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/**
* Copyright (C) 2020-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/platform/basic.h"
#include "mongo/db/query/sbe_runtime_planner.h"
#include "mongo/db/catalog/collection.h"
#include "mongo/db/exec/sbe/expressions/expression.h"
#include "mongo/db/exec/trial_period_utils.h"
#include "mongo/db/exec/trial_run_tracker.h"
#include "mongo/db/query/plan_executor_sbe.h"
namespace mongo::sbe {
namespace {
/**
* Fetches a next document form the given plan stage tree and returns 'true' if the plan stage
* returns EOF, or throws 'TrialRunTracker::EarlyExitException' exception. Otherwise, the
* loaded document is placed into the candidate's plan result queue.
*
* If the plan stage throws a 'QueryExceededMemoryLimitNoDiskUseAllowed', it will be caught and the
* 'candidate->failed' flag will be set to 'true', and the 'numFailures' parameter incremented by 1.
* This failure is considered recoverable, as another candidate plan may require less memory, or may
* not contain a stage requiring spilling to disk at all.
*/
bool fetchNextDocument(plan_ranker::CandidatePlan* candidate,
const std::pair<value::SlotAccessor*, value::SlotAccessor*>& slots) {
try {
BSONObj obj;
RecordId recordId;
auto [resultSlot, recordIdSlot] = slots;
auto state = fetchNext(candidate->root.get(),
resultSlot,
recordIdSlot,
&obj,
recordIdSlot ? &recordId : nullptr,
true /* must return owned BSON */);
if (state == PlanState::IS_EOF) {
candidate->root->close();
return true;
}
invariant(state == PlanState::ADVANCED);
invariant(obj.isOwned());
candidate->results.push({obj, {recordIdSlot != nullptr, recordId}});
} catch (const ExceptionFor<ErrorCodes::QueryTrialRunCompleted>&) {
candidate->exitedEarly = true;
return true;
} catch (const ExceptionFor<ErrorCodes::QueryExceededMemoryLimitNoDiskUseAllowed>& ex) {
candidate->root->close();
candidate->status = ex.toStatus();
}
return false;
}
} // namespace
StatusWith<std::tuple<value::SlotAccessor*, value::SlotAccessor*, bool>>
BaseRuntimePlanner::prepareExecutionPlan(PlanStage* root,
stage_builder::PlanStageData* data) const {
invariant(root);
invariant(data);
root->prepare(data->ctx);
value::SlotAccessor* resultSlot{nullptr};
if (auto slot = data->outputs.getIfExists(stage_builder::PlanStageSlots::kResult); slot) {
resultSlot = root->getAccessor(data->ctx, *slot);
tassert(4822871, "Query does not have a result slot.", resultSlot);
}
value::SlotAccessor* recordIdSlot{nullptr};
if (auto slot = data->outputs.getIfExists(stage_builder::PlanStageSlots::kRecordId); slot) {
recordIdSlot = root->getAccessor(data->ctx, *slot);
tassert(4822872, "Query does not have a recordId slot.", recordIdSlot);
}
auto exitedEarly{false};
try {
root->open(false);
} catch (const ExceptionFor<ErrorCodes::QueryTrialRunCompleted>&) {
exitedEarly = true;
} catch (const ExceptionFor<ErrorCodes::QueryExceededMemoryLimitNoDiskUseAllowed>& ex) {
root->close();
return ex.toStatus();
}
return std::make_tuple(resultSlot, recordIdSlot, exitedEarly);
}
std::vector<plan_ranker::CandidatePlan> BaseRuntimePlanner::collectExecutionStats(
std::vector<std::unique_ptr<QuerySolution>> solutions,
std::vector<std::pair<std::unique_ptr<PlanStage>, stage_builder::PlanStageData>> roots,
size_t maxTrialPeriodNumReads) {
invariant(solutions.size() == roots.size());
std::vector<plan_ranker::CandidatePlan> candidates;
std::vector<std::pair<value::SlotAccessor*, value::SlotAccessor*>> accessors;
std::vector<std::pair<PlanStage*, std::unique_ptr<TrialRunTracker>>> trialRunTrackers;
ON_BLOCK_EXIT([&] {
// Detach each SBE plan's TrialRunTracker.
