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.hadoop.mapreduce.lib.input; import java.io.IOException; import java.util.ArrayList; import java.util.Collection; import java.util.Collections; import java.util.LinkedHashSet; import java.util.HashSet; import java.util.List; import java.util.HashMap; import java.util.Set; import java.util.Iterator; import java.util.Map; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.LocatedFileStatus; import org.apache.hadoop.fs.Path; import org.apache.hadoop.fs.BlockLocation; import org.apache.hadoop.fs.FileStatus; import org.apache.hadoop.fs.PathFilter; import org.apache.hadoop.io.compress.CompressionCodec; import org.apache.hadoop.io.compress.CompressionCodecFactory; import org.apache.hadoop.io.compress.SplittableCompressionCodec; import org.apache.hadoop.mapreduce.InputFormat; import org.apache.hadoop.mapreduce.InputSplit; import org.apache.hadoop.mapreduce.JobContext; import org.apache.hadoop.mapreduce.RecordReader; import org.apache.hadoop.mapreduce.TaskAttemptContext; import org.apache.hadoop.net.NodeBase; import org.apache.hadoop.net.NetworkTopology; import com.google.common.annotations.VisibleForTesting; import com.google.common.collect.HashMultiset; import com.google.common.collect.Multiset; /** * An abstract {@link InputFormat} that returns {@link CombineFileSplit}'s in * {@link InputFormat#getSplits(JobContext)} method. * * Splits are constructed from the files under the input paths. * A split cannot have files from different pools. * Each split returned may contain blocks from different files. * If a maxSplitSize is specified, then blocks on the same node are * combined to form a single split. Blocks that are left over are * then combined with other blocks in the same rack. * If maxSplitSize is not specified, then blocks from the same rack * are combined in a single split; no attempt is made to create * node-local splits. * If the maxSplitSize is equal to the block size, then this class * is similar to the default splitting behavior in Hadoop: each * block is a locally processed split. * Subclasses implement * {@link InputFormat#createRecordReader(InputSplit, TaskAttemptContext)} * to construct <code>RecordReader</code>'s for * <code>CombineFileSplit</code>'s. * * @see CombineFileSplit */ @InterfaceAudience.Public @InterfaceStability.Stable public abstract class CombineFileInputFormat<K, V> extends FileInputFormat<K, V> { private static final Log LOG = LogFactory.getLog(CombineFileInputFormat.class); public static final String SPLIT_MINSIZE_PERNODE = "mapreduce.input.fileinputformat.split.minsize.per.node"; public static final String SPLIT_MINSIZE_PERRACK = "mapreduce.input.fileinputformat.split.minsize.per.rack"; // ability to limit the size of a single split private long maxSplitSize = 0; private long minSplitSizeNode = 0; private long minSplitSizeRack = 0; // A pool of input paths filters. A split cannot have blocks from files // across multiple pools. private ArrayList<MultiPathFilter> pools = new ArrayList<MultiPathFilter>(); // mapping from a rack name to the set of Nodes in the rack private HashMap<String, Set<String>> rackToNodes = new HashMap<String, Set<String>>(); /** * Specify the maximum size (in bytes) of each split. Each split is * approximately equal to the specified size. */ protected void setMaxSplitSize(long maxSplitSize) { this.maxSplitSize = maxSplitSize; } /** * Specify the minimum size (in bytes) of each split per node. * This applies to data that is left over after combining data on a single * node into splits that are of maximum size specified by maxSplitSize. * This leftover data will be combined into its own split if its size * exceeds minSplitSizeNode. */ protected void setMinSplitSizeNode(long minSplitSizeNode) { this.minSplitSizeNode = minSplitSizeNode; } /** * Specify the minimum size (in bytes) of each split per rack. * This applies to data that is left over after combining data on a single * rack into splits that are of maximum size specified by maxSplitSize. * This