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balancer.cpp
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balancer.cpp
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/**
* Copyright (C) 2018-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.
*/
#include "mongo/db/s/balancer/balancer.h"
#include <absl/container/node_hash_set.h>
#include <boost/cstdint.hpp>
#include <boost/move/utility_core.hpp>
#include <boost/none.hpp>
#include <boost/none_t.hpp>
#include <boost/optional/optional.hpp>
#include <boost/smart_ptr.hpp>
// IWYU pragma: no_include "cxxabi.h"
#include <algorithm>
#include <cmath>
#include <iterator>
#include <map>
#include <memory>
#include <mutex>
#include <ratio>
#include <string>
#include <tuple>
#include <type_traits>
#include <utility>
#include <variant>
#include <vector>
#include "mongo/base/error_codes.h"
#include "mongo/base/status_with.h"
#include "mongo/base/string_data.h"
#include "mongo/bson/bsonelement.h"
#include "mongo/bson/bsonmisc.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/bson/bsonobjbuilder.h"
#include "mongo/client/read_preference.h"
#include "mongo/db/client.h"
#include "mongo/db/database_name.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/repl/read_concern_level.h"
#include "mongo/db/repl/repl_client_info.h"
#include "mongo/db/repl/replication_coordinator.h"
#include "mongo/db/s/balancer/actions_stream_policy.h"
#include "mongo/db/s/balancer/auto_merger_policy.h"
#include "mongo/db/s/balancer/balancer_commands_scheduler.h"
#include "mongo/db/s/balancer/balancer_commands_scheduler_impl.h"
#include "mongo/db/s/balancer/balancer_defragmentation_policy.h"
#include "mongo/db/s/balancer/cluster_statistics_impl.h"
#include "mongo/db/s/config/sharding_catalog_manager.h"
#include "mongo/db/s/sharding_config_server_parameters_gen.h"
#include "mongo/db/s/sharding_logging.h"
#include "mongo/db/server_feature_flags_gen.h"
#include "mongo/db/shard_id.h"
#include "mongo/db/write_concern_options.h"
#include "mongo/executor/scoped_task_executor.h"
#include "mongo/executor/task_executor_pool.h"
#include "mongo/logv2/log.h"
#include "mongo/logv2/log_attr.h"
#include "mongo/logv2/log_component.h"
#include "mongo/logv2/redaction.h"
#include "mongo/platform/random.h"
#include "mongo/s/balancer_configuration.h"
#include "mongo/s/catalog/sharding_catalog_client.h"
#include "mongo/s/catalog/type_chunk.h"
#include "mongo/s/catalog/type_collection.h"
#include "mongo/s/catalog/type_shard.h"
#include "mongo/s/catalog_cache.h"
#include "mongo/s/chunk.h"
#include "mongo/s/chunk_manager.h"
#include "mongo/s/chunk_version.h"
#include "mongo/s/client/shard.h"
#include "mongo/s/client/shard_registry.h"
#include "mongo/s/grid.h"
#include "mongo/s/request_types/balancer_collection_status_gen.h"
#include "mongo/s/request_types/migration_secondary_throttle_options.h"
#include "mongo/s/shard_util.h"
#include "mongo/stdx/variant.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/concurrency/idle_thread_block.h"
#include "mongo/util/debug_util.h"
#include "mongo/util/decorable.h"
#include "mongo/util/future.h"
#include "mongo/util/future_impl.h"
#include "mongo/util/pcre.h"
#include "mongo/util/scopeguard.h"
#include "mongo/util/testing_proctor.h"
#include "mongo/util/time_support.h"
#include "mongo/util/timer.h"
#include "mongo/util/version.h"
#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kSharding
namespace mongo {
using std::map;
using std::string;
using std::vector;
namespace {
const Milliseconds kBalanceRoundDefaultInterval(10 * 1000);
/**
* Balancer status response
*/
static constexpr StringData kBalancerPolicyStatusDraining = "draining"_sd;
static constexpr StringData kBalancerPolicyStatusZoneViolation = "zoneViolation"_sd;
static constexpr StringData kBalancerPolicyStatusChunksImbalance = "chunksImbalance"_sd;
static constexpr StringData kBalancerPolicyStatusDefragmentingChunks = "defragmentingChunks"_sd;
// Time interval between checks on draining shards.
constexpr Minutes kDrainingShardsCheckInterval{10};
/**
* Utility class to generate timing and statistics for a single balancer round.
