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/*
* 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.
*
* 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.
*
*
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.
*
*
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).
*
*
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);
}