flink-core/src/main/java/org/apache/flink/api/common/distributions/DataDistribution.java

/*
 * 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.flink.api.common.distributions;

import java.io.Serializable;

import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.core.io.IOReadableWritable;

@PublicEvolving
public interface DataDistribution extends IOReadableWritable, Serializable {
	
	/**
	 * Returns the i'th bucket's upper bound, given that the distribution is to be
	 * split into {@code totalBuckets} buckets.
	 * <p>
	 * Assuming <i>n</i> buckets, let {@code B_i} be the result from calling {@code getBucketBoundary(i, n)},
	 * then the distribution will partition the data domain in the following fashion:
	 * <pre>
	 * (-inf, B_1] (B_1, B_2] ... (B_n-2, B_n-1] (B_n-1, inf)
	 * </pre>
	 * 
	 * <p>
	 * Note: The last bucket's upper bound is actually discarded by many algorithms.
	 * The last bucket is assumed to hold all values <i>v</i> such that
	 * {@code v > getBucketBoundary(n-1, n)}, where <i>n</i> is the number of buckets.
	 * 
	 * @param bucketNum The number of the bucket for which to get the upper bound.
	 * @param totalNumBuckets The number of buckets to split the data into.
	 * 
	 * @return A record whose values act as bucket boundaries for the specified bucket.
	 */
	Object[] getBucketBoundary(int bucketNum, int totalNumBuckets);
	
	/**
	 * The number of fields in the (composite) key. This determines how many fields in the records define
	 * the bucket. The number of fields must be the size of the array returned by the function
	 * {@link #getBucketBoundary(int, int)}.
	 * 
	 * @return The number of fields in the (composite) key.
	 */
	int getNumberOfFields();

	/**
	 * Gets the type of the key by which the dataSet is partitioned. 
	 * @return The type of the key by which the dataSet is partitioned.
	 */
	TypeInformation[] getKeyTypes();
}