*/
class BalanceRoundDetails {
public:
BalanceRoundDetails() : _executionTimer() {}
void setSucceeded(int numCandidateChunks,
int numChunksMoved,
int numImbalancedCachedCollections,
Milliseconds selectionTime,
Milliseconds throttleTime,
Milliseconds migrationTime) {
invariant(!_errMsg);
_numCandidateChunks = numCandidateChunks;
_numChunksMoved = numChunksMoved;
_numImbalancedCachedCollections = numImbalancedCachedCollections;
_selectionTime = selectionTime;
_throttleTime = throttleTime;
_migrationTime = migrationTime;
}
void setFailed(const string& errMsg) {
_errMsg = errMsg;
}
BSONObj toBSON() const {
BSONObjBuilder builder;
builder.append("executionTimeMillis", _executionTimer.millis());
builder.append("errorOccurred", _errMsg.has_value());
if (_errMsg) {
builder.append("errmsg", *_errMsg);
} else {
builder.append("candidateChunks", _numCandidateChunks);
builder.append("chunksMoved", _numChunksMoved);
builder.append("imbalancedCachedCollections", _numImbalancedCachedCollections);
BSONObjBuilder timeInfo{builder.subobjStart("times"_sd)};
timeInfo.append("selectionTimeMillis"_sd, _selectionTime.count());
timeInfo.append("throttleTimeMillis"_sd, _throttleTime.count());
timeInfo.append("migrationTimeMillis"_sd, _migrationTime.count());
timeInfo.done();
}
return builder.obj();
}
private:
const Timer _executionTimer;
Milliseconds _selectionTime;
Milliseconds _throttleTime;
Milliseconds _migrationTime;
// Set only on success
int _numCandidateChunks{0};
int _numChunksMoved{0};
int _numImbalancedCachedCollections{0};
// Set only on failure
boost::optional<string> _errMsg;
};
/**
* Occasionally prints a log message with shard versions if the versions are not the same
* in the cluster.
*/
void warnOnMultiVersion(const vector<ClusterStatistics::ShardStatistics>& clusterStats) {
static const auto& majorMinorRE = *new pcre::Regex(R"re(^(\d+)\.(\d+)\.)re");
auto&& vii = VersionInfoInterface::instance();
auto hasMyVersion = [&](auto&& stat) {
auto m = majorMinorRE.match(stat.mongoVersion);
return m && std::stoi(std::string{m[1]}) == vii.majorVersion() &&
std::stoi(std::string{m[2]}) == vii.minorVersion();
};
// If we're all the same version, don't message
if (std::all_of(clusterStats.begin(), clusterStats.end(), hasMyVersion))
return;
BSONObjBuilder shardVersions;
for (const auto& stat : clusterStats) {
shardVersions << stat.shardId << stat.mongoVersion;
}
LOGV2_WARNING(21875,
"Multiversion cluster detected",
"localVersion"_attr = vii.version(),
"shardVersions"_attr = shardVersions.done());
}
Chunk getChunkForMaxBound(const ChunkManager& cm, const BSONObj& max) {
boost::optional<Chunk> chunkWithMaxBound;
cm.forEachChunk([&](const auto& chunk) {
if (chunk.getMax().woCompare(max) == 0) {
chunkWithMaxBound.emplace(chunk);
return false;
}
return true;
});
if (chunkWithMaxBound) {
return *chunkWithMaxBound;
}
return cm.findIntersectingChunkWithSimpleCollation(max);
}
Status processManualMigrationOutcome(OperationContext* opCtx,
const boost::optional<BSONObj>& min,
const boost::optional<BSONObj>& max,
const NamespaceString& nss,
const ShardId& destination,
Status outcome) {
// Since the commands scheduler uses a separate thread to remotely execute a
// request, the resulting clusterTime needs to be explicitly retrieved and set on the
// original context of the requestor to ensure it will be propagated back to the router.
auto& replClient = repl::ReplClientInfo::forClient(opCtx->getClient());
replClient.setLastOpToSystemLastOpTime(opCtx);
if (outcome.isOK()) {
return outcome;
}
auto swCM =
Grid::get(opCtx)->catalogCache()->getShardedCollectionRoutingInfoWithPlacementRefresh(opCtx,
nss);
if (!swCM.isOK()) {
return swCM.getStatus();
}
const auto& cm = swCM.getValue().cm;
const auto currentChunkInfo =
min ? cm.findIntersectingChunkWithSimpleCollation(*min) : getChunkForMaxBound(cm, *max);
if (currentChunkInfo.getShardId() == destination &&
outcome != ErrorCodes::BalancerInterrupted) {
// Migration calls can be interrupted after the metadata is committed but before the command
// finishes the waitForDelete stage. Any failovers, therefore, must always cause the
// moveChunk command to be retried so as to assure that the waitForDelete promise of a
// successful command has been fulfilled.
