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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/pipeline/sharded_agg_helpers.h"
#include "mongo/db/curop.h"
#include "mongo/db/pipeline/aggregate_command_gen.h"
#include "mongo/db/pipeline/aggregation_request_helper.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/document_source_change_stream.h"
#include "mongo/db/pipeline/document_source_change_stream_handle_topology_change.h"
#include "mongo/db/pipeline/document_source_group.h"
#include "mongo/db/pipeline/document_source_limit.h"
#include "mongo/db/pipeline/document_source_match.h"
#include "mongo/db/pipeline/document_source_merge.h"
#include "mongo/db/pipeline/document_source_out.h"
#include "mongo/db/pipeline/document_source_project.h"
#include "mongo/db/pipeline/document_source_sequential_document_cache.h"
#include "mongo/db/pipeline/document_source_set_variable_from_subpipeline.h"
#include "mongo/db/pipeline/document_source_skip.h"
#include "mongo/db/pipeline/document_source_sort.h"
#include "mongo/db/pipeline/document_source_unwind.h"
#include "mongo/db/pipeline/lite_parsed_pipeline.h"
#include "mongo/db/pipeline/search_helper.h"
#include "mongo/db/pipeline/semantic_analysis.h"
#include "mongo/db/query/cursor_response_gen.h"
#include "mongo/db/vector_clock.h"
#include "mongo/logv2/log.h"
#include "mongo/rpc/get_status_from_command_result.h"
#include "mongo/s/cluster_commands_helpers.h"
#include "mongo/s/collection_uuid_mismatch.h"
#include "mongo/s/is_mongos.h"
#include "mongo/s/query/cluster_query_knobs_gen.h"
#include "mongo/s/query/document_source_merge_cursors.h"
#include "mongo/s/query/establish_cursors.h"
#include "mongo/s/router.h"
#include "mongo/s/stale_exception.h"
#include "mongo/s/transaction_router.h"
#include "mongo/util/fail_point.h"
#include "mongo/util/visit_helper.h"
#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kQuery
namespace mongo {
namespace sharded_agg_helpers {
namespace {
MONGO_FAIL_POINT_DEFINE(shardedAggregateHangBeforeEstablishingShardCursors);
/**
* Given a document representing an aggregation command such as
* {aggregate: "myCollection", pipeline: [], ...},
*
* produces the corresponding explain command:
* {explain: {aggregate: "myCollection", pipline: [], ...}, $queryOptions: {...}, verbosity: ...}
*/
Document wrapAggAsExplain(Document aggregateCommand, ExplainOptions::Verbosity verbosity) {
MutableDocument explainCommandBuilder;
explainCommandBuilder["explain"] = Value(aggregateCommand);
// Downstream host targeting code expects queryOptions at the top level of the command object.
explainCommandBuilder[query_request_helper::kUnwrappedReadPrefField] =
Value(aggregateCommand[query_request_helper::kUnwrappedReadPrefField]);
// readConcern needs to be promoted to the top-level of the request.
explainCommandBuilder[repl::ReadConcernArgs::kReadConcernFieldName] =
Value(aggregateCommand[repl::ReadConcernArgs::kReadConcernFieldName]);
// Add explain command options.
for (auto&& explainOption : ExplainOptions::toBSON(verbosity)) {
explainCommandBuilder[explainOption.fieldNameStringData()] = Value(explainOption);
}
return explainCommandBuilder.freeze();
}
/**
* Open a $changeStream cursor on the 'config.shards' collection to watch for new shards.
*/
RemoteCursor openChangeStreamNewShardMonitor(const boost::intrusive_ptr<ExpressionContext>& expCtx,
Timestamp startMonitoringAtTime) {
const auto& configShard = Grid::get(expCtx->opCtx)->shardRegistry()->getConfigShard();
// Pipeline: {$changeStream: {startAtOperationTime: [now], allowToRunOnConfigDB: true}}
AggregateCommandRequest aggReq(
ShardType::ConfigNS,
{BSON(DocumentSourceChangeStream::kStageName
<< BSON(DocumentSourceChangeStreamSpec::kStartAtOperationTimeFieldName
<< startMonitoringAtTime
<< DocumentSourceChangeStreamSpec::kAllowToRunOnConfigDBFieldName << true))});
aggReq.setFromMongos(true);
aggReq.setNeedsMerge(true);
// TODO SERVER-65369: This code block can be removed after 7.0.
if (isMongos() && expCtx->changeStreamTokenVersion == 1) {
// A request for v1 resume tokens on mongos should only be allowed in test mode.
tassert(6497000, "Invalid request for v1 resume tokens", getTestCommandsEnabled());
aggReq.setGenerateV2ResumeTokens(false);
}
SimpleCursorOptions cursor;
cursor.setBatchSize(0);
aggReq.setCursor(cursor);
auto cmdObjWithRWC =
applyReadWriteConcern(expCtx->opCtx,
true, /* appendRC */
!expCtx->explain, /* appendWC */
aggregation_request_helper::serializeToCommandObj(aggReq));
auto configCursor = establishCursors(expCtx->opCtx,
expCtx->mongoProcessInterface->taskExecutor,
aggReq.getNamespace(),
ReadPreferenceSetting{ReadPreference::SecondaryPreferred},
{{configShard->getId(), cmdObjWithRWC}},
false);
invariant(configCursor.size() == 1);
return std::move(*configCursor.begin());
}
BSONObj genericTransformForShards(MutableDocument&& cmdForShards,
const boost::intrusive_ptr<ExpressionContext>& expCtx,
boost::optional<ExplainOptions::Verbosity> explainVerbosity,
BSONObj collationObj,
boost::optional<BSONObj> readConcern) {
cmdForShards[AggregateCommandRequest::kLetFieldName] =
Value(expCtx->variablesParseState.serialize(expCtx->variables));
cmdForShards[AggregateCommandRequest::kFromMongosFieldName] = Value(expCtx->inMongos);
if (!collationObj.isEmpty()) {
cmdForShards[AggregateCommandRequest::kCollationFieldName] = Value(collationObj);
}
// If this is a request for an aggregation explain, then we must wrap the aggregate inside an
// explain command.
if (explainVerbosity) {
cmdForShards.reset(wrapAggAsExplain(cmdForShards.freeze(), *explainVerbosity));
}
if (expCtx->opCtx->getTxnNumber()) {
invariant(cmdForShards.peek()[OperationSessionInfo::kTxnNumberFieldName].missing(),
str::stream() << "Command for shards unexpectedly had the "
<< OperationSessionInfo::kTxnNumberFieldName
<< " field set: " << cmdForShards.peek().toString());
cmdForShards[OperationSessionInfo::kTxnNumberFieldName] =
Value(static_cast<long long>(*expCtx->opCtx->getTxnNumber()));
}
if (readConcern) {
cmdForShards["readConcern"] = Value(std::move(*readConcern));
}
return cmdForShards.freeze().toBson();
}
std::vector<RemoteCursor> establishShardCursors(OperationContext* opCtx,
std::shared_ptr<executor::TaskExecutor> executor,
const NamespaceString& nss,
bool mustRunOnAll,
boost::optional<ChunkManager>& cm,
const std::set<ShardId>& shardIds,
const BSONObj& cmdObj,
const ReadPreferenceSetting& readPref) {
LOGV2_DEBUG(20904,
1,
"Dispatching command {cmdObj} to establish cursors on shards",
"cmdObj"_attr = redact(cmdObj));
std::vector<std::pair<ShardId, BSONObj>> requests;
// If we don't need to run on all shards, then we should always have a valid routing table.
invariant(cm || mustRunOnAll);
if (mustRunOnAll) {
// The pipeline contains a stage which must be run on all shards. Skip versioning and
// enqueue the raw command objects.
for (const auto& shardId : shardIds) {
requests.emplace_back(shardId, cmdObj);
}
} else if (cm->isSharded()) {
// The collection is sharded. Use the routing table to decide which shards to target
// based on the query and collation, and build versioned requests for them.
for (const auto& shardId : shardIds) {
auto versionedCmdObj = appendShardVersion(cmdObj, cm->getVersion(shardId));
requests.emplace_back(shardId, std::move(versionedCmdObj));
}
} else {
// The collection is unsharded. Target only the primary shard for the database.
