foundationdb/fdbserver/Ratekeeper.actor.cpp

/*
 * Ratekeeper.actor.cpp
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2022 Apple Inc. and the FoundationDB project authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "fdbserver/DataDistribution.actor.h"
#include "fdbserver/Ratekeeper.h"
#include "fdbserver/TagThrottler.h"
#include "fdbserver/WaitFailure.h"

#include "flow/actorcompiler.h" // must be last include

const char* limitReasonName[] = { "workload",
	                              "storage_server_write_queue_size",
	                              "storage_server_write_bandwidth_mvcc",
	                              "storage_server_readable_behind",
	                              "log_server_mvcc_write_bandwidth",
	                              "log_server_write_queue",
	                              "storage_server_min_free_space",
	                              "storage_server_min_free_space_ratio",
	                              "log_server_min_free_space",
	                              "log_server_min_free_space_ratio",
	                              "storage_server_durability_lag",
	                              "storage_server_list_fetch_failed" };
static_assert(sizeof(limitReasonName) / sizeof(limitReasonName[0]) == limitReason_t_end, "limitReasonDesc table size");

int limitReasonEnd = limitReason_t_end;

// NOTE: This has a corresponding table in Script.cs (see RatekeeperReason graph)
// IF UPDATING THIS ARRAY, UPDATE SCRIPT.CS!
const char* limitReasonDesc[] = { "Workload or read performance.",
	                              "Storage server performance (storage queue).",
	                              "Storage server MVCC memory.",
	                              "Storage server version falling behind.",
	                              "Log server MVCC memory.",
	                              "Storage server performance (log queue).",
	                              "Storage server running out of space (approaching 100MB limit).",
	                              "Storage server running out of space (approaching 5% limit).",
	                              "Log server running out of space (approaching 100MB limit).",
	                              "Log server running out of space (approaching 5% limit).",
	                              "Storage server durable version falling behind.",
	                              "Unable to fetch storage server list." };

static_assert(sizeof(limitReasonDesc) / sizeof(limitReasonDesc[0]) == limitReason_t_end, "limitReasonDesc table size");

ACTOR static Future<Void> splitError(Future<Void> in, Promise<Void> errOut) {
	try {
		wait(in);
		return Void();
	} catch (Error& e) {
		if (e.code() != error_code_actor_cancelled && !errOut.isSet())
			errOut.sendError(e);
		throw;
	}
}

class RatekeeperImpl {
public:
	ACTOR static Future<Void> configurationMonitor(Ratekeeper* self) {
		loop {
			state ReadYourWritesTransaction tr(self->db);

			loop {
				try {
					tr.setOption(FDBTransactionOptions::ACCESS_SYSTEM_KEYS);
					tr.setOption(FDBTransactionOptions::PRIORITY_SYSTEM_IMMEDIATE);
					RangeResult results = wait(tr.getRange(configKeys, CLIENT_KNOBS->TOO_MANY));
					ASSERT(!results.more && results.size() < CLIENT_KNOBS->TOO_MANY);

					self->configuration.fromKeyValues((VectorRef<KeyValueRef>)results);

					state Future<Void> watchFuture =
					    tr.watch(moveKeysLockOwnerKey) || tr.watch(excludedServersVersionKey) ||
					    tr.watch(failedServersVersionKey) || tr.watch(excludedLocalityVersionKey) ||
					    tr.watch(failedLocalityVersionKey);
					wait(tr.commit());
					wait(watchFuture);
					break;
				} catch (Error& e) {
					wait(tr.onError(e));
				}
			}
		}
	}

	ACTOR static Future<Void> monitorServerListChange(
	    Ratekeeper* self,
	    PromiseStream<std::pair<UID, Optional<StorageServerInterface>>> serverChanges) {
		state std::map<UID, StorageServerInterface> oldServers;
		state Transaction tr(self->db);

		loop {
			try {
				if (now() - self->lastSSListFetchedTimestamp > 2 * SERVER_KNOBS->SERVER_LIST_DELAY) {
					TraceEvent(SevWarnAlways, "RatekeeperGetSSListLongLatency", self->id)
					    .detail("Latency", now() - self->lastSSListFetchedTimestamp);
				}
				tr.setOption(FDBTransactionOptions::PRIORITY_SYSTEM_IMMEDIATE);
				std::vector<std::pair<StorageServerInterface, ProcessClass>> results =
				    wait(getServerListAndProcessClasses(&tr));
				self->lastSSListFetchedTimestamp = now();

				std::map<UID, StorageServerInterface> newServers;
				for (const auto& [ssi, _] : results) {
					const UID serverId = ssi.id();
					newServers[serverId] = ssi;

					if (oldServers.count(serverId)) {
						if (ssi.getValue.getEndpoint() != oldServers[serverId].getValue.getEndpoint()) {
							serverChanges.send(std::make_pair(serverId, Optional<StorageServerInterface>(ssi)));
						}
						oldServers.erase(serverId);
					} else {
						serverChanges.send(std::make_pair(serverId, Optional<StorageServerInterface>(ssi)));
					}
				}

				for (const auto& it : oldServers) {
					serverChanges.send(std::make_pair(it.first, Optional<StorageServerInterface>()));
				}

				oldServers.swap(newServers);
				tr = Transaction(self->db);
				wait(delay(SERVER_KNOBS->SERVER_LIST_DELAY));
			} catch (Error& e) {
				TraceEvent("RatekeeperGetSSListError", self->id).error(e).suppressFor(1.0);
				wait(tr.onError(e));
			}
		}
	}

	ACTOR static Future<Void> trackStorageServerQueueInfo(Ratekeeper* self, StorageServerInterface ssi) {
		self->storageQueueInfo.insert(mapPair(ssi.id(), StorageQueueInfo(ssi.id(), ssi.locality)));
		state Map<UID, StorageQueueInfo>::iterator myQueueInfo = self->storageQueueInfo.find(ssi.id());
		TraceEvent("RkTracking", self->id)
		    .detail("StorageServer", ssi.id())
		    .detail("Locality", ssi.locality.toString());
		try {
			loop {
				ErrorOr<StorageQueuingMetricsReply> reply = wait(ssi.getQueuingMetrics.getReplyUnlessFailedFor(
				    StorageQueuingMetricsRequest(), 0, 0)); // SOMEDAY: or tryGetReply?
				if (reply.present()) {
					myQueueInfo->value.valid = true;
					myQueueInfo->value.prevReply = myQueueInfo->value.lastReply;
					myQueueInfo->value.lastReply = reply.get();
					if (myQueueInfo->value.prevReply.instanceID != reply.get().instanceID) {
						myQueueInfo->value.smoothDurableBytes.reset(reply.get().bytesDurable);
						myQueueInfo->value.verySmoothDurableBytes.reset(reply.get().bytesDurable);
						myQueueInfo->value.smoothInputBytes.reset(reply.get().bytesInput);
						myQueueInfo->value.smoothFreeSpace.reset(reply.get().storageBytes.available);
						myQueueInfo->value.smoothTotalSpace.reset(reply.get().storageBytes.total);
						myQueueInfo->value.smoothDurableVersion.reset(reply.get().durableVersion);
						myQueueInfo->value.smoothLatestVersion.reset(reply.get().version);
					} else {
						self->smoothTotalDurableBytes.addDelta(reply.get().bytesDurable -
						                                       myQueueInfo->value.prevReply.bytesDurable);
						myQueueInfo->value.smoothDurableBytes.setTotal(reply.get().bytesDurable);
						myQueueInfo->value.verySmoothDurableBytes.setTotal(reply.get().bytesDurable);
						myQueueInfo->value.smoothInputBytes.setTotal(reply.get().bytesInput);
						myQueueInfo->value.smoothFreeSpace.setTotal(reply.get().storageBytes.available);
						myQueueInfo->value.smoothTotalSpace.setTotal(reply.get().storageBytes.total);
						myQueueInfo->value.smoothDurableVersion.setTotal(reply.get().durableVersion);
						myQueueInfo->value.smoothLatestVersion.setTotal(reply.get().version);
					}