LOGV2(6036622,
"Migration outcome is not OK, but the transaction was committed. Returning success");
outcome = Status::OK();
}
return outcome;
}
uint64_t getMaxChunkSizeBytes(OperationContext* opCtx, const CollectionType& coll) {
const auto balancerConfig = Grid::get(opCtx)->getBalancerConfiguration();
uassertStatusOK(balancerConfig->refreshAndCheck(opCtx));
return coll.getMaxChunkSizeBytes().value_or(balancerConfig->getMaxChunkSizeBytes());
}
int64_t getMaxChunkSizeMB(OperationContext* opCtx, const CollectionType& coll) {
return getMaxChunkSizeBytes(opCtx, coll) / (1024 * 1024);
}
// Returns a boolean flag indicating whether secondary throttling is enabled and the write concern
// to apply for migrations
std::tuple<bool, WriteConcernOptions> getSecondaryThrottleAndWriteConcern(
const boost::optional<MigrationSecondaryThrottleOptions>& secondaryThrottle) {
if (secondaryThrottle &&
secondaryThrottle->getSecondaryThrottle() == MigrationSecondaryThrottleOptions::kOn) {
if (secondaryThrottle->isWriteConcernSpecified()) {
return {true, secondaryThrottle->getWriteConcern()};
}
return {true, WriteConcernOptions()};
}
return {false, WriteConcernOptions()};
}
const auto _balancerDecoration = ServiceContext::declareDecoration<Balancer>();
const ReplicaSetAwareServiceRegistry::Registerer<Balancer> _balancerRegisterer("Balancer");
/**
* Returns the names of shards that are currently draining. When the balancer is disabled, draining
* shards are stuck in this state as chunks cannot be migrated.
*/
std::vector<std::string> getDrainingShardNames(OperationContext* opCtx) {
// Find the shards that are currently draining.
const auto& configShard = ShardingCatalogManager::get(opCtx)->localConfigShard();
const auto drainingShardsDocs{
uassertStatusOK(
configShard->exhaustiveFindOnConfig(opCtx,
ReadPreferenceSetting{ReadPreference::Nearest},
repl::ReadConcernLevel::kMajorityReadConcern,
NamespaceString::kConfigsvrShardsNamespace,
BSON(ShardType::draining << true),
BSONObj() /* No sorting */,
boost::none /* No limit */))
.docs};
// Build the list of the draining shard names.
std::vector<std::string> drainingShardNames;
std::transform(drainingShardsDocs.begin(),
drainingShardsDocs.end(),
std::back_inserter(drainingShardNames),
[](const auto& shardDoc) {
const auto shardEntry{uassertStatusOK(ShardType::fromBSON(shardDoc))};
return shardEntry.getName();
});
return drainingShardNames;
}
} // namespace
Balancer* Balancer::get(ServiceContext* serviceContext) {
return &_balancerDecoration(serviceContext);
}
Balancer* Balancer::get(OperationContext* operationContext) {
return get(operationContext->getServiceContext());
}
Balancer::Balancer()
: _balancedLastTime(0),
_clusterStats(std::make_unique<ClusterStatisticsImpl>()),
_chunkSelectionPolicy(std::make_unique<BalancerChunkSelectionPolicy>(_clusterStats.get())),
_commandScheduler(std::make_unique<BalancerCommandsSchedulerImpl>()),
_defragmentationPolicy(std::make_unique<BalancerDefragmentationPolicy>(
_clusterStats.get(), [this]() { _onActionsStreamPolicyStateUpdate(); })),
_autoMergerPolicy(
std::make_unique<AutoMergerPolicy>([this]() { _onActionsStreamPolicyStateUpdate(); })),
_imbalancedCollectionsCache(std::make_unique<stdx::unordered_set<NamespaceString>>()) {}
Balancer::~Balancer() {
onShutdown();
}
void Balancer::onStepUpBegin(OperationContext* opCtx, long long term) {
// Before starting step-up, ensure the balancer is ready to start. Specifically, that there is
// not an outstanding termination sequence requested during a previous step down of this node.
joinTermination();
}
void Balancer::onStepUpComplete(OperationContext* opCtx, long long term) {
initiate(opCtx);
}
void Balancer::onStepDown() {
// Asynchronously request to terminate all the worker threads and allow the stepdown sequence to
// continue.
requestTermination();
}
void Balancer::onShutdown() {
// Terminate the balancer thread so it doesn't leak memory.
requestTermination();
joinTermination();
}
void Balancer::onBecomeArbiter() {
// The Balancer is only active on config servers, and arbiters are not permitted in config
// server replica sets.
