eu.stratosphere.api.common.distributions.DataDistribution Maven / Gradle / Ivy
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* Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
*
* 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.
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package eu.stratosphere.api.common.distributions;
import java.io.Serializable;
import eu.stratosphere.core.io.IOReadableWritable;
import eu.stratosphere.types.Key;
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.
*
* Assuming n 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:
*
* (-inf, B_1] (B_1, B_2] ... (B_n-2, B_n-1] (B_n-1, inf)
*
*
*
* Note: The last bucket's upper bound is actually discarded by many algorithms.
* The last bucket is assumed to hold all values v such that
* {@code v > getBucketBoundary(n-1, n)}, where n 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.
*/
Key[] 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();
}