					myQueueInfo->value.busiestReadTag = reply.get().busiestTag;
					myQueueInfo->value.busiestReadTagFractionalBusyness = reply.get().busiestTagFractionalBusyness;
					myQueueInfo->value.busiestReadTagRate = reply.get().busiestTagRate;
				} else {
					if (myQueueInfo->value.valid) {
						TraceEvent("RkStorageServerDidNotRespond", self->id).detail("StorageServer", ssi.id());
					}
					myQueueInfo->value.valid = false;
				}

				wait(delayJittered(SERVER_KNOBS->METRIC_UPDATE_RATE) &&
				     IFailureMonitor::failureMonitor().onStateEqual(ssi.getQueuingMetrics.getEndpoint(),
				                                                    FailureStatus(false)));
			}
		} catch (...) {
			// including cancellation
			self->storageQueueInfo.erase(myQueueInfo);
			throw;
		}
	}

	ACTOR static Future<Void> trackTLogQueueInfo(Ratekeeper* self, TLogInterface tli) {
		self->tlogQueueInfo.insert(mapPair(tli.id(), TLogQueueInfo(tli.id())));
		state Map<UID, TLogQueueInfo>::iterator myQueueInfo = self->tlogQueueInfo.find(tli.id());
		TraceEvent("RkTracking", self->id).detail("TransactionLog", tli.id());
		try {
			loop {
				ErrorOr<TLogQueuingMetricsReply> reply = wait(tli.getQueuingMetrics.getReplyUnlessFailedFor(
				    TLogQueuingMetricsRequest(), 0, 0)); // SOMEDAY: or tryGetReply?
				if (reply.present()) {
					myQueueInfo->value.valid = true;
					myQueueInfo->value.prevReply = myQueueInfo->value.lastReply;
					myQueueInfo->value.lastReply = reply.get();
					if (myQueueInfo->value.prevReply.instanceID != reply.get().instanceID) {
						myQueueInfo->value.smoothDurableBytes.reset(reply.get().bytesDurable);
						myQueueInfo->value.verySmoothDurableBytes.reset(reply.get().bytesDurable);
						myQueueInfo->value.smoothInputBytes.reset(reply.get().bytesInput);
						myQueueInfo->value.smoothFreeSpace.reset(reply.get().storageBytes.available);
						myQueueInfo->value.smoothTotalSpace.reset(reply.get().storageBytes.total);
					} else {
						self->smoothTotalDurableBytes.addDelta(reply.get().bytesDurable -
						                                       myQueueInfo->value.prevReply.bytesDurable);
						myQueueInfo->value.smoothDurableBytes.setTotal(reply.get().bytesDurable);
						myQueueInfo->value.verySmoothDurableBytes.setTotal(reply.get().bytesDurable);
						myQueueInfo->value.smoothInputBytes.setTotal(reply.get().bytesInput);
						myQueueInfo->value.smoothFreeSpace.setTotal(reply.get().storageBytes.available);
						myQueueInfo->value.smoothTotalSpace.setTotal(reply.get().storageBytes.total);
					}
				} else {
					if (myQueueInfo->value.valid) {
						TraceEvent("RkTLogDidNotRespond", self->id).detail("TransactionLog", tli.id());
					}
					myQueueInfo->value.valid = false;
				}

				wait(delayJittered(SERVER_KNOBS->METRIC_UPDATE_RATE) &&
				     IFailureMonitor::failureMonitor().onStateEqual(tli.getQueuingMetrics.getEndpoint(),
				                                                    FailureStatus(false)));
			}
		} catch (...) {
			// including cancellation
			self->tlogQueueInfo.erase(myQueueInfo);
			throw;
		}
	}

	ACTOR static Future<Void> trackEachStorageServer(
	    Ratekeeper* self,
	    FutureStream<std::pair<UID, Optional<StorageServerInterface>>> serverChanges) {
		state Map<UID, Future<Void>> actors;
		state Promise<Void> err;
		loop choose {
			when(state std::pair<UID, Optional<StorageServerInterface>> change = waitNext(serverChanges)) {
				wait(delay(0)); // prevent storageServerTracker from getting cancelled while on the call stack
				if (change.second.present()) {
					if (!change.second.get().isTss()) {
						auto& a = actors[change.first];
						a = Future<Void>();
						a = splitError(trackStorageServerQueueInfo(self, change.second.get()), err);
					}
				} else
					actors.erase(change.first);
			}
			when(wait(err.getFuture())) {}
		}
	}

	ACTOR static Future<Void> monitorThrottlingChanges(Ratekeeper* self) {
		wait(self->tagThrottler->monitorThrottlingChanges());
		return Void();
	}

	ACTOR static Future<Void> run(RatekeeperInterface rkInterf, Reference<AsyncVar<ServerDBInfo> const> dbInfo) {
		state Ratekeeper self(rkInterf.id(), openDBOnServer(dbInfo, TaskPriority::DefaultEndpoint, LockAware::True));
		state Future<Void> timeout = Void();
		state std::vector<Future<Void>> tlogTrackers;
		state std::vector<TLogInterface> tlogInterfs;
		state Promise<Void> err;
		state Future<Void> collection = actorCollection(self.addActor.getFuture());

		TraceEvent("RatekeeperStarting", rkInterf.id());
		self.addActor.send(waitFailureServer(rkInterf.waitFailure.getFuture()));
		self.addActor.send(self.configurationMonitor());

		PromiseStream<std::pair<UID, Optional<StorageServerInterface>>> serverChanges;
		self.addActor.send(self.monitorServerListChange(serverChanges));
		self.addActor.send(self.trackEachStorageServer(serverChanges.getFuture()));
		self.addActor.send(traceRole(Role::RATEKEEPER, rkInterf.id()));

		self.addActor.send(self.monitorThrottlingChanges());
		Ratekeeper* selfPtr = &self; // let flow compiler capture self
		self.addActor.send(recurring([selfPtr]() { selfPtr->refreshStorageServerCommitCost(); },
		                             SERVER_KNOBS->TAG_MEASUREMENT_INTERVAL));

