lbug 0.16.1

An in-process property graph database management system built for query speed and scalability
Documentation 
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#pragma once

#include "logical_operator_visitor.h"
#include "planner/operator/logical_plan.h"

namespace lbug {
namespace optimizer {

/* When UNWIND is followed by MERGE, duplicate values in the UNWIND list can cause
 * issues because the MERGE's HASH_JOIN doesn't see newly created nodes within the same batch.
 * This optimizer inserts a UNWIND_DEDUP operator to deduplicate UNWIND output before MERGE.
 *
 * E.g., UNWIND [1, 1, 2] AS x MERGE (a:A {val: x})
 * Before: UNWIND -> HASH_JOIN (for optional match) -> MERGE
 * After:  UNWIND -> UNWIND_DEDUP -> HASH_JOIN -> MERGE
 */
class UnwindDedupOptimizer : public LogicalOperatorVisitor {
public:
    void rewrite(planner::LogicalPlan* plan);

private:
    std::shared_ptr<planner::LogicalOperator> visitOperator(
        const std::shared_ptr<planner::LogicalOperator>& op);

    std::shared_ptr<planner::LogicalOperator> visitMergeReplace(
        std::shared_ptr<planner::LogicalOperator> op) override;
};

} // namespace optimizer
} // namespace lbug