// Don't append shard version info when contacting the config servers.
const auto cmdObjWithShardVersion = cm->dbPrimary() != ShardId::kConfigServerId
? appendShardVersion(cmdObj, ChunkVersion::UNSHARDED())
: cmdObj;
requests.emplace_back(cm->dbPrimary(),
appendDbVersionIfPresent(cmdObjWithShardVersion, cm->dbVersion()));
}
if (MONGO_unlikely(shardedAggregateHangBeforeEstablishingShardCursors.shouldFail())) {
LOGV2(20905,
"shardedAggregateHangBeforeEstablishingShardCursors fail point enabled. Blocking "
"until fail point is disabled.");
while (MONGO_unlikely(shardedAggregateHangBeforeEstablishingShardCursors.shouldFail())) {
sleepsecs(1);
}
}
return establishCursors(opCtx,
std::move(executor),
nss,
readPref,
requests,
false /* do not allow partial results */,
getDesiredRetryPolicy(opCtx));
}
std::set<ShardId> getTargetedShards(boost::intrusive_ptr<ExpressionContext> expCtx,
bool mustRunOnAllShards,
const boost::optional<ChunkManager>& cm,
const BSONObj shardQuery,
const BSONObj collation) {
if (mustRunOnAllShards) {
// The pipeline begins with a stage which must be run on all shards.
auto shardIds = Grid::get(expCtx->opCtx)->shardRegistry()->getAllShardIds(expCtx->opCtx);
return {std::make_move_iterator(shardIds.begin()), std::make_move_iterator(shardIds.end())};
}
invariant(cm);
return getTargetedShardsForQuery(expCtx, *cm, shardQuery, collation);
}
/**
* Helpers to check and move stages from a DistributedPlanLogic.
*/
void addMaybeNullStageToFront(Pipeline* pipe, boost::intrusive_ptr<DocumentSource> ds) {
if (ds) {
pipe->addInitialSource(std::move(ds));
}
}
void addMaybeNullStageToBack(Pipeline* pipe, boost::intrusive_ptr<DocumentSource> ds) {
if (ds) {
pipe->addFinalSource(std::move(ds));
}
}
boost::optional<BSONObj> getOwnedOrNone(boost::optional<BSONObj> obj) {
if (obj) {
return obj->getOwned();
}
return boost::none;
}
void addSplitStages(const DocumentSource::DistributedPlanLogic& distributedPlanLogic,
Pipeline* mergePipe,
Pipeline* shardPipe) {
// This stage must be split, split it normally.
// Add in reverse order since we add each to the front and this would flip the order otherwise.
for (auto reverseIt = distributedPlanLogic.mergingStages.rbegin();
reverseIt != distributedPlanLogic.mergingStages.rend();
++reverseIt) {
tassert(6448012,
"A stage cannot simultaneously be present on both sides of a pipeline split",
distributedPlanLogic.shardsStage != *reverseIt);
mergePipe->addInitialSource(*reverseIt);
}
addMaybeNullStageToBack(shardPipe, distributedPlanLogic.shardsStage);
}
/**
* Helper for find split point that handles the split after a stage that must be on
* the merging half of the pipeline defers being added to the merging pipeline.
*/
std::pair<std::unique_ptr<Pipeline, PipelineDeleter>, boost::optional<BSONObj>>
finishFindSplitPointAfterDeferral(
Pipeline* mergePipe,
std::unique_ptr<Pipeline, PipelineDeleter> shardPipe,
boost::intrusive_ptr<DocumentSource> deferredStage,
boost::optional<BSONObj> mergeSort,
DocumentSource::DistributedPlanLogic::movePastFunctionType moveCheckFunc) {
tassert(6253723, "Expected shard pipeline", shardPipe);
tassert(6253724, "Expected original pipeline", mergePipe);
while (!mergePipe->getSources().empty()) {
boost::intrusive_ptr<DocumentSource> current = mergePipe->popFront();
if (!moveCheckFunc(*current)) {
mergePipe->addInitialSource(std::move(current));
break;
}
// If this stage also would like to split, split here. Don't defer multiple stages.
if (auto distributedPlanLogic = current->distributedPlanLogic()) {
addSplitStages(*distributedPlanLogic, mergePipe, shardPipe.get());
// The sort that was earlier in the pipeline takes precedence.
if (!mergeSort) {
mergeSort = getOwnedOrNone(distributedPlanLogic->mergeSortPattern);
}
break;
}
// Move the source from the merger _sources to the shard _sources.
shardPipe->addFinalSource(current);
}
// We got to the end of the pipeline or found a split point.
addMaybeNullStageToFront(mergePipe, std::move(deferredStage));
return {std::move(shardPipe), getOwnedOrNone(mergeSort)};
}
/**
* Moves everything before a splittable stage to the shards. If there are no splittable stages,
* moves everything to the shards.
*
* It is not safe to call this optimization multiple times.
*
* Returns {shardPipe, sortSpec}. The original passed in pipeline retains all stages after the split
* point and becomes the merge pipeline.
*/
std::pair<std::unique_ptr<Pipeline, PipelineDeleter>, boost::optional<BSONObj>> findSplitPoint(
Pipeline* mergePipe) {
const auto& expCtx = mergePipe->getContext();
auto shardPipe = Pipeline::create({}, expCtx);
while (!mergePipe->getSources().empty()) {
boost::intrusive_ptr<DocumentSource> current = mergePipe->popFront();
auto distributedPlanLogic = current->distributedPlanLogic();
// Check if this source is splittable.
if (!distributedPlanLogic) {
// Move the source from the merger _sources to the shard _sources.
shardPipe->addFinalSource(current);
continue;
}
// If we got a plan logic which doesn't require a split, save it and keep going.
if (!distributedPlanLogic->needsSplit) {
addMaybeNullStageToBack(shardPipe.get(), std::move(distributedPlanLogic->shardsStage));
tassert(6253721,
"Must have deferral function if deferring pipeline split",
distributedPlanLogic->canMovePast);
auto mergingStageList = distributedPlanLogic->mergingStages;
tassert(6448007,
"Only support deferring at most one stage for now.",
mergingStageList.size() <= 1);
// We know these are all currently null/none, as if we had deferred something and
// 'current' did not need split we would have returned above.
return finishFindSplitPointAfterDeferral(
mergePipe,
std::move(shardPipe),
mergingStageList.empty() ? nullptr : std::move(*mergingStageList.begin()),
getOwnedOrNone(distributedPlanLogic->mergeSortPattern),
distributedPlanLogic->canMovePast);
}
addSplitStages(*distributedPlanLogic, mergePipe, shardPipe.get());
return {std::move(shardPipe), getOwnedOrNone(distributedPlanLogic->mergeSortPattern)};
}
return {std::move(shardPipe), boost::none};
}
/**
* If the final stage on shards is to unwind an array, move that stage to the merger. This cuts down
* on network traffic and allows us to take advantage of reduced copying in unwind.
*/
void moveFinalUnwindFromShardsToMerger(Pipeline* shardPipe, Pipeline* mergePipe) {
while (!shardPipe->getSources().empty() &&
dynamic_cast<DocumentSourceUnwind*>(shardPipe->getSources().back().get())) {
mergePipe->addInitialSource(shardPipe->popBack());
}
}
/**
* When the last stage of shard pipeline is $sort, move stages that can run on shards and don't
* rename or modify the fields in $sort from merge pipeline. The function starts from the beginning
* of the merge pipeline and finds the first consecutive eligible stages.
*/
void moveEligibleStreamingStagesBeforeSortOnShards(Pipeline* shardPipe,
Pipeline* mergePipe,
const BSONObj& sortPattern) {
tassert(5363800,
"Expected non-empty shardPipe consisting of at least a $sort stage",
!shardPipe->getSources().empty());
if (!dynamic_cast<DocumentSourceSort*>(shardPipe->getSources().back().get())) {
// Expected last stage on the shards to be a $sort.
return;
}
auto sortPaths = sortPattern.getFieldNames<std::set<std::string>>();
auto firstMergeStage = mergePipe->getSources().cbegin();
std::function<bool(DocumentSource*)> distributedPlanLogicCallback = [](DocumentSource* stage) {
return !static_cast<bool>(stage->distributedPlanLogic());
};
auto [lastUnmodified, renameMap] = semantic_analysis::findLongestViablePrefixPreservingPaths(
firstMergeStage, mergePipe->getSources().cend(), sortPaths, distributedPlanLogicCallback);
for (const auto& sortPath : sortPaths) {
auto pair = renameMap.find(sortPath);
if (pair == renameMap.end() || pair->first != pair->second) {
return;
}
}
shardPipe->getSources().insert(shardPipe->getSources().end(), firstMergeStage, lastUnmodified);
mergePipe->getSources().erase(firstMergeStage, lastUnmodified);
}
/**
* Returns true if the final stage of the pipeline limits the number of documents it could output
* (such as a $limit stage).