		TraceEvent("RkTLogQueueSizeParameters", rkInterf.id())
		    .detail("Target", SERVER_KNOBS->TARGET_BYTES_PER_TLOG)
		    .detail("Spring", SERVER_KNOBS->SPRING_BYTES_TLOG)
		    .detail(
		        "Rate",
		        (SERVER_KNOBS->TARGET_BYTES_PER_TLOG - SERVER_KNOBS->SPRING_BYTES_TLOG) /
		            ((((double)SERVER_KNOBS->MAX_READ_TRANSACTION_LIFE_VERSIONS) / SERVER_KNOBS->VERSIONS_PER_SECOND) +
		             2.0));

		TraceEvent("RkStorageServerQueueSizeParameters", rkInterf.id())
		    .detail("Target", SERVER_KNOBS->TARGET_BYTES_PER_STORAGE_SERVER)
		    .detail("Spring", SERVER_KNOBS->SPRING_BYTES_STORAGE_SERVER)
		    .detail("EBrake", SERVER_KNOBS->STORAGE_HARD_LIMIT_BYTES)
		    .detail(
		        "Rate",
		        (SERVER_KNOBS->TARGET_BYTES_PER_STORAGE_SERVER - SERVER_KNOBS->SPRING_BYTES_STORAGE_SERVER) /
		            ((((double)SERVER_KNOBS->MAX_READ_TRANSACTION_LIFE_VERSIONS) / SERVER_KNOBS->VERSIONS_PER_SECOND) +
		             2.0));

		tlogInterfs = dbInfo->get().logSystemConfig.allLocalLogs();
		tlogTrackers.reserve(tlogInterfs.size());
		for (int i = 0; i < tlogInterfs.size(); i++) {
			tlogTrackers.push_back(splitError(self.trackTLogQueueInfo(tlogInterfs[i]), err));
		}

		self.remoteDC = dbInfo->get().logSystemConfig.getRemoteDcId();

		try {
			state bool lastLimited = false;
			loop choose {
				when(wait(timeout)) {
					self.updateRate(&self.normalLimits);
					self.updateRate(&self.batchLimits);

					lastLimited = self.smoothReleasedTransactions.smoothRate() >
					              SERVER_KNOBS->LAST_LIMITED_RATIO * self.batchLimits.tpsLimit;
					double tooOld = now() - 1.0;
					for (auto p = self.grvProxyInfo.begin(); p != self.grvProxyInfo.end();) {
						if (p->second.lastUpdateTime < tooOld)
							p = self.grvProxyInfo.erase(p);
						else
							++p;
					}
					timeout = delayJittered(SERVER_KNOBS->METRIC_UPDATE_RATE);
				}
				when(GetRateInfoRequest req = waitNext(rkInterf.getRateInfo.getFuture())) {
					GetRateInfoReply reply;

					auto& p = self.grvProxyInfo[req.requesterID];
					//TraceEvent("RKMPU", req.requesterID).detail("TRT", req.totalReleasedTransactions).detail("Last", p.totalTransactions).detail("Delta", req.totalReleasedTransactions - p.totalTransactions);
					if (p.totalTransactions > 0) {
						self.smoothReleasedTransactions.addDelta(req.totalReleasedTransactions - p.totalTransactions);

						for (auto const& [tag, count] : req.throttledTagCounts) {
							self.tagThrottler->addRequests(tag, count);
						}
					}
					if (p.batchTransactions > 0) {
						self.smoothBatchReleasedTransactions.addDelta(req.batchReleasedTransactions -
						                                              p.batchTransactions);
					}

					p.totalTransactions = req.totalReleasedTransactions;
					p.batchTransactions = req.batchReleasedTransactions;
					p.lastUpdateTime = now();

					reply.transactionRate = self.normalLimits.tpsLimit / self.grvProxyInfo.size();
					reply.batchTransactionRate = self.batchLimits.tpsLimit / self.grvProxyInfo.size();
					reply.leaseDuration = SERVER_KNOBS->METRIC_UPDATE_RATE;

					if (p.lastThrottledTagChangeId != self.tagThrottler->getThrottledTagChangeId() ||
					    now() > p.lastTagPushTime + SERVER_KNOBS->TAG_THROTTLE_PUSH_INTERVAL) {
						p.lastThrottledTagChangeId = self.tagThrottler->getThrottledTagChangeId();
						p.lastTagPushTime = now();

						reply.throttledTags = self.tagThrottler->getClientRates();
						bool returningTagsToProxy =
						    reply.throttledTags.present() && reply.throttledTags.get().size() > 0;
						TEST(returningTagsToProxy); // Returning tag throttles to a proxy
					}

					reply.healthMetrics.update(self.healthMetrics, true, req.detailed);
					reply.healthMetrics.tpsLimit = self.normalLimits.tpsLimit;
					reply.healthMetrics.batchLimited = lastLimited;

					req.reply.send(reply);
				}
				when(HaltRatekeeperRequest req = waitNext(rkInterf.haltRatekeeper.getFuture())) {
					req.reply.send(Void());
					TraceEvent("RatekeeperHalted", rkInterf.id()).detail("ReqID", req.requesterID);
					break;
				}
				when(ReportCommitCostEstimationRequest req =
				         waitNext(rkInterf.reportCommitCostEstimation.getFuture())) {
					self.updateCommitCostEstimation(req.ssTrTagCommitCost);
					req.reply.send(Void());
				}
				when(wait(err.getFuture())) {}
				when(wait(dbInfo->onChange())) {
					if (tlogInterfs != dbInfo->get().logSystemConfig.allLocalLogs()) {
						tlogInterfs = dbInfo->get().logSystemConfig.allLocalLogs();
						tlogTrackers = std::vector<Future<Void>>();
						for (int i = 0; i < tlogInterfs.size(); i++)
							tlogTrackers.push_back(splitError(self.trackTLogQueueInfo(tlogInterfs[i]), err));
					}
					self.remoteDC = dbInfo->get().logSystemConfig.getRemoteDcId();
				}
				when(wait(collection)) {
					ASSERT(false);
					throw internal_error();
				}
			}
		} catch (Error& err) {
			TraceEvent("RatekeeperDied", rkInterf.id()).error(err, true);
		}
		return Void();
	}

}; // class RatekeeperImpl

Future<Void> Ratekeeper::configurationMonitor() {
	return RatekeeperImpl::configurationMonitor(this);
}

Future<Void> Ratekeeper::monitorServerListChange(
    PromiseStream<std::pair<UID, Optional<StorageServerInterface>>> serverChanges) {
	return RatekeeperImpl::monitorServerListChange(this, serverChanges);
}

Future<Void> Ratekeeper::trackEachStorageServer(
    FutureStream<std::pair<UID, Optional<StorageServerInterface>>> serverChanges) {
	return RatekeeperImpl::trackEachStorageServer(this, serverChanges);
}

