content: /*
   * 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.arrow.vector;
  
  /**
   * Vector that support density aware initial capacity settings. We use this for ListVector and
   * VarCharVector as of now to control the memory allocated.
   *
   * <p>For ListVector, we have been using a multiplier of 5 to compute the initial capacity of the
   * inner data vector. For deeply nested lists and lists with lots of NULL values, this is
   * over-allocation upfront. So density helps to be conservative when computing the value capacity of
   * the inner vector.
   *
   * <p>For example, a density value of 10 implies each position in the list vector has a list of 10
   * values. So we will provision an initial capacity of (valuecount * 10) for the inner vector. A
   * density value of 0.1 implies out of 10 positions in the list vector, 1 position has a list of
   * size 1 and remaining positions are null (no lists) or empty lists. This helps in tightly
   * controlling the memory we provision for inner data vector.
   *
   * <p>Similar analogy is applicable for VarCharVector where the capacity of the data buffer can be
   * controlled using density multiplier instead of default multiplier of 8 (default size of average
   * varchar length).
   *
   * <p>Also from container vectors, we propagate the density down the inner vectors so that they can
   * use it appropriately.
   */
  public interface DensityAwareVector {
  
    /**
     * Set value with density.
     *
     * @param valueCount the number of values in this vector
     * @param density the density of the vector
     */
    void setInitialCapacity(int valueCount, double density);
  }
  