org.apache.hadoop.io.MapFile Maven / Gradle / Ivy
/**
* 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.io;
import java.io.EOFException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.HadoopIllegalArgumentException;
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.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.SequenceFile.CompressionType;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.util.Options;
import org.apache.hadoop.util.Progressable;
import org.apache.hadoop.util.ReflectionUtils;
/** A file-based map from keys to values.
*
* A map is a directory containing two files, the data file,
* containing all keys and values in the map, and a smaller index
* file, containing a fraction of the keys. The fraction is determined by
* {@link Writer#getIndexInterval()}.
*
*
The index file is read entirely into memory. Thus key implementations
* should try to keep themselves small.
*
*
Map files are created by adding entries in-order. To maintain a large
* database, perform updates by copying the previous version of a database and
* merging in a sorted change list, to create a new version of the database in
* a new file. Sorting large change lists can be done with {@link
* SequenceFile.Sorter}.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class MapFile {
private static final Log LOG = LogFactory.getLog(MapFile.class);
/** The name of the index file. */
public static final String INDEX_FILE_NAME = "index";
/** The name of the data file. */
public static final String DATA_FILE_NAME = "data";
protected MapFile() {} // no public ctor
/** Writes a new map. */
public static class Writer implements java.io.Closeable {
private SequenceFile.Writer data;
private SequenceFile.Writer index;
final private static String INDEX_INTERVAL = "io.map.index.interval";
private int indexInterval = 128;
private long size;
private LongWritable position = new LongWritable();
// the following fields are used only for checking key order
private WritableComparator comparator;
private DataInputBuffer inBuf = new DataInputBuffer();
private DataOutputBuffer outBuf = new DataOutputBuffer();
private WritableComparable lastKey;
/** What's the position (in bytes) we wrote when we got the last index */
private long lastIndexPos = -1;
/**
* What was size when we last wrote an index. Set to MIN_VALUE to ensure that
* we have an index at position zero -- midKey will throw an exception if this
* is not the case
*/
private long lastIndexKeyCount = Long.MIN_VALUE;
/** Create the named map for keys of the named class.
* @deprecated Use Writer(Configuration, Path, Option...) instead.
*/
@Deprecated
public Writer(Configuration conf, FileSystem fs, String dirName,
Class keyClass,
Class valClass) throws IOException {
this(conf, new Path(dirName), keyClass(keyClass), valueClass(valClass));
}
/** Create the named map for keys of the named class.
* @deprecated Use Writer(Configuration, Path, Option...) instead.
*/
@Deprecated
public Writer(Configuration conf, FileSystem fs, String dirName,
Class keyClass, Class valClass,
CompressionType compress,
Progressable progress) throws IOException {
this(conf, new Path(dirName), keyClass(keyClass), valueClass(valClass),
compression(compress), progressable(progress));
}
/** Create the named map for keys of the named class.
* @deprecated Use Writer(Configuration, Path, Option...) instead.
*/
@Deprecated
public Writer(Configuration conf, FileSystem fs, String dirName,
Class keyClass, Class valClass,
CompressionType compress, CompressionCodec codec,
Progressable progress) throws IOException {
this(conf, new Path(dirName), keyClass(keyClass), valueClass(valClass),
compression(compress, codec), progressable(progress));
}
/** Create the named map for keys of the named class.
* @deprecated Use Writer(Configuration, Path, Option...) instead.
*/
@Deprecated
public Writer(Configuration conf, FileSystem fs, String dirName,
Class keyClass, Class valClass,
CompressionType compress) throws IOException {
this(conf, new Path(dirName), keyClass(keyClass),
valueClass(valClass), compression(compress));
}
/** Create the named map using the named key comparator.
* @deprecated Use Writer(Configuration, Path, Option...) instead.
*/
@Deprecated
public Writer(Configuration conf, FileSystem fs, String dirName,
WritableComparator comparator, Class valClass
) throws IOException {
this(conf, new Path(dirName), comparator(comparator),
valueClass(valClass));
}
/** Create the named map using the named key comparator.