Future<Void> Ratekeeper::trackStorageServerQueueInfo(StorageServerInterface ssi) {
	return RatekeeperImpl::trackStorageServerQueueInfo(this, ssi);
}

Future<Void> Ratekeeper::trackTLogQueueInfo(TLogInterface tli) {
	return RatekeeperImpl::trackTLogQueueInfo(this, tli);
}

Future<Void> Ratekeeper::monitorThrottlingChanges() {
	return RatekeeperImpl::monitorThrottlingChanges(this);
}

Future<Void> Ratekeeper::run(RatekeeperInterface rkInterf, Reference<AsyncVar<ServerDBInfo> const> dbInfo) {
	return RatekeeperImpl::run(rkInterf, dbInfo);
}

Ratekeeper::Ratekeeper(UID id, Database db)
  : id(id), db(db), smoothReleasedTransactions(SERVER_KNOBS->SMOOTHING_AMOUNT),
    smoothBatchReleasedTransactions(SERVER_KNOBS->SMOOTHING_AMOUNT),
    smoothTotalDurableBytes(SERVER_KNOBS->SLOW_SMOOTHING_AMOUNT),
    actualTpsMetric(LiteralStringRef("Ratekeeper.ActualTPS")), lastWarning(0), lastSSListFetchedTimestamp(now()),
    normalLimits(TransactionPriority::DEFAULT,
                 "",
                 SERVER_KNOBS->TARGET_BYTES_PER_STORAGE_SERVER,
                 SERVER_KNOBS->SPRING_BYTES_STORAGE_SERVER,
                 SERVER_KNOBS->TARGET_BYTES_PER_TLOG,
                 SERVER_KNOBS->SPRING_BYTES_TLOG,
                 SERVER_KNOBS->MAX_TL_SS_VERSION_DIFFERENCE,
                 SERVER_KNOBS->TARGET_DURABILITY_LAG_VERSIONS),
    batchLimits(TransactionPriority::BATCH,
                "Batch",
                SERVER_KNOBS->TARGET_BYTES_PER_STORAGE_SERVER_BATCH,
                SERVER_KNOBS->SPRING_BYTES_STORAGE_SERVER_BATCH,
                SERVER_KNOBS->TARGET_BYTES_PER_TLOG_BATCH,
                SERVER_KNOBS->SPRING_BYTES_TLOG_BATCH,
                SERVER_KNOBS->MAX_TL_SS_VERSION_DIFFERENCE_BATCH,
                SERVER_KNOBS->TARGET_DURABILITY_LAG_VERSIONS_BATCH) {
	tagThrottler = std::make_unique<TagThrottler>(this);
	expiredTagThrottleCleanup = recurring([this]() { ThrottleApi::expire(this->db.getReference()); },
	                                      SERVER_KNOBS->TAG_THROTTLE_EXPIRED_CLEANUP_INTERVAL);
}

void Ratekeeper::updateCommitCostEstimation(
    UIDTransactionTagMap<TransactionCommitCostEstimation> const& costEstimation) {
	for (auto it = storageQueueInfo.begin(); it != storageQueueInfo.end(); ++it) {
		auto tagCostIt = costEstimation.find(it->key);
		if (tagCostIt == costEstimation.end())
			continue;
		for (const auto& [tagName, cost] : tagCostIt->second) {
			it->value.tagCostEst[tagName] += cost;
			it->value.totalWriteCosts += cost.getCostSum();
			it->value.totalWriteOps += cost.getOpsSum();
		}
	}
}

void Ratekeeper::updateRate(RatekeeperLimits* limits) {
	// double controlFactor = ;  // dt / eFoldingTime

	double actualTps = smoothReleasedTransactions.smoothRate();
	actualTpsMetric = (int64_t)actualTps;
	// SOMEDAY: Remove the max( 1.0, ... ) since the below calculations _should_ be able to recover back up from this
	// value
	actualTps =
	    std::max(std::max(1.0, actualTps), smoothTotalDurableBytes.smoothRate() / CLIENT_KNOBS->TRANSACTION_SIZE_LIMIT);

	if (actualTpsHistory.size() > SERVER_KNOBS->MAX_TPS_HISTORY_SAMPLES) {
		actualTpsHistory.pop_front();
	}
	actualTpsHistory.push_back(actualTps);

	limits->tpsLimit = std::numeric_limits<double>::infinity();
	UID reasonID = UID();
	limitReason_t limitReason = limitReason_t::unlimited;

	int sscount = 0;

	int64_t worstFreeSpaceStorageServer = std::numeric_limits<int64_t>::max();
	int64_t worstStorageQueueStorageServer = 0;
	int64_t limitingStorageQueueStorageServer = 0;
	int64_t worstDurabilityLag = 0;

	std::multimap<double, StorageQueueInfo*> storageTpsLimitReverseIndex;
	std::multimap<int64_t, StorageQueueInfo*> storageDurabilityLagReverseIndex;

	std::map<UID, limitReason_t> ssReasons;

	bool printRateKeepLimitReasonDetails =
	    SERVER_KNOBS->RATEKEEPER_PRINT_LIMIT_REASON &&
	    (deterministicRandom()->random01() < SERVER_KNOBS->RATEKEEPER_LIMIT_REASON_SAMPLE_RATE);

	// Look at each storage server's write queue and local rate, compute and store the desired rate ratio
	for (auto i = storageQueueInfo.begin(); i != storageQueueInfo.end(); ++i) {
		auto& ss = i->value;
		if (!ss.valid || (remoteDC.present() && ss.locality.dcId() == remoteDC))
			continue;
		++sscount;

		limitReason_t ssLimitReason = limitReason_t::unlimited;

		int64_t minFreeSpace =
		    std::max(SERVER_KNOBS->MIN_AVAILABLE_SPACE,
		             (int64_t)(SERVER_KNOBS->MIN_AVAILABLE_SPACE_RATIO * ss.smoothTotalSpace.smoothTotal()));

		worstFreeSpaceStorageServer =
		    std::min(worstFreeSpaceStorageServer, (int64_t)ss.smoothFreeSpace.smoothTotal() - minFreeSpace);

		int64_t springBytes = std::max<int64_t>(
		    1, std::min<int64_t>(limits->storageSpringBytes, (ss.smoothFreeSpace.smoothTotal() - minFreeSpace) * 0.2));
		int64_t targetBytes = std::max<int64_t>(
		    1, std::min(limits->storageTargetBytes, (int64_t)ss.smoothFreeSpace.smoothTotal() - minFreeSpace));
		if (targetBytes != limits->storageTargetBytes) {
			if (minFreeSpace == SERVER_KNOBS->MIN_AVAILABLE_SPACE) {
				ssLimitReason = limitReason_t::storage_server_min_free_space;
			} else {
				ssLimitReason = limitReason_t::storage_server_min_free_space_ratio;
			}
			if (printRateKeepLimitReasonDetails) {
				TraceEvent("RatekeeperLimitReasonDetails")
				    .detail("Reason", ssLimitReason)
				    .detail("SSID", ss.id)
				    .detail("SSSmoothTotalSpace", ss.smoothTotalSpace.smoothTotal())
				    .detail("SSSmoothFreeSpace", ss.smoothFreeSpace.smoothTotal())
				    .detail("TargetBytes", targetBytes)
				    .detail("LimitsStorageTargetBytes", limits->storageTargetBytes)
				    .detail("MinFreeSpace", minFreeSpace);
			}
		}