*
* This function is not meant to exhaustively catch every single case where a pipeline might have
* some kind of limit. It's only here so that propagateDocLimitsToShards() can avoid adding an
* obviously unnecessary $limit to a shard's pipeline.
*/
boost::optional<long long> getPipelineLimit(Pipeline* pipeline) {
for (auto source_it = pipeline->getSources().rbegin();
source_it != pipeline->getSources().rend();
++source_it) {
const auto source = source_it->get();
auto limitStage = dynamic_cast<DocumentSourceLimit*>(source);
if (limitStage) {
return limitStage->getLimit();
}
auto sortStage = dynamic_cast<DocumentSourceSort*>(source);
if (sortStage) {
return sortStage->getLimit();
}
auto cursorStage = dynamic_cast<DocumentSourceSort*>(source);
if (cursorStage) {
return cursorStage->getLimit();
}
// If this stage is one that can swap with a $limit stage, then we can look at the previous
// stage to see if it includes a limit. Otherwise, we give up trying to find a limit on this
// stage's output.
if (!source->constraints().canSwapWithSkippingOrLimitingStage) {
break;
}
}
return boost::none;
}
/**
* If the merging pipeline includes a $limit stage that creates an upper bound on how many input
* documents it needs to compute the aggregation, we can use that as an upper bound on how many
* documents each of the shards needs to produce. Propagating that upper bound to the shards (using
* a $limit in the shard pipeline) can reduce the number of documents the shards need to process and
* transfer over the network (see SERVER-36881).
*
* If there are $skip stages before the $limit, the skipped documents also contribute to the upper
* bound.
*/
void propagateDocLimitToShards(Pipeline* shardPipe, Pipeline* mergePipe) {
long long numDocumentsNeeded = 0;
for (auto&& source : mergePipe->getSources()) {
auto skipStage = dynamic_cast<DocumentSourceSkip*>(source.get());
if (skipStage) {
numDocumentsNeeded += skipStage->getSkip();
continue;
}
auto limitStage = dynamic_cast<DocumentSourceLimit*>(source.get());
if (limitStage) {
numDocumentsNeeded += limitStage->getLimit();
auto existingShardLimit = getPipelineLimit(shardPipe);
if (existingShardLimit && *existingShardLimit <= numDocumentsNeeded) {
// The sharding pipeline already has a limit that is no greater than the limit we
// were going to add, so no changes are necessary.
return;
}
auto shardLimit =
DocumentSourceLimit::create(mergePipe->getContext(), numDocumentsNeeded);
shardPipe->addFinalSource(shardLimit);
// We have successfully applied a limit to the number of documents we need from each
// shard.
return;
}
// If there are any stages in the merge pipeline before the $skip and $limit stages, then we
// cannot use the $limit to determine an upper bound, unless those stages could be swapped
// with the $limit.
if (!source->constraints().canSwapWithSkippingOrLimitingStage) {
return;
}
}
// We did not find any limit in the merge pipeline that would allow us to set an upper bound on
// the number of documents we need from each shard.
return;
}
/**
* Adds a stage to the end of 'shardPipe' explicitly requesting all fields that 'mergePipe' needs.
* This is only done if it heuristically determines that it is needed. This optimization can reduce
* the amount of network traffic and can also enable the shards to convert less source BSON into
* Documents.
*/
void limitFieldsSentFromShardsToMerger(Pipeline* shardPipe, Pipeline* mergePipe) {
DepsTracker mergeDeps(mergePipe->getDependencies(DepsTracker::kNoMetadata));
if (mergeDeps.needWholeDocument)
return; // the merge needs all fields, so nothing we can do.
// Empty project is "special" so if no fields are needed, we just ask for _id instead.
if (mergeDeps.fields.empty())
mergeDeps.fields.insert("_id");
// HEURISTIC: only apply optimization if none of the shard stages have an exhaustive list of
// field dependencies. While this may not be 100% ideal in all cases, it is simple and
// avoids the worst cases by ensuring that:
// 1) Optimization IS applied when the shards wouldn't have known their exhaustive list of
// dependencies. This situation can happen when a $sort is before the first $project or
// $group. Without the optimization, the shards would have to reify and transmit full
// objects even though only a subset of fields are needed.
// 2) Optimization IS NOT applied immediately following a $project or $group since it would
// add an unnecessary project (and therefore a deep-copy).
for (auto&& source : shardPipe->getSources()) {
DepsTracker dt(DepsTracker::kNoMetadata);
if (source->getDependencies(&dt) & DepsTracker::State::EXHAUSTIVE_FIELDS)
return;
}
// if we get here, add the project.
boost::intrusive_ptr<DocumentSource> project = DocumentSourceProject::createFromBson(
BSON("$project" << mergeDeps.toProjectionWithoutMetadata()).firstElement(),
shardPipe->getContext());
shardPipe->pushBack(project);
}
bool stageCanRunInParallel(const boost::intrusive_ptr<DocumentSource>& stage,
const std::set<std::string>& nameOfShardKeyFieldsUponEntryToStage) {
if (stage->distributedPlanLogic()) {
return stage->canRunInParallelBeforeWriteStage(nameOfShardKeyFieldsUponEntryToStage);
} else {
// This stage is fine to execute in parallel on each stream. For example, a $match can be
// applied to each stream in parallel.
return true;
}
}
std::string mapToString(const StringMap<std::string>& map) {
StringBuilder sb;
sb << "{";
for (auto&& entry : map) {
if (sb.len() != 1) {
sb << ", ";
}
sb << entry.first << ": " << entry.second;
}
sb << "}";
return sb.str();
}
BSONObj buildNewKeyPattern(const ShardKeyPattern& shardKey, StringMap<std::string> renames) {
BSONObjBuilder newPattern;
for (auto&& elem : shardKey.getKeyPattern().toBSON()) {
auto it = renames.find(elem.fieldNameStringData());
invariant(it != renames.end(),
str::stream() << "Could not find new name of shard key field \""
<< elem.fieldName() << "\": rename map was "
<< mapToString(renames));
newPattern.appendAs(elem, it->second);
}
return newPattern.obj();
}
StringMap<std::string> computeShardKeyRenameMap(const Pipeline* mergePipeline,
std::set<std::string>&& pathsOfShardKey) {
auto traversalStart = mergePipeline->getSources().crbegin();
auto traversalEnd = mergePipeline->getSources().crend();
const auto leadingGroup =
dynamic_cast<DocumentSourceGroup*>(mergePipeline->getSources().front().get());
if (leadingGroup && leadingGroup->doingMerge()) {
// A leading $group stage will not report to preserve any fields, since it blows away the
// _id and replaces it with something new. It possibly renames some fields, but when
// computing the new shard key we are interested in the name of the shard key *in the middle
// of the $group*. The $exchange will be inserted between the shard-local groups and the
// global groups. Thus we want to exclude this stage from our rename tracking.
traversalEnd = std::prev(traversalEnd);
}
auto renameMap = semantic_analysis::renamedPaths(traversalStart, traversalEnd, pathsOfShardKey);
invariant(renameMap,
str::stream()
<< "Analyzed pipeline was thought to preserve the shard key fields, but did not: "
<< Value(mergePipeline->serialize()).toString());
return *renameMap;
}
/**
* Returns true if any stage in the pipeline would modify any of the fields in 'shardKeyPaths', or
* if there is any stage in the pipeline requires a unified stream to do its computation like a
* $limit would.
*
* Purposefully takes 'shardKeyPaths' by value so that it can be modified throughout.
*/
bool anyStageModifiesShardKeyOrNeedsMerge(std::set<std::string> shardKeyPaths,
const Pipeline* mergePipeline) {
const auto& stages = mergePipeline->getSources();
for (auto it = stages.crbegin(); it != stages.crend(); ++it) {
const auto& stage = *it;
auto renames = semantic_analysis::renamedPaths(
std::move(shardKeyPaths), *stage, semantic_analysis::Direction::kBackward);
if (!renames) {
return true;
}
shardKeyPaths.clear();
for (auto&& rename : *renames) {
shardKeyPaths.insert(rename.second);
}
if (!stageCanRunInParallel(stage, shardKeyPaths)) {
// In order for this stage to work it needs a single input stream which it wouldn't get
// if we inserted an exchange before it.
return true;
}
}
return false;
}
boost::optional<ShardedExchangePolicy> walkPipelineBackwardsTrackingShardKey(
OperationContext* opCtx, const Pipeline* mergePipeline, const ChunkManager& chunkManager) {
const ShardKeyPattern& shardKey = chunkManager.getShardKeyPattern();
std::set<std::string> shardKeyPaths;
for (auto&& path : shardKey.getKeyPatternFields()) {
shardKeyPaths.emplace(path->dottedField().toString());
}
if (anyStageModifiesShardKeyOrNeedsMerge(shardKeyPaths, mergePipeline)) {
return boost::none;
}
// All the fields of the shard key are preserved by the pipeline, but they might be renamed. To
// set up the $exchange, we need to build a fake shard key pattern which uses the names of the
// shard key fields as they are at the split point of the pipeline.
auto renames = computeShardKeyRenameMap(mergePipeline, std::move(shardKeyPaths));
ShardKeyPattern newShardKey(buildNewKeyPattern(shardKey, renames));
// Append the boundaries with the new names from the new shard key.
auto translateBoundary = [&renames](const BSONObj& oldBoundary) {
BSONObjBuilder bob;
for (auto&& elem : oldBoundary) {
bob.appendAs(elem, renames[elem.fieldNameStringData()]);
}
return bob.obj();
};
// Given the new shard key fields, build the distribution map.