* @deprecated Use Writer(Configuration, Path, Option...) instead.
*/
@Deprecated
public Writer(Configuration conf, FileSystem fs, String dirName,
WritableComparator comparator, Class valClass,
SequenceFile.CompressionType compress) throws IOException {
this(conf, new Path(dirName), comparator(comparator),
valueClass(valClass), compression(compress));
}
/** Create the named map using the named key comparator.
* @deprecated Use Writer(Configuration, Path, Option...)} instead.
*/
@Deprecated
public Writer(Configuration conf, FileSystem fs, String dirName,
WritableComparator comparator, Class valClass,
SequenceFile.CompressionType compress,
Progressable progress) throws IOException {
this(conf, new Path(dirName), comparator(comparator),
valueClass(valClass), compression(compress),
progressable(progress));
}
/** Create the named map using the named key comparator.
* @deprecated Use Writer(Configuration, Path, Option...) instead.
*/
@Deprecated
public Writer(Configuration conf, FileSystem fs, String dirName,
WritableComparator comparator, Class valClass,
SequenceFile.CompressionType compress, CompressionCodec codec,
Progressable progress) throws IOException {
this(conf, new Path(dirName), comparator(comparator),
valueClass(valClass), compression(compress, codec),
progressable(progress));
}
// our options are a superset of sequence file writer options
public static interface Option extends SequenceFile.Writer.Option { }
private static class KeyClassOption extends Options.ClassOption
implements Option {
KeyClassOption(Class value) {
super(value);
}
}
private static class ComparatorOption implements Option {
private final WritableComparator value;
ComparatorOption(WritableComparator value) {
this.value = value;
}
WritableComparator getValue() {
return value;
}
}
public static Option keyClass(Class value) {
return new KeyClassOption(value);
}
public static Option comparator(WritableComparator value) {
return new ComparatorOption(value);
}
public static SequenceFile.Writer.Option valueClass(Class value) {
return SequenceFile.Writer.valueClass(value);
}
public static
SequenceFile.Writer.Option compression(CompressionType type) {
return SequenceFile.Writer.compression(type);
}
public static
SequenceFile.Writer.Option compression(CompressionType type,
CompressionCodec codec) {
return SequenceFile.Writer.compression(type, codec);
}
public static SequenceFile.Writer.Option progressable(Progressable value) {
return SequenceFile.Writer.progressable(value);
}
@SuppressWarnings("unchecked")
public Writer(Configuration conf,
Path dirName,
SequenceFile.Writer.Option... opts
) throws IOException {
KeyClassOption keyClassOption =
Options.getOption(KeyClassOption.class, opts);
ComparatorOption comparatorOption =
Options.getOption(ComparatorOption.class, opts);
if ((keyClassOption == null) == (comparatorOption == null)) {
throw new IllegalArgumentException("key class or comparator option "
+ "must be set");
}
this.indexInterval = conf.getInt(INDEX_INTERVAL, this.indexInterval);
Class keyClass;
if (keyClassOption == null) {
this.comparator = comparatorOption.getValue();
keyClass = comparator.getKeyClass();
} else {
keyClass=
(Class) keyClassOption.getValue();
this.comparator = WritableComparator.get(keyClass, conf);
}
this.lastKey = comparator.newKey();
FileSystem fs = dirName.getFileSystem(conf);
if (!fs.mkdirs(dirName)) {
throw new IOException("Mkdirs failed to create directory " + dirName);
}
Path dataFile = new Path(dirName, DATA_FILE_NAME);
Path indexFile = new Path(dirName, INDEX_FILE_NAME);
SequenceFile.Writer.Option[] dataOptions =
Options.prependOptions(opts,
SequenceFile.Writer.file(dataFile),
SequenceFile.Writer.keyClass(keyClass));
this.data = SequenceFile.createWriter(conf, dataOptions);
SequenceFile.Writer.Option[] indexOptions =
Options.prependOptions(opts, SequenceFile.Writer.file(indexFile),
SequenceFile.Writer.keyClass(keyClass),
SequenceFile.Writer.valueClass(LongWritable.class),
SequenceFile.Writer.compression(CompressionType.BLOCK));
this.index = SequenceFile.createWriter(conf, indexOptions);
}
/** The number of entries that are added before an index entry is added.*/
public int getIndexInterval() { return indexInterval; }
/** Sets the index interval.