		int64_t storageQueue = ss.lastReply.bytesInput - ss.smoothDurableBytes.smoothTotal();
		worstStorageQueueStorageServer = std::max(worstStorageQueueStorageServer, storageQueue);

		int64_t storageDurabilityLag = ss.smoothLatestVersion.smoothTotal() - ss.smoothDurableVersion.smoothTotal();
		worstDurabilityLag = std::max(worstDurabilityLag, storageDurabilityLag);

		storageDurabilityLagReverseIndex.insert(std::make_pair(-1 * storageDurabilityLag, &ss));

		auto& ssMetrics = healthMetrics.storageStats[ss.id];
		ssMetrics.storageQueue = storageQueue;
		ssMetrics.storageDurabilityLag = storageDurabilityLag;
		ssMetrics.cpuUsage = ss.lastReply.cpuUsage;
		ssMetrics.diskUsage = ss.lastReply.diskUsage;

		double targetRateRatio = std::min((storageQueue - targetBytes + springBytes) / (double)springBytes, 2.0);

		if (limits->priority == TransactionPriority::DEFAULT) {
			tryAutoThrottleTag(ss, storageQueue, storageDurabilityLag);
		}

		double inputRate = ss.smoothInputBytes.smoothRate();
		// inputRate = std::max( inputRate, actualTps / SERVER_KNOBS->MAX_TRANSACTIONS_PER_BYTE );

		/*if( deterministicRandom()->random01() < 0.1 ) {
		  std::string name = "RatekeeperUpdateRate" + limits.context;
		  TraceEvent(name, ss.id)
		  .detail("MinFreeSpace", minFreeSpace)
		  .detail("SpringBytes", springBytes)
		  .detail("TargetBytes", targetBytes)
		  .detail("SmoothTotalSpaceTotal", ss.smoothTotalSpace.smoothTotal())
		  .detail("SmoothFreeSpaceTotal", ss.smoothFreeSpace.smoothTotal())
		  .detail("LastReplyBytesInput", ss.lastReply.bytesInput)
		  .detail("SmoothDurableBytesTotal", ss.smoothDurableBytes.smoothTotal())
		  .detail("TargetRateRatio", targetRateRatio)
		  .detail("SmoothInputBytesRate", ss.smoothInputBytes.smoothRate())
		  .detail("ActualTPS", actualTps)
		  .detail("InputRate", inputRate)
		  .detail("VerySmoothDurableBytesRate", ss.verySmoothDurableBytes.smoothRate())
		  .detail("B", b);
		  }*/

		// Don't let any storage server use up its target bytes faster than its MVCC window!
		double maxBytesPerSecond =
		    (targetBytes - springBytes) /
		    ((((double)SERVER_KNOBS->MAX_READ_TRANSACTION_LIFE_VERSIONS) / SERVER_KNOBS->VERSIONS_PER_SECOND) + 2.0);
		double limitTps = std::min(actualTps * maxBytesPerSecond / std::max(1.0e-8, inputRate),
		                           maxBytesPerSecond * SERVER_KNOBS->MAX_TRANSACTIONS_PER_BYTE);
		if (ssLimitReason == limitReason_t::unlimited)
			ssLimitReason = limitReason_t::storage_server_write_bandwidth_mvcc;

		if (targetRateRatio > 0 && inputRate > 0) {
			ASSERT(inputRate != 0);
			double smoothedRate =
			    std::max(ss.verySmoothDurableBytes.smoothRate(), actualTps / SERVER_KNOBS->MAX_TRANSACTIONS_PER_BYTE);
			double x = smoothedRate / (inputRate * targetRateRatio);
			double lim = actualTps * x;
			if (lim < limitTps) {
				double oldLimitTps = limitTps;
				limitTps = lim;
				if (ssLimitReason == limitReason_t::unlimited ||
				    ssLimitReason == limitReason_t::storage_server_write_bandwidth_mvcc) {
					if (printRateKeepLimitReasonDetails) {
						TraceEvent("RatekeeperLimitReasonDetails")
						    .detail("Reason", limitReason_t::storage_server_write_queue_size)
						    .detail("FromReason", ssLimitReason)
						    .detail("SSID", ss.id)
						    .detail("SSSmoothTotalSpace", ss.smoothTotalSpace.smoothTotal())
						    .detail("LimitsStorageTargetBytes", limits->storageTargetBytes)
						    .detail("LimitsStorageSpringBytes", limits->storageSpringBytes)
						    .detail("SSSmoothFreeSpace", ss.smoothFreeSpace.smoothTotal())
						    .detail("MinFreeSpace", minFreeSpace)
						    .detail("SSLastReplyBytesInput", ss.lastReply.bytesInput)
						    .detail("SSSmoothDurableBytes", ss.smoothDurableBytes.smoothTotal())
						    .detail("StorageQueue", storageQueue)
						    .detail("TargetBytes", targetBytes)
						    .detail("SpringBytes", springBytes)
						    .detail("SSVerySmoothDurableBytesSmoothRate", ss.verySmoothDurableBytes.smoothRate())
						    .detail("SmoothedRate", smoothedRate)
						    .detail("X", x)
						    .detail("ActualTps", actualTps)
						    .detail("Lim", lim)
						    .detail("LimitTps", oldLimitTps)
						    .detail("InputRate", inputRate)
						    .detail("TargetRateRatio", targetRateRatio);
					}
					ssLimitReason = limitReason_t::storage_server_write_queue_size;
				}
			}
		}

		storageTpsLimitReverseIndex.insert(std::make_pair(limitTps, &ss));

		if (limitTps < limits->tpsLimit && (ssLimitReason == limitReason_t::storage_server_min_free_space ||
		                                    ssLimitReason == limitReason_t::storage_server_min_free_space_ratio)) {
			reasonID = ss.id;
			limits->tpsLimit = limitTps;
			limitReason = ssLimitReason;
		}

		ssReasons[ss.id] = ssLimitReason;
	}

	std::set<Optional<Standalone<StringRef>>> ignoredMachines;
	for (auto ss = storageTpsLimitReverseIndex.begin();
	     ss != storageTpsLimitReverseIndex.end() && ss->first < limits->tpsLimit;
	     ++ss) {
		if (ignoredMachines.size() <
		    std::min(configuration.storageTeamSize - 1, SERVER_KNOBS->MAX_MACHINES_FALLING_BEHIND)) {
			ignoredMachines.insert(ss->second->locality.zoneId());
			continue;
		}
		if (ignoredMachines.count(ss->second->locality.zoneId()) > 0) {
			continue;
		}

		limitingStorageQueueStorageServer =
		    ss->second->lastReply.bytesInput - ss->second->smoothDurableBytes.smoothTotal();
		limits->tpsLimit = ss->first;
		reasonID = storageTpsLimitReverseIndex.begin()->second->id; // Although we aren't controlling based on the worst
		// SS, we still report it as the limiting process
		limitReason = ssReasons[reasonID];
		break;
	}