leftover data will be combined into its own split if its size * exceeds minSplitSizeRack. */ protected void setMinSplitSizeRack(long minSplitSizeRack) { this.minSplitSizeRack = minSplitSizeRack; } /** * Create a new pool and add the filters to it. * A split cannot have files from different pools. */ protected void createPool(List<PathFilter> filters) { pools.add(new MultiPathFilter(filters)); } /** * Create a new pool and add the filters to it. * A pathname can satisfy any one of the specified filters. * A split cannot have files from different pools. */ protected void createPool(PathFilter... filters) { MultiPathFilter multi = new MultiPathFilter(); for (PathFilter f : filters) { multi.add(f); } pools.add(multi); } @Override protected boolean isSplitable(JobContext context, Path file) { final CompressionCodec codec = new CompressionCodecFactory(context.getConfiguration()).getCodec(file); if (null == codec) { return true; } return codec instanceof SplittableCompressionCodec; } /** * default constructor */ public CombineFileInputFormat() { } @Override public List<InputSplit> getSplits(JobContext job) throws IOException { long minSizeNode = 0; long minSizeRack = 0; long maxSize = 0; Configuration conf = job.getConfiguration(); // the values specified by setxxxSplitSize() takes precedence over the // values that might have been specified in the config if (minSplitSizeNode != 0) { minSizeNode = minSplitSizeNode; } else { minSizeNode = conf.getLong(SPLIT_MINSIZE_PERNODE, 0); } if (minSplitSizeRack != 0) { minSizeRack = minSplitSizeRack; } else { minSizeRack = conf.getLong(SPLIT_MINSIZE_PERRACK, 0); } if (maxSplitSize != 0) { maxSize = maxSplitSize; } else { maxSize = conf.getLong("mapreduce.input.fileinputformat.split.maxsize", 0); // If maxSize is not configured, a single split will be generated per // node. } if (minSizeNode != 0 && maxSize != 0 && minSizeNode > maxSize) { throw new IOException("Minimum split size pernode " + minSizeNode + " cannot be larger than maximum split size " + maxSize); } if (minSizeRack != 0 && maxSize != 0 && minSizeRack > maxSize) { throw new IOException("Minimum split size per rack " + minSizeRack + " cannot be larger than maximum split size " + maxSize); } if (minSizeRack != 0 && minSizeNode > minSizeRack) { throw new IOException("Minimum split size per node " + minSizeNode + " cannot be larger than minimum split " + "size per rack " + minSizeRack); } // all the files in input set List<FileStatus> stats = listStatus(job); List<InputSplit> splits = new ArrayList<InputSplit>(); if (stats.size() == 0) { return splits; } // In one single iteration, process all the paths in a single pool. // Processing one pool at a time ensures that a split contains paths // from a single pool only. for (MultiPathFilter onepool : pools) { ArrayList<FileStatus> myPaths = new ArrayList<FileStatus>(); // pick one input path. If it matches all the filters in a pool, // add it to the output set for (Iterator<FileStatus> iter = stats.iterator(); iter.hasNext();) { FileStatus p = iter.next(); if (onepool.accept(p.getPath())) { myPaths.add(p); // add it to my output set iter.remove(); } } // create splits for all files in this pool. getMoreSplits(job, myPaths, maxSize, minSizeNode, minSizeRack, splits); } // create splits for all files that are not in any pool. getMoreSplits(job, stats, maxSize, minSizeNode, minSizeRack, splits); // free up rackToNodes map rackToNodes.clear(); return splits; } /** * Return all the splits in the specified set of paths */ private void getMoreSplits(JobContext job, List<FileStatus> stats, long maxSize, long minSizeNode, long minSizeRack, List<InputSplit> splits) throws IOException { Configuration conf = job.getConfiguration(); // all blocks for all the files in input set OneFileInfo[] files; // mapping from a rack name to the list of blocks it has HashMap<String, List<OneBlockInfo>> rackToBlocks = new HashMap<String, List<OneBlockInfo>>(); // mapping from a block to the nodes on which it has replicas