MONGO_UNREACHABLE;
}
void Balancer::initiate(OperationContext* opCtx) {
stdx::lock_guard<Latch> scopedLock(_mutex);
_imbalancedCollectionsCache->clear();
invariant(_threadSetState == ThreadSetState::Terminated);
_threadSetState = ThreadSetState::Running;
invariant(!_thread.joinable());
invariant(!_actionStreamConsumerThread.joinable());
invariant(!_threadOperationContext);
_thread = stdx::thread([this] { _mainThread(); });
}
void Balancer::requestTermination() {
stdx::lock_guard<Latch> scopedLock(_mutex);
if (_threadSetState != ThreadSetState::Running) {
return;
}
_threadSetState = ThreadSetState::Terminating;
// Interrupt the balancer thread if it has been started. We are guaranteed that the operation
// context of that thread is still alive, because we hold the balancer mutex.
if (_threadOperationContext) {
stdx::lock_guard<Client> scopedClientLock(*_threadOperationContext->getClient());
_threadOperationContext->markKilled(ErrorCodes::InterruptedDueToReplStateChange);
}
_condVar.notify_all();
_actionStreamCondVar.notify_all();
}
void Balancer::joinTermination() {
stdx::unique_lock<Latch> scopedLock(_mutex);
_joinCond.wait(scopedLock, [this] { return _threadSetState == ThreadSetState::Terminated; });
if (_thread.joinable()) {
_thread.join();
}
}
void Balancer::joinCurrentRound(OperationContext* opCtx) {
stdx::unique_lock<Latch> scopedLock(_mutex);
const auto numRoundsAtStart = _numBalancerRounds;
opCtx->waitForConditionOrInterrupt(_condVar, scopedLock, [&] {
return !_inBalancerRound || _numBalancerRounds != numRoundsAtStart;
});
}
Status Balancer::moveRange(OperationContext* opCtx,
const NamespaceString& nss,
const ConfigsvrMoveRange& request,
bool issuedByRemoteUser) {
const auto catalogClient = ShardingCatalogManager::get(opCtx)->localCatalogClient();
auto coll =
catalogClient->getCollection(opCtx, nss, repl::ReadConcernLevel::kMajorityReadConcern);
if (coll.getUnsplittable())
return {ErrorCodes::NamespaceNotSharded,
str::stream() << "Can't execute moveRange on unsharded collection "
<< nss.toStringForErrorMsg()};
const auto maxChunkSize = getMaxChunkSizeBytes(opCtx, coll);
const auto fromShardId = [&]() {
const auto [cm, _] = uassertStatusOK(
Grid::get(opCtx)->catalogCache()->getShardedCollectionRoutingInfoWithPlacementRefresh(
opCtx, nss));
if (request.getMin()) {
const auto& chunk = cm.findIntersectingChunkWithSimpleCollation(*request.getMin());
return chunk.getShardId();
} else {
return getChunkForMaxBound(cm, *request.getMax()).getShardId();
}
}();
ShardsvrMoveRange shardSvrRequest(nss);
shardSvrRequest.setDbName(DatabaseName::kAdmin);
shardSvrRequest.setMoveRangeRequestBase(request.getMoveRangeRequestBase());
shardSvrRequest.setMaxChunkSizeBytes(maxChunkSize);
shardSvrRequest.setFromShard(fromShardId);
shardSvrRequest.setCollectionTimestamp(coll.getTimestamp());
shardSvrRequest.setEpoch(coll.getEpoch());
const auto [secondaryThrottle, wc] =
getSecondaryThrottleAndWriteConcern(request.getSecondaryThrottle());
shardSvrRequest.setSecondaryThrottle(secondaryThrottle);
shardSvrRequest.setForceJumbo(request.getForceJumbo());
auto response =
_commandScheduler->requestMoveRange(opCtx, shardSvrRequest, wc, issuedByRemoteUser)
.getNoThrow(opCtx);
return processManualMigrationOutcome(opCtx,
request.getMin(),
request.getMax(),
nss,
shardSvrRequest.getToShard(),
std::move(response));
}
void Balancer::report(OperationContext* opCtx, BSONObjBuilder* builder) {
auto balancerConfig = Grid::get(opCtx)->getBalancerConfiguration();
balancerConfig->refreshAndCheck(opCtx).ignore();
const auto mode = balancerConfig->getBalancerMode();
stdx::lock_guard<Latch> scopedLock(_mutex);
builder->append("mode", BalancerSettingsType::kBalancerModes[mode]);
builder->append("inBalancerRound", _inBalancerRound);
builder->append("numBalancerRounds", _numBalancerRounds);
builder->append("term", repl::ReplicationCoordinator::get(opCtx)->getTerm());
}
void Balancer::_consumeActionStreamLoop() {
Client::initThread("BalancerSecondary",
getGlobalServiceContext()->getService(ClusterRole::ShardServer));
auto opCtx = cc().makeOperationContext();
executor::ScopedTaskExecutor executor(
Grid::get(opCtx.get())->getExecutorPool()->getFixedExecutor());
ScopeGuard onExitCleanup([this, &executor] {
_defragmentationPolicy->interruptAllDefragmentations();
_autoMergerPolicy->disable();
// Explicitly cancel and drain any outstanding streaming action already dispatched to the
// task executor.