	// Calculate limited durability lag
	int64_t limitingDurabilityLag = 0;

	std::set<Optional<Standalone<StringRef>>> ignoredDurabilityLagMachines;
	for (auto ss = storageDurabilityLagReverseIndex.begin(); ss != storageDurabilityLagReverseIndex.end(); ++ss) {
		if (ignoredDurabilityLagMachines.size() <
		    std::min(configuration.storageTeamSize - 1, SERVER_KNOBS->MAX_MACHINES_FALLING_BEHIND)) {
			ignoredDurabilityLagMachines.insert(ss->second->locality.zoneId());
			continue;
		}
		if (ignoredDurabilityLagMachines.count(ss->second->locality.zoneId()) > 0) {
			continue;
		}

		limitingDurabilityLag = -1 * ss->first;
		if (limitingDurabilityLag > limits->durabilityLagTargetVersions &&
		    actualTpsHistory.size() > SERVER_KNOBS->NEEDED_TPS_HISTORY_SAMPLES) {
			if (limits->durabilityLagLimit == std::numeric_limits<double>::infinity()) {
				double maxTps = 0;
				for (int i = 0; i < actualTpsHistory.size(); i++) {
					maxTps = std::max(maxTps, actualTpsHistory[i]);
				}
				limits->durabilityLagLimit = SERVER_KNOBS->INITIAL_DURABILITY_LAG_MULTIPLIER * maxTps;
			}
			if (limitingDurabilityLag > limits->lastDurabilityLag) {
				limits->durabilityLagLimit = SERVER_KNOBS->DURABILITY_LAG_REDUCTION_RATE * limits->durabilityLagLimit;
			}
			if (limits->durabilityLagLimit < limits->tpsLimit) {
				if (printRateKeepLimitReasonDetails) {
					TraceEvent("RatekeeperLimitReasonDetails")
					    .detail("SSID", ss->second->id)
					    .detail("Reason", limitReason_t::storage_server_durability_lag)
					    .detail("LimitsDurabilityLagLimit", limits->durabilityLagLimit)
					    .detail("LimitsTpsLimit", limits->tpsLimit)
					    .detail("LimitingDurabilityLag", limitingDurabilityLag)
					    .detail("LimitsLastDurabilityLag", limits->lastDurabilityLag);
				}
				limits->tpsLimit = limits->durabilityLagLimit;
				limitReason = limitReason_t::storage_server_durability_lag;
			}
		} else if (limits->durabilityLagLimit != std::numeric_limits<double>::infinity() &&
		           limitingDurabilityLag >
		               limits->durabilityLagTargetVersions - SERVER_KNOBS->DURABILITY_LAG_UNLIMITED_THRESHOLD) {
			limits->durabilityLagLimit = SERVER_KNOBS->DURABILITY_LAG_INCREASE_RATE * limits->durabilityLagLimit;
		} else {
			limits->durabilityLagLimit = std::numeric_limits<double>::infinity();
		}
		limits->lastDurabilityLag = limitingDurabilityLag;
		break;
	}

	healthMetrics.worstStorageQueue = worstStorageQueueStorageServer;
	healthMetrics.limitingStorageQueue = limitingStorageQueueStorageServer;
	healthMetrics.worstStorageDurabilityLag = worstDurabilityLag;
	healthMetrics.limitingStorageDurabilityLag = limitingDurabilityLag;

	double writeToReadLatencyLimit = 0;
	Version worstVersionLag = 0;
	Version limitingVersionLag = 0;

	{
		Version minSSVer = std::numeric_limits<Version>::max();
		Version minLimitingSSVer = std::numeric_limits<Version>::max();
		for (const auto& it : storageQueueInfo) {
			auto& ss = it.value;
			if (!ss.valid || (remoteDC.present() && ss.locality.dcId() == remoteDC))
				continue;

			minSSVer = std::min(minSSVer, ss.lastReply.version);

			// Machines that ratekeeper isn't controlling can fall arbitrarily far behind
			if (ignoredMachines.count(it.value.locality.zoneId()) == 0) {
				minLimitingSSVer = std::min(minLimitingSSVer, ss.lastReply.version);
			}
		}

		Version maxTLVer = std::numeric_limits<Version>::min();
		for (const auto& it : tlogQueueInfo) {
			auto& tl = it.value;
			if (!tl.valid)
				continue;
			maxTLVer = std::max(maxTLVer, tl.lastReply.v);
		}

		if (minSSVer != std::numeric_limits<Version>::max() && maxTLVer != std::numeric_limits<Version>::min()) {
			// writeToReadLatencyLimit: 0 = infinte speed; 1 = TL durable speed ; 2 = half TL durable speed
			writeToReadLatencyLimit =
			    ((maxTLVer - minLimitingSSVer) - limits->maxVersionDifference / 2) / (limits->maxVersionDifference / 4);
			worstVersionLag = std::max((Version)0, maxTLVer - minSSVer);
			limitingVersionLag = std::max((Version)0, maxTLVer - minLimitingSSVer);
		}
	}

	int64_t worstFreeSpaceTLog = std::numeric_limits<int64_t>::max();
	int64_t worstStorageQueueTLog = 0;
	int tlcount = 0;
	for (auto& it : tlogQueueInfo) {
		auto& tl = it.value;
		if (!tl.valid)
			continue;
		++tlcount;

		limitReason_t tlogLimitReason = limitReason_t::log_server_write_queue;

		int64_t minFreeSpace =
		    std::max(SERVER_KNOBS->MIN_AVAILABLE_SPACE,
		             (int64_t)(SERVER_KNOBS->MIN_AVAILABLE_SPACE_RATIO * tl.smoothTotalSpace.smoothTotal()));

		worstFreeSpaceTLog = std::min(worstFreeSpaceTLog, (int64_t)tl.smoothFreeSpace.smoothTotal() - minFreeSpace);

