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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/pipeline.h"
#include "mongo/s/async_requests_sender.h"
#include "mongo/s/catalog_cache.h"
#include "mongo/s/query/owned_remote_cursor.h"
namespace mongo {
class CachedCollectionRoutingInfo;
namespace sharded_agg_helpers {
/**
* 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;
};
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;
};
struct DispatchShardPipelineResults {
// True if this pipeline was split, and the second half of the pipeline needs to be run on
// the primary shard for the database.
bool needsPrimaryShardMerge;
// Populated if this *is not* an explain, this vector represents the cursors on the remote
// shards.
std::vector<OwnedRemoteCursor> remoteCursors;
// Populated if this *is* an explain, this vector represents the results from each shard.
std::vector<AsyncRequestsSender::Response> remoteExplainOutput;
// The split version of the pipeline if more than one shard was targeted, otherwise
// boost::none.
boost::optional<SplitPipeline> splitPipeline;
// If the pipeline targeted a single shard, this is the pipeline to run on that shard.
std::unique_ptr<Pipeline, PipelineDeleter> pipelineForSingleShard;
// The command object to send to the targeted shards.
BSONObj commandForTargetedShards;
// How many exchange producers are running the shard part of splitPipeline.
size_t numProducers;
// The exchange specification if the query can run with the exchange otherwise boost::none.
boost::optional<ShardedExchangePolicy> exchangeSpec;
};
/**
* 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);
/**
* 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);
/**
* Targets shards for the pipeline and returns a struct with the remote cursors or results, and
* the pipeline that will need to be executed to merge the results from the remotes. If a stale
* shard version is encountered, refreshes the routing table and tries again.
*/
DispatchShardPipelineResults dispatchShardPipeline(
Document serializedCommand,
bool hasChangeStream,
std::unique_ptr<Pipeline, PipelineDeleter> pipeline);
BSONObj createPassthroughCommandForShard(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
Document serializedCommand,
boost::optional<ExplainOptions::Verbosity> explainVerbosity,
const boost::optional<RuntimeConstants>& constants,
Pipeline* pipeline,
BSONObj collationObj);
BSONObj createCommandForTargetedShards(const boost::intrusive_ptr<ExpressionContext>& expCtx,
Document serializedCommand,
const SplitPipeline& splitPipeline,
const boost::optional<ShardedExchangePolicy> exchangeSpec,
bool needsMerge);
/**
* Creates a new DocumentSourceMergeCursors from the provided 'remoteCursors' and adds it to the
* front of 'mergePipeline'.
*/
void addMergeCursorsSource(Pipeline* mergePipeline,
BSONObj cmdSentToShards,
std::vector<OwnedRemoteCursor> ownedCursors,
const std::vector<ShardId>& targetedShards,
boost::optional<BSONObj> shardCursorsSortSpec,
std::shared_ptr<executor::TaskExecutor> executor,
bool hasChangeStream);
/**
* For a sharded collection, establishes remote cursors on each shard that may have results, and
* creates a DocumentSourceMergeCursors stage to merge the remove cursors. Returns a pipeline
* beginning with that DocumentSourceMergeCursors stage. Note that one of the 'remote' cursors might
* be this node itself.
*/
std::unique_ptr<Pipeline, PipelineDeleter> targetShardsAndAddMergeCursors(
const boost::intrusive_ptr<ExpressionContext>& expCtx, Pipeline* ownedPipeline);
/**
* Returns the proper routing table to use for targeting shards: either a historical routing table
* based on the global read timestamp if there is an active transaction with snapshot level read
* concern or the latest routing table otherwise.
*
* Returns 'ShardNotFound' or 'NamespaceNotFound' if there are no shards in the cluster or if
* collection 'execNss' does not exist, respectively.
*/
StatusWith<CachedCollectionRoutingInfo> getExecutionNsRoutingInfo(OperationContext* opCtx,
const NamespaceString& execNss);
/**
* Returns true if an aggregation over 'nss' must run on all shards.
*/
bool mustRunOnAllShards(const NamespaceString& nss, bool hasChangeStream);
/**
* Retrieves the desired retry policy based on whether the default writeConcern is set on 'opCtx'.
*/
Shard::RetryPolicy getDesiredRetryPolicy(OperationContext* opCtx);
} // namespace sharded_agg_helpers
} // namespace mongo
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