* @see #getIndexInterval()
*/
public void setIndexInterval(int interval) { indexInterval = interval; }
/** Sets the index interval and stores it in conf
* @see #getIndexInterval()
*/
public static void setIndexInterval(Configuration conf, int interval) {
conf.setInt(INDEX_INTERVAL, interval);
}
/** Close the map. */
@Override
public synchronized void close() throws IOException {
data.close();
index.close();
}
/** Append a key/value pair to the map. The key must be greater or equal
* to the previous key added to the map. */
public synchronized void append(WritableComparable key, Writable val)
throws IOException {
checkKey(key);
long pos = data.getLength();
// Only write an index if we've changed positions. In a block compressed
// file, this means we write an entry at the start of each block
if (size >= lastIndexKeyCount + indexInterval && pos > lastIndexPos) {
position.set(pos); // point to current eof
index.append(key, position);
lastIndexPos = pos;
lastIndexKeyCount = size;
}
data.append(key, val); // append key/value to data
size++;
}
private void checkKey(WritableComparable key) throws IOException {
// check that keys are well-ordered
if (size != 0 && comparator.compare(lastKey, key) > 0)
throw new IOException("key out of order: "+key+" after "+lastKey);
// update lastKey with a copy of key by writing and reading
outBuf.reset();
key.write(outBuf); // write new key
inBuf.reset(outBuf.getData(), outBuf.getLength());
lastKey.readFields(inBuf); // read into lastKey
}
}
/** Provide access to an existing map. */
public static class Reader implements java.io.Closeable {
/** Number of index entries to skip between each entry. Zero by default.
* Setting this to values larger than zero can facilitate opening large map
* files using less memory. */
private int INDEX_SKIP = 0;
private WritableComparator comparator;
private WritableComparable nextKey;
private long seekPosition = -1;
private int seekIndex = -1;
private long firstPosition;
// the data, on disk
private SequenceFile.Reader data;
private SequenceFile.Reader index;
// whether the index Reader was closed
private boolean indexClosed = false;
// the index, in memory
private int count = -1;
private WritableComparable[] keys;
private long[] positions;
/** Returns the class of keys in this file. */
public Class getKeyClass() { return data.getKeyClass(); }
/** Returns the class of values in this file. */
public Class getValueClass() { return data.getValueClass(); }
public static interface Option extends SequenceFile.Reader.Option {}
public static Option comparator(WritableComparator value) {
return new ComparatorOption(value);
}
static class ComparatorOption implements Option {
private final WritableComparator value;
ComparatorOption(WritableComparator value) {
this.value = value;
}
WritableComparator getValue() {
return value;
}
}
public Reader(Path dir, Configuration conf,
SequenceFile.Reader.Option... opts) throws IOException {
ComparatorOption comparatorOption =
Options.getOption(ComparatorOption.class, opts);
WritableComparator comparator =
comparatorOption == null ? null : comparatorOption.getValue();
INDEX_SKIP = conf.getInt("io.map.index.skip", 0);
open(dir, comparator, conf, opts);
}
/** Construct a map reader for the named map.
* @deprecated
*/
@Deprecated
public Reader(FileSystem fs, String dirName,
Configuration conf) throws IOException {
this(new Path(dirName), conf);
}
/** Construct a map reader for the named map using the named comparator.