executor->shutdown();
executor->join();
// When shutting down, the task executor may or may not invoke the
// applyActionResponseTo()callback for canceled streaming actions: to ensure a consistent
// state of the balancer after a step down, _outstandingStreamingOps needs then to be reset
// to 0 once all the tasks have been drained.
_outstandingStreamingOps.store(0);
});
// Lambda function to sleep for throttling
auto applyThrottling =
[lastActionTime = Date_t::fromMillisSinceEpoch(0)](const Milliseconds throttle) mutable {
auto timeSinceLastAction = Date_t::now() - lastActionTime;
if (throttle > timeSinceLastAction) {
auto sleepingTime = throttle - timeSinceLastAction;
LOGV2_DEBUG(6443700,
2,
"Applying throttling on balancer secondary thread",
"sleepingTime"_attr = sleepingTime);
sleepFor(sleepingTime);
}
lastActionTime = Date_t::now();
};
auto backOff = Backoff(Seconds(1), Milliseconds::max());
bool errorOccurred = false;
while (true) {
{
stdx::unique_lock<Latch> ul(_mutex);
// Keep asking for more actions if we meet all these conditions:
// - Balancer is in kRunning state
// - There are less than kMaxOutstandingStreamingOperations
// - There were actions to schedule on the previous iteration or there is an update on
// the streams state
auto stopWaitingCondition = [&] {
return _threadSetState != ThreadSetState::Running ||
(_outstandingStreamingOps.load() <= kMaxOutstandingStreamingOperations &&
_actionStreamsStateUpdated.load());
};
if (!errorOccurred) {
_actionStreamCondVar.wait(ul, stopWaitingCondition);
} else {
// Enable retries in case of error by performing a backoff
_actionStreamCondVar.wait_for(
ul, backOff.nextSleep().toSystemDuration(), stopWaitingCondition);
}
if (_threadSetState != ThreadSetState::Running) {
break;
}
}
// Clear flags
errorOccurred = false;
_actionStreamsStateUpdated.store(false);
// Get active streams
auto activeStreams = [&]() -> std::vector<ActionsStreamPolicy*> {
auto balancerConfig = Grid::get(opCtx.get())->getBalancerConfiguration();
std::vector<ActionsStreamPolicy*> streams;
if (balancerConfig->shouldBalanceForAutoMerge() && _autoMergerPolicy->isEnabled()) {
streams.push_back(_autoMergerPolicy.get());
}
if (balancerConfig->shouldBalance()) {
streams.push_back(_defragmentationPolicy.get());
}
return streams;
}();
// Get next action from a random stream together with its stream
auto [nextAction, sourcedStream] =
[&]() -> std::tuple<boost::optional<BalancerStreamAction>, ActionsStreamPolicy*> {
auto client = opCtx->getClient();
std::shuffle(activeStreams.begin(), activeStreams.end(), client->getPrng().urbg());
for (auto stream : activeStreams) {
try {
auto action = stream->getNextStreamingAction(opCtx.get());
if (action.has_value()) {
return std::make_tuple(std::move(action), stream);
}
} catch (const DBException& e) {
LOGV2_WARNING(7435001,
"Failed to get next action from action stream",
"error"_attr = redact(e),
"stream"_attr = stream->getName());
errorOccurred = true;
}
}
return std::make_tuple(boost::none, nullptr);
}();
if (!nextAction.has_value()) {
continue;
}
// Signal there are still actions to be consumed by next iteration
_actionStreamsStateUpdated.store(true);
_outstandingStreamingOps.fetchAndAdd(1);
stdx::visit(
OverloadedVisitor{
[&, stream = sourcedStream](MergeInfo&& mergeAction) {
applyThrottling(Milliseconds(chunkDefragmentationThrottlingMS.load()));
auto result =
_commandScheduler
->requestMergeChunks(opCtx.get(),
mergeAction.nss,
mergeAction.shardId,
mergeAction.chunkRange,
mergeAction.collectionPlacementVersion)
.thenRunOn(*executor)
.onCompletion([this, stream, action = std::move(mergeAction)](
const Status& status) {
_applyStreamingActionResponseToPolicy(action, status, stream);
});
},
[&, stream = sourcedStream](DataSizeInfo&& dataSizeAction) {
