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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.
*/
#pragma once
#include <memory>
#include <string>
#include <vector>
#include "mongo/base/owned_pointer_vector.h"
#include "mongo/base/status.h"
#include "mongo/base/string_data.h"
#include "mongo/db/exec/requires_all_indices_stage.h"
#include "mongo/db/query/canonical_query.h"
#include "mongo/db/query/plan_cache.h"
#include "mongo/db/query/plan_yield_policy.h"
#include "mongo/db/query/query_planner_params.h"
#include "mongo/db/query/query_solution.h"
#include "mongo/db/record_id.h"
#include "mongo/stdx/memory.h"
namespace mongo {
class OperationContext;
/**
* The SubplanStage is used for rooted $or queries. It plans each clause of the $or
* individually, and then creates an overall query plan based on the winning plan from
* each clause.
*
* Uses the MultiPlanStage in order to rank plans for the individual clauses.
*
* Notes on caching strategy:
*
* --Interaction with the plan cache is done on a per-clause basis. For a given clause C,
* if there is a plan in the cache for shape C, then C is planned using the index tags
* obtained from the plan cache entry. If no cached plan is found for C, then a MultiPlanStage
* is used to determine the best plan for the clause; unless there is a tie between multiple
* candidate plans, the winner is inserted into the plan cache and used to plan subsequent
* executions of C. These subsequent executions of shape C could be either as a clause in
* another rooted $or query, or shape C as its own query.
*
* --Plans for entire rooted $or queries are neither written to nor read from the plan cache.
*/
class SubplanStage final : public RequiresAllIndicesStage {
public:
SubplanStage(OperationContext* opCtx,
const Collection* collection,
WorkingSet* ws,
const QueryPlannerParams& params,
CanonicalQuery* cq);
static bool canUseSubplanning(const CanonicalQuery& query);
bool isEOF() final;
StageState doWork(WorkingSetID* out) final;
StageType stageType() const final {
return STAGE_SUBPLAN;
}
std::unique_ptr<PlanStageStats> getStats();
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
/**
* Selects a plan using subplanning. First uses the query planning results from
* planSubqueries() and the multi plan stage to select the best plan for each branch.
*
* If this effort fails, then falls back on planning the whole query normally rather
* then planning $or branches independently.
*
* If 'yieldPolicy' is non-NULL, then all locks may be yielded in between round-robin
* works of the candidate plans. By default, 'yieldPolicy' is NULL and no yielding will
* take place.
*
* Returns a non-OK status if query planning fails. In particular, this function returns
* ErrorCodes::QueryPlanKilled if the query plan was killed during a yield, or
* ErrorCodes::MaxTimeMSExpired if the operation has exceeded its time limit.
*/
Status pickBestPlan(PlanYieldPolicy* yieldPolicy);
//
// For testing.
//
/**
* Returns true if the i-th branch was planned by retrieving a cached solution,
* otherwise returns false.
*/
bool branchPlannedFromCache(size_t i) const;
/**
* Provide access to the query solution for our composite solution. Does not relinquish
* ownership.
*/
QuerySolution* compositeSolution() const {
return _compositeSolution.get();
}
private:
/**
* A class used internally in order to keep track of the results of planning
* a particular $or branch.
*/
struct BranchPlanningResult {
MONGO_DISALLOW_COPYING(BranchPlanningResult);
public:
BranchPlanningResult() {}
// A parsed version of one branch of the $or.
std::unique_ptr<CanonicalQuery> canonicalQuery;
// If there is cache data available, then we store it here rather than generating
// a set of alternate plans for the branch. The index tags from the cache data
// can be applied directly to the parent $or MatchExpression when generating the
// composite solution.
std::unique_ptr<CachedSolution> cachedSolution;
// Query solutions resulting from planning the $or branch.
std::vector<std::unique_ptr<QuerySolution>> solutions;
};
/**
* Plan each branch of the $or independently, and store the resulting
* lists of query solutions in '_solutions'.
*
* Called from SubplanStage::make so that construction of the subplan stage
* fails immediately, rather than returning a plan executor and subsequently
* through getNext(...).
*/
Status planSubqueries();
/**
* Uses the query planning results from planSubqueries() and the multi plan stage
* to select the best plan for each branch.
*
* Helper for pickBestPlan().
*/
Status choosePlanForSubqueries(PlanYieldPolicy* yieldPolicy);
/**
* Used as a fallback if subplanning fails. Helper for pickBestPlan().
*/
Status choosePlanWholeQuery(PlanYieldPolicy* yieldPolicy);
// Not owned here.
WorkingSet* _ws;
QueryPlannerParams _plannerParams;
// Not owned here.
CanonicalQuery* _query;
// The copy of the query that we will annotate with tags and use to construct the composite
// solution. Must be a rooted $or query, or a contained $or that has been rewritten to a
// rooted $or.
std::unique_ptr<MatchExpression> _orExpression;
// If we successfully create a "composite solution" by planning each $or branch
// independently, that solution is owned here.
std::unique_ptr<QuerySolution> _compositeSolution;
// Holds a list of the results from planning each branch.
std::vector<std::unique_ptr<BranchPlanningResult>> _branchResults;
// We need this to extract cache-friendly index data from the index assignments.
std::map<IndexEntry::Identifier, size_t> _indexMap;
};
} // namespace mongo
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