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/**
* Copyright (C) 2020-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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.
*/
#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kDefault
#include "mongo/platform/basic.h"
#include "mongo/db/logical_time_validator.h"
#include "mongo/db/persistent_task_store.h"
#include "mongo/db/repl/replica_set_aware_service.h"
#include "mongo/db/repl/replication_coordinator.h"
#include "mongo/db/s/sharding_state.h"
#include "mongo/db/vector_clock_document_gen.h"
#include "mongo/db/vector_clock_mutable.h"
#include "mongo/executor/scoped_task_executor.h"
#include "mongo/logv2/log.h"
#include "mongo/s/grid.h"
namespace mongo {
namespace {
class VectorClockMongoD : public VectorClockMutable,
public ReplicaSetAwareService<VectorClockMongoD> {
VectorClockMongoD(const VectorClockMongoD&) = delete;
VectorClockMongoD& operator=(const VectorClockMongoD&) = delete;
public:
static VectorClockMongoD* get(ServiceContext* serviceContext);
VectorClockMongoD();
virtual ~VectorClockMongoD();
private:
// VectorClock methods implementation
ComponentSet _gossipOutInternal() const override;
ComponentSet _gossipInInternal() const override;
bool _permitRefreshDuringGossipOut() const override {
return false;
}
// VectorClockMutable methods implementation
SharedSemiFuture<void> waitForDurableConfigTime() override;
SharedSemiFuture<void> waitForDurableTopologyTime() override;
SharedSemiFuture<void> waitForDurable() override;
SharedSemiFuture<void> recover() override;
LogicalTime _tick(Component component, uint64_t nTicks) override;
void _tickTo(Component component, LogicalTime newTime) override;
// ReplicaSetAwareService methods implementation
void onStartup(OperationContext* opCtx) override {}
void onStepUpBegin(OperationContext* opCtx, long long term) override;
void onStepUpComplete(OperationContext* opCtx, long long term) override {}
void onStepDown() override;
void onBecomeArbiter() override;
/**
* Structure used as keys for the map of waiters for VectorClock durability.
*/
struct ComparableVectorTime {
bool operator<(const ComparableVectorTime& other) const {
return vt.configTime() < other.vt.configTime() ||
vt.topologyTime() < other.vt.topologyTime();
}
bool operator>(const ComparableVectorTime& other) const {
return vt.configTime() > other.vt.configTime() ||
vt.topologyTime() > other.vt.topologyTime();
}
bool operator==(const ComparableVectorTime& other) const {
return vt.configTime() == other.vt.configTime() &&
vt.topologyTime() == other.vt.topologyTime();
}
VectorTime vt;
};
/**
* The way the VectorClock durability works is by maintaining an `_queue` of callers, which wait
* for a particular VectorTime to become durable.
*
* When the queue is empty, there is no persistence activity going on. The first caller, who
* finds `_loopScheduled` to be false, will set it to true, indicating it will schedule the
* asynchronous persistence task. The asynchronous persistence task is effectively the following
* loop:
*
* while (!_queue.empty()) {
* timeToPersist = getTime();
* persistTime(timeToPersist);
* _durableTime = timeToPersist;
* // Notify entries in _queue, whose time is <= _durableTime and remove them
* }
*/
SharedSemiFuture<void> _enqueueWaiterAndScheduleLoopIfNeeded(stdx::unique_lock<Mutex> ul,
VectorTime time);
Future<void> _doWhileQueueNotEmptyOrError(ServiceContext* service);
// Protects the shared state below
Mutex _mutex = MONGO_MAKE_LATCH("VectorClockMongoD::_mutex");
// This value is incremented every time the node changes its role between primary and secondary
uint64_t _generation{0};
// If set to true, means that another operation already scheduled the `_queue` draining loop, if
// false it means that this operation must do it
bool _loopScheduled{false};
// This value is only boost::none once, just after the object is constructuted. From the moment,
// the first operation schedules the `_queue`-draining loop, it will be set to a future, which
// will be signaled when the previously-scheduled `_queue` draining loop completes.
boost::optional<Future<void>> _currentWhileLoop;
// If boost::none, means the durable time needs to be recovered from disk, otherwise contains
// the latest-known durable time
boost::optional<VectorTime> _durableTime;
// Queue ordered in increasing order of the VectorTimes, which are waiting to be persisted
using Queue = std::map<ComparableVectorTime, std::unique_ptr<SharedPromise<void>>>;
Queue _queue;
};
const auto vectorClockMongoDDecoration = ServiceContext::declareDecoration<VectorClockMongoD>();
const ReplicaSetAwareServiceRegistry::Registerer<VectorClockMongoD>
vectorClockMongoDServiceRegisterer("VectorClockMongoD-ReplicaSetAwareServiceRegistration");
const ServiceContext::ConstructorActionRegisterer vectorClockMongoDRegisterer(
"VectorClockMongoD-VectorClockRegistration",
{},
[](ServiceContext* service) {
VectorClockMongoD::registerVectorClockOnServiceContext(
service, &vectorClockMongoDDecoration(service));
},
{});
VectorClockMongoD* VectorClockMongoD::get(ServiceContext* serviceContext) {
return &vectorClockMongoDDecoration(serviceContext);
}
VectorClockMongoD::VectorClockMongoD() = default;
VectorClockMongoD::~VectorClockMongoD() = default;
void VectorClockMongoD::onStepUpBegin(OperationContext* opCtx, long long term) {
stdx::lock_guard lg(_mutex);
++_generation;
_durableTime.reset();
}
void VectorClockMongoD::onStepDown() {
stdx::lock_guard lg(_mutex);
++_generation;
_durableTime.reset();
}
void VectorClockMongoD::onBecomeArbiter() {
// The node has become an arbiter, hence will not need logical clock for external operations.