* @deprecated
*/
@Deprecated
public Reader(FileSystem fs, String dirName, WritableComparator comparator,
Configuration conf) throws IOException {
this(new Path(dirName), conf, comparator(comparator));
}
protected synchronized void open(Path dir,
WritableComparator comparator,
Configuration conf,
SequenceFile.Reader.Option... options
) throws IOException {
Path dataFile = new Path(dir, DATA_FILE_NAME);
Path indexFile = new Path(dir, INDEX_FILE_NAME);
// open the data
this.data = createDataFileReader(dataFile, conf, options);
this.firstPosition = data.getPosition();
if (comparator == null) {
Class cls;
cls = data.getKeyClass().asSubclass(WritableComparable.class);
this.comparator = WritableComparator.get(cls, conf);
} else {
this.comparator = comparator;
}
// open the index
SequenceFile.Reader.Option[] indexOptions =
Options.prependOptions(options, SequenceFile.Reader.file(indexFile));
this.index = new SequenceFile.Reader(conf, indexOptions);
}
/**
* Override this method to specialize the type of
* {@link SequenceFile.Reader} returned.
*/
protected SequenceFile.Reader
createDataFileReader(Path dataFile, Configuration conf,
SequenceFile.Reader.Option... options
) throws IOException {
SequenceFile.Reader.Option[] newOptions =
Options.prependOptions(options, SequenceFile.Reader.file(dataFile));
return new SequenceFile.Reader(conf, newOptions);
}
private void readIndex() throws IOException {
// read the index entirely into memory
if (this.keys != null)
return;
this.count = 0;
this.positions = new long[1024];
try {
int skip = INDEX_SKIP;
LongWritable position = new LongWritable();
WritableComparable lastKey = null;
long lastIndex = -1;
ArrayList keyBuilder = new ArrayList(1024);
while (true) {
WritableComparable k = comparator.newKey();
if (!index.next(k, position))
break;
// check order to make sure comparator is compatible
if (lastKey != null && comparator.compare(lastKey, k) > 0)
throw new IOException("key out of order: "+k+" after "+lastKey);
lastKey = k;
if (skip > 0) {
skip--;
continue; // skip this entry
} else {
skip = INDEX_SKIP; // reset skip
}
// don't read an index that is the same as the previous one. Block
// compressed map files used to do this (multiple entries would point
// at the same block)
if (position.get() == lastIndex)
continue;
if (count == positions.length) {
positions = Arrays.copyOf(positions, positions.length * 2);
}
keyBuilder.add(k);
positions[count] = position.get();
count++;
}
this.keys = keyBuilder.toArray(new WritableComparable[count]);
positions = Arrays.copyOf(positions, count);
} catch (EOFException e) {
LOG.warn("Unexpected EOF reading " + index +
" at entry #" + count + ". Ignoring.");
} finally {
indexClosed = true;
index.close();
}
}
/** Re-positions the reader before its first key. */
public synchronized void reset() throws IOException {
data.seek(firstPosition);
}
/** Get the key at approximately the middle of the file. Or null if the
* file is empty.
*/
public synchronized WritableComparable midKey() throws IOException {
readIndex();
if (count == 0) {
return null;
}
return keys[(count - 1) / 2];
}
/** Reads the final key from the file.
*
* @param key key to read into
*/
public synchronized void finalKey(WritableComparable key)
throws IOException {
long originalPosition = data.getPosition(); // save position
try {
readIndex(); // make sure index is valid
if (count > 0) {
data.seek(positions[count-1]); // skip to last indexed entry
} else {
reset(); // start at the beginning
}
while (data.next(key)) {} // scan to eof
} finally {
data.seek(originalPosition); // restore position
}
}
/** Positions the reader at the named key, or if none such exists, at the
* first entry after the named key. Returns true iff the named key exists
* in this map.
*/
public synchronized boolean seek(WritableComparable key) throws IOException {
return seekInternal(key) == 0;
}
/**
* Positions the reader at the named key, or if none such exists, at the
* first entry after the named key.
*
* @return 0 - exact match found
* < 0 - positioned at next record
* 1 - no more records in file
*/
private synchronized int seekInternal(WritableComparable key)
throws IOException {
return seekInternal(key, false);
}
/**
* Positions the reader at the named key, or if none such exists, at the
* key that falls just before or just after dependent on how the
* before parameter is set.