		int64_t springBytes = std::max<int64_t>(
		    1, std::min<int64_t>(limits->logSpringBytes, (tl.smoothFreeSpace.smoothTotal() - minFreeSpace) * 0.2));
		int64_t targetBytes = std::max<int64_t>(
		    1, std::min(limits->logTargetBytes, (int64_t)tl.smoothFreeSpace.smoothTotal() - minFreeSpace));
		if (targetBytes != limits->logTargetBytes) {
			if (minFreeSpace == SERVER_KNOBS->MIN_AVAILABLE_SPACE) {
				tlogLimitReason = limitReason_t::log_server_min_free_space;
			} else {
				tlogLimitReason = limitReason_t::log_server_min_free_space_ratio;
			}
			if (printRateKeepLimitReasonDetails) {
				TraceEvent("RatekeeperLimitReasonDetails")
				    .detail("TLogID", tl.id)
				    .detail("Reason", tlogLimitReason)
				    .detail("TLSmoothFreeSpace", tl.smoothFreeSpace.smoothTotal())
				    .detail("TLSmoothTotalSpace", tl.smoothTotalSpace.smoothTotal())
				    .detail("LimitsLogTargetBytes", limits->logTargetBytes)
				    .detail("TargetBytes", targetBytes)
				    .detail("MinFreeSpace", minFreeSpace);
			}
		}

		int64_t queue = tl.lastReply.bytesInput - tl.smoothDurableBytes.smoothTotal();
		healthMetrics.tLogQueue[tl.id] = queue;
		int64_t b = queue - targetBytes;
		worstStorageQueueTLog = std::max(worstStorageQueueTLog, queue);

		if (tl.lastReply.bytesInput - tl.lastReply.bytesDurable > tl.lastReply.storageBytes.free - minFreeSpace / 2) {
			if (now() - lastWarning > 5.0) {
				lastWarning = now();
				TraceEvent(SevWarnAlways, "RkTlogMinFreeSpaceZero", id).detail("ReasonId", tl.id);
			}
			reasonID = tl.id;
			limitReason = limitReason_t::log_server_min_free_space;
			limits->tpsLimit = 0.0;
		}

		double targetRateRatio = std::min((b + springBytes) / (double)springBytes, 2.0);

		if (writeToReadLatencyLimit > targetRateRatio) {
			if (printRateKeepLimitReasonDetails) {
				TraceEvent("RatekeeperLimitReasonDetails")
				    .detail("TLogID", tl.id)
				    .detail("Reason", limitReason_t::storage_server_readable_behind)
				    .detail("TLSmoothFreeSpace", tl.smoothFreeSpace.smoothTotal())
				    .detail("TLSmoothTotalSpace", tl.smoothTotalSpace.smoothTotal())
				    .detail("LimitsLogSpringBytes", limits->logSpringBytes)
				    .detail("LimitsLogTargetBytes", limits->logTargetBytes)
				    .detail("SpringBytes", springBytes)
				    .detail("TargetBytes", targetBytes)
				    .detail("TLLastReplyBytesInput", tl.lastReply.bytesInput)
				    .detail("TLSmoothDurableBytes", tl.smoothDurableBytes.smoothTotal())
				    .detail("Queue", queue)
				    .detail("B", b)
				    .detail("TargetRateRatio", targetRateRatio)
				    .detail("WriteToReadLatencyLimit", writeToReadLatencyLimit)
				    .detail("MinFreeSpace", minFreeSpace)
				    .detail("LimitsMaxVersionDifference", limits->maxVersionDifference);
			}
			targetRateRatio = writeToReadLatencyLimit;
			tlogLimitReason = limitReason_t::storage_server_readable_behind;
		}

		double inputRate = tl.smoothInputBytes.smoothRate();

		if (targetRateRatio > 0) {
			double smoothedRate =
			    std::max(tl.verySmoothDurableBytes.smoothRate(), actualTps / SERVER_KNOBS->MAX_TRANSACTIONS_PER_BYTE);
			double x = smoothedRate / (inputRate * targetRateRatio);
			if (targetRateRatio < .75) //< FIXME: KNOB for 2.0
				x = std::max(x, 0.95);
			double lim = actualTps * x;
			if (lim < limits->tpsLimit) {
				limits->tpsLimit = lim;
				reasonID = tl.id;
				limitReason = tlogLimitReason;
			}
		}
		if (inputRate > 0) {
			// Don't let any tlogs use up its target bytes faster than its MVCC window!
			double x =
			    ((targetBytes - springBytes) /
			     ((((double)SERVER_KNOBS->MAX_READ_TRANSACTION_LIFE_VERSIONS) / SERVER_KNOBS->VERSIONS_PER_SECOND) +
			      2.0)) /
			    inputRate;
			double lim = actualTps * x;
			if (lim < limits->tpsLimit) {
				if (printRateKeepLimitReasonDetails) {
					TraceEvent("RatekeeperLimitReasonDetails")
					    .detail("Reason", limitReason_t::log_server_mvcc_write_bandwidth)
					    .detail("TLogID", tl.id)
					    .detail("MinFreeSpace", minFreeSpace)
					    .detail("TLSmoothFreeSpace", tl.smoothFreeSpace.smoothTotal())
					    .detail("TLSmoothTotalSpace", tl.smoothTotalSpace.smoothTotal())
					    .detail("LimitsLogSpringBytes", limits->logSpringBytes)
					    .detail("LimitsLogTargetBytes", limits->logTargetBytes)
					    .detail("SpringBytes", springBytes)
					    .detail("TargetBytes", targetBytes)
					    .detail("InputRate", inputRate)
					    .detail("X", x)
					    .detail("ActualTps", actualTps)
					    .detail("Lim", lim)
					    .detail("LimitsTpsLimit", limits->tpsLimit);
				}
				limits->tpsLimit = lim;
				reasonID = tl.id;
				limitReason = limitReason_t::log_server_mvcc_write_bandwidth;
			}
		}
	}

	healthMetrics.worstTLogQueue = worstStorageQueueTLog;

	limits->tpsLimit = std::max(limits->tpsLimit, 0.0);

	if (g_network->isSimulated() && g_simulator.speedUpSimulation) {
		limits->tpsLimit = std::max(limits->tpsLimit, 100.0);
	}

	int64_t totalDiskUsageBytes = 0;
	for (auto& t : tlogQueueInfo) {
		if (t.value.valid) {
			totalDiskUsageBytes += t.value.lastReply.storageBytes.used;
		}
	}
	for (auto& s : storageQueueInfo) {
		if (s.value.valid) {
			totalDiskUsageBytes += s.value.lastReply.storageBytes.used;
		}
	}

	if (now() - lastSSListFetchedTimestamp > SERVER_KNOBS->STORAGE_SERVER_LIST_FETCH_TIMEOUT) {
		limits->tpsLimit = 0.0;
		limitReason = limitReason_t::storage_server_list_fetch_failed;
		reasonID = UID();
		TraceEvent(SevWarnAlways, "RkSSListFetchTimeout", id).suppressFor(1.0);
	} else if (limits->tpsLimit == std::numeric_limits<double>::infinity()) {
		limits->tpsLimit = SERVER_KNOBS->RATEKEEPER_DEFAULT_LIMIT;
	}

	limits->tpsLimitMetric = std::min(limits->tpsLimit, 1e6);
	limits->reasonMetric = limitReason;

