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A module that is everything required to understands Druid Segments

There is a newer version: 31.0.0

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.druid.query.topn;

import org.apache.druid.query.aggregation.BufferAggregator;
import org.apache.druid.segment.Cursor;
import org.apache.druid.segment.DimensionSelector;

import java.nio.ByteBuffer;

public interface Generic2AggPooledTopNScanner
{
  /**
   * @param aggregator1Size number of bytes required by aggregator1 for a single aggregation
   * @param aggregator2Size number of bytes required by aggregator2 for a single aggregation
   * @param positions a cache for positions in resultsBuffer, where specific (indexed) dimension values are aggregated
   * @return number of scanned rows, i. e. number of steps made with the given cursor
   */
  long scanAndAggregate(
      DimensionSelector dimensionSelector,
      BufferAggregator aggregator1,
      int aggregator1Size,
      BufferAggregator aggregator2,
      int aggregator2Size,
      Cursor cursor,
      int[] positions,
      ByteBuffer resultsBuffer
  );
}