/*
* 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.openjpa.slice;
import java.util.List;
import java.util.Random;
/**
* Policy to select one of the physical databases referred as <em>slice</em>
* in which a given persistent instance will be stored.
*
* The user application is required to implement this interface. Slice will
* invoke the single method of this interface to determine the target slice for
* a newly persistent or a detached instance being merged.
*
* @author Pinaki Poddar
*
*/
public interface DistributionPolicy {
/**
* Gets the name of the target slice where the given newly persistent or
* the detached, to-be-merged instance will be stored.
* <br>
* If the current state of the given instance is sufficient to determine
* the target slice, return null. In that case, the runtime will callback
* this method again before the instance being flushed to the datastore.
* By then, the policy <em>must</em> be able to determine the target slice.
*
* @param pc The newly persistent or to-be-merged object.
* @param slices list of names of the active slices. The ordering of
* the list is either explicit <code>openjpa.slice.Names</code> property
* or implicit i.e. alphabetic order of available identifiers if
* <code>openjpa.slice.Names</code> is unspecified.
* @param context the generic persistence context managing the given
* instance.
*
* @return identifier of the slice. This name must match one of the
* given slice names.
* @see DistributedConfiguration#getActiveSliceNames()
*/
String distribute(Object pc, List<String> slices, Object context);
/**
* Implements a default distribution policy to store the given
* instance to a randomly selected available slice.
*
*/
public static class Default implements DistributionPolicy {
private static Random RNG = new Random();
public String distribute(Object pc, List<String> slices, Object ctx) {
return slices.get(RNG.nextInt(slices.size()));
}
}
}