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.net.URI; import java.util.Hashtable; import java.util.Iterator; import java.util.Enumeration; import org.apache.hadoop.fs.*; import org.apache.hadoop.io.*; 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; import org.apache.hadoop.filecache.DistributedCache; /** The fragment-replicate join (map-side join) physical operator */ final public class MapJoinOperation extends MapReducePlan { /** the mapper of the MapJoin */ private final static class mapJoinMapper extends Mapper<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 Function probe_map_fnc; private static Hashtable<MRData, Bag> built_table; private static Function acc_fnc; // aggregator private static MRData result; // aggregation result private static Tuple pair = new Tuple(2); private static MRContainer container = new MRContainer(new MR_int(0)); private static Bag empty_bag = new Bag(); private static boolean mapJoinReduce = false; 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 map(MRContainer key, MRContainer value, Context context) throws IOException, InterruptedException { for (MRData e : (Bag) probe_map_fnc.eval(value.data())) { Tuple p = (Tuple) e; MRData pd = built_table.get(p.first()); if (pd == null) pd = empty_bag; pair.set(0, p.second()); pair.set(1, pd); for (MRData v : (Bag) reduce_fnc.eval(pair)) write(key, v, context); } } @Override protected void setup(Context context) throws IOException, InterruptedException { super.setup(context); try { conf = context.getConfiguration(); Plan.conf = conf; Config.read(Plan.conf); if (conf.get("mrql.mapJoinReduce") != null) mapJoinReduce = true; Tree code = Tree.parse(conf.get("mrql.inMap.reducer")); reduce_fnc = functional_argument(conf, code); code = Tree.parse(conf.get("mrql.probe_mapper")); probe_map_fnc = functional_argument(conf, code); if (!mapJoinReduce && 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"); built_table = new Hashtable<MRData, Bag>(Config.map_cache_size); Bag res = new Bag(); URI[] uris = DistributedCache.getCacheFiles(conf); Path[] local_paths = DistributedCache.getLocalCacheFiles(conf); final FileSystem fs = FileSystem.getLocal(conf); final Configuration fconf = conf; for (int i = 0; i < local_paths.length; i++) { // hadoop 0.20.2 distributed cache doesn't work in stand-alone final Path path = (conf.get("mapred.job.tracker").equals("local")) ? new Path(uris[i].toString()) : local_paths[i]; if (path.getName().endsWith(".jar")) continue; res = res.union(new Bag(new BagIterator() { final SequenceFile.Reader reader = new SequenceFile.Reader(fs, path, fconf); final MRContainer key = new MRContainer(new MR_int(0)); final MRContainer value = new MRContainer(new MR_int(0)); public boolean hasNext() { try { boolean done = reader.next(key, value); if (!done) reader.close(); return done; } catch (IOException e) { throw new Error("Cannot collect values from distributed cache"); } } public MRData next() { return value.data(); } })); } ; for (MRData e : res) { Tuple p = (Tuple) e; Bag entries = built_table.get(p.first()); built_table.put(p.first(), (entries == null) ? (new Bag(p.second())) : entries.add_element(p.second())); } } catch (Exception e) { throw new Error("Cannot setup the mapJoin: " + e); } } @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)); built_table = null; // garbage-collect it super.cleanup(context); } } /** The fragment-replicate join (map-side join) physical operator * @param probe_map_fnc left mapper function * @param built_map_fnc right mapper function * @param reduce_fnc reducer function * @param acc_fnc optional accumulator function * @param zero optional the zero value for the accumulator * @param probe_dataset the map source * @param built_dataset stored in distributed cache * @param stop_counter optional counter used in repeat operation * @return a new data source that contains the result */ public final static DataSet mapJoin(Tree probe_map_fnc, // left mapper function Tree built_map_fnc, // right mapper function Tree reduce_fnc, // reducer function Tree acc_fnc, // optional accumulator function Tree zero, // optional the zero value for the accumulator DataSet probe_dataset, // the map source DataSet built_dataset, // stored in distributed cache String stop_counter) // optional counter used in repeat operation throws Exception { DataSet ds = MapOperation.cMap(built_map_fnc, null, null, built_dataset, "-"); conf = MapReduceEvaluator.clear_configuration(conf); String newpath = new_path(conf); conf.set("mrql.inMap.reducer", reduce_fnc.toString()); conf.set("mrql.probe_mapper", probe_map_fnc.toString()); conf.set("mrql.counter", stop_counter); if (zero != null) { conf.set("mrql.accumulator", acc_fnc.toString()); conf.set("mrql.zero", zero.toString()); } else conf.set("mrql.zero", ""); setupSplits(new DataSet[] { probe_dataset, built_dataset }, 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.setOutputFormatClass(SequenceFileOutputFormat.class); PathFilter pf = new PathFilter() { public boolean accept(Path path) { return !path.getName().startsWith("_"); } }; for (DataSource p : ds.source) { // distribute the built dataset Path path = new Path(p.path); for (FileStatus s : path.getFileSystem(conf).listStatus(path, pf)) DistributedCache.addCacheFile(s.getPath().toUri(), job.getConfiguration()); } ; for (DataSource p : probe_dataset.source) MultipleInputs.addInputPath(job, new Path(p.path), (Class<? extends MapReduceMRQLFileInputFormat>) p.inputFormat, mapJoinMapper.class); FileOutputFormat.setOutputPath(job, new Path(newpath)); job.setNumReduceTasks(0); job.waitForCompletion(true); long c = (stop_counter.equals("-")) ? 0 : job.getCounters().findCounter("mrql", stop_counter).getValue(); return new DataSet(new BinaryDataSource(newpath, conf), c, outputRecords(job)); } }