while (!trialRunTrackers.empty()) {
trialRunTrackers.back().first->detachFromTrialRunTracker();
trialRunTrackers.pop_back();
}
});
const auto maxNumResults{trial_period::getTrialPeriodNumToReturn(_cq)};
// Determine which plans are blocking and which are non blocking. The non blocking plans will
// be run first in order to provide an upper bound on the number of reads allowed for the
// blocking plans.
std::vector<size_t> nonBlockingPlanIndexes;
std::vector<size_t> blockingPlanIndexes;
for (size_t index = 0; index < solutions.size(); ++index) {
if (solutions[index]->hasBlockingStage) {
blockingPlanIndexes.push_back(index);
} else {
nonBlockingPlanIndexes.push_back(index);
}
}
// If all the plans are blocking, then the trial period risks going on for too long. Because the
// plans are blocking, they may not provide 'maxNumResults' within the allotted budget of reads.
// We could end up in a situation where each plan's trial period runs for a long time,
// substantially slowing down the multi-planning process. For this reason, when all the plans
// are blocking, we pass 'maxNumResults' to the trial run tracker. This causes the sort stage to
// exit early as soon as it sees 'maxNumResults' _input_ values, which keeps the trial period
// shorter.
//
// On the other hand, if we have a mix of blocking and non-blocking plans, we don't want the
// sort stage to exit early based on the number of input rows it observes. This could cause the
// trial period for the blocking plans to run for a much shorter timeframe than the non-blocking
// plans. This leads to an apples-to-oranges comparison between the blocking and non-blocking
// plans which could artificially favor the blocking plans.
const size_t trackerResultsBudget = nonBlockingPlanIndexes.empty() ? maxNumResults : 0;
auto runPlans = [&](const std::vector<size_t>& planIndexes, size_t& maxNumReads) -> void {
for (auto planIndex : planIndexes) {
// Prepare the plan.
auto&& [root, data] = roots[planIndex];
// Attach a unique TrialRunTracker to the plan, which is configured to use at most
// 'maxNumReads' reads.
auto tracker = std::make_unique<TrialRunTracker>(trackerResultsBudget, maxNumReads);
root->attachToTrialRunTracker(tracker.get());
trialRunTrackers.emplace_back(root.get(), std::move(tracker));
// Before preparing our plan, verify that none of the required indexes were dropped.
// This can occur if a yield occurred during a previously trialed plan.
_indexExistenceChecker.check();
auto status = prepareExecutionPlan(root.get(), &data);
auto [resultAccessor, recordIdAccessor, exitedEarly] =
[&]() -> std::tuple<value::SlotAccessor*, value::SlotAccessor*, bool> {
if (status.isOK()) {
return status.getValue();
}
// The candidate plan returned a failure that is not fatal to the execution of the
// query, as long as we have other candidates that haven't failed. We will mark the
// candidate as failed and keep preparing any remaining candidate plans.
return {};
}();
candidates.push_back({std::move(solutions[planIndex]),
std::move(root),
std::move(data),
exitedEarly,
status.getStatus()});
accessors.push_back({resultAccessor, recordIdAccessor});
// The current candidate is located at the end of each vector.
auto endIdx = candidates.size() - 1;
// Run the plan until the plan finishes, uses up its allowed budget of storage reads,
// or returns 'maxNumResults' results.
for (size_t it = 0; it < maxNumResults; ++it) {
// Even if we had a candidate plan that exited early, we still want continue the
// trial run for the remaining plans as the early exited plan may not be the best.
// For example, it could be blocked in a SORT stage until one of the trial period
// metrics was reached, causing the plan to raise an early exit exception and return
// control back to the runtime planner. If that happens, we need to continue and
// complete the trial period for all candidates, as some of them may have a better
// cost.
if (!candidates[endIdx].status.isOK() || candidates[endIdx].exitedEarly) {
break;
}
bool candidateDone = fetchNextDocument(&candidates[endIdx], accessors[endIdx]);
bool reachedMaxNumResults = (it == maxNumResults - 1);
// If this plan finished or returned 'maxNumResults', then use its number of reads
// as the value for 'maxNumReads' if it's the smallest we've seen.
if (candidateDone || reachedMaxNumResults) {
maxNumReads = std::min(
maxNumReads,
trialRunTrackers[endIdx]
.second->getMetric<TrialRunTracker::TrialRunMetric::kNumReads>());
break;
}
}
}
};
runPlans(nonBlockingPlanIndexes, maxTrialPeriodNumReads);
runPlans(blockingPlanIndexes, maxTrialPeriodNumReads);
return candidates;
}
} // namespace mongo::sbe
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