	if (deterministicRandom()->random01() < 0.1) {
		const std::string& name = limits->rkUpdateEventCacheHolder.getPtr()->trackingKey;
		TraceEvent(name.c_str(), id)
		    .detail("TPSLimit", limits->tpsLimit)
		    .detail("Reason", limitReason)
		    .detail("ReasonServerID", reasonID == UID() ? std::string() : Traceable<UID>::toString(reasonID))
		    .detail("ReleasedTPS", smoothReleasedTransactions.smoothRate())
		    .detail("ReleasedBatchTPS", smoothBatchReleasedTransactions.smoothRate())
		    .detail("TPSBasis", actualTps)
		    .detail("StorageServers", sscount)
		    .detail("GrvProxies", grvProxyInfo.size())
		    .detail("TLogs", tlcount)
		    .detail("WorstFreeSpaceStorageServer", worstFreeSpaceStorageServer)
		    .detail("WorstFreeSpaceTLog", worstFreeSpaceTLog)
		    .detail("WorstStorageServerQueue", worstStorageQueueStorageServer)
		    .detail("LimitingStorageServerQueue", limitingStorageQueueStorageServer)
		    .detail("WorstTLogQueue", worstStorageQueueTLog)
		    .detail("TotalDiskUsageBytes", totalDiskUsageBytes)
		    .detail("WorstStorageServerVersionLag", worstVersionLag)
		    .detail("LimitingStorageServerVersionLag", limitingVersionLag)
		    .detail("WorstStorageServerDurabilityLag", worstDurabilityLag)
		    .detail("LimitingStorageServerDurabilityLag", limitingDurabilityLag)
		    .detail("TagsAutoThrottled", tagThrottler->autoThrottleCount())
		    .detail("TagsAutoThrottledBusyRead", tagThrottler->busyReadTagCount())
		    .detail("TagsAutoThrottledBusyWrite", tagThrottler->busyWriteTagCount())
		    .detail("TagsManuallyThrottled", tagThrottler->manualThrottleCount())
		    .detail("AutoThrottlingEnabled", tagThrottler->isAutoThrottlingEnabled())
		    .trackLatest(name);
	}
}

Future<Void> Ratekeeper::refreshStorageServerCommitCost() {
	if (tagThrottler->getLastBusiestCommitTagPick() == 0) { // the first call should be skipped
		tagThrottler->updateLastBusiestCommitTagPick();
		return Void();
	}
	double elapsed = now() - tagThrottler->getLastBusiestCommitTagPick();
	// for each SS, select the busiest commit tag from ssTrTagCommitCost
	for (auto it = storageQueueInfo.begin(); it != storageQueueInfo.end(); ++it) {
		it->value.busiestWriteTag.reset();
		TransactionTag busiestTag;
		TransactionCommitCostEstimation maxCost;
		double maxRate = 0, maxBusyness = 0;
		for (const auto& [tag, cost] : it->value.tagCostEst) {
			double rate = cost.getCostSum() / elapsed;
			if (rate > maxRate) {
				busiestTag = tag;
				maxRate = rate;
				maxCost = cost;
			}
		}
		if (maxRate > SERVER_KNOBS->MIN_TAG_WRITE_PAGES_RATE) {
			it->value.busiestWriteTag = busiestTag;
			// TraceEvent("RefreshSSCommitCost").detail("TotalWriteCost", it->value.totalWriteCost).detail("TotalWriteOps",it->value.totalWriteOps);
			ASSERT(it->value.totalWriteCosts > 0);
			maxBusyness = double(maxCost.getCostSum()) / it->value.totalWriteCosts;
			it->value.busiestWriteTagFractionalBusyness = maxBusyness;
			it->value.busiestWriteTagRate = maxRate;
		}

		TraceEvent("BusiestWriteTag", it->key)
		    .detail("Elapsed", elapsed)
		    .detail("Tag", printable(busiestTag))
		    .detail("TagOps", maxCost.getOpsSum())
		    .detail("TagCost", maxCost.getCostSum())
		    .detail("TotalCost", it->value.totalWriteCosts)
		    .detail("Reported", it->value.busiestWriteTag.present())
		    .trackLatest(it->value.busiestWriteTagEventHolder->trackingKey);

		// reset statistics
		it->value.tagCostEst.clear();
		it->value.totalWriteOps = 0;
		it->value.totalWriteCosts = 0;
	}
	tagThrottler->updateLastBusiestCommitTagPick();
	return Void();
}

void Ratekeeper::tryAutoThrottleTag(TransactionTag tag, double rate, double busyness, TagThrottledReason reason) {
	// NOTE: before the comparison with MIN_TAG_COST, the busiest tag rate also compares with MIN_TAG_PAGES_RATE
	// currently MIN_TAG_PAGES_RATE > MIN_TAG_COST in our default knobs.
	if (busyness > SERVER_KNOBS->AUTO_THROTTLE_TARGET_TAG_BUSYNESS && rate > SERVER_KNOBS->MIN_TAG_COST) {
		TEST(true); // Transaction tag auto-throttled
		Optional<double> clientRate = tagThrottler->autoThrottleTag(id, tag, busyness);
		if (clientRate.present()) {
			TagSet tags;
			tags.addTag(tag);

			Reference<DatabaseContext> dbRef = Reference<DatabaseContext>::addRef(db.getPtr());
			addActor.send(ThrottleApi::throttleTags(dbRef,
			                                        tags,
			                                        clientRate.get(),
			                                        SERVER_KNOBS->AUTO_TAG_THROTTLE_DURATION,
			                                        TagThrottleType::AUTO,
			                                        TransactionPriority::DEFAULT,
			                                        now() + SERVER_KNOBS->AUTO_TAG_THROTTLE_DURATION,
			                                        reason));
		}
	}
}

void Ratekeeper::tryAutoThrottleTag(StorageQueueInfo& ss, int64_t storageQueue, int64_t storageDurabilityLag) {
	// NOTE: we just keep it simple and don't differentiate write-saturation and read-saturation at the moment. In most
	// of situation, this works. More indicators besides queue size and durability lag could be investigated in the
	// future
	if (storageQueue > SERVER_KNOBS->AUTO_TAG_THROTTLE_STORAGE_QUEUE_BYTES ||
	    storageDurabilityLag > SERVER_KNOBS->AUTO_TAG_THROTTLE_DURABILITY_LAG_VERSIONS) {
		if (ss.busiestWriteTag.present()) {
			tryAutoThrottleTag(ss.busiestWriteTag.get(),
			                   ss.busiestWriteTagRate,
			                   ss.busiestWriteTagFractionalBusyness,
			                   TagThrottledReason::BUSY_WRITE);
		}
		if (ss.busiestReadTag.present()) {
			tryAutoThrottleTag(ss.busiestReadTag.get(),
			                   ss.busiestReadTagRate,
			                   ss.busiestReadTagFractionalBusyness,
			                   TagThrottledReason::BUSY_READ);
		}
	}
}

ACTOR Future<Void> ratekeeper(RatekeeperInterface rkInterf, Reference<AsyncVar<ServerDBInfo> const> dbInfo) {
	wait(Ratekeeper::run(rkInterf, dbInfo));
	return Void();
}