HashMap<OneBlockInfo, String[]> blockToNodes = new HashMap<OneBlockInfo, String[]>(); // mapping from a node to the list of blocks that it contains HashMap<String, Set<OneBlockInfo>> nodeToBlocks = new HashMap<String, Set<OneBlockInfo>>(); files = new OneFileInfo[stats.size()]; if (stats.size() == 0) { return; } // populate all the blocks for all files long totLength = 0; int i = 0; for (FileStatus stat : stats) { files[i] = new OneFileInfo(stat, conf, isSplitable(job, stat.getPath()), rackToBlocks, blockToNodes, nodeToBlocks, rackToNodes, maxSize); totLength += files[i].getLength(); } createSplits(nodeToBlocks, blockToNodes, rackToBlocks, totLength, maxSize, minSizeNode, minSizeRack, splits); } /** * Process all the nodes and create splits that are local to a node. * Generate one split per node iteration, and walk over nodes multiple times * to distribute the splits across nodes. * <p> * Note: The order of processing the nodes is undetermined because the * implementation of nodeToBlocks is {@link java.util.HashMap} and its order * of the entries is undetermined. * @param nodeToBlocks Mapping from a node to the list of blocks that * it contains. * @param blockToNodes Mapping from a block to the nodes on which * it has replicas. * @param rackToBlocks Mapping from a rack name to the list of blocks it has. * @param totLength Total length of the input files. * @param maxSize Max size of each split. * If set to 0, disable smoothing load. * @param minSizeNode Minimum split size per node. * @param minSizeRack Minimum split size per rack. * @param splits New splits created by this method are added to the list. */ @VisibleForTesting void createSplits(Map<String, Set<OneBlockInfo>> nodeToBlocks, Map<OneBlockInfo, String[]> blockToNodes, Map<String, List<OneBlockInfo>> rackToBlocks, long totLength, long maxSize, long minSizeNode, long minSizeRack, List<InputSplit> splits) { ArrayList<OneBlockInfo> validBlocks = new ArrayList<OneBlockInfo>(); long curSplitSize = 0; int totalNodes = nodeToBlocks.size(); long totalLength = totLength; Multiset<String> splitsPerNode = HashMultiset.create(); Set<String> completedNodes = new HashSet<String>(); while (true) { for (Iterator<Map.Entry<String, Set<OneBlockInfo>>> iter = nodeToBlocks.entrySet().iterator(); iter .hasNext();) { Map.Entry<String, Set<OneBlockInfo>> one = iter.next(); String node = one.getKey(); // Skip the node if it has previously been marked as completed. if (completedNodes.contains(node)) { continue; } Set<OneBlockInfo> blocksInCurrentNode = one.getValue(); // for each block, copy it into validBlocks. Delete it from // blockToNodes so that the same block does not appear in // two different splits. Iterator<OneBlockInfo> oneBlockIter = blocksInCurrentNode.iterator(); while (oneBlockIter.hasNext()) { OneBlockInfo oneblock = oneBlockIter.next(); // Remove all blocks which may already have been assigned to other // splits. if (!blockToNodes.containsKey(oneblock)) { oneBlockIter.remove(); continue; } validBlocks.add(oneblock); blockToNodes.remove(oneblock); curSplitSize += oneblock.length; // if the accumulated split size exceeds the maximum, then // create this split. if (maxSize != 0 && curSplitSize >= maxSize) { // create an input split and add it to the splits array addCreatedSplit(splits, Collections.singleton(node), validBlocks); totalLength -= curSplitSize; curSplitSize = 0; splitsPerNode.add(node); // Remove entries from blocksInNode so that we don't walk these // again. blocksInCurrentNode.removeAll(validBlocks); validBlocks.clear(); // Done creating a single split for this node. Move on to the next // node so that splits are distributed across nodes. break; } } if (validBlocks.size() != 0) { // This implies that the last few blocks (or all in case maxSize=0) // were not part of a split. The node is complete. // if there were any blocks left over and their combined size is // larger than minSplitNode, then combine them into one split. // Otherwise add them back to the unprocessed pool. It is likely // that they will be combined with other blocks from the // same rack later on. // This condition also kicks in when max split size is not set. All // blocks on a node will be grouped together into a single split. if (minSizeNode != 0 && curSplitSize >= minSizeNode && splitsPerNode.count(node) == 0) { // haven't created any split on this machine. so its ok to add a // smaller one for parallelism. Otherwise group it in the rack for // balanced size create an input split and add it to the splits // array addCreatedSplit(splits, Collections.singleton(node), validBlocks); totalLength -= curSplitSize; splitsPerNode.add(node); // Remove entries from blocksInNode so that we don't walk this again. blocksInCurrentNode.removeAll(validBlocks); // The node is done. This was the last set of blocks for this node. } else { // Put the unplaced blocks back into the pool for later rack-allocation. for (OneBlockInfo oneblock : validBlocks) { blockToNodes.put(oneblock, oneblock.hosts); } } validBlocks.clear(); curSplitSize = 0; completedNodes.add(node); } else { // No in-flight blocks. if (blocksInCurrentNode.size() == 0) { // Node is done. All blocks were fit into node-local splits. completedNodes.add(node); } // else Run through the node again. } } // Check if node-local assignments are complete. if (completedNodes.size() == totalNodes || totalLength == 0) { // All nodes have been walked over and marked as completed or all blocks // have been assigned. The rest should be handled via rackLock assignment. LOG.info("DEBUG: Terminated node allocation with : CompletedNodes: " + completedNodes.size() + ", size left: " + totalLength); break; } } // if blocks in a rack are below the specified minimum size, then keep them // in 'overflow'. After the processing of all racks is complete, these // overflow blocks will be combined into splits. ArrayList<OneBlockInfo> overflowBlocks = new ArrayList<OneBlockInfo>(); Set<String> racks = new HashSet<String>(); // Process all racks over and over again until there is no more work to do. while (blockToNodes.size() > 0) { // Create one split for this rack before moving over to the next rack. // Come back to this rack after creating a single split for each of the // remaining racks. // Process one rack location at a time, Combine all possible blocks that // reside on this rack as one split. (constrained by minimum and maximum // split size). // iterate over all racks for (Iterator<Map.Entry<String, List<OneBlockInfo>>> iter = rackToBlocks.entrySet().iterator(); iter .hasNext();) { Map.Entry<String, List<OneBlockInfo>> one = iter.next(); racks.add(one.getKey()); List<OneBlockInfo> blocks = one.getValue(); // for each block, copy it into validBlocks. Delete it from // blockToNodes so that the same block does not appear in // two different splits. boolean createdSplit = false; for (OneBlockInfo oneblock : blocks) { if (blockToNodes.containsKey(oneblock)) { validBlocks.add(oneblock); blockToNodes.remove(oneblock); curSplitSize += oneblock.length; // if the accumulated split size exceeds the maximum, then // create this split. if (maxSize != 0 && curSplitSize >= maxSize) { // create an input split and add it to the splits array addCreatedSplit(splits, getHosts(racks), validBlocks); createdSplit = true; break; } } } // if we created a split, then just go to the next rack if (createdSplit) { curSplitSize = 0; validBlocks.clear(); racks.clear(); continue; } if (!validBlocks.isEmpty()) { if (minSizeRack != 0 && curSplitSize >= minSizeRack) { // if there is a minimum size specified, then create a single split // otherwise, store these blocks into overflow data structure addCreatedSplit(splits, getHosts(racks), validBlocks); } else { // There were a few blocks in this rack that // remained to be processed. Keep them in 'overflow' block list. // These will be combined later. overflowBlocks.addAll(validBlocks); } } curSplitSize = 0; validBlocks.clear(); racks.clear(); } } assert blockToNodes.isEmpty(); assert curSplitSize == 0; assert validBlocks.isEmpty(); assert