Function checkBetterSingletons

fdbserver/ClusterController.actor.cpp:590–728

Checks if there exists a better process for each singleton (e.g. DD) compared to the process it is currently on. Note: there is a lot of extra logic here to only recruit the blob manager when gate is open. When adding new singletons, just follow the ratekeeper/data distributor examples.

// Note: there is a lot of extra logic here to only recruit the blob manager when gate is open.
// When adding new singletons, just follow the ratekeeper/data distributor examples.
void checkBetterSingletons(ClusterControllerData* self) {
	if (!self->masterProcessId.present() ||
	    self->db.serverInfo->get().recoveryState < RecoveryState::ACCEPTING_COMMITS) {
		return;
	}

	// note: this map doesn't consider pids used by existing singletons
	std::map<Optional<Standalone<StringRef>>, int> id_used = self->getUsedIds();

	// We prefer spreading out other roles more than separating singletons on their own process
	// so we artificially amplify the pid count for the processes used by non-singleton roles.
	// In other words, we make the processes used for other roles less desirable to be used
	// by singletons as well.
	for (auto& it : id_used) {
		it.second *= PID_USED_AMP_FOR_NON_SINGLETON;
	}

	// Try to find a new process for each singleton.
	WorkerDetails newRKWorker = findNewProcessForSingleton(self, ProcessClass::Ratekeeper, id_used);
	WorkerDetails newDDWorker = findNewProcessForSingleton(self, ProcessClass::DataDistributor, id_used);

	WorkerDetails newBMWorker;
	if (self->db.blobGranulesEnabled.get()) {
		newBMWorker = findNewProcessForSingleton(self, ProcessClass::BlobManager, id_used);
	}

	WorkerDetails newEKPWorker;
	if (SERVER_KNOBS->ENABLE_ENCRYPTION) {
		newEKPWorker = findNewProcessForSingleton(self, ProcessClass::EncryptKeyProxy, id_used);
	}

	// Find best possible fitnesses for each singleton.
	auto bestFitnessForRK = findBestFitnessForSingleton(self, newRKWorker, ProcessClass::Ratekeeper);
	auto bestFitnessForDD = findBestFitnessForSingleton(self, newDDWorker, ProcessClass::DataDistributor);

	ProcessClass::Fitness bestFitnessForBM;
	if (self->db.blobGranulesEnabled.get()) {
		bestFitnessForBM = findBestFitnessForSingleton(self, newBMWorker, ProcessClass::BlobManager);
	}

	ProcessClass::Fitness bestFitnessForEKP;
	if (SERVER_KNOBS->ENABLE_ENCRYPTION) {
		bestFitnessForEKP = findBestFitnessForSingleton(self, newEKPWorker, ProcessClass::EncryptKeyProxy);
	}

	auto& db = self->db.serverInfo->get();
	auto rkSingleton = RatekeeperSingleton(db.ratekeeper);
	auto ddSingleton = DataDistributorSingleton(db.distributor);
	BlobManagerSingleton bmSingleton(db.blobManager);
	EncryptKeyProxySingleton ekpSingleton(db.encryptKeyProxy);

	// Check if the singletons are healthy.
	// side effect: try to rerecruit the singletons to more optimal processes
	bool rkHealthy = isHealthySingleton<RatekeeperInterface>(
	    self, newRKWorker, rkSingleton, bestFitnessForRK, self->recruitingRatekeeperID);

	bool ddHealthy = isHealthySingleton<DataDistributorInterface>(
	    self, newDDWorker, ddSingleton, bestFitnessForDD, self->recruitingDistributorID);