_disable();
if (auto validator = LogicalTimeValidator::get(_service)) {
validator->stopKeyManager();
}
}
SharedSemiFuture<void> VectorClockMongoD::waitForDurableConfigTime() {
auto time = getTime();
stdx::unique_lock ul(_mutex);
if (_durableTime && _durableTime->configTime() >= time.configTime())
return SharedSemiFuture<void>();
return _enqueueWaiterAndScheduleLoopIfNeeded(std::move(ul), std::move(time));
}
SharedSemiFuture<void> VectorClockMongoD::waitForDurableTopologyTime() {
auto time = getTime();
stdx::unique_lock ul(_mutex);
if (_durableTime && _durableTime->topologyTime() >= time.topologyTime())
return SharedSemiFuture<void>();
return _enqueueWaiterAndScheduleLoopIfNeeded(std::move(ul), std::move(time));
}
SharedSemiFuture<void> VectorClockMongoD::waitForDurable() {
auto time = getTime();
stdx::unique_lock ul(_mutex);
if (_durableTime && _durableTime->configTime() >= time.configTime() &&
_durableTime->topologyTime() >= time.topologyTime())
return SharedSemiFuture<void>();
return _enqueueWaiterAndScheduleLoopIfNeeded(std::move(ul), std::move(time));
}
SharedSemiFuture<void> VectorClockMongoD::recover() {
stdx::unique_lock ul(_mutex);
if (_durableTime)
return SharedSemiFuture<void>();
return _enqueueWaiterAndScheduleLoopIfNeeded(std::move(ul), VectorTime());
}
SharedSemiFuture<void> VectorClockMongoD::_enqueueWaiterAndScheduleLoopIfNeeded(
stdx::unique_lock<Mutex> ul, VectorTime time) {
auto [it, unusedEmplaced] =
_queue.try_emplace({std::move(time)}, std::make_unique<SharedPromise<void>>());
if (!_loopScheduled) {
_loopScheduled = true;
auto joinPreviousLoop(_currentWhileLoop ? std::move(*_currentWhileLoop)
: Future<void>::makeReady());
_currentWhileLoop.emplace(std::move(joinPreviousLoop).onCompletion([this](auto) {
return _doWhileQueueNotEmptyOrError(vectorClockMongoDDecoration.owner(this));
}));
}
return it->second->getFuture();
}
Future<void> VectorClockMongoD::_doWhileQueueNotEmptyOrError(ServiceContext* service) {
auto [p, f] = makePromiseFuture<std::pair<uint64_t, VectorTime>>();
auto future = std::move(f)
.then([this](std::pair<uint64_t, VectorTime> newDurableTime) {
stdx::unique_lock ul(_mutex);
uassert(ErrorCodes::InterruptedDueToReplStateChange,
"VectorClock failed to persist due to stepdown",
newDurableTime.first == _generation);
_durableTime.emplace(newDurableTime.second);
ComparableVectorTime time{*_durableTime};
std::vector<Queue::value_type::second_type> promises;
for (auto it = _queue.begin(); it != _queue.end();) {
if (it->first > time)
break;
promises.emplace_back(std::move(it->second));
it = _queue.erase(it);
}
ul.unlock();
// Make sure the VectorClock advances at least up to the just recovered
// durable time
_advanceTime({newDurableTime.second.clusterTime(),
newDurableTime.second.configTime(),
newDurableTime.second.topologyTime()});
for (auto& p : promises)
p->emplaceValue();
})
.onError([this](Status status) {
stdx::unique_lock ul(_mutex);
std::vector<Queue::value_type::second_type> promises;
for (auto it = _queue.begin(); it != _queue.end();) {
promises.emplace_back(std::move(it->second));
it = _queue.erase(it);
}
ul.unlock();
for (auto& p : promises)
p->setError(status);
})
.onCompletion([this, service](auto) {
{
stdx::lock_guard lg(_mutex);
if (_queue.empty()) {
_loopScheduled = false;
return Future<void>::makeReady();
}
}
return _doWhileQueueNotEmptyOrError(service);
});
// Blocking work to recover and/or persist the current vector time
ExecutorFuture<void>(Grid::get(service)->getExecutorPool()->getFixedExecutor())
.then([this, service] {
auto [generation, mustRecoverDurableTime] = [&] {
stdx::lock_guard lg(_mutex);
return std::make_pair(_generation, !_durableTime);
}();
ThreadClient tc("VectorClockStateOperation", service);
{
stdx::lock_guard<Client> lk(*tc.get());
tc->setSystemOperationKillableByStepdown(lk);
}
const auto opCtxHolder = tc->makeOperationContext();
auto* const opCtx = opCtxHolder.get();
if (mustRecoverDurableTime) {
VectorClockDocument durableVectorClock;
PersistentTaskStore<VectorClockDocument> store(
NamespaceString::kVectorClockNamespace);