ExchangeSpec exchangeSpec;
std::vector<BSONObj> boundaries;
std::vector<int> consumerIds;
std::map<ShardId, int> shardToConsumer;
std::vector<ShardId> consumerShards;
int numConsumers = 0;
// The chunk manager enumerates the chunks in the ascending order from MinKey to MaxKey. Every
// chunk has an associated range [from, to); i.e. inclusive lower bound and exclusive upper
// bound. The chunk ranges must cover all domain without any holes. For the exchange we coalesce
// ranges into a single vector of points. E.g. chunks [min,5], [5,10], [10,max] will produce
// [min,5,10,max] vector. Number of points in the vector is always one greater than number of
// chunks.
// We also compute consumer indices for every chunk. From the example above (3 chunks) we may
// get the vector [0,1,2]; i.e. the first chunk goes to the consumer 0 and so on. Note that
// the consumer id may be repeated if the consumer hosts more than 1 chunk.
chunkManager.forEachChunk([&](const auto& chunk) {
if (boundaries.empty())
boundaries.emplace_back(translateBoundary(chunk.getMin()));
boundaries.emplace_back(translateBoundary(chunk.getMax()));
if (shardToConsumer.find(chunk.getShardId()) == shardToConsumer.end()) {
shardToConsumer.emplace(chunk.getShardId(), numConsumers++);
consumerShards.emplace_back(chunk.getShardId());
}
consumerIds.emplace_back(shardToConsumer[chunk.getShardId()]);
return true;
});
exchangeSpec.setPolicy(ExchangePolicyEnum::kKeyRange);
exchangeSpec.setKey(newShardKey.toBSON());
exchangeSpec.setBoundaries(std::move(boundaries));
exchangeSpec.setConsumers(shardToConsumer.size());
exchangeSpec.setConsumerIds(std::move(consumerIds));
return ShardedExchangePolicy{std::move(exchangeSpec), std::move(consumerShards)};
}
/**
* Non-correlated pipeline caching is only supported locally. When the
* DocumentSourceSequentialDocumentCache stage has been moved to the shards pipeline, abandon the
* associated local cache.
*/
void abandonCacheIfSentToShards(Pipeline* shardsPipeline) {
for (auto&& stage : shardsPipeline->getSources()) {
if (StringData(stage->getSourceName()) ==
DocumentSourceSequentialDocumentCache::kStageName) {
static_cast<DocumentSourceSequentialDocumentCache*>(stage.get())->abandonCache();
}
}
}
} // namespace
std::unique_ptr<Pipeline, PipelineDeleter> targetShardsAndAddMergeCursors(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
stdx::variant<std::unique_ptr<Pipeline, PipelineDeleter>, AggregateCommandRequest>
targetRequest,
boost::optional<BSONObj> shardCursorsSortSpec,
ShardTargetingPolicy shardTargetingPolicy,
boost::optional<BSONObj> readConcern) {
auto&& [aggRequest, pipeline] = [&] {
return stdx::visit(
visit_helper::Overloaded{
[&](std::unique_ptr<Pipeline, PipelineDeleter>&& pipeline) {
return std::make_pair(
AggregateCommandRequest(expCtx->ns, pipeline->serializeToBson()),
std::move(pipeline));
},
[&](AggregateCommandRequest&& aggRequest) {
auto rawPipeline = aggRequest.getPipeline();
return std::make_pair(std::move(aggRequest),
Pipeline::parse(std::move(rawPipeline), expCtx));
}},
std::move(targetRequest));
}();
invariant(pipeline->getSources().empty() ||
!dynamic_cast<DocumentSourceMergeCursors*>(pipeline->getSources().front().get()));
// The default value for 'allowDiskUse' and 'maxTimeMS' in the AggregateCommandRequest may not
// match what was set on the originating command, so copy it from the ExpressionContext.
aggRequest.setAllowDiskUse(expCtx->allowDiskUse);
if (auto maxTimeMS = expCtx->opCtx->getRemainingMaxTimeMillis();
maxTimeMS < Microseconds::max()) {
aggRequest.setMaxTimeMS(durationCount<Milliseconds>(maxTimeMS));
}
LiteParsedPipeline liteParsedPipeline(aggRequest);
auto hasChangeStream = liteParsedPipeline.hasChangeStream();
auto shardDispatchResults =
dispatchShardPipeline(aggregation_request_helper::serializeToCommandDoc(aggRequest),
hasChangeStream,
std::move(pipeline),
shardTargetingPolicy,
std::move(readConcern));
std::vector<ShardId> targetedShards;
targetedShards.reserve(shardDispatchResults.remoteCursors.size());
for (auto&& remoteCursor : shardDispatchResults.remoteCursors) {
targetedShards.emplace_back(remoteCursor->getShardId().toString());
}
std::unique_ptr<Pipeline, PipelineDeleter> mergePipeline;
if (shardDispatchResults.splitPipeline) {
mergePipeline = std::move(shardDispatchResults.splitPipeline->mergePipeline);
if (shardDispatchResults.splitPipeline->shardCursorsSortSpec) {
uassert(4929304, "Split pipeline provides its own sort already", !shardCursorsSortSpec);
shardCursorsSortSpec = shardDispatchResults.splitPipeline->shardCursorsSortSpec;
}
} else {
// We have not split the pipeline, and will execute entirely on the remote shards. Set up an
// empty local pipeline which we will attach the merge cursors stage to.
mergePipeline = Pipeline::parse(std::vector<BSONObj>(), expCtx);
}
partitionAndAddMergeCursorsSource(
mergePipeline.get(), std::move(shardDispatchResults.remoteCursors), shardCursorsSortSpec);
return mergePipeline;
}
std::unique_ptr<Pipeline, PipelineDeleter> runPipelineDirectlyOnSingleShard(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
AggregateCommandRequest request,
ShardId shardId) {
invariant(!request.getExplain());
auto readPreference = uassertStatusOK(ReadPreferenceSetting::fromContainingBSON(
request.getUnwrappedReadPref().value_or(BSONObj())));
auto* opCtx = expCtx->opCtx;
auto* catalogCache = Grid::get(opCtx)->catalogCache();
auto cm =
uassertStatusOK(catalogCache->getCollectionRoutingInfo(opCtx, request.getNamespace()));
auto versionedCmdObj = [&] {
if (cm.isSharded()) {
return appendShardVersion(aggregation_request_helper::serializeToCommandObj(request),
cm.getVersion(shardId));
} else {
// The collection is unsharded. Don't append shard version info when contacting the
// config servers.
const auto cmdObjWithShardVersion = (shardId != ShardId::kConfigServerId)
? appendShardVersion(aggregation_request_helper::serializeToCommandObj(request),
ChunkVersion::UNSHARDED())
: aggregation_request_helper::serializeToCommandObj(request);
return appendDbVersionIfPresent(std::move(cmdObjWithShardVersion), cm.dbVersion());
}
}();
auto cursors = establishCursors(opCtx,
expCtx->mongoProcessInterface->taskExecutor,
request.getNamespace(),
std::move(readPreference),
{{shardId, versionedCmdObj}},
false /* allowPartialResults */,
Shard::RetryPolicy::kIdempotent);
invariant(cursors.size() == 1);
// Convert remote cursors into a vector of "owned" cursors.
std::vector<OwnedRemoteCursor> ownedCursors;
for (auto&& cursor : cursors) {
auto cursorNss = cursor.getCursorResponse().getNSS();
ownedCursors.emplace_back(opCtx, std::move(cursor), std::move(cursorNss));
}
// We have not split the pipeline, and will execute entirely on the remote shard. Set up an
// empty local pipeline which we will attach the merge cursors stage to.
auto mergePipeline = Pipeline::parse(std::vector<BSONObj>{}, expCtx);
partitionAndAddMergeCursorsSource(mergePipeline.get(), std::move(ownedCursors), boost::none);
return mergePipeline;
}
boost::optional<ShardedExchangePolicy> checkIfEligibleForExchange(OperationContext* opCtx,
const Pipeline* mergePipeline) {
if (internalQueryDisableExchange.load()) {
return boost::none;
}
if (mergePipeline->getSources().empty()) {
return boost::none;
}
auto mergeStage = dynamic_cast<DocumentSourceMerge*>(mergePipeline->getSources().back().get());
if (!mergeStage) {
// If there's no $merge stage we won't try to do an $exchange. For the $out stage there's no
// point doing an $exchange because all the writes will go to a single node, so we should
// just perform the merge on that host.
return boost::none;
}
const auto cm =
uassertStatusOK(getCollectionRoutingInfoForTxnCmd(opCtx, mergeStage->getOutputNs()));
if (!cm.isSharded()) {
return boost::none;
}
// The collection is sharded and we have a $merge stage! Here we assume the $merge stage has
// already verified that the shard key pattern is compatible with the unique key being used.