*
* @param before - IF true, and key does not exist, position
* file at entry that falls just before key. Otherwise,
* position file at record that sorts just after.
* @return 0 - exact match found
* < 0 - positioned at next record
* 1 - no more records in file
*/
private synchronized int seekInternal(WritableComparable key,
final boolean before)
throws IOException {
readIndex(); // make sure index is read
if (seekIndex != -1 // seeked before
&& seekIndex+1 < count
&& comparator.compare(key, keys[seekIndex+1])<0 // before next indexed
&& comparator.compare(key, nextKey)
>= 0) { // but after last seeked
// do nothing
} else {
seekIndex = binarySearch(key);
if (seekIndex < 0) // decode insertion point
seekIndex = -seekIndex-2;
if (seekIndex == -1) // belongs before first entry
seekPosition = firstPosition; // use beginning of file
else
seekPosition = positions[seekIndex]; // else use index
}
data.seek(seekPosition);
if (nextKey == null)
nextKey = comparator.newKey();
// If we're looking for the key before, we need to keep track
// of the position we got the current key as well as the position
// of the key before it.
long prevPosition = -1;
long curPosition = seekPosition;
while (data.next(nextKey)) {
int c = comparator.compare(key, nextKey);
if (c <= 0) { // at or beyond desired
if (before && c != 0) {
if (prevPosition == -1) {
// We're on the first record of this index block
// and we've already passed the search key. Therefore
// we must be at the beginning of the file, so seek
// to the beginning of this block and return c
data.seek(curPosition);
} else {
// We have a previous record to back up to
data.seek(prevPosition);
data.next(nextKey);
// now that we've rewound, the search key must be greater than this key
return 1;
}
}
return c;
}
if (before) {
prevPosition = curPosition;
curPosition = data.getPosition();
}
}
return 1;
}
private int binarySearch(WritableComparable key) {
int low = 0;
int high = count-1;
while (low <= high) {
int mid = (low + high) >>> 1;
WritableComparable midVal = keys[mid];
int cmp = comparator.compare(midVal, key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found.
}
/** Read the next key/value pair in the map into key and
* val. Returns true if such a pair exists and false when at
* the end of the map */
public synchronized boolean next(WritableComparable key, Writable val)
throws IOException {
return data.next(key, val);
}
/** Return the value for the named key, or null if none exists. */
public synchronized Writable get(WritableComparable key, Writable val)
throws IOException {
if (seek(key)) {
data.getCurrentValue(val);
return val;
} else
return null;
}
/**
* Finds the record that is the closest match to the specified key.
* Returns key or if it does not exist, at the first entry
* after the named key.
*
- * @param key - key that we're trying to find
- * @param val - data value if key is found
- * @return - the key that was the closest match or null if eof.
*/
public synchronized WritableComparable getClosest(WritableComparable key,
Writable val)
throws IOException {
return getClosest(key, val, false);
}
/**
* Finds the record that is the closest match to the specified key.
*
* @param key - key that we're trying to find
* @param val - data value if key is found
* @param before - IF true, and key does not exist, return
* the first entry that falls just before the key. Otherwise,
* return the record that sorts just after.
* @return - the key that was the closest match or null if eof.
*/
public synchronized WritableComparable getClosest(WritableComparable key,
Writable val, final boolean before)
throws IOException {
int c = seekInternal(key, before);
// If we didn't get an exact match, and we ended up in the wrong
// direction relative to the query key, return null since we
// must be at the beginning or end of the file.
if ((!before && c > 0) ||
(before && c < 0)) {
return null;
}
data.getCurrentValue(val);
return nextKey;
}
/** Close the map. */
@Override
public synchronized void close() throws IOException {
if (!indexClosed) {
index.close();
}
data.close();
}
}
/** Renames an existing map directory. */
public static void rename(FileSystem fs, String oldName, String newName)
throws IOException {
Path oldDir = new Path(oldName);
Path newDir = new Path(newName);
if (!fs.rename(oldDir, newDir)) {
throw new IOException("Could not rename " + oldDir + " to " + newDir);
}
}
/** Deletes the named map file. */
public static void delete(FileSystem fs, String name) throws IOException {
Path dir = new Path(name);
Path data = new Path(dir, DATA_FILE_NAME);
Path index = new Path(dir, INDEX_FILE_NAME);
fs.delete(data, true);
fs.delete(index, true);
fs.delete(dir, true);
}
/**
* This method attempts to fix a corrupt MapFile by re-creating its index.
