private void writeIndexRecord(
FSDataOutputStream indexOut, FSDataOutputStream out, long start, Writer<K, V> writer)
throws IOException {
// when we write the offset/decompressed-length/compressed-length to
// the final index file, we write longs for both compressed and
// decompressed lengths. This helps us to reliably seek directly to
// the offset/length for a partition when we start serving the
// byte-ranges to the reduces. We probably waste some space in the
// file by doing this as opposed to writing VLong but it helps us later on.
// index record: <offset, raw-length, compressed-length>
// StringBuffer sb = new StringBuffer();
indexOut.writeLong(start);
indexOut.writeLong(writer.getRawLength());
long segmentLength = out.getPos() - start;
indexOut.writeLong(segmentLength);
LOG.info("Index: (" + start + ", " + writer.getRawLength() + ", " + segmentLength + ")");
}
@Override
public void merge(List<CompressAwarePath> inputs) throws IOException {
// sanity check
if (inputs == null || inputs.isEmpty()) {
LOG.info("No ondisk files to merge...");
return;
}
long approxOutputSize = 0;
int bytesPerSum = jobConf.getInt("io.bytes.per.checksum", 512);
LOG.info(
"OnDiskMerger: We have " + inputs.size() + " map outputs on disk. Triggering merge...");
// 1. Prepare the list of files to be merged.
for (CompressAwarePath file : inputs) {
approxOutputSize += localFS.getFileStatus(file).getLen();
}
// add the checksum length
approxOutputSize += ChecksumFileSystem.getChecksumLength(approxOutputSize, bytesPerSum);
// 2. Start the on-disk merge process
Path outputPath =
localDirAllocator
.getLocalPathForWrite(inputs.get(0).toString(), approxOutputSize, jobConf)
.suffix(Task.MERGED_OUTPUT_PREFIX);
Writer<K, V> writer =
new Writer<K, V>(
jobConf,
rfs,
outputPath,
(Class<K>) jobConf.getMapOutputKeyClass(),
(Class<V>) jobConf.getMapOutputValueClass(),
codec,
null);
RawKeyValueIterator iter = null;
CompressAwarePath compressAwarePath;
Path tmpDir = new Path(reduceId.toString());
try {
iter =
Merger.merge(
jobConf,
rfs,
(Class<K>) jobConf.getMapOutputKeyClass(),
(Class<V>) jobConf.getMapOutputValueClass(),
codec,
inputs.toArray(new Path[inputs.size()]),
true,
ioSortFactor,
tmpDir,
(RawComparator<K>) jobConf.getOutputKeyComparator(),
reporter,
spilledRecordsCounter,
null,
mergedMapOutputsCounter,
null);
Merger.writeFile(iter, writer, reporter, jobConf);
writer.close();
compressAwarePath =
new CompressAwarePath(outputPath, writer.getRawLength(), writer.getCompressedLength());
} catch (IOException e) {
localFS.delete(outputPath, true);
throw e;
}
closeOnDiskFile(compressAwarePath);
LOG.info(
reduceId
+ " Finished merging "
+ inputs.size()
+ " map output files on disk of total-size "
+ approxOutputSize
+ "."
+ " Local output file is "
+ outputPath
+ " of size "
+ localFS.getFileStatus(outputPath).getLen());
}
private RawKeyValueIterator finalMerge(
JobConf job,
FileSystem fs,
List<InMemoryMapOutput<K, V>> inMemoryMapOutputs,
List<CompressAwarePath> onDiskMapOutputs)
throws IOException {
LOG.info(
"finalMerge called with "
+ inMemoryMapOutputs.size()
+ " in-memory map-outputs and "
+ onDiskMapOutputs.size()
+ " on-disk map-outputs");
final float maxRedPer = job.getFloat(MRJobConfig.REDUCE_INPUT_BUFFER_PERCENT, 0f);
if (maxRedPer > 1.0 || maxRedPer < 0.0) {
throw new IOException(MRJobConfig.REDUCE_INPUT_BUFFER_PERCENT + maxRedPer);
}
int maxInMemReduce =
(int) Math.min(Runtime.getRuntime().maxMemory() * maxRedPer, Integer.MAX_VALUE);
// merge config params
Class<K> keyClass = (Class<K>) job.getMapOutputKeyClass();
Class<V> valueClass = (Class<V>) job.getMapOutputValueClass();
boolean keepInputs = job.getKeepFailedTaskFiles();
final Path tmpDir = new Path(reduceId.toString());
final RawComparator<K> comparator = (RawComparator<K>) job.getOutputKeyComparator();
// segments required to vacate memory