// Assuming this, we just have to make sure the shard key is preserved (though possibly renamed)
// all the way to the front of the merge pipeline. If this is the case then for any document
// entering the merging pipeline we can predict which shard it will need to end up being
// inserted on. With this ability we can insert an exchange on the shards to partition the
// documents based on which shard will end up owning them. Then each shard can perform a merge
// of only those documents which belong to it (optimistically, barring chunk migrations).
return walkPipelineBackwardsTrackingShardKey(opCtx, mergePipeline, cm);
}
SplitPipeline splitPipeline(std::unique_ptr<Pipeline, PipelineDeleter> pipeline) {
// Re-brand 'pipeline' as the merging pipeline. We will move stages one by one from the merging
// half to the shards, as possible.
auto mergePipeline = std::move(pipeline);
auto [shardsPipeline, inputsSort] = findSplitPoint(mergePipeline.get());
// The order in which optimizations are applied can have significant impact on the efficiency of
// the final pipeline. Be Careful!
if (inputsSort) {
moveEligibleStreamingStagesBeforeSortOnShards(
shardsPipeline.get(), mergePipeline.get(), *inputsSort);
}
moveFinalUnwindFromShardsToMerger(shardsPipeline.get(), mergePipeline.get());
propagateDocLimitToShards(shardsPipeline.get(), mergePipeline.get());
limitFieldsSentFromShardsToMerger(shardsPipeline.get(), mergePipeline.get());
abandonCacheIfSentToShards(shardsPipeline.get());
shardsPipeline->setSplitState(Pipeline::SplitState::kSplitForShards);
mergePipeline->setSplitState(Pipeline::SplitState::kSplitForMerge);
return {std::move(shardsPipeline), std::move(mergePipeline), std::move(inputsSort)};
}
BSONObj createPassthroughCommandForShard(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
Document serializedCommand,
boost::optional<ExplainOptions::Verbosity> explainVerbosity,
Pipeline* pipeline,
BSONObj collationObj,
boost::optional<BSONObj> readConcern,
boost::optional<int> overrideBatchSize) {
// Create the command for the shards.
MutableDocument targetedCmd(serializedCommand);
if (pipeline) {
targetedCmd[AggregateCommandRequest::kPipelineFieldName] = Value(pipeline->serialize());
}
if (overrideBatchSize.has_value()) {
if (serializedCommand[AggregateCommandRequest::kCursorFieldName].missing()) {
targetedCmd[AggregateCommandRequest::kCursorFieldName] =
Value(DOC(SimpleCursorOptions::kBatchSizeFieldName << Value(*overrideBatchSize)));
} else {
targetedCmd[AggregateCommandRequest::kCursorFieldName]
[SimpleCursorOptions::kBatchSizeFieldName] = Value(*overrideBatchSize);
}
}
auto shardCommand = genericTransformForShards(std::move(targetedCmd),
expCtx,
explainVerbosity,
std::move(collationObj),
std::move(readConcern));
// Apply filter and RW concern to the final shard command.
return CommandHelpers::filterCommandRequestForPassthrough(
applyReadWriteConcern(expCtx->opCtx,
true, /* appendRC */
!explainVerbosity, /* appendWC */
shardCommand));
}
BSONObj createCommandForTargetedShards(const boost::intrusive_ptr<ExpressionContext>& expCtx,
Document serializedCommand,
const SplitPipeline& splitPipeline,
const boost::optional<ShardedExchangePolicy> exchangeSpec,
bool needsMerge,
boost::optional<BSONObj> readConcern) {
// Create the command for the shards.
MutableDocument targetedCmd(serializedCommand);
// If we've parsed a pipeline on mongos, always override the pipeline, in case parsing it
// has defaulted any arguments or otherwise changed the spec. For example, $listSessions may
// have detected a logged in user and appended that user name to the $listSessions spec to
// send to the shards.
targetedCmd[AggregateCommandRequest::kPipelineFieldName] =
Value(splitPipeline.shardsPipeline->serialize());
// When running on many shards with the exchange we may not need merging.
if (needsMerge) {
targetedCmd[AggregateCommandRequest::kNeedsMergeFieldName] = Value(true);
// If there aren't any stages like $out in the pipeline being sent to the shards, remove the
// write concern. The write concern should only be applied when there are writes performed
// to avoid mistakenly waiting for writes which didn't happen.
const auto& shardsPipe = splitPipeline.shardsPipeline->getSources();
if (!std::any_of(shardsPipe.begin(), shardsPipe.end(), [](const auto& stage) {
return stage->constraints().writesPersistentData();
})) {
targetedCmd[WriteConcernOptions::kWriteConcernField] = Value();
}
}
targetedCmd[AggregateCommandRequest::kCursorFieldName] =
Value(DOC(aggregation_request_helper::kBatchSizeField << 0));
targetedCmd[AggregateCommandRequest::kExchangeFieldName] =
exchangeSpec ? Value(exchangeSpec->exchangeSpec.toBSON()) : Value();
auto shardCommand = genericTransformForShards(std::move(targetedCmd),
expCtx,
expCtx->explain,
expCtx->getCollatorBSON(),
std::move(readConcern));
// Apply RW concern to the final shard command.
return applyReadWriteConcern(expCtx->opCtx,
true, /* appendRC */
!expCtx->explain, /* appendWC */
shardCommand);
}
/**
* Targets shards for the pipeline and returns a struct with the remote cursors or results, and
* the pipeline that will need to be executed to merge the results from the remotes. If a stale
* shard version is encountered, refreshes the routing table and tries again.
*/
DispatchShardPipelineResults dispatchShardPipeline(
Document serializedCommand,
bool hasChangeStream,
std::unique_ptr<Pipeline, PipelineDeleter> pipeline,
ShardTargetingPolicy shardTargetingPolicy,
boost::optional<BSONObj> readConcern) {
auto expCtx = pipeline->getContext();
// The process is as follows:
// - First, determine whether we need to target more than one shard. If so, we split the
// pipeline; if not, we retain the existing pipeline.
// - Call establishShardCursors to dispatch the aggregation to the targeted shards.
// - Stale shard version errors are thrown up to the top-level handler, causing a retry on the
// entire aggregation command.
auto cursors = std::vector<RemoteCursor>();
auto shardResults = std::vector<AsyncRequestsSender::Response>();
auto opCtx = expCtx->opCtx;
const bool needsPrimaryShardMerge =
(pipeline->needsPrimaryShardMerger() || internalQueryAlwaysMergeOnPrimaryShard.load());
const bool needsMongosMerge = pipeline->needsMongosMerger();
const auto shardQuery = pipeline->getInitialQuery();
auto executionNsRoutingInfoStatus = getExecutionNsRoutingInfo(opCtx, expCtx->ns);
// If this is a $changeStream, we swallow NamespaceNotFound exceptions and continue.