auto result =
_commandScheduler
->requestDataSize(opCtx.get(),
dataSizeAction.nss,
dataSizeAction.shardId,
dataSizeAction.chunkRange,
dataSizeAction.version,
dataSizeAction.keyPattern,
dataSizeAction.estimatedValue,
dataSizeAction.maxSize)
.thenRunOn(*executor)
.onCompletion([this, stream, action = std::move(dataSizeAction)](
const StatusWith<DataSizeResponse>& swDataSize) {
_applyStreamingActionResponseToPolicy(action, swDataSize, stream);
});
},
[&, stream = sourcedStream](MergeAllChunksOnShardInfo&& mergeAllChunksAction) {
if (mergeAllChunksAction.applyThrottling) {
applyThrottling(Milliseconds(autoMergerThrottlingMS.load()));
}
auto result =
_commandScheduler
->requestMergeAllChunksOnShard(
opCtx.get(), mergeAllChunksAction.nss, mergeAllChunksAction.shardId)
.thenRunOn(*executor)
.onCompletion(
[this, stream, action = mergeAllChunksAction](
const StatusWith<NumMergedChunks>& swNumMergedChunks) {
_applyStreamingActionResponseToPolicy(
action, swNumMergedChunks, stream);
});
},
[](MigrateInfo&& _) {
uasserted(ErrorCodes::BadValue,
"Migrations cannot be processed as Streaming Actions");
}},
std::move(nextAction.value()));
}
}
void Balancer::_mainThread() {
ON_BLOCK_EXIT([this] {
{
stdx::lock_guard<Latch> scopedLock(_mutex);
_threadSetState = ThreadSetState::Terminated;
LOGV2_DEBUG(21855, 1, "Balancer thread set terminated");
}
_joinCond.notify_all();
});
Client::initThread("Balancer", getGlobalServiceContext()->getService(ClusterRole::ShardServer));
// TODO(SERVER-74658): Please revisit if this thread could be made killable.
{
stdx::lock_guard<Client> lk(cc());
cc().setSystemOperationUnkillableByStepdown(lk);
}
auto opCtx = cc().makeOperationContext();
auto shardingContext = Grid::get(opCtx.get());
LOGV2(21856, "CSRS balancer is starting");
{
stdx::lock_guard<Latch> scopedLock(_mutex);
_threadOperationContext = opCtx.get();
}
const Seconds kInitBackoffInterval(10);
auto balancerConfig = shardingContext->getBalancerConfiguration();
while (!_terminationRequested()) {
Status refreshStatus = balancerConfig->refreshAndCheck(opCtx.get());
if (!refreshStatus.isOK()) {
LOGV2_WARNING(21876,
"Got error while refreshing balancer settings, will retry with a backoff",
"backoffInterval"_attr = Milliseconds(kInitBackoffInterval),
"error"_attr = refreshStatus);
_sleepFor(opCtx.get(), kInitBackoffInterval);
continue;
}
break;
}
LOGV2(6036605, "Starting command scheduler");
_commandScheduler->start(opCtx.get());
_actionStreamConsumerThread = stdx::thread([&] { _consumeActionStreamLoop(); });
LOGV2(6036606, "Balancer worker thread initialised. Entering main loop.");
// Main balancer loop
auto lastMigrationTime = Date_t::fromMillisSinceEpoch(0);
auto lastDrainingShardsCheckTime{Date_t::fromMillisSinceEpoch(0)};
while (!_terminationRequested()) {
BalanceRoundDetails roundDetails;
_beginRound(opCtx.get());
try {
shardingContext->shardRegistry()->reload(opCtx.get());
uassert(13258, "oids broken after resetting!", _checkOIDs(opCtx.get()));
Status refreshStatus = balancerConfig->refreshAndCheck(opCtx.get());
if (!refreshStatus.isOK()) {
LOGV2_WARNING(21877, "Skipping balancing round", "error"_attr = refreshStatus);
_endRound(opCtx.get(), kBalanceRoundDefaultInterval);
continue;
}
if (!balancerConfig->shouldBalance() || _terminationRequested()) {
if (balancerConfig->getBalancerMode() == BalancerSettingsType::BalancerMode::kOff &&
Date_t::now() - lastDrainingShardsCheckTime >= kDrainingShardsCheckInterval) {
const auto drainingShardNames{getDrainingShardNames(opCtx.get())};
if (!drainingShardNames.empty()) {
LOGV2_WARNING(6434000,
"Draining of removed shards cannot be completed because the "
"balancer is disabled",
"shards"_attr = drainingShardNames);
}
lastDrainingShardsCheckTime = Date_t::now();
