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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.
*/
#pragma once
#include "mongo/db/exec/plan_stats.h"
#include "mongo/db/query/canonical_query.h"
#include "mongo/db/query/collection_query_info.h"
#include "mongo/db/query/plan_explainer_factory.h"
#include "mongo/db/query/sbe_plan_ranker.h"
namespace mongo {
/**
* Specifies how the multi-planner should interact with the plan cache.
*/
enum class PlanCachingMode {
// Always write a cache entry for the winning plan to the plan cache, overwriting any
// previously existing cache entry for the query shape.
AlwaysCache,
// Write a cache entry for the query shape *unless* we encounter one of the following edge
// cases:
// - Two or more plans tied for the win.
// - The winning plan returned zero query results during the plan ranking trial period.
SometimesCache,
// Do not write to the plan cache.
NeverCache,
};
namespace plan_cache_util {
// The logging facility enforces the rule that logging should not be done in a header file. Since
// the template classes and functions below must be defined in the header file and since they do use
// the logging facility, we have to define the helper functions below to perform the actual logging
// operation from template code.
namespace log_detail {
void logTieForBest(std::string&& query,
double winnerScore,
double runnerUpScore,
std::string winnerPlanSummary,
std::string runnerUpPlanSummary);
void logNotCachingZeroResults(std::string&& query, double score, std::string winnerPlanSummary);
void logNotCachingNoData(std::string&& solution);
} // namespace log_detail
/**
* Caches the best candidate plan, chosen from the given 'candidates' based on the 'ranking'
* decision, if the 'query' is of a type that can be cached. Otherwise, does nothing.
*
* The 'cachingMode' specifies whether the query should be:
* * Always cached.
* * Never cached.
* * Cached, except in certain special cases.
*/
template <typename PlanStageType, typename ResultType, typename Data>
void updatePlanCache(
OperationContext* opCtx,
const CollectionPtr& collection,
PlanCachingMode cachingMode,
const CanonicalQuery& query,
std::unique_ptr<plan_ranker::PlanRankingDecision> ranking,
const std::vector<plan_ranker::BaseCandidatePlan<PlanStageType, ResultType, Data>>&
candidates) {
auto winnerIdx = ranking->candidateOrder[0];
invariant(winnerIdx >= 0 && winnerIdx < candidates.size());
// Even if the query is of a cacheable shape, the caller might have indicated that we shouldn't
// write to the plan cache.
//
// TODO: We can remove this if we introduce replanning logic to the SubplanStage.
bool canCache = (cachingMode == PlanCachingMode::AlwaysCache);
if (cachingMode == PlanCachingMode::SometimesCache) {
// In "sometimes cache" mode, we cache unless we hit one of the special cases below.
canCache = true;
if (ranking->tieForBest) {
// The winning plan tied with the runner-up and we're using "sometimes cache" mode. We
// will not write a plan cache entry.
canCache = false;
// These arrays having two or more entries is implied by 'tieForBest'.
invariant(ranking->scores.size() > 1U);
invariant(ranking->candidateOrder.size() > 1U);
auto runnerUpIdx = ranking->candidateOrder[1];
auto&& [winnerExplainer, runnerUpExplainer] = [&]() {
if constexpr (std::is_same_v<PlanStageType, std::unique_ptr<sbe::PlanStage>>) {
return std::make_pair(
plan_explainer_factory::make(candidates[winnerIdx].root.get(),
&candidates[winnerIdx].data,
candidates[winnerIdx].solution.get()),
plan_explainer_factory::make(candidates[runnerUpIdx].root.get(),
&candidates[runnerUpIdx].data,
candidates[runnerUpIdx].solution.get()));
} else {
static_assert(std::is_same_v<PlanStageType, PlanStage*>);
return std::make_pair(
plan_explainer_factory::make(candidates[winnerIdx].root),
plan_explainer_factory::make(candidates[runnerUpIdx].root));
}
}();
log_detail::logTieForBest(query.toStringShort(),
ranking->scores[0],
ranking->scores[1],
winnerExplainer->getPlanSummary(),
runnerUpExplainer->getPlanSummary());
}
if (candidates[winnerIdx].results.empty()) {
// We're using the "sometimes cache" mode, and the winning plan produced no results
// during the plan ranking trial period. We will not write a plan cache entry.
canCache = false;
auto winnerExplainer = [&]() {
if constexpr (std::is_same_v<PlanStageType, std::unique_ptr<sbe::PlanStage>>) {
return plan_explainer_factory::make(candidates[winnerIdx].root.get(),
&candidates[winnerIdx].data,
candidates[winnerIdx].solution.get());
} else {
static_assert(std::is_same_v<PlanStageType, PlanStage*>);
return plan_explainer_factory::make(candidates[winnerIdx].root);
}
}();
log_detail::logNotCachingZeroResults(
query.toStringShort(), ranking->scores[0], winnerExplainer->getPlanSummary());
}
}
// Store the choice we just made in the cache, if the query is of a type that is safe to
// cache.
if (PlanCache::shouldCacheQuery(query) && canCache) {
// Create list of candidate solutions for the cache with the best solution at the front.
std::vector<QuerySolution*> solutions;
// Generate solutions and ranking decisions sorted by score.
for (auto&& ix : ranking->candidateOrder) {
solutions.push_back(candidates[ix].solution.get());
}
// Insert the failed plans in the back.
for (auto&& ix : ranking->failedCandidates) {
solutions.push_back(candidates[ix].solution.get());
}
// Check solution cache data. Do not add to cache if we have any invalid SolutionCacheData
// data. One known example is 2D queries.
bool validSolutions = true;
for (size_t ix = 0; ix < solutions.size(); ++ix) {
if (nullptr == solutions[ix]->cacheData.get()) {
log_detail::logNotCachingNoData(solutions[ix]->toString());
validSolutions = false;
break;
}
}
if (validSolutions) {
uassertStatusOK(CollectionQueryInfo::get(collection)
.getPlanCache()
->set(query,
solutions,
std::move(ranking),
opCtx->getServiceContext()->getPreciseClockSource()->now()));
}
}
}
} // namespace plan_cache_util
} // namespace mongo
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