// Otherwise, uassert on all exceptions here.
if (!(hasChangeStream && executionNsRoutingInfoStatus == ErrorCodes::NamespaceNotFound)) {
uassertStatusOK(executionNsRoutingInfoStatus);
}
auto executionNsRoutingInfo = executionNsRoutingInfoStatus.isOK()
? std::move(executionNsRoutingInfoStatus.getValue())
: boost::optional<ChunkManager>{};
// A $changeStream update lookup attempts to retrieve a single document by documentKey. In this
// case, we wish to target a single shard using the simple collation, but we also want to ensure
// that we use the collection-default collation on the shard so that the lookup can use the _id
// index. We therefore ignore the collation on the expCtx.
const auto& shardTargetingCollation =
shardTargetingPolicy == ShardTargetingPolicy::kForceTargetingWithSimpleCollation
? CollationSpec::kSimpleSpec
: expCtx->getCollatorBSON();
// Determine whether we can run the entire aggregation on a single shard.
const bool mustRunOnAll = mustRunOnAllShards(expCtx->ns, hasChangeStream);
std::set<ShardId> shardIds = getTargetedShards(
expCtx, mustRunOnAll, executionNsRoutingInfo, shardQuery, shardTargetingCollation);
// Don't need to split the pipeline if we are only targeting a single shard, unless:
// - There is a stage that needs to be run on the primary shard and the single target shard
// is not the primary.
// - The pipeline contains one or more stages which must always merge on mongoS.
const bool needsSplit = (shardIds.size() > 1u || needsMongosMerge ||
(needsPrimaryShardMerge && executionNsRoutingInfo &&
*(shardIds.begin()) != executionNsRoutingInfo->dbPrimary()));
boost::optional<ShardedExchangePolicy> exchangeSpec;
boost::optional<SplitPipeline> splitPipelines;
// If set, the pipeline is not valid to be run if the collection is sharded. The given string
// is the error message to print if the collection is sharded.
boost::optional<std::string> errMsgOnShardedCollection = boost::none;
auto srvcCtxt = opCtx->getServiceContext();
if (srvcCtxt && pipeline) {
errMsgOnShardedCollection =
getSearchHelpers(srvcCtxt)->validatePipelineForShardedCollection(*pipeline.get());
}
if (needsSplit) {
LOGV2_DEBUG(20906,
5,
"Splitting pipeline: targeting = {shardIds_size} shards, needsMongosMerge = "
"{needsMongosMerge}, needsPrimaryShardMerge = {needsPrimaryShardMerge}",
"shardIds_size"_attr = shardIds.size(),
"needsMongosMerge"_attr = needsMongosMerge,
"needsPrimaryShardMerge"_attr = needsPrimaryShardMerge);
splitPipelines = splitPipeline(std::move(pipeline));
// If the first stage of the pipeline is a $search stage, exchange optimization isn't
// possible.
// TODO SERVER-65349 Investigate relaxing this restriction.
if (!splitPipelines || !splitPipelines->shardsPipeline ||
!splitPipelines->shardsPipeline->peekFront() ||
splitPipelines->shardsPipeline->peekFront()->getSourceName() !=
"$_internalSearchMongotRemote"_sd) {
exchangeSpec = checkIfEligibleForExchange(opCtx, splitPipelines->mergePipeline.get());
}
}
// Generate the command object for the targeted shards.
BSONObj targetedCommand =
(splitPipelines ? createCommandForTargetedShards(expCtx,
serializedCommand,
*splitPipelines,
exchangeSpec,
true /* needsMerge */,
std::move(readConcern))
: createPassthroughCommandForShard(expCtx,
serializedCommand,
expCtx->explain,
pipeline.get(),
expCtx->getCollatorBSON(),
std::move(readConcern),
boost::none));
// A $changeStream pipeline must run on all shards, and will also open an extra cursor on the
// config server in order to monitor for new shards. To guarantee that we do not miss any
// shards, we must ensure that the list of shards to which we initially dispatch the pipeline is
// at least as current as the logical time at which the stream begins scanning for new shards.
// We therefore set 'shardRegistryReloadTime' to the current clusterTime and then hard-reload
// the shard registry. We don't refresh for other pipelines that must run on all shards (e.g.
// $currentOp) because, unlike $changeStream, those pipelines may not have been forced to split
// if there was only one shard in the cluster when the command began execution. If a shard was
// added since the earlier targeting logic ran, then refreshing here may cause us to illegally
// target an unsplit pipeline to more than one shard.
const auto currentTime = VectorClock::get(opCtx)->getTime();
auto shardRegistryReloadTime = currentTime.clusterTime().asTimestamp();
if (hasChangeStream) {
Grid::get(opCtx)->shardRegistry()->reload(opCtx);
// Rebuild the set of shards as the shard registry might have changed.
shardIds = getTargetedShards(
expCtx, mustRunOnAll, executionNsRoutingInfo, shardQuery, shardTargetingCollation);
}
// If there were no shards when we began execution, we wouldn't have run this aggregation in the
// first place. Here, we double-check that the shards have not been removed mid-operation.
uassert(ErrorCodes::ShardNotFound,
"Unexpectedly found 0 shards while preparing to dispatch aggregation requests. Were "
"the shards removed mid-operation?",
shardIds.size() > 0);
// Explain does not produce a cursor, so instead we scatter-gather commands to the shards.
if (expCtx->explain) {
if (mustRunOnAll) {
// Some stages (such as $currentOp) need to be broadcast to all shards, and
// should not participate in the shard version protocol.
shardResults =
scatterGatherUnversionedTargetAllShards(opCtx,
expCtx->ns.db(),
targetedCommand,
ReadPreferenceSetting::get(opCtx),
Shard::RetryPolicy::kIdempotent);
} else {
// Aggregations on a real namespace should use the routing table to target
// shards, and should participate in the shard version protocol.
invariant(executionNsRoutingInfo);
shardResults =
scatterGatherVersionedTargetByRoutingTable(opCtx,
expCtx->ns.db(),
expCtx->ns,
*executionNsRoutingInfo,
targetedCommand,
ReadPreferenceSetting::get(opCtx),
Shard::RetryPolicy::kIdempotent,
shardQuery,
shardTargetingCollation);
}
} else {
try {
cursors = establishShardCursors(opCtx,
expCtx->mongoProcessInterface->taskExecutor,
expCtx->ns,
mustRunOnAll,
executionNsRoutingInfo,
shardIds,
targetedCommand,
ReadPreferenceSetting::get(opCtx));
} catch (const StaleConfigException& e) {
// Check to see if the command failed because of a stale shard version or something
// else.
auto staleInfo = e.extraInfo<StaleConfigInfo>();
tassert(6441003, "StaleConfigInfo was null during sharded aggregation", staleInfo);
if (errMsgOnShardedCollection && staleInfo->getVersionWanted() &&
staleInfo->getVersionWanted() != ChunkVersion::UNSHARDED()) {
// If we thought the collection was not sharded, we were wrong. Collection must be
// sharded.
uassert(5858100, *errMsgOnShardedCollection, executionNsRoutingInfo->isSharded());
}
throw;
} catch (const ExceptionFor<ErrorCodes::CollectionUUIDMismatch>& ex) {
uassertStatusOK(populateCollectionUUIDMismatch(opCtx, ex.toStatus()));
MONGO_UNREACHABLE_TASSERT(6487201);
}
// If we thought the collection was sharded and the shard confirmed this, fail if the query
// isn't valid on a sharded collection.
uassert(6347900,
*errMsgOnShardedCollection,
!errMsgOnShardedCollection || !executionNsRoutingInfo->isSharded());
invariant(cursors.size() % shardIds.size() == 0,
str::stream() << "Number of cursors (" << cursors.size()
<< ") is not a multiple of producers (" << shardIds.size() << ")");
// For $changeStream, we must open an extra cursor on the 'config.shards' collection, so
// that we can monitor for the addition of new shards inline with real events.
if (hasChangeStream && expCtx->ns.db() != ShardType::ConfigNS.db()) {
cursors.emplace_back(openChangeStreamNewShardMonitor(expCtx, shardRegistryReloadTime));
}
}
// Convert remote cursors into a vector of "owned" cursors.
std::vector<OwnedRemoteCursor> ownedCursors;
for (auto&& cursor : cursors) {
auto cursorNss = cursor.getCursorResponse().getNSS();
ownedCursors.emplace_back(opCtx, std::move(cursor), std::move(cursorNss));
}
// Record the number of shards involved in the aggregation. If we are required to merge on
// the primary shard, but the primary shard was not in the set of targeted shards, then we
// must increment the number of involved shards.
CurOp::get(opCtx)->debug().nShards = shardIds.size() +
(needsPrimaryShardMerge && executionNsRoutingInfo &&
!shardIds.count(executionNsRoutingInfo->dbPrimary()));
return DispatchShardPipelineResults{needsPrimaryShardMerge,
std::move(ownedCursors),
std::move(shardResults),
std::move(splitPipelines),
std::move(pipeline),
targetedCommand,
shardIds.size(),
exchangeSpec};
}
/**
* Build the AsyncResultsMergerParams from the cursor set and sort spec.
