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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 <string>
#include "mongo/db/query/explain_options.h"
#include "mongo/s/async_requests_sender.h"
#include "mongo/s/commands/strategy.h"
namespace mongo {
class OperationContext;
/**
* Namespace for the collection of static methods used by commands in the implementation of
* explain on mongos.
*/
class ClusterExplain {
public:
/**
* Temporary crutch to allow a single implementation of the methods in this file. Since
* AsyncRequestsSender::Response is a strict superset of Strategy::CommandResult, we leave the
* implementations in terms of Strategy::CommandResult and convert down.
*
* TODO(esha): remove once Strategy::commandOp is removed, and make these methods take
* vector<AsyncRequestsSender::Response>.
*/
static std::vector<Strategy::CommandResult> downconvert(
OperationContext* opCtx, const std::vector<AsyncRequestsSender::Response>& responses);
/**
* Returns an explain command request wrapping the passed in command at the given verbosity
* level, propagating generic top-level command arguments.
*/
static BSONObj wrapAsExplain(const BSONObj& cmdObj, ExplainOptions::Verbosity verbosity);
/**
* Determines the kind of "execution stage" that mongos would use in order to collect
* the results from the shards, assuming that the command being explained is a read
* operation such as find or count.
*/
static const char* getStageNameForReadOp(size_t numShards, const BSONObj& explainObj);
/**
* Command implementations on mongos use this method to construct the sharded explain
* output format based on the results from the shards in 'shardResults'.
*
* On success, the output is added to the BSONObj builder 'out'.
*/
static Status buildExplainResult(OperationContext* opCtx,
const std::vector<Strategy::CommandResult>& shardResults,
const char* mongosStageName,
long long millisElapsed,
BSONObjBuilder* out);
//
// Names of mock mongos execution stages.
//
static const char* kSingleShard;
static const char* kMergeFromShards;
static const char* kMergeSortFromShards;
static const char* kWriteOnShards;
private:
/**
* Returns an OK status if all shards support the explain command and returned sensible
* results. Otherwise, returns a non-OK status and the entire explain should fail.
*/
static Status validateShardResults(const std::vector<Strategy::CommandResult>& shardResults);
/**
* Populates the BSONObj builder 'out' with query planner explain information, based on
* the results from the shards contained in 'shardResults'.
*
* The planner info will display 'mongosStageName' as the name of the execution stage
* performed by mongos after gathering results from the shards.
*/
static void buildPlannerInfo(OperationContext* opCtx,
const std::vector<Strategy::CommandResult>& shardResults,
const char* mongosStageName,
BSONObjBuilder* out);
/**
* Populates the BSONObj builder 'out' with execution stats explain information,
* if the results from the shards in 'shardsResults' contain this info.
*
* Will display 'mongosStageName' as the name of the execution stage performed by mongos,
* and 'millisElapsed' as the execution time of the mongos stage.
*/
static void buildExecStats(const std::vector<Strategy::CommandResult>& shardResults,
const char* mongosStageName,
long long millisElapsed,
BSONObjBuilder* out);
};
} // namespace mongo
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