racks.isEmpty(); // Process all overflow blocks for (OneBlockInfo oneblock : overflowBlocks) { validBlocks.add(oneblock); curSplitSize += oneblock.length; // This might cause an exiting rack location to be re-added, // but it should be ok. for (int i = 0; i < oneblock.racks.length; i++) { racks.add(oneblock.racks[i]); } // if the accumulated split size exceeds the maximum, then // create this split. if (maxSize != 0 && curSplitSize >= maxSize) { // create an input split and add it to the splits array addCreatedSplit(splits, getHosts(racks), validBlocks); curSplitSize = 0; validBlocks.clear(); racks.clear(); } } // Process any remaining blocks, if any. if (!validBlocks.isEmpty()) { addCreatedSplit(splits, getHosts(racks), validBlocks); } } /** * Create a single split from the list of blocks specified in validBlocks * Add this new split into splitList. */ private void addCreatedSplit(List<InputSplit> splitList, Collection<String> locations, ArrayList<OneBlockInfo> validBlocks) { // create an input split Path[] fl = new Path[validBlocks.size()]; long[] offset = new long[validBlocks.size()]; long[] length = new long[validBlocks.size()]; for (int i = 0; i < validBlocks.size(); i++) { fl[i] = validBlocks.get(i).onepath; offset[i] = validBlocks.get(i).offset; length[i] = validBlocks.get(i).length; } // add this split to the list that is returned CombineFileSplit thissplit = new CombineFileSplit(fl, offset, length, locations.toArray(new String[0])); splitList.add(thissplit); } /** * This is not implemented yet. */ public abstract RecordReader<K, V> createRecordReader(InputSplit split, TaskAttemptContext context) throws IOException; /** * information about one file from the File System */ @VisibleForTesting static class OneFileInfo { private long fileSize; // size of the file private OneBlockInfo[] blocks; // all blocks in this file OneFileInfo(FileStatus stat, Configuration conf, boolean isSplitable, HashMap<String, List<OneBlockInfo>> rackToBlocks, HashMap<OneBlockInfo, String[]> blockToNodes, HashMap<String, Set<OneBlockInfo>> nodeToBlocks, HashMap<String, Set<String>> rackToNodes, long maxSize) throws IOException { this.fileSize = 0; // get block locations from file system BlockLocation[] locations; if (stat instanceof LocatedFileStatus) { locations = ((LocatedFileStatus) stat).getBlockLocations(); } else { FileSystem fs = stat.getPath().getFileSystem(conf); locations = fs.getFileBlockLocations(stat, 0, stat.getLen()); } // create a list of all block and their locations if (locations == null) { blocks = new OneBlockInfo[0]; } else { if (locations.length == 0 && !stat.isDirectory()) { locations = new BlockLocation[] { new BlockLocation() }; } if (!isSplitable) { // if the file is not splitable, just create the one block with // full file length blocks = new OneBlockInfo[1]; fileSize = stat.getLen(); blocks[0] = new OneBlockInfo(stat.getPath(), 0, fileSize, locations[0].getHosts(), locations[0].getTopologyPaths()); } else { ArrayList<OneBlockInfo> blocksList = new ArrayList<OneBlockInfo>(locations.length); for (int i = 0; i < locations.length; i++) { fileSize += locations[i].getLength(); // each split can be a maximum of maxSize long left = locations[i].getLength(); long myOffset = locations[i].getOffset(); long myLength = 0; do { if (maxSize == 0) { myLength = left; } else { if (left > maxSize && left < 2 * maxSize) { // if remainder is between max and 2*max - then // instead of creating splits of size max, left-max we // create splits of size left/2 and left/2. This is // a heuristic to avoid creating really really small // splits. myLength = left / 2; } else { myLength = Math.min(maxSize, left); } } OneBlockInfo oneblock = new OneBlockInfo(stat.getPath(), myOffset, myLength, locations[i].getHosts(), locations[i].getTopologyPaths()); left -= myLength; myOffset += myLength; blocksList.add(oneblock); } while (left > 0); } blocks = blocksList.toArray(new OneBlockInfo[blocksList.size()]); } populateBlockInfo(blocks, rackToBlocks, blockToNodes, nodeToBlocks, rackToNodes); } } @VisibleForTesting