*/
AsyncResultsMergerParams buildArmParams(boost::intrusive_ptr<ExpressionContext> expCtx,
std::vector<OwnedRemoteCursor> ownedCursors,
boost::optional<BSONObj> shardCursorsSortSpec) {
AsyncResultsMergerParams armParams;
armParams.setSort(std::move(shardCursorsSortSpec));
armParams.setTailableMode(expCtx->tailableMode);
armParams.setNss(expCtx->ns);
OperationSessionInfoFromClient sessionInfo;
boost::optional<LogicalSessionFromClient> lsidFromClient;
auto lsid = expCtx->opCtx->getLogicalSessionId();
if (lsid) {
lsidFromClient.emplace(lsid->getId());
lsidFromClient->setUid(lsid->getUid());
}
sessionInfo.setSessionId(lsidFromClient);
sessionInfo.setTxnNumber(expCtx->opCtx->getTxnNumber());
if (TransactionRouter::get(expCtx->opCtx)) {
sessionInfo.setAutocommit(false);
}
armParams.setOperationSessionInfo(sessionInfo);
// Convert owned cursors into a vector of remote cursors to be transferred to the merge
// pipeline.
std::vector<RemoteCursor> remoteCursors;
for (auto&& cursor : ownedCursors) {
// Transfer ownership of the remote cursor to the $mergeCursors stage.
remoteCursors.emplace_back(cursor.releaseCursor());
}
armParams.setRemotes(std::move(remoteCursors));
return armParams;
}
// Anonnymous namespace for helpers of partitionCursorsAndAddMergeCursors.
namespace {
/**
* Given the owned cursors vector, partitions the cursors into either one or two vectors. If
* untyped cursors are present, returned pair will be {results, boost::none}. If results or meta are
* present, the returned pair will be {results, meta}.
*/
std::pair<std::vector<OwnedRemoteCursor>, boost::optional<std::vector<OwnedRemoteCursor>>>
partitionCursors(std::vector<OwnedRemoteCursor> ownedCursors) {
// Partition cursor set based on type/label.
std::vector<OwnedRemoteCursor> resultsCursors;
std::vector<OwnedRemoteCursor> metaCursors;
std::vector<OwnedRemoteCursor> untypedCursors;
for (OwnedRemoteCursor& ownedCursor : ownedCursors) {
auto cursor = *ownedCursor;
auto maybeCursorType = cursor->getCursorResponse().getCursorType();
if (!maybeCursorType) {
untypedCursors.push_back(std::move(ownedCursor));
} else {
auto cursorType = CursorType_parse(IDLParserErrorContext("ShardedAggHelperCursorType"),
maybeCursorType.get());
if (cursorType == CursorTypeEnum::DocumentResult) {
resultsCursors.push_back(std::move(ownedCursor));
} else if (cursorType == CursorTypeEnum::SearchMetaResult) {
metaCursors.push_back(std::move(ownedCursor));
} else {
tasserted(625304, "Received unknown cursor type from mongot.");
}
}
}
// Verify we don't have illegal mix of types and untyped cursors from the shards.
bool haveTypedCursors = !resultsCursors.empty() || !metaCursors.empty();
if (haveTypedCursors) {
tassert(625305,
"Received unexpected mix of labelled and unlabelled cursors.",
untypedCursors.empty());
}
if (haveTypedCursors) {
return {std::move(resultsCursors), std::move(metaCursors)};
}
return {std::move(untypedCursors), boost::none};
}
/**
* Adds a merge cursors stage to the pipeline for metadata cursors. Should not be called if
* the query did not generate metadata cursors.
*/
void injectMetaCursor(Pipeline* mergePipeline, std::vector<OwnedRemoteCursor> metaCursors) {
// Provide the "meta" cursors to the $setVariableFromSubPipeline stage.
for (auto source : mergePipeline->getSources()) {
if (auto* setVarStage =
dynamic_cast<DocumentSourceSetVariableFromSubPipeline*>(source.get())) {
// If $setVar is present, we must have a non-empty set of "meta" cursors.
tassert(625307, "Missing meta cursor set.", !metaCursors.empty());
auto armParams = sharded_agg_helpers::buildArmParams(
mergePipeline->getContext(), std::move(metaCursors), {});
setVarStage->addSubPipelineInitialSource(DocumentSourceMergeCursors::create(
mergePipeline->getContext(), std::move(armParams)));
break;
}
}
}
/**
* Adds a mergeCursors stage to the front of the pipeline to handle merging cursors from each
* shard.
*/
void addMergeCursorsSource(Pipeline* mergePipeline,
std::vector<OwnedRemoteCursor> cursorsToMerge,
boost::optional<BSONObj> shardCursorsSortSpec) {
auto armParams = sharded_agg_helpers::buildArmParams(
mergePipeline->getContext(), std::move(cursorsToMerge), std::move(shardCursorsSortSpec));
mergePipeline->addInitialSource(
DocumentSourceMergeCursors::create(mergePipeline->getContext(), std::move(armParams)));
}
} // namespace
void partitionAndAddMergeCursorsSource(Pipeline* mergePipeline,
std::vector<OwnedRemoteCursor> cursors,
boost::optional<BSONObj> shardCursorsSortSpec) {
auto [resultsCursors, metaCursors] = partitionCursors(std::move(cursors));
// Whether or not cursors are typed/untyped, the first is always the results cursor.
addMergeCursorsSource(mergePipeline, std::move(resultsCursors), shardCursorsSortSpec);
if (metaCursors) {
injectMetaCursor(mergePipeline, std::move(*metaCursors));
}
}
Status appendExplainResults(DispatchShardPipelineResults&& dispatchResults,
const boost::intrusive_ptr<ExpressionContext>& mergeCtx,
BSONObjBuilder* result) {
if (dispatchResults.splitPipeline) {
auto* mergePipeline = dispatchResults.splitPipeline->mergePipeline.get();
const char* mergeType = [&]() {
if (mergePipeline->canRunOnMongos()) {
if (mergeCtx->inMongos) {
return "mongos";
}
return "local";
} else if (dispatchResults.exchangeSpec) {
return "exchange";
} else if (mergePipeline->needsPrimaryShardMerger()) {
return "primaryShard";
} else {
return "anyShard";
}
}();
*result << "mergeType" << mergeType;
MutableDocument pipelinesDoc;
// We specify "queryPlanner" verbosity when building the output for "shardsPart" because
// execution stats are reported by each shard individually.
pipelinesDoc.addField("shardsPart",
Value(dispatchResults.splitPipeline->shardsPipeline->writeExplainOps(
ExplainOptions::Verbosity::kQueryPlanner)));
if (dispatchResults.exchangeSpec) {
BSONObjBuilder bob;
dispatchResults.exchangeSpec->exchangeSpec.serialize(&bob);
bob.append("consumerShards", dispatchResults.exchangeSpec->consumerShards);
pipelinesDoc.addField("exchange", Value(bob.obj()));
}
// We specify "queryPlanner" verbosity because execution stats are not currently
// supported when building the output for "mergerPart".
auto explainOps = mergePipeline->writeExplainOps(ExplainOptions::Verbosity::kQueryPlanner);
// No cursors to remote shards are established for an explain, and the $mergeCursors
// aggregation stage which is normally built in addMergeCursorsSource() requires vectors of
// cursors and ShardIDs. For explain output, we construct the armParams that would normally
// be used in the serialization of the $mergeCursors stage and add it to the serialization
// of the pipeline.
auto armParams =
// Since no cursors are actually established for an explain, construct ARM params with
// an empty vector and then remove it from the explain BSON.
buildArmParams(dispatchResults.splitPipeline->mergePipeline->getContext(),
std::vector<OwnedRemoteCursor>(),
std::move(dispatchResults.splitPipeline->shardCursorsSortSpec))
.toBSON()
.removeField(AsyncResultsMergerParams::kRemotesFieldName);
// See DocumentSourceMergeCursors::serialize().