}
_autoMergerPolicy->disable();
LOGV2_DEBUG(21859, 1, "Skipping balancing round because balancing is disabled");
_endRound(opCtx.get(), kBalanceRoundDefaultInterval);
continue;
}
if (balancerConfig->shouldBalanceForAutoMerge()) {
_autoMergerPolicy->enable();
}
LOGV2_DEBUG(21860,
1,
"Start balancing round",
"waitForDelete"_attr = balancerConfig->waitForDelete(),
"secondaryThrottle"_attr = balancerConfig->getSecondaryThrottle().toBSON());
static Occasionally sampler;
if (sampler.tick()) {
warnOnMultiVersion(uassertStatusOK(_clusterStats->getStats(opCtx.get())));
}
// Collect and apply up-to-date configuration values on the cluster collections.
_defragmentationPolicy->startCollectionDefragmentations(opCtx.get());
// Reactivate the Automerger if needed.
_autoMergerPolicy->checkInternalUpdates();
// The current configuration is allowing the balancer to perform operations.
// Unblock the secondary thread if needed.
_actionStreamCondVar.notify_all();
// Split chunk to match zones boundaries
{
Status status = _splitChunksIfNeeded(opCtx.get());
if (!status.isOK()) {
LOGV2_WARNING(21878, "Failed to split chunks", "error"_attr = status);
} else {
LOGV2_DEBUG(21861, 1, "Done enforcing zone range boundaries.");
}
}
// Select and migrate chunks
{
Timer selectionTimer;
const std::vector<ClusterStatistics::ShardStatistics> shardStats =
uassertStatusOK(_clusterStats->getStats(opCtx.get()));
stdx::unordered_set<ShardId> availableShards;
availableShards.reserve(shardStats.size());
std::transform(
shardStats.begin(),
shardStats.end(),
std::inserter(availableShards, availableShards.end()),
[](const ClusterStatistics::ShardStatistics& shardStatistics) -> ShardId {
return shardStatistics.shardId;
});
const auto chunksToDefragment =
_defragmentationPolicy->selectChunksToMove(opCtx.get(), &availableShards);
const auto chunksToRebalance = uassertStatusOK(
_chunkSelectionPolicy->selectChunksToMove(opCtx.get(),
shardStats,
&availableShards,
_imbalancedCollectionsCache.get()));
const Milliseconds selectionTimeMillis{selectionTimer.millis()};
if (chunksToRebalance.empty() && chunksToDefragment.empty()) {
LOGV2_DEBUG(21862, 1, "No need to move any chunk");
_balancedLastTime = 0;
LOGV2_DEBUG(21863, 1, "End balancing round");
// Set to 100ms when executed in context of a test
_endRound(opCtx.get(),
TestingProctor::instance().isEnabled()
? Milliseconds(100)
: kBalanceRoundDefaultInterval);
} else {
// Sleep according to the migration throttling settings
const auto throttleTimeMillis = [&] {
const auto& minRoundinterval =
Milliseconds(balancerMigrationsThrottlingMs.load());
const auto timeSinceLastMigration = Date_t::now() - lastMigrationTime;
if (timeSinceLastMigration < minRoundinterval) {
return minRoundinterval - timeSinceLastMigration;
}
return Milliseconds::zero();
}();
_sleepFor(opCtx.get(), throttleTimeMillis);
// Migrate chunks
Timer migrationTimer;
_balancedLastTime =
_moveChunks(opCtx.get(), chunksToRebalance, chunksToDefragment);
lastMigrationTime = Date_t::now();
const Milliseconds migrationTimeMillis{migrationTimer.millis()};
// Complete round
roundDetails.setSucceeded(
static_cast<int>(chunksToRebalance.size() + chunksToDefragment.size()),
_balancedLastTime,
_imbalancedCollectionsCache->size(),
selectionTimeMillis,
throttleTimeMillis,
migrationTimeMillis);
auto catalogManager = ShardingCatalogManager::get(opCtx.get());
ShardingLogging::get(opCtx.get())
->logAction(opCtx.get(),
"balancer.round",
NamespaceString::kEmpty,
roundDetails.toBSON(),
catalogManager->localConfigShard(),
catalogManager->localCatalogClient())
.ignore();
LOGV2_DEBUG(6679500, 1, "End balancing round");
// Migration throttling of `balancerMigrationsThrottlingMs` will be applied
// before the next call to _moveChunks, so don't sleep here.
