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/**
* Copyright (C) 2021-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 "mongo/db/pipeline/change_stream_constants.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/document_source_change_stream.h"
#include "mongo/db/shard_id.h"
#include "mongo/s/query/document_source_merge_cursors.h"
namespace mongo {
/**
* An internal stage used as part of the change streams infrastructure to listen for an event
* signaling that a new shard now has potentially matching data. For example, this stage will
* detect if a collection is being watched and a chunk for that collection migrates to a shard for
* the first time. When this event is detected, this stage will establish a new cursor on that
* shard and add it to the cursors being merged.
*/
class DocumentSourceChangeStreamHandleTopologyChange final : public DocumentSource {
public:
static constexpr StringData kStageName = "$_internalChangeStreamHandleTopologyChange"_sd;
/**
* Creates a new stage which will establish a new cursor and add it to the cursors being merged
* by 'mergeCursorsStage' whenever a new shard is detected by a change stream.
*/
static boost::intrusive_ptr<DocumentSourceChangeStreamHandleTopologyChange> create(
const boost::intrusive_ptr<ExpressionContext>&);
const char* getSourceName() const final {
return kStageName.rawData();
}
Value serialize(SerializationOptions opts = SerializationOptions()) const final override;
StageConstraints constraints(Pipeline::SplitState) const final;
GetModPathsReturn getModifiedPaths() const final {
// This stage neither modifies nor renames any field.
return {GetModPathsReturn::Type::kFiniteSet, OrderedPathSet{}, {}};
}
boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
return DistributedPlanLogic{nullptr, this, change_stream_constants::kSortSpec};
}
void addVariableRefs(std::set<Variables::Id>* refs) const final {}
private:
DocumentSourceChangeStreamHandleTopologyChange(const boost::intrusive_ptr<ExpressionContext>&);
GetNextResult doGetNext() final;
/**
* Establish the new cursors and tell the RouterStageMerge about them.
*/
void addNewShardCursors(const Document& newShardDetectedObj);
/**
* Open the cursors on the new shards.
*/
std::vector<RemoteCursor> establishShardCursorsOnNewShards(const Document& newShardDetectedObj);
/**
* Updates the $changeStream stage in the '_originalAggregateCommand' to reflect the start time
* for the newly-added shard(s), then generates the final command object to be run on those
* shards.
*/
BSONObj createUpdatedCommandForNewShard(Timestamp shardAddedTime);
/**
* Given the '_originalAggregateCommand' and a resume token, returns a new BSON object with the
* same command except with the addition of a resumeAfter option containing the resume token.
* If there was a previous resumeAfter option, it will be removed.
*/
BSONObj replaceResumeTokenInCommand(Document resumeToken);
boost::intrusive_ptr<DocumentSourceMergeCursors> _mergeCursors;
BSONObj _originalAggregateCommand;
};
} // namespace mongo
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