explainOps.insert(explainOps.begin(), Value(Document{{"$mergeCursors"_sd, armParams}}));
pipelinesDoc.addField("mergerPart", Value(explainOps));
*result << "splitPipeline" << pipelinesDoc.freeze();
} else {
*result << "splitPipeline" << BSONNULL;
}
BSONObjBuilder shardExplains(result->subobjStart("shards"));
for (const auto& shardResult : dispatchResults.remoteExplainOutput) {
invariant(shardResult.shardHostAndPort);
uassertStatusOK(shardResult.swResponse.getStatus());
uassertStatusOK(getStatusFromCommandResult(shardResult.swResponse.getValue().data));
auto shardId = shardResult.shardId.toString();
const auto& data = shardResult.swResponse.getValue().data;
BSONObjBuilder explain(shardExplains.subobjStart(shardId));
explain << "host" << shardResult.shardHostAndPort->toString();
if (auto stagesElement = data["stages"]) {
explain << "stages" << stagesElement;
} else {
auto queryPlannerElement = data["queryPlanner"];
uassert(51157,
str::stream() << "Malformed explain response received from shard " << shardId
<< ": " << data.toString(),
queryPlannerElement);
explain << "queryPlanner" << queryPlannerElement;
if (auto executionStatsElement = data["executionStats"]) {
explain << "executionStats" << executionStatsElement;
}
}
}
return Status::OK();
}
BSONObj targetShardsForExplain(Pipeline* ownedPipeline) {
auto expCtx = ownedPipeline->getContext();
std::unique_ptr<Pipeline, PipelineDeleter> pipeline(ownedPipeline,
PipelineDeleter(expCtx->opCtx));
// The pipeline is going to be explained on the shards, and we don't want to send a
// mergeCursors stage.
invariant(pipeline->getSources().empty() ||
!dynamic_cast<DocumentSourceMergeCursors*>(pipeline->getSources().front().get()));
invariant(expCtx->explain);
// Generate the command object for the targeted shards.
auto rawStages = [&pipeline]() {
auto serialization = pipeline->serialize();
std::vector<BSONObj> stages;
stages.reserve(serialization.size());
for (const auto& stageObj : serialization) {
invariant(stageObj.getType() == BSONType::Object);
stages.push_back(stageObj.getDocument().toBson());
}
return stages;
}();
AggregateCommandRequest aggRequest(expCtx->ns, rawStages);
LiteParsedPipeline liteParsedPipeline(aggRequest);
auto hasChangeStream = liteParsedPipeline.hasChangeStream();
auto shardDispatchResults =
dispatchShardPipeline(aggregation_request_helper::serializeToCommandDoc(aggRequest),
hasChangeStream,
std::move(pipeline));
BSONObjBuilder explainBuilder;
auto appendStatus =
appendExplainResults(std::move(shardDispatchResults), expCtx, &explainBuilder);
uassertStatusOK(appendStatus);
return BSON("pipeline" << explainBuilder.done());
}
StatusWith<ChunkManager> getExecutionNsRoutingInfo(OperationContext* opCtx,
const NamespaceString& execNss) {
// First, verify that there are shards present in the cluster. If not, then we return the
// stronger 'ShardNotFound' error rather than 'NamespaceNotFound'. We must do this because
// $changeStream aggregations ignore NamespaceNotFound in order to allow streams to be opened on
// a collection before its enclosing database is created. However, if there are no shards
// present, then $changeStream should immediately return an empty cursor just as other
// aggregations do when the database does not exist.
const auto shardIds = Grid::get(opCtx)->shardRegistry()->getAllShardIds(opCtx);
if (shardIds.empty()) {
return {ErrorCodes::ShardNotFound, "No shards are present in the cluster"};
}
// This call to getCollectionRoutingInfoForTxnCmd will return !OK if the database does not exist
return getCollectionRoutingInfoForTxnCmd(opCtx, execNss);
}
Shard::RetryPolicy getDesiredRetryPolicy(OperationContext* opCtx) {
// The idempotent retry policy will retry even for writeConcern failures, so only set it if the
// pipeline does not support writeConcern.
if (!opCtx->getWriteConcern().usedDefaultConstructedWC) {
return Shard::RetryPolicy::kNotIdempotent;
}
return Shard::RetryPolicy::kIdempotent;
}
bool mustRunOnAllShards(const NamespaceString& nss, bool hasChangeStream) {
// The following aggregations must be routed to all shards:
// - Any collectionless aggregation, such as non-localOps $currentOp.
// - Any aggregation which begins with a $changeStream stage.
return nss.isCollectionlessAggregateNS() || hasChangeStream;
}
std::unique_ptr<Pipeline, PipelineDeleter> attachCursorToPipeline(
Pipeline* ownedPipeline,
ShardTargetingPolicy shardTargetingPolicy,
boost::optional<BSONObj> readConcern) {
auto expCtx = ownedPipeline->getContext();
std::unique_ptr<Pipeline, PipelineDeleter> pipeline(ownedPipeline,
PipelineDeleter(expCtx->opCtx));
boost::optional<DocumentSource*> hasFirstStage = pipeline->getSources().empty()
? boost::optional<DocumentSource*>{}
: pipeline->getSources().front().get();
if (hasFirstStage) {
// Make sure the first stage isn't already a $mergeCursors, and also check if it is a stage
// which needs to actually get a cursor attached or not.
const auto* firstStage = *hasFirstStage;
invariant(!dynamic_cast<const DocumentSourceMergeCursors*>(firstStage));
// Here we check the hostRequirment because there is at least one stage ($indexStats) which
// does not require input data, but is still expected to fan out and contact remote shards
// nonetheless.
if (auto constraints = firstStage->constraints(); !constraints.requiresInputDocSource &&
(constraints.hostRequirement == StageConstraints::HostTypeRequirement::kLocalOnly)) {
// There's no need to attach a cursor here - the first stage provides its own data and
// is meant to be run locally (e.g. $documents).
return pipeline;
}
}
// Helper to decide whether we should ignore the given shardTargetingPolicy for this namespace.
// Certain namespaces are shard-local; that is, they exist independently on every shard. For
// these namespaces, a local cursor should always be used.
// TODO SERVER-59957: use NamespaceString::isPerShardNamespace instead.
auto shouldAlwaysAttachLocalCursorForNamespace = [](const NamespaceString& ns) {
return (ns.isLocal() || ns.isConfigDotCacheDotChunks() ||
ns.isReshardingLocalOplogBufferCollection() ||
ns == NamespaceString::kConfigImagesNamespace ||
ns == NamespaceString::kChangeStreamPreImagesNamespace);
};
if (shardTargetingPolicy == ShardTargetingPolicy::kNotAllowed ||
shouldAlwaysAttachLocalCursorForNamespace(expCtx->ns)) {
auto pipelineToTarget = pipeline->clone();
return expCtx->mongoProcessInterface->attachCursorSourceToPipelineForLocalRead(
pipelineToTarget.release());
}
sharding::router::CollectionRouter router(expCtx->opCtx->getServiceContext(), expCtx->ns);
return router.route(
expCtx->opCtx,
"targeting pipeline to attach cursors"_sd,
[&](OperationContext* opCtx, const ChunkManager& cm) {
auto pipelineToTarget = pipeline->clone();
if (!cm.isSharded()) {
// If the collection is unsharded and we are on the primary, we should be able to
// do a local read. The primary may be moved right after the primary shard check,
// but the local read path will do a db version check before it establishes a cursor
// to catch this case and ensure we fail to read locally.
try {
auto expectUnshardedCollection(
expCtx->mongoProcessInterface->expectUnshardedCollectionInScope(
expCtx->opCtx, expCtx->ns, cm.dbVersion()));
expCtx->mongoProcessInterface->checkOnPrimaryShardForDb(expCtx->opCtx,
expCtx->ns);
LOGV2_DEBUG(5837600,
3,
"Performing local read",
logAttrs(expCtx->ns),
"pipeline"_attr = pipelineToTarget->serializeToBson(),
"comment"_attr = expCtx->opCtx->getComment());
return expCtx->mongoProcessInterface->attachCursorSourceToPipelineForLocalRead(
pipelineToTarget.release());
} catch (ExceptionFor<ErrorCodes::IllegalOperation>&) {
// The current node isn't the primary for or has stale information about this
// collection, proceed with shard targeting.
} catch (ExceptionFor<ErrorCodes::StaleDbVersion>&) {
// The current node has stale information about this collection, proceed with
// shard targeting, which has logic to handle refreshing that may be needed.
} catch (ExceptionForCat<ErrorCategory::StaleShardVersionError>&) {
// The current node has stale information about this collection, proceed with
// shard targeting, which has logic to handle refreshing that may be needed.
} catch (ExceptionFor<ErrorCodes::CommandNotSupportedOnView>&) {
// The current node may be trying to run a pipeline on a namespace which is an
// unresolved view, proceed with shard targeting,
}
// The local read failed. Recreate 'pipelineToTarget' if it was released above.
if (!pipelineToTarget) {
pipelineToTarget = pipeline->clone();
}
}
return targetShardsAndAddMergeCursors(expCtx,
std::move(pipelineToTarget),
boost::none,
shardTargetingPolicy,
std::move(readConcern));
});
}
} // namespace sharded_agg_helpers
} // namespace mongo
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