_endRound(opCtx.get(), Milliseconds(0));
}
}
} catch (const DBException& e) {
LOGV2(21865, "Error while doing balance", "error"_attr = e);
// Just to match the opening statement if in log level 1
LOGV2_DEBUG(21866, 1, "End balancing round");
// This round failed, tell the world!
roundDetails.setFailed(e.what());
auto catalogManager = ShardingCatalogManager::get(opCtx.get());
ShardingLogging::get(opCtx.get())
->logAction(opCtx.get(),
"balancer.round",
NamespaceString::kEmpty,
roundDetails.toBSON(),
catalogManager->localConfigShard(),
catalogManager->localCatalogClient())
.ignore();
// Sleep a fair amount before retrying because of the error
_endRound(opCtx.get(), kBalanceRoundDefaultInterval);
}
}
{
stdx::lock_guard<Latch> scopedLock(_mutex);
invariant(_threadSetState == ThreadSetState::Terminating);
}
_commandScheduler->stop();
_actionStreamConsumerThread.join();
{
stdx::lock_guard<Latch> scopedLock(_mutex);
_threadOperationContext = nullptr;
}
LOGV2(21867, "CSRS balancer is now stopped");
}
void Balancer::_applyStreamingActionResponseToPolicy(const BalancerStreamAction& action,
const BalancerStreamActionResponse& response,
ActionsStreamPolicy* policy) {
invariant(_outstandingStreamingOps.addAndFetch(-1) >= 0);
ThreadClient tc("BalancerSecondaryThread::applyActionResponse",
getGlobalServiceContext()->getService(ClusterRole::ShardServer));
auto opCtx = tc->makeOperationContext();
policy->applyActionResult(opCtx.get(), action, response);
};
bool Balancer::_terminationRequested() {
stdx::lock_guard<Latch> scopedLock(_mutex);
return (_threadSetState != ThreadSetState::Running);
}
void Balancer::_beginRound(OperationContext* opCtx) {
stdx::unique_lock<Latch> lock(_mutex);
_inBalancerRound = true;
_condVar.notify_all();
}
void Balancer::_endRound(OperationContext* opCtx, Milliseconds waitTimeout) {
{
stdx::lock_guard<Latch> lock(_mutex);
_inBalancerRound = false;
_numBalancerRounds++;
_condVar.notify_all();
}
MONGO_IDLE_THREAD_BLOCK;
_sleepFor(opCtx, waitTimeout);
}
void Balancer::_sleepFor(OperationContext* opCtx, Milliseconds waitTimeout) {
stdx::unique_lock<Latch> lock(_mutex);
_condVar.wait_for(lock, waitTimeout.toSystemDuration(), [&] {
return _threadSetState != ThreadSetState::Running;
});
}
bool Balancer::_checkOIDs(OperationContext* opCtx) {
auto shardingContext = Grid::get(opCtx);
const auto all = shardingContext->shardRegistry()->getAllShardIds(opCtx);
// map of OID machine ID => shardId
map<int, ShardId> oids;
for (const ShardId& shardId : all) {
if (_terminationRequested()) {
return false;
}
auto shardStatus = shardingContext->shardRegistry()->getShard(opCtx, shardId);
if (!shardStatus.isOK()) {
continue;
}
const auto s = std::move(shardStatus.getValue());
auto result = uassertStatusOK(
s->runCommandWithFixedRetryAttempts(opCtx,