdown attempts succeed or fail.
*/
bool _canCompleteStepDownAttempt(Date_t now, Date_t waitUntil, bool force);
void _stepDownSelfAndReplaceWith(int newPrimary);
/**
* Looks up the provided member in the blacklist and returns true if the member's blacklist
* expire time is after 'now'. If the member is found but the expire time is before 'now',
* the function returns false. If the member is not found in the blacklist, the function
* returns false.
**/
bool _memberIsBlacklisted(const MemberConfig& memberConfig, Date_t now) const;
/**
* Returns true if we are a one-node replica set, we're the one member,
* we're electable, we're not in maintenance mode, and we are currently in followerMode
* SECONDARY.
*
* This is used to decide if we should transition to Role::candidate in a one-node replica set.
*/
bool _isElectableNodeInSingleNodeReplicaSet() const;
// This node's role in the replication protocol.
Role _role;
// This is a unique id that is generated and set each time we transition to PRIMARY, as the
// result of an election.
OID _electionId;
// The time at which the current PRIMARY was elected.
Timestamp _electionTime;
// This node's election term. The term is used as part of the consensus algorithm to elect
// and maintain one primary (leader) node in the cluster.
long long _term;
// the index of the member we currently believe is primary, if one exists, otherwise -1
int _currentPrimaryIndex;
// the hostandport we are currently syncing from
// empty if no sync source (we are primary, or we cannot connect to anyone yet)
HostAndPort _syncSource;
// These members are not chosen as sync sources for a period of time, due to connection
// issues with them
std::map<HostAndPort, Date_t> _syncSourceBlacklist;
// The next sync source to be chosen, requested via a replSetSyncFrom command
int _forceSyncSourceIndex;
// Options for this TopologyCoordinator
Options _options;
// "heartbeat message"
// sent in requestHeartbeat respond in field "hbm"
std::string _hbmsg;
Date_t _hbmsgTime; // when it was logged
// heartbeat msg to send to others; descriptive diagnostic info
std::string _getHbmsg(Date_t now) const;
int _selfIndex; // this node's index in _members and _currentConfig
ReplSetConfig _rsConfig; // The current config, including a vector of MemberConfigs
// Heartbeat, current applied/durable optime, and other state data for each member. It is
// guaranteed that this vector will be maintained in the same order as the MemberConfigs in
// _currentConfig, therefore the member config index can be used to index into this vector as
// well.
std::vector<MemberData> _memberData;
// Time when stepDown command expires
Date_t _stepDownUntil;
// A time before which this node will not stand for election.
// In protocol version 1, this is used to prevent running for election after seeing
// a new term.
Date_t _electionSleepUntil;
// OpTime of the latest committed operation.
OpTime _lastCommittedOpTime;
// OpTime representing our transition to PRIMARY and the start of our term.
// _lastCommittedOpTime cannot be set to an earlier OpTime.
OpTime _firstOpTimeOfMyTerm;
// The number of calls we have had to enter maintenance mode
int _maintenanceModeCalls;
// The sub-mode of follower that we are in. Legal values are RS_SECONDARY, RS_RECOVERING,
// RS_STARTUP2 (initial sync) and RS_ROLLBACK. Only meaningful if _role == Role::follower.
// Configured via setFollowerMode(). If the sub-mode is RS_SECONDARY, then the effective
// sub-mode is either RS_SECONDARY or RS_RECOVERING, depending on _maintenanceModeCalls.
// Rather than accesing this variable direclty, one should use the getMemberState() method,
// which computes the replica set node state on the fly.
MemberState::MS _followerMode;
// What type of PRIMARY this node currently is. Don't set this directly, call _setLeaderMode
// instead.
LeaderMode _leaderMode = LeaderMode::kNotLeader;
typedef std::map<HostAndPort, PingStats> PingMap;
// Ping stats for each member by HostAndPort;
PingMap _pings;
// Last vote info from the election
struct VoteLease {
static const Seconds leaseTime;
Date_t when;
int whoId = -1;
HostAndPort whoHostAndPort;
} _voteLease;
// V1 last vote info for elections
LastVote _lastVote{OpTime::kInitialTerm, -1};
enum class ReadCommittedSupport {
kUnknown,
kNo,
kYes,
};
// Whether or not the storage engine supports read committed.
ReadCommittedSupport _storageEngineSupportsReadCommitted{ReadCommittedSupport::kUnknown};
};
/**
* A PingStats object stores data about heartbeat attempts to a particular target node. Over the
* course of its lifetime, it may be used for multiple rounds of heartbeats. This allows for the
* collection of statistics like average heartbeat latency to a target. The heartbeat latency
* measurement it stores for each replica set member is an average weighted 80% to the old value,
* and 20% to the new value.