static void populateBlockInfo(OneBlockInfo[] blocks, Map<String, List<OneBlockInfo>> rackToBlocks, Map<OneBlockInfo, String[]> blockToNodes, Map<String, Set<OneBlockInfo>> nodeToBlocks, Map<String, Set<String>> rackToNodes) { for (OneBlockInfo oneblock : blocks) { // add this block to the block --> node locations map blockToNodes.put(oneblock, oneblock.hosts); // For blocks that do not have host/rack information, // assign to default rack. String[] racks = null; if (oneblock.hosts.length == 0) { racks = new String[] { NetworkTopology.DEFAULT_RACK }; } else { racks = oneblock.racks; } // add this block to the rack --> block map for (int j = 0; j < racks.length; j++) { String rack = racks[j]; List<OneBlockInfo> blklist = rackToBlocks.get(rack); if (blklist == null) { blklist = new ArrayList<OneBlockInfo>(); rackToBlocks.put(rack, blklist); } blklist.add(oneblock); if (!racks[j].equals(NetworkTopology.DEFAULT_RACK)) { // Add this host to rackToNodes map addHostToRack(rackToNodes, racks[j], oneblock.hosts[j]); } } // add this block to the node --> block map for (int j = 0; j < oneblock.hosts.length; j++) { String node = oneblock.hosts[j]; Set<OneBlockInfo> blklist = nodeToBlocks.get(node); if (blklist == null) { blklist = new LinkedHashSet<OneBlockInfo>(); nodeToBlocks.put(node, blklist); } blklist.add(oneblock); } } } long getLength() { return fileSize; } OneBlockInfo[] getBlocks() { return blocks; } } /** * information about one block from the File System */ @VisibleForTesting static class OneBlockInfo { Path onepath; // name of this file long offset; // offset in file long length; // length of this block String[] hosts; // nodes on which this block resides String[] racks; // network topology of hosts OneBlockInfo(Path path, long offset, long len, String[] hosts, String[] topologyPaths) { this.onepath = path; this.offset = offset; this.hosts = hosts; this.length = len; assert (hosts.length == topologyPaths.length || topologyPaths.length == 0); // if the file system does not have any rack information, then // use dummy rack location. if (topologyPaths.length == 0) { topologyPaths = new String[hosts.length]; for (int i = 0; i < topologyPaths.length; i++) { topologyPaths[i] = (new NodeBase(hosts[i], NetworkTopology.DEFAULT_RACK)).toString(); } } // The topology paths have the host name included as the last // component. Strip it. this.racks = new String[topologyPaths.length]; for (int i = 0; i < topologyPaths.length; i++) { this.racks[i] = (new NodeBase(topologyPaths[i])).getNetworkLocation(); } } } protected BlockLocation[] getFileBlockLocations(FileSystem fs, FileStatus stat) throws IOException { if (stat instanceof LocatedFileStatus) { return ((LocatedFileStatus) stat).getBlockLocations(); } return fs.getFileBlockLocations(stat, 0, stat.getLen()); } private static void addHostToRack(Map<String, Set<String>> rackToNodes, String rack, String host) { Set<String> hosts = rackToNodes.get(rack); if (hosts == null) { hosts = new HashSet<String>(); rackToNodes.put(rack, hosts); } hosts.add(host); } private Set<String> getHosts(Set<String> racks) { Set<String> hosts = new HashSet<String>(); for (String rack : racks) { if (rackToNodes.containsKey(rack)) { hosts.addAll(rackToNodes.get(rack)); } } return hosts; } /** * Accept a path only if any one of filters given in the * constructor do. */ private static class MultiPathFilter implements PathFilter { private List<PathFilter> filters; public MultiPathFilter() { this.filters = new ArrayList<PathFilter>(); } public MultiPathFilter(List<PathFilter> filters) { this.filters = filters; } public void add(PathFilter one) { filters.add(one); } public boolean accept(Path path) { for (PathFilter filter : filters) { if (filter.accept(path)) { return true; } } return false; } public String toString() { StringBuffer buf = new StringBuffer(); buf.append("["); for (PathFilter f : filters) { buf.append(f); buf.append(","); } buf.append("]"); return buf.toString(); } } }