store.forEach(
opCtx,
QUERY(VectorClockDocument::k_idFieldName << durableVectorClock.get_id()),
[&, numDocsFound = 0](const auto& doc) mutable {
invariant(++numDocsFound == 1);
durableVectorClock = doc;
return true;
});
return std::make_pair(
generation,
VectorTime({LogicalTime(Timestamp(0)),
LogicalTime(durableVectorClock.getConfigTime()),
LogicalTime(durableVectorClock.getTopologyTime())}));
} else {
auto vectorTime = getTime();
auto* const replCoord = repl::ReplicationCoordinator::get(opCtx);
if (replCoord->getMemberState().primary()) {
// Persist as primary
const VectorClockDocument vcd(vectorTime.configTime().asTimestamp(),
vectorTime.topologyTime().asTimestamp());
PersistentTaskStore<VectorClockDocument> store(
NamespaceString::kVectorClockNamespace);
store.upsert(opCtx,
QUERY(VectorClockDocument::k_idFieldName << vcd.get_id()),
vcd.toBSON(),
WriteConcerns::kMajorityWriteConcern);
} else {
// Persist as secondary, by asking the primary
auto const shardingState = ShardingState::get(opCtx);
invariant(shardingState->enabled());
auto selfShard = uassertStatusOK(Grid::get(opCtx)->shardRegistry()->getShard(
opCtx, shardingState->shardId()));
auto cmdResponse = uassertStatusOK(selfShard->runCommandWithFixedRetryAttempts(
opCtx,
ReadPreferenceSetting{ReadPreference::PrimaryOnly},
NamespaceString::kVectorClockNamespace.toString(),
BSON("_vectorClockPersist" << 1),
Seconds{30},
Shard::RetryPolicy::kIdempotent));
uassertStatusOK(cmdResponse.commandStatus);
}
return std::make_pair(generation, vectorTime);
}
})
.getAsync([this, promise = std::move(p)](
StatusWith<std::pair<uint64_t, VectorTime>> swResult) mutable {
promise.setFromStatusWith(std::move(swResult));
});
return future;
}
VectorClock::ComponentSet VectorClockMongoD::_gossipOutInternal() const {
VectorClock::ComponentSet toGossip{Component::ClusterTime};
if (serverGlobalParams.clusterRole == ClusterRole::ShardServer ||
serverGlobalParams.clusterRole == ClusterRole::ConfigServer) {
toGossip.insert(Component::ConfigTime);
toGossip.insert(Component::TopologyTime);
}
return toGossip;
}
VectorClock::ComponentSet VectorClockMongoD::_gossipInInternal() const {
VectorClock::ComponentSet toGossip{Component::ClusterTime};
if (serverGlobalParams.clusterRole == ClusterRole::ShardServer) {
toGossip.insert(Component::ConfigTime);
toGossip.insert(Component::TopologyTime);
}
return toGossip;
}
LogicalTime VectorClockMongoD::_tick(Component component, uint64_t nTicks) {
if (component == Component::ClusterTime) {
// Although conceptually ClusterTime can only be ticked when a mongod is able to take writes
// (ie. primary, or standalone), this is handled at a higher layer.
//
// ClusterTime is ticked when replacing zero-valued Timestamps with the current time, which
// is usually but not necessarily associated with writes.
//
// ClusterTime is ticked after winning an election, while persisting the stepUp to the
// oplog, which is slightly before the repl state is changed to primary.
//
// As such, ticking ClusterTime is not restricted here based on repl state.
return _advanceComponentTimeByTicks(component, nTicks);
}
// tick is not permitted in other circumstances.
MONGO_UNREACHABLE;
}
void VectorClockMongoD::_tickTo(Component component, LogicalTime newTime) {
if (component == Component::ClusterTime) {
// The ClusterTime is allowed to tickTo in certain very limited and trusted cases (eg.
// initializing based on oplog timestamps), so we have to allow it here.
_advanceComponentTimeTo(component, std::move(newTime));
return;
}
if (component == Component::ConfigTime &&
serverGlobalParams.clusterRole == ClusterRole::ConfigServer) {
_advanceComponentTimeTo(component, std::move(newTime));
return;
}
if (component == Component::TopologyTime &&
serverGlobalParams.clusterRole == ClusterRole::ConfigServer) {
_advanceComponentTimeTo(component, std::move(newTime));
return;
}
// tickTo is not permitted in other circumstances.
MONGO_UNREACHABLE;
}
} // namespace
} // namespace mongo
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