lbug 0.16.1

An in-process property graph database management system built for query speed and scalability
Documentation 
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#include "optimizer/limit_push_down_optimizer.h"

#include "binder/expression/expression_util.h"
#include "common/exception/runtime.h"
#include "planner/operator/extend/logical_recursive_extend.h"
#include "planner/operator/logical_distinct.h"
#include "planner/operator/logical_hash_join.h"
#include "planner/operator/logical_limit.h"
#include "planner/operator/logical_table_function_call.h"

using namespace lbug::binder;
using namespace lbug::common;
using namespace lbug::planner;

namespace lbug {
namespace optimizer {

void LimitPushDownOptimizer::rewrite(LogicalPlan* plan) {
    visitOperator(plan->getLastOperator().get());
}

void LimitPushDownOptimizer::visitOperator(planner::LogicalOperator* op) {
    switch (op->getOperatorType()) {
    case LogicalOperatorType::LIMIT: {
        auto& limit = op->constCast<LogicalLimit>();
        if (limit.hasSkipNum() && ExpressionUtil::canEvaluateAsLiteral(*limit.getSkipNum())) {
            skipNumber = ExpressionUtil::evaluateAsSkipLimit(*limit.getSkipNum());
        }
        if (limit.hasLimitNum() && ExpressionUtil::canEvaluateAsLiteral(*limit.getLimitNum())) {
            limitNumber = ExpressionUtil::evaluateAsSkipLimit(*limit.getLimitNum());
        }
        visitOperator(limit.getChild(0).get());
        return;
    }
    case LogicalOperatorType::MULTIPLICITY_REDUCER:
    case LogicalOperatorType::EXPLAIN:
    case LogicalOperatorType::ACCUMULATE:
    case LogicalOperatorType::FILTER:
    case LogicalOperatorType::PROJECTION: {
        visitOperator(op->getChild(0).get());
        return;
    }
    case LogicalOperatorType::TABLE_FUNCTION_CALL: {
        if (limitNumber == INVALID_LIMIT && skipNumber == 0) {
            return;
        }
        auto& tableFuncCall = op->cast<LogicalTableFunctionCall>();
        if (tableFuncCall.getTableFunc().supportsPushDownFunc()) {
            tableFuncCall.setLimitNum(skipNumber + limitNumber);
        }
        return;
    }
    case LogicalOperatorType::DISTINCT: {
        if (limitNumber == INVALID_LIMIT && skipNumber == 0) {
            return;
        }
        auto& distinctOp = op->cast<LogicalDistinct>();
        distinctOp.setLimitNum(limitNumber);
        distinctOp.setSkipNum(skipNumber);
        return;
    }
    case LogicalOperatorType::HASH_JOIN: {
        if (limitNumber == INVALID_LIMIT && skipNumber == 0) {
            return;
        }
        if (op->getChild(0)->getOperatorType() == LogicalOperatorType::HASH_JOIN) {
            op->ptrCast<LogicalHashJoin>()->getSIPInfoUnsafe().position = SemiMaskPosition::NONE;
            // OP is the hash join reading destination node property. Continue push limit down.
            op = op->getChild(0).get();
        }
        if (op->getChild(0)->getOperatorType() == LogicalOperatorType::PATH_PROPERTY_PROBE) {
            // LCOV_EXCL_START
            if (op->getChild(0)->getChild(0)->getOperatorType() !=
                LogicalOperatorType::RECURSIVE_EXTEND) {
                throw RuntimeException("Trying to push limit to a non RECURSIVE_EXTEND operator. "
                                       "This should never happen.");
            }
            // LCOV_EXCL_STOP
            auto& extend = op->getChild(0)->getChild(0)->cast<LogicalRecursiveExtend>();
            extend.setLimitNum(skipNumber + limitNumber);
        }
        return;
    }
    case LogicalOperatorType::UNION_ALL: {
        for (auto i = 0u; i < op->getNumChildren(); ++i) {
            auto optimizer = LimitPushDownOptimizer();
            optimizer.visitOperator(op->getChild(i).get());
        }
        return;
    }
    default:
        return;
    }
}

} // namespace optimizer
} // namespace lbug