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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 "mongo/db/pipeline/exchange_spec_gen.h"
#include "mongo/db/pipeline/lite_parsed_pipeline.h"
#include "mongo/db/pipeline/pipeline.h"
#include "mongo/s/catalog/type_chunk.h"
#include "mongo/s/query/cluster_client_cursor_impl.h"
#include "mongo/s/query/owned_remote_cursor.h"
#include "mongo/s/shard_id.h"
namespace mongo {
namespace cluster_aggregation_planner {
/**
* Represents the two halves of a pipeline that will execute in a sharded cluster. 'shardsPipeline'
* will execute in parallel on each shard, and 'mergePipeline' will execute on the merge host -
* either one of the shards or a mongos.
*/
struct SplitPipeline {
SplitPipeline(std::unique_ptr<Pipeline, PipelineDeleter> shardsPipeline,
std::unique_ptr<Pipeline, PipelineDeleter> mergePipeline,
boost::optional<BSONObj> shardCursorsSortSpec)
: shardsPipeline(std::move(shardsPipeline)),
mergePipeline(std::move(mergePipeline)),
shardCursorsSortSpec(std::move(shardCursorsSortSpec)) {}
std::unique_ptr<Pipeline, PipelineDeleter> shardsPipeline;
std::unique_ptr<Pipeline, PipelineDeleter> mergePipeline;
// If set, the cursors from the shards are expected to be sorted according to this spec, and to
// have populated a "$sortKey" metadata field which can be used to compare the results.
boost::optional<BSONObj> shardCursorsSortSpec;
};
/**
* Split the current Pipeline into a Pipeline for each shard, and a Pipeline that combines the
* results within a merging process. This call also performs optimizations with the aim of reducing
* computing time and network traffic when a pipeline has been split into two pieces.
*
* The 'mergePipeline' returned as part of the SplitPipeline here is not ready to execute until the
* 'shardsPipeline' has been sent to the shards and cursors have been established. Once cursors have
* been established, the merge pipeline can be made executable by calling 'addMergeCursorsSource()'
*/
SplitPipeline splitPipeline(std::unique_ptr<Pipeline, PipelineDeleter> pipeline);
/**
* Creates a new DocumentSourceMergeCursors from the provided 'remoteCursors' and adds it to the
* front of 'mergePipeline'.
*/
void addMergeCursorsSource(Pipeline* mergePipeline,
const LiteParsedPipeline&,
BSONObj cmdSentToShards,
std::vector<OwnedRemoteCursor> remoteCursors,
const std::vector<ShardId>& targetedShards,
boost::optional<BSONObj> shardCursorsSortSpec,
executor::TaskExecutor*);
/**
* Builds a ClusterClientCursor which will execute 'pipeline'. If 'pipeline' consists entirely of
* $skip and $limit stages, the pipeline is eliminated entirely and replaced with a RouterExecStage
* tree that does same thing but will avoid using a RouterStagePipeline. Avoiding a
* RouterStagePipeline will remove an expensive conversion from BSONObj -> Document for each result.
*/
ClusterClientCursorGuard buildClusterCursor(OperationContext* opCtx,
std::unique_ptr<Pipeline, PipelineDeleter> pipeline,
ClusterClientCursorParams&&);
struct ShardedExchangePolicy {
// The exchange specification that will be sent to shards as part of the aggregate command.
// It will be used by producers to determine how to distribute documents to consumers.
ExchangeSpec exchangeSpec;
// Shards that will run the consumer part of the exchange.
std::vector<ShardId> consumerShards;
};
/**
* If the merging pipeline is eligible for an $exchange merge optimization, returns the information
* required to set that up.
*/
boost::optional<ShardedExchangePolicy> checkIfEligibleForExchange(OperationContext* opCtx,
const Pipeline* mergePipeline);
} // namespace cluster_aggregation_planner
} // namespace mongo
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