*
*/
class TopologyCoordinator::PingStats {
public:
/**
* Starts a new round of heartbeat attempts by transitioning to 'TRYING' and resetting the
* failure count. Also records that a new heartbeat request started at "now".
*/
void start(Date_t now);
/**
* Records that a heartbeat request completed successfully, and that "millis" milliseconds
* were spent for a single network roundtrip plus remote processing time.
*/
void hit(Milliseconds millis);
/**
* Records that a heartbeat request failed.
*/
void miss();
/**
* Gets the number of hit() calls.
*/
unsigned int getCount() const {
return hitCount;
}
/**
* Gets the weighted average round trip time for heartbeat messages to the target.
* Returns 0 if there have been no pings recorded yet.
*/
Milliseconds getMillis() const {
return averagePingTimeMs == UninitializedPingTime ? Milliseconds(0) : averagePingTimeMs;
}
/**
* Gets the date at which start() was last called, which is used to determine if
* a heartbeat should be retried or if the time limit has expired.
*/
Date_t getLastHeartbeatStartDate() const {
return _lastHeartbeatStartDate;
}
/**
* Returns true if the number of failed heartbeats for the most recent round of attempts has
* exceeded the max number of heartbeat retries.
*/
bool failed() const {
return _state == FAILED;
}
/**
* Returns true if a good heartbeat has been received for the most recent round of heartbeat
* attempts before the maximum number of retries has been exceeded. Returns false otherwise.
*/
bool succeeded() const {
return _state == SUCCEEDED;
}
/**
* Returns true if a heartbeat attempt is currently in progress and there are still retries
* left.
*/
bool trying() const {
return _state == TRYING;
}
/**
* Returns true if 'start' has never been called on this instance of PingStats. Otherwise
* returns false.
*/
bool uninitialized() const {
return _state == UNINITIALIZED;
}
/**
* Gets the number of retries left for this heartbeat attempt. Invalid to call if the current
* state is 'UNINITIALIZED'.
*/
int retriesLeft() const {
return kMaxHeartbeatRetries - _numFailuresSinceLastStart;
}
private:
/**
* Represents the current state of this PingStats object.
*
* At creation time, a PingStats object is in the 'UNINITIALIZED' state, and will remain so
* until the first heartbeat attempt is initiated. Heartbeat attempts are initiated by calls to
* 'start', which puts the object into 'TRYING' state. If all heartbeat retries are used up
* before receiving a good response, it will enter the 'FAILED' state. If a good heartbeat
* response is received before exceeding the maximum number of retries, the object enters the
* 'SUCCEEDED' state. From either the 'SUCCEEDED' or 'FAILED' state, the object can go back into
* 'TRYING' state, to begin a new heartbeat attempt. The following is a simple state transition
* table illustrating this behavior:
*
* UNINITIALIZED: [TRYING]
* TRYING: [SUCCEEDED, FAILED]
* SUCCEEDED: [TRYING]
* FAILED: [TRYING]
*
*/
enum HeartbeatState { UNINITIALIZED, TRYING, SUCCEEDED, FAILED };
// The current state of this PingStats object.
HeartbeatState _state = UNINITIALIZED;
// Represents the uninitialized value of a counter that should only ever be >=0 after
// initialization.
static constexpr int UninitializedCount{-1};
// The value of 'averagePingTimeMs' before any good heartbeats have been received.
static constexpr Milliseconds UninitializedPingTime{UninitializedCount};
// The number of successful heartbeats that have ever been received i.e. the total number of
// calls to 'PingStats::hit'.
unsigned int hitCount = 0;
// The running, weighted average round trip time for heartbeat messages to the target node.
// Weighted 80% to the old round trip ping time, and 20% to the new round trip ping time.
Milliseconds averagePingTimeMs = UninitializedPingTime;
// The time of the most recent call to 'PingStats::start'.
Date_t _lastHeartbeatStartDate;
// The number of failed heartbeat attempts since the most recent call to 'PingStats::start'.
int _numFailuresSinceLastStart = UninitializedCount;
};
//
// Convenience method for unittest code. Please use accessors otherwise.
//
std::ostream& operator<<(std::ostream& os, TopologyCoordinator::Role role);
std::ostream& operator<<(std::ostream& os, TopologyCoordinator::PrepareFreezeResponseResult result);
} // namespace repl
} // namespace mongo
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