/*
* 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.solr.hadoop.dedup;
import java.util.Iterator;
import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.Reducer.Context;
import org.apache.solr.common.SolrInputDocument;
/**
* Interface that enables deduplication and ordering of a series of document
* updates for the same unique document key.
*
* For example, a MapReduce batch job might index multiple files in the same job
* where some of the files contain old and new versions of the very same
* document, using the same unique document key.
*
* Typically, implementations of this interface forbid collisions by throwing an
* exception, or ignore all but the most recent document version, or, in the
* general case, order colliding updates ascending from least recent to most
* recent (partial) update.
*
* The caller of this interface (i.e. the Hadoop Reducer) will then apply the
* updates to Solr in the order returned by the orderUpdates() method.
*
* Configuration: If an UpdateConflictResolver implementation also implements
* {@link Configurable} then the Hadoop Reducer will call
* {@link Configurable#setConf(org.apache.hadoop.conf.Configuration)} on
* instance construction and pass the standard Hadoop configuration information.
*/
public interface UpdateConflictResolver {
/**
* Given a list of all colliding document updates for the same unique document
* key, this method returns zero or more documents in an application specific
* order.
*
* The caller will then apply the updates for this key to Solr in the order
* returned by the orderUpdate() method.
*
* @param uniqueKey
* the document key common to all collidingUpdates mentioned below
* @param collidingUpdates
* all updates in the MapReduce job that have a key equal to
* {@code uniqueKey} mentioned above. The input order is unspecified.
* @param context
* The <code>Context</code> passed from the {@link Reducer}
* implementations.
* @return the order in which the updates shall be applied to Solr
*/
Iterator<SolrInputDocument> orderUpdates(
Text uniqueKey, Iterator<SolrInputDocument> collidingUpdates, Context context);
}