io.trino.cost.LimitStatsRule Maven / Gradle / Ivy

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/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.trino.cost;

import io.trino.cost.StatsCalculator.Context;
import io.trino.matching.Pattern;
import io.trino.sql.planner.plan.LimitNode;

import java.util.Optional;

import static io.trino.sql.planner.plan.Patterns.limit;

public class LimitStatsRule
        extends SimpleStatsRule
{
    private static final Pattern PATTERN = limit();

    public LimitStatsRule(StatsNormalizer normalizer)
    {
        super(normalizer);
    }

    @Override
    public Pattern getPattern()
    {
        return PATTERN;
    }

    @Override
    protected Optional doCalculate(LimitNode node, Context context)
    {
        PlanNodeStatsEstimate sourceStats = context.statsProvider().getStats(node.getSource());
        if (sourceStats.getOutputRowCount() <= node.getCount()) {
            return Optional.of(sourceStats);
        }

        // LIMIT actually limits (or when there was no row count estimated for source)
        return Optional.of(PlanNodeStatsEstimate.buildFrom(sourceStats)
                .setOutputRowCount(node.getCount())
                .build());
    }
}