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/**
* Copyright (C) 2020-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 <queue>
#include "mongo/db/exec/sbe/stages/stages.h"
namespace mongo::sbe {
/**
* This stage deduplicates by a given key. Unlike a HashAgg, this stage is not blocking and rows are
* returned in the same order as they appear in the input stream.
*
* TODO: It is possible to optimize this stage in the case where the input is sorted by key X, we
* are "uniquing" by key Y, and we are guaranteed that all identical values of Y appear are
* associated with the same key X. In this case the hash table of seen elements can be cleared each
* time a new key X is encountered.
*
* For example, this optimization is possible when the UniqueStage is uniquing by record ID and
* below it there are non-multikey index scans merged via a SortMerge stage. Each duplicate record
* ID will be associated with the same sort key.
*
* Debug string representation:
*
* unique [<keys>] childStage
*/
class UniqueStage final : public PlanStage {
public:
UniqueStage(std::unique_ptr<PlanStage> input,
value::SlotVector keys,
PlanNodeId planNodeId,
bool participateInTrialRunTracking = true);
std::unique_ptr<PlanStage> clone() const final;
void prepare(CompileCtx& ctx) final;
value::SlotAccessor* getAccessor(CompileCtx& ctx, value::SlotId slot) final;
void open(bool reOpen) final;
PlanState getNext() final;
void close() final;
std::unique_ptr<PlanStageStats> getStats(bool includeDebugInfo) const final;
const SpecificStats* getSpecificStats() const final;
std::vector<DebugPrinter::Block> debugPrint() const final;
size_t estimateCompileTimeSize() const final;
private:
const value::SlotVector _keySlots;
std::vector<value::SlotAccessor*> _inKeyAccessors;
// Table of keys that have been seen.
stdx::unordered_set<value::MaterializedRow,
value::MaterializedRowHasher,
value::MaterializedRowEq>
_seen;
UniqueStats _specificStats;
};
} // namespace mongo::sbe
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