* @param fs filesystem
* @param dir directory containing the MapFile data and index
* @param keyClass key class (has to be a subclass of Writable)
* @param valueClass value class (has to be a subclass of Writable)
* @param dryrun do not perform any changes, just report what needs to be done
* @return number of valid entries in this MapFile, or -1 if no fixing was needed
* @throws Exception
*/
public static long fix(FileSystem fs, Path dir,
Class keyClass,
Class valueClass, boolean dryrun,
Configuration conf) throws Exception {
String dr = (dryrun ? "[DRY RUN ] " : "");
Path data = new Path(dir, DATA_FILE_NAME);
Path index = new Path(dir, INDEX_FILE_NAME);
int indexInterval = conf.getInt(Writer.INDEX_INTERVAL, 128);
if (!fs.exists(data)) {
// there's nothing we can do to fix this!
throw new Exception(dr + "Missing data file in " + dir + ", impossible to fix this.");
}
if (fs.exists(index)) {
// no fixing needed
return -1;
}
SequenceFile.Reader dataReader =
new SequenceFile.Reader(conf, SequenceFile.Reader.file(data));
if (!dataReader.getKeyClass().equals(keyClass)) {
throw new Exception(dr + "Wrong key class in " + dir + ", expected" + keyClass.getName() +
", got " + dataReader.getKeyClass().getName());
}
if (!dataReader.getValueClass().equals(valueClass)) {
throw new Exception(dr + "Wrong value class in " + dir + ", expected" + valueClass.getName() +
", got " + dataReader.getValueClass().getName());
}
long cnt = 0L;
Writable key = ReflectionUtils.newInstance(keyClass, conf);
Writable value = ReflectionUtils.newInstance(valueClass, conf);
SequenceFile.Writer indexWriter = null;
if (!dryrun) {
indexWriter =
SequenceFile.createWriter(conf,
SequenceFile.Writer.file(index),
SequenceFile.Writer.keyClass(keyClass),
SequenceFile.Writer.valueClass
(LongWritable.class));
}
try {
long pos = 0L;
LongWritable position = new LongWritable();
while(dataReader.next(key, value)) {
cnt++;
if (cnt % indexInterval == 0) {
position.set(pos);
if (!dryrun) indexWriter.append(key, position);
}
pos = dataReader.getPosition();
}
} catch(Throwable t) {
// truncated data file. swallow it.
}
dataReader.close();
if (!dryrun) indexWriter.close();
return cnt;
}
/**
* Class to merge multiple MapFiles of same Key and Value types to one MapFile
*/
public static class Merger {
private Configuration conf;
private WritableComparator comparator = null;
private Reader[] inReaders;
private Writer outWriter;
private Class valueClass = null;
private Class keyClass = null;
public Merger(Configuration conf) throws IOException {
this.conf = conf;
}
/**
* Merge multiple MapFiles to one Mapfile
*
* @param inMapFiles
* @param outMapFile
* @throws IOException
*/
public void merge(Path[] inMapFiles, boolean deleteInputs,
Path outMapFile) throws IOException {
try {
open(inMapFiles, outMapFile);
mergePass();
} finally {
close();
}
if (deleteInputs) {
for (int i = 0; i < inMapFiles.length; i++) {
Path path = inMapFiles[i];
delete(path.getFileSystem(conf), path.toString());
}
}
}
/*
* Open all input files for reading and verify the key and value types. And
* open Output file for writing
*/
@SuppressWarnings("unchecked")
private void open(Path[] inMapFiles, Path outMapFile) throws IOException {
inReaders = new Reader[inMapFiles.length];
for (int i = 0; i < inMapFiles.length; i++) {
Reader reader = new Reader(inMapFiles[i], conf);
if (keyClass == null || valueClass == null) {
keyClass = (Class) reader.getKeyClass();
valueClass = (Class) reader.getValueClass();
} else if (keyClass != reader.getKeyClass()
|| valueClass != reader.getValueClass()) {
throw new HadoopIllegalArgumentException(
"Input files cannot be merged as they"
+ " have different Key and Value classes");
}
inReaders[i] = reader;
}
if (comparator == null) {
Class cls;
cls = keyClass.asSubclass(WritableComparable.class);
this.comparator = WritableComparator.get(cls, conf);
} else if (comparator.getKeyClass() != keyClass) {
throw new HadoopIllegalArgumentException(
"Input files cannot be merged as they"
+ " have different Key class compared to"
+ " specified comparator");
}
outWriter = new MapFile.Writer(conf, outMapFile,
MapFile.Writer.keyClass(keyClass),
MapFile.Writer.valueClass(valueClass));
}
/**
* Merge all input files to output map file.
