Java tutorial
package org.apache.cassandra.hadoop; /* * * 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. * */ import java.io.IOException; import java.net.InetAddress; import java.nio.ByteBuffer; import java.util.*; import java.util.concurrent.Callable; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; import org.apache.commons.lang.StringUtils; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.apache.cassandra.db.IColumn; import org.apache.cassandra.thrift.Cassandra; import org.apache.cassandra.thrift.InvalidRequestException; import org.apache.cassandra.thrift.TokenRange; import org.apache.cassandra.thrift.TBinaryProtocol; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.mapreduce.*; import org.apache.thrift.TException; import org.apache.thrift.transport.TFramedTransport; import org.apache.thrift.transport.TSocket; import org.apache.thrift.transport.TTransport; import org.apache.thrift.transport.TTransportException; /** * Hadoop InputFormat allowing map/reduce against Cassandra rows within one ColumnFamily. * * At minimum, you need to set the CF and predicate (description of columns to extract from each row) * in your Hadoop job Configuration. The ConfigHelper class is provided to make this * simple: * ConfigHelper.setColumnFamily * ConfigHelper.setSlicePredicate * * You can also configure the number of rows per InputSplit with * ConfigHelper.setInputSplitSize * This should be "as big as possible, but no bigger." Each InputSplit is read from Cassandra * with multiple get_slice_range queries, and the per-call overhead of get_slice_range is high, * so larger split sizes are better -- but if it is too large, you will run out of memory. * * The default split size is 64k rows. */ public class ColumnFamilyInputFormat extends InputFormat<ByteBuffer, SortedMap<ByteBuffer, IColumn>> { private static final Logger logger = LoggerFactory.getLogger(ColumnFamilyInputFormat.class); private String keyspace; private String cfName; private static void validateConfiguration(Configuration conf) { if (ConfigHelper.getInputKeyspace(conf) == null || ConfigHelper.getInputColumnFamily(conf) == null) { throw new UnsupportedOperationException( "you must set the keyspace and columnfamily with setColumnFamily()"); } if (ConfigHelper.getInputSlicePredicate(conf) == null) { throw new UnsupportedOperationException("you must set the predicate with setPredicate"); } } public List<InputSplit> getSplits(JobContext context) throws IOException { Configuration conf = context.getConfiguration(); validateConfiguration(conf); // cannonical ranges and nodes holding replicas List<TokenRange> masterRangeNodes = getRangeMap(conf); keyspace = ConfigHelper.getInputKeyspace(context.getConfiguration()); cfName = ConfigHelper.getInputColumnFamily(context.getConfiguration()); // cannonical ranges, split into pieces, fetching the splits in parallel ExecutorService executor = Executors.newCachedThreadPool(); List<InputSplit> splits = new ArrayList<InputSplit>(); try { List<Future<List<InputSplit>>> splitfutures = new ArrayList<Future<List<InputSplit>>>(); for (TokenRange range : masterRangeNodes) { // for each range, pick a live owner and ask it to compute bite-sized splits splitfutures.add(executor.submit(new SplitCallable(range, conf))); } // wait until we have all the results back for (Future<List<InputSplit>> futureInputSplits : splitfutures) { try { splits.addAll(futureInputSplits.get()); } catch (Exception e) { throw new IOException("Could not get input splits", e); } } } finally { executor.shutdownNow(); } assert splits.size() > 0; Collections.shuffle(splits, new Random(System.nanoTime())); return splits; } /** * Gets a token range and splits it up according to the suggested * size into input splits that Hadoop can use. */ class SplitCallable implements Callable<List<InputSplit>> { private final TokenRange range; private final Configuration conf; public SplitCallable(TokenRange tr, Configuration conf) { this.range = tr; this.conf = conf; } public List<InputSplit> call() throws Exception { ArrayList<InputSplit> splits = new ArrayList<InputSplit>(); List<String> tokens = getSubSplits(keyspace, cfName, range, conf); // turn the sub-ranges into InputSplits String[] endpoints = range.endpoints.toArray(new String[range.endpoints.size()]); // hadoop needs hostname, not ip for (int i = 0; i < endpoints.length; i++) { endpoints[i] = InetAddress.getByName(endpoints[i]).getHostName(); } for (int i = 1; i < tokens.size(); i++) { ColumnFamilySplit split = new ColumnFamilySplit(tokens.get(i - 1), tokens.get(i), endpoints); logger.debug("adding " + split); splits.add(split); } return splits; } } private List<String> getSubSplits(String keyspace, String cfName, TokenRange range, Configuration conf) throws IOException { int splitsize = ConfigHelper.getInputSplitSize(conf); for (String host : range.endpoints) { try { Cassandra.Client client = createConnection(host, ConfigHelper.getRpcPort(conf), true); client.set_keyspace(keyspace); return client.describe_splits(cfName, range.start_token, range.end_token, splitsize); } catch (IOException e) { logger.debug("failed connect to endpoint " + host, e); } catch (TException e) { throw new RuntimeException(e); } catch (InvalidRequestException e) { throw new RuntimeException(e); } } throw new IOException("failed connecting to all endpoints " + StringUtils.join(range.endpoints, ",")); } private static Cassandra.Client createConnection(String host, Integer port, boolean framed) throws IOException { TSocket socket = new TSocket(host, port); TTransport trans = framed ? new TFramedTransport(socket) : socket; try { trans.open(); } catch (TTransportException e) { throw new IOException("unable to connect to server", e); } return new Cassandra.Client(new TBinaryProtocol(trans)); } private List<TokenRange> getRangeMap(Configuration conf) throws IOException { Cassandra.Client client = createConnection(ConfigHelper.getInitialAddress(conf), ConfigHelper.getRpcPort(conf), true); List<TokenRange> map; try { map = client.describe_ring(ConfigHelper.getInputKeyspace(conf)); } catch (TException e) { throw new RuntimeException(e); } catch (InvalidRequestException e) { throw new RuntimeException(e); } return map; } public RecordReader<ByteBuffer, SortedMap<ByteBuffer, IColumn>> createRecordReader(InputSplit inputSplit, TaskAttemptContext taskAttemptContext) throws IOException, InterruptedException { return new ColumnFamilyRecordReader(); } }