Java tutorial
/** * 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.mrql; import org.apache.mrql.gen.*; import java.io.*; import java.util.Hashtable; import java.util.Iterator; import java.util.Enumeration; import org.apache.hadoop.fs.*; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.mapreduce.*; import org.apache.hadoop.mapreduce.lib.input.MultipleInputs; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; import org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat; /** The MapReduce operation that uses an in-mapper combiner to partially reduce groups during mapping */ final public class MapReduceOperation extends MapReducePlan { public final static class MRContainerPartitioner extends Partitioner<MRContainer, MRContainer> { final public int getPartition(MRContainer key, MRContainer value, int numPartitions) { return Math.abs(key.hashCode()) % numPartitions; } } /** The mapper of the MapReduce operation */ private final static class MRMapper extends Mapper<MRContainer, MRContainer, MRContainer, MRContainer> { private static Function map_fnc; // the map function private static Function combine_fnc; // the combiner function private static Hashtable<MRData, MRData> hashTable; // in-mapper combiner private static int index; private static Tuple tkey = new Tuple(2); private static Bag tbag = new Bag(2); private static MRContainer ckey = new MRContainer(new MR_int(0)); private static MRContainer cvalue = new MRContainer(new MR_int(0)); @Override public void map(MRContainer key, MRContainer value, Context context) throws IOException, InterruptedException { for (MRData e : (Bag) map_fnc.eval(value.data())) { Tuple p = (Tuple) e; if (hashTable == null) { ckey.set(p.first()); cvalue.set(p.second()); context.write(ckey, cvalue); } else { // in-mapper combiner MRData old = hashTable.get(p.first()); if (old == null) { if (index++ == Config.map_cache_size) flush_table(context); hashTable.put(p.first(), p.second()); } else { tkey.set(0, p.first()); tbag.clear(); tbag.add_element(p.second()).add_element(old); tkey.set(1, tbag); for (MRData x : (Bag) combine_fnc.eval(tkey)) hashTable.put(p.first(), x); // normally, done once } } } } private static void flush_table(Context context) throws IOException, InterruptedException { Enumeration<MRData> en = hashTable.keys(); while (en.hasMoreElements()) { MRData key = en.nextElement(); ckey.set(key); MRData value = hashTable.get(key); cvalue.set(value); if (value != null) context.write(ckey, cvalue); } ; index = 0; hashTable.clear(); } @Override protected void setup(Context context) throws IOException, InterruptedException { super.setup(context); try { Configuration conf = context.getConfiguration(); Config.read(conf); if (Plan.conf == null) Plan.conf = conf; Tree code = Tree.parse(conf.get("mrql.mapper")); map_fnc = functional_argument(conf, code); code = Tree.parse(conf.get("mrql.combiner")); hashTable = null; if (code != null && !code.equals(new VariableLeaf("null"))) { combine_fnc = functional_argument(conf, code); hashTable = new Hashtable<MRData, MRData>(Config.map_cache_size); index = 0; } } catch (Exception e) { throw new Error("Cannot retrieve the mapper plan"); } } @Override protected void cleanup(Context context) throws IOException, InterruptedException { if (hashTable != null) flush_table(context); hashTable = null; // garbage-collect it super.cleanup(context); } } /** The reducer of the MapReduce operation */ private final static class MRReducer extends Reducer<MRContainer, MRContainer, MRContainer, MRContainer> { private static String counter; // a Hadoop user-defined counter used in the repeat operation private static Function reduce_fnc; // the reduce function private static Bag s = new Bag(); // a cached bag of input fragments private static Function acc_fnc; // aggregator private static MRData result; // aggregation result private static boolean streamed = false; private static Tuple pair = new Tuple(2); private static MRContainer container = new MRContainer(new MR_int(0)); private void write(MRContainer key, MRData value, Context context) throws IOException, InterruptedException { if (result != null) { // aggregation pair.set(0, result); pair.set(1, value); result = acc_fnc.eval(pair); } else if (counter.equals("-")) { container.set(value); context.write(key, container); } else { // increment the repetition counter if the repeat condition is true Tuple t = (Tuple) value; if (((MR_bool) t.second()).get()) context.getCounter("mrql", counter).increment(1); container.set(t.first()); context.write(key, container); } } @Override public void reduce(MRContainer key, Iterable<MRContainer> values, Context context) throws IOException, InterruptedException { if (!streamed) { // store the values in a Bag and then reduce s.clear(); for (MRContainer val : values) s.add(val.data()); pair.set(0, key.data()); pair.set(1, s); for (MRData e : (Bag) reduce_fnc.eval(pair)) write(key, e, context); } else { // it accesses the values in stream-like fashion final Iterator<MRContainer> iterator = values.iterator(); Bag s = new Bag(new BagIterator() { public boolean hasNext() { return iterator.hasNext(); } public MRData next() { return iterator.next().data(); } }); pair.set(0, key.data()); pair.set(1, s); for (MRData e : (Bag) reduce_fnc.eval(pair)) write(key, e, context); } } @Override protected void setup(Context context) throws IOException, InterruptedException { super.setup(context); try { conf = context.getConfiguration(); Plan.conf = conf; Config.read(Plan.conf); Tree code = Tree.parse(conf.get("mrql.reducer")); reduce_fnc = functional_argument(conf, code); streamed = PlanGeneration.streamed_MapReduce_reducer(code); if (conf.get("mrql.zero") != null) { code = Tree.parse(conf.get("mrql.zero")); result = Interpreter.evalE(code); code = Tree.parse(conf.get("mrql.accumulator")); acc_fnc = functional_argument(conf, code); } else result = null; counter = conf.get("mrql.counter"); } catch (Exception e) { throw new Error("Cannot retrieve the reduce plan"); } } @Override protected void cleanup(Context context) throws IOException, InterruptedException { if (result != null) // emit the result of aggregation context.write(new MRContainer(new MR_int(0)), new MRContainer(result)); super.cleanup(context); } } /** * The MapReduce physical operator * @param map_fnc the mapper function * @param combine_fnc optional in-mapper combiner function * @param reduce_fnc the reducer function * @param acc_fnc optional accumulator function * @param zero optional the zero value for the accumulator * @param source the input data source * @param num_reduces number of reducers * @param stop_counter optional counter used in repeat operation * @param orderp does the result need to be ordered? * @return a new data source that contains the result */ public final static DataSet mapReduce(Tree map_fnc, // mapper function Tree combine_fnc, // optional in-mapper combiner function Tree reduce_fnc, // reducer function Tree acc_fnc, // optional accumulator function Tree zero, // optional the zero value for the accumulator DataSet source, // input data source int num_reduces, // number of reducers String stop_counter, // optional counter used in repeat operation boolean orderp) // does the result need to be ordered? throws Exception { conf = MapReduceEvaluator.clear_configuration(conf); String newpath = new_path(conf); conf.set("mrql.mapper", map_fnc.toString()); if (combine_fnc != null) conf.set("mrql.combiner", combine_fnc.toString()); conf.set("mrql.reducer", reduce_fnc.toString()); if (zero != null) { // will use in-mapper combiner conf.set("mrql.accumulator", acc_fnc.toString()); conf.set("mrql.zero", zero.toString()); } else conf.set("mrql.zero", ""); conf.set("mrql.counter", stop_counter); setupSplits(source, conf); Job job = new Job(conf, newpath); distribute_compiled_arguments(job.getConfiguration()); job.setJarByClass(MapReducePlan.class); job.setOutputKeyClass(MRContainer.class); job.setOutputValueClass(MRContainer.class); job.setPartitionerClass(MRContainerPartitioner.class); job.setSortComparatorClass(MRContainerKeyComparator.class); job.setGroupingComparatorClass(MRContainerKeyComparator.class); job.setOutputFormatClass(SequenceFileOutputFormat.class); for (DataSource p : source.source) MultipleInputs.addInputPath(job, new Path(p.path), (Class<? extends MapReduceMRQLFileInputFormat>) p.inputFormat, MRMapper.class); FileOutputFormat.setOutputPath(job, new Path(newpath)); job.setReducerClass(MRReducer.class); if (Config.trace && PlanGeneration.streamed_MapReduce_reducer(reduce_fnc)) System.out.println("Streamed MapReduce reducer"); if (num_reduces > 0) job.setNumReduceTasks(num_reduces); job.waitForCompletion(true); long c = (stop_counter.equals("-")) ? 0 : job.getCounters().findCounter("mrql", stop_counter).getValue(); DataSource s = new BinaryDataSource(newpath, conf); s.to_be_merged = orderp; return new DataSet(s, c, outputRecords(job)); } }