* 1. Read first key/value from all input files to keys/values array.
* 2. Select the least key and corresponding value.
* 3. Write the selected key and value to output file.
* 4. Replace the already written key/value in keys/values arrays with the
* next key/value from the selected input
* 5. Repeat step 2-4 till all keys are read.
*/
private void mergePass() throws IOException {
// re-usable array
WritableComparable[] keys = new WritableComparable[inReaders.length];
Writable[] values = new Writable[inReaders.length];
// Read first key/value from all inputs
for (int i = 0; i < inReaders.length; i++) {
keys[i] = ReflectionUtils.newInstance(keyClass, null);
values[i] = ReflectionUtils.newInstance(valueClass, null);
if (!inReaders[i].next(keys[i], values[i])) {
// Handle empty files
keys[i] = null;
values[i] = null;
}
}
do {
int currentEntry = -1;
WritableComparable currentKey = null;
Writable currentValue = null;
for (int i = 0; i < keys.length; i++) {
if (keys[i] == null) {
// Skip Readers reached EOF
continue;
}
if (currentKey == null || comparator.compare(currentKey, keys[i]) > 0) {
currentEntry = i;
currentKey = keys[i];
currentValue = values[i];
}
}
if (currentKey == null) {
// Merge Complete
break;
}
// Write the selected key/value to merge stream
outWriter.append(currentKey, currentValue);
// Replace the already written key/value in keys/values arrays with the
// next key/value from the selected input
if (!inReaders[currentEntry].next(keys[currentEntry],
values[currentEntry])) {
// EOF for this file
keys[currentEntry] = null;
values[currentEntry] = null;
}
} while (true);
}
private void close() throws IOException {
for (int i = 0; i < inReaders.length; i++) {
IOUtils.closeStream(inReaders[i]);
inReaders[i] = null;
}
if (outWriter != null) {
outWriter.close();
outWriter = null;
}
}
}
public static void main(String[] args) throws Exception {
String usage = "Usage: MapFile inFile outFile";
if (args.length != 2) {
System.err.println(usage);
System.exit(-1);
}
String in = args[0];
String out = args[1];
Configuration conf = new Configuration();
FileSystem fs = FileSystem.getLocal(conf);
MapFile.Reader reader = null;
MapFile.Writer writer = null;
try {
reader = new MapFile.Reader(fs, in, conf);
writer =
new MapFile.Writer(conf, fs, out,
reader.getKeyClass().asSubclass(WritableComparable.class),
reader.getValueClass());
WritableComparable key = ReflectionUtils.newInstance(reader.getKeyClass()
.asSubclass(WritableComparable.class), conf);
Writable value = ReflectionUtils.newInstance(reader.getValueClass()
.asSubclass(Writable.class), conf);
while (reader.next(key, value)) // copy all entries
writer.append(key, value);
} finally {
IOUtils.cleanup(LOG, writer, reader);
}
}
}