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/**
* Copyright (C) 2013-2014 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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_stage.h"
#include "mongo/db/exec/plan_stats.h"
#include "mongo/db/query/canonical_query.h"
#include "mongo/db/query/plan_executor.h"
#include "mongo/db/query/query_planner_params.h"
#include "mongo/db/query/query_solution.h"
#include "mongo/db/query/type_explain.h"
namespace mongo {
class Collection;
class OperationContext;
// Temporarily hide the new explain implementation behind a setParameter.
// TODO: take this out, and make the new implementation the default.
extern bool enableNewExplain;
/**
* A container for the summary statistics that the profiler, slow query log, and
* other non-explain debug mechanisms may want to collect.
*/
struct PlanSummaryStats {
PlanSummaryStats() : nReturned(0),
totalKeysExamined(0),
totalDocsExamined(0),
isIdhack(false),
hasSortStage(false),
summaryStr("") { }
// The number of results returned by the plan.
size_t nReturned;
// The total number of index keys examined by the plan.
size_t totalKeysExamined;
// The total number of documents examined by the plan.
size_t totalDocsExamined;
// The number of milliseconds spent inside the root stage's work() method.
long long executionTimeMillis;
// Did this plan use the fast path for key-value retrievals on the _id index?
bool isIdhack;
// Did this plan use an in-memory sort stage?
bool hasSortStage;
// A string summarizing the plan selected.
std::string summaryStr;
};
/**
* Namespace for the collection of static methods used to generate explain information.
*/
class Explain {
public:
/**
* The various supported verbosity levels for explain. The order is
* significant: the enum values are assigned in order of increasing verbosity.
*/
enum Verbosity {
// At all verbosities greater than or equal to QUERY_PLANNER, we display information
// about the plan selected and alternate rejected plans. Does not include any execution-
// related info. String alias is "queryPlanner".
QUERY_PLANNER = 0,
// At all verbosities greater than or equal to EXEC_STATS, we display a section of
// output containing both overall execution stats, and stats per stage in the
// execution tree. String alias is "execStats".
EXEC_STATS = 1,
// At this second-highest verbosity level, we generate the execution stats for each
// rejected plan as well as the winning plan. String alias is "allPlansExecution".
EXEC_ALL_PLANS = 2,
// This is the highest verbosity level. It has the same behavior as EXEC_ALL_PLANS,
// except it includes more detailed stats. String alias is "full".
//
// The FULL verbosity level is used to generate detailed debug information for the
// plan cache and for logging. It includes metrics like "works", "isEOF", and "advanced"
// that are omitted at lesser verbosities.
FULL = 3,
};
/**
* Get explain BSON for the execution stages contained by 'exec'. Use this function if you
* have a PlanExecutor and want to convert it into a human readable explain format. Any
* operation which has a query component (e.g. find, update, group) can be explained via
* this function.
*
* The explain information is extracted from 'exec' and added to the out-parameter 'out'.
*
* The explain information is generated with the level of detail specified by 'verbosity'.
*
* Does not take ownership of its arguments.
*/
static Status explainStages(PlanExecutor* exec,
Explain::Verbosity verbosity,
BSONObjBuilder* out);
/**
* Converts the stats tree 'stats' into a corresponding BSON object containing
* explain information.
*
* Generates the BSON stats at a verbosity specified by 'verbosity'. Defaults
* to the highest verbosity (FULL).
*/
static BSONObj statsToBSON(const PlanStageStats& stats,
Explain::Verbosity verbosity = FULL);
/**
* This version of stats tree to BSON conversion returns the result through the
* out-parameter 'bob' rather than returning a BSONObj.
*
* Generates the BSON stats at a verbosity specified by 'verbosity'. Defaults
* to the highest verbosity (FULL).
*/
static void statsToBSON(const PlanStageStats& stats,
BSONObjBuilder* bob,
Explain::Verbosity verbosity = FULL);
/**
* Returns a short plan summary std::string describing the leaves of the query plan.
*/
static std::string getPlanSummary(PlanStage* root);
/**
* Fills out 'statsOut' with summary stats using the execution tree contained
* in 'exec'.
*
* The summary stats are consumed by debug mechanisms such as the profiler and
* the slow query log.
*
* This is a lightweight alternative for explainStages(...) above which is useful
* when operations want to request debug information without doing all the work
* to generate a full explain.
*
* Does not take ownership of its arguments.
*/
static void getSummaryStats(PlanExecutor* exec, PlanSummaryStats* statsOut);
//
// Helpers for special-case explains.
//
/**
* If you have an empty query with a count, then there are no execution stages.
* We just get the number of records and then apply skip/limit. Since there
* are no stages, this requires a special explain format.
*/
static void explainCountEmptyQuery(BSONObjBuilder* out);
/**
* Generate the legacy explain format from a PlanExecutor.
*
* On success, the caller owns 'explain'.
*
* TODO: THIS IS TEMPORARY. Once the legacy explain code is deleted, we won't
* need this anymore.
*/
static Status legacyExplain(PlanExecutor* exec, TypeExplain** explain);
private:
/**
* Private helper that does the heavy-lifting for the public statsToBSON(...) functions
* declared above.
*
* Not used except as a helper to the public statsToBSON(...) functions.
*/
static void statsToBSON(const PlanStageStats& stats,
Explain::Verbosity verbosity,
BSONObjBuilder* bob,
BSONObjBuilder* topLevelBob);
/**
* Adds the 'queryPlanner' explain section to the BSON object being built
* by 'out'.
*
* This is a helper for generating explain BSON. It is used by explainStages(...).
*
* @param query -- the query part of the operation being explained.
* @param winnerStats -- the stats tree for the winning plan.
* @param rejectedStats -- an array of stats trees, one per rejected plan
*/
static void generatePlannerInfo(CanonicalQuery* query,
PlanStageStats* winnerStats,
const vector<PlanStageStats*>& rejectedStats,
BSONObjBuilder* out);
/**
* Generates the execution stats section for the stats tree 'stats',
* adding the resulting BSON to 'out'.
*
* Stats are generated at the verbosity specified by 'verbosity'.
*
* This is a helper for generating explain BSON. It is used by explainStages(...).
*/
static void generateExecStats(PlanStageStats* stats,
Explain::Verbosity verbosity,
BSONObjBuilder* out);
/**
* Adds the 'serverInfo' explain section to the BSON object being build
* by 'out'.
*
* This is a helper for generating explain BSON. It is used by explainStages(...).
*/
static void generateServerInfo(BSONObjBuilder* out);
};
} // namespace
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