List<Segment<K, V>> memDiskSegments = new ArrayList<Segment<K, V>>();
long inMemToDiskBytes = 0;
boolean mergePhaseFinished = false;
if (inMemoryMapOutputs.size() > 0) {
TaskID mapId = inMemoryMapOutputs.get(0).getMapId().getTaskID();
inMemToDiskBytes =
createInMemorySegments(inMemoryMapOutputs, memDiskSegments, maxInMemReduce);
final int numMemDiskSegments = memDiskSegments.size();
if (numMemDiskSegments > 0 && ioSortFactor > onDiskMapOutputs.size()) {
// If we reach here, it implies that we have less than io.sort.factor
// disk segments and this will be incremented by 1 (result of the
// memory segments merge). Since this total would still be
// <= io.sort.factor, we will not do any more intermediate merges,
// the merge of all these disk segments would be directly fed to the
// reduce method
mergePhaseFinished = true;
// must spill to disk, but can't retain in-mem for intermediate merge
final Path outputPath =
mapOutputFile
.getInputFileForWrite(mapId, inMemToDiskBytes)
.suffix(Task.MERGED_OUTPUT_PREFIX);
final RawKeyValueIterator rIter =
Merger.merge(
job,
fs,
keyClass,
valueClass,
memDiskSegments,
numMemDiskSegments,
tmpDir,
comparator,
reporter,
spilledRecordsCounter,
null,
mergePhase);
Writer<K, V> writer =
new Writer<K, V>(job, fs, outputPath, keyClass, valueClass, codec, null);
try {
Merger.writeFile(rIter, writer, reporter, job);
writer.close();
onDiskMapOutputs.add(
new CompressAwarePath(
outputPath, writer.getRawLength(), writer.getCompressedLength()));
writer = null;
// add to list of final disk outputs.
} catch (IOException e) {
if (null != outputPath) {
try {
fs.delete(outputPath, true);
} catch (IOException ie) {
// NOTHING
}
}
throw e;
} finally {
if (null != writer) {
writer.close();
}
}
LOG.info(
"Merged "
+ numMemDiskSegments
+ " segments, "
+ inMemToDiskBytes
+ " bytes to disk to satisfy "
+ "reduce memory limit");
inMemToDiskBytes = 0;
memDiskSegments.clear();
} else if (inMemToDiskBytes != 0) {
LOG.info(
"Keeping "
+ numMemDiskSegments
+ " segments, "
+ inMemToDiskBytes
+ " bytes in memory for "
+ "intermediate, on-disk merge");
}
}
// segments on disk
List<Segment<K, V>> diskSegments = new ArrayList<Segment<K, V>>();
long onDiskBytes = inMemToDiskBytes;
long rawBytes = inMemToDiskBytes;
CompressAwarePath[] onDisk =
onDiskMapOutputs.toArray(new CompressAwarePath[onDiskMapOutputs.size()]);
for (CompressAwarePath file : onDisk) {
long fileLength = fs.getFileStatus(file).getLen();
onDiskBytes += fileLength;
rawBytes += (file.getRawDataLength() > 0) ? file.getRawDataLength() : fileLength;
LOG.debug("Disk file: " + file + " Length is " + fileLength);
diskSegments.add(
new Segment<K, V>(
job,
fs,
file,
codec,
keepInputs,
(file.toString().endsWith(Task.MERGED_OUTPUT_PREFIX)
? null
: mergedMapOutputsCounter),
file.getRawDataLength()));
}
LOG.info("Merging " + onDisk.length + " files, " + onDiskBytes + " bytes from disk");
Collections.sort(
diskSegments,
new Comparator<Segment<K, V>>() {
public int compare(Segment<K, V> o1, Segment<K, V> o2) {
if (o1.getLength() == o2.getLength()) {
return 0;
}
return o1.getLength() < o2.getLength() ? -1 : 1;
}
});
// build final list of segments from merged backed by disk + in-mem
List<Segment<K, V>> finalSegments = new ArrayList<Segment<K, V>>();
long inMemBytes = createInMemorySegments(inMemoryMapOutputs, finalSegments, 0);
LOG.info(
"Merging "
+ finalSegments.size()
+ " segments, "
+ inMemBytes
+ " bytes from memory into reduce");
if (0 != onDiskBytes) {
final int numInMemSegments = memDiskSegments.size();
diskSegments.addAll(0, memDiskSegments);
memDiskSegments.clear();
// Pass mergePhase only if there is a going to be intermediate
// merges. See comment where mergePhaseFinished is being set
Progress thisPhase = (mergePhaseFinished) ? null : mergePhase;
RawKeyValueIterator diskMerge =
Merger.merge(
job,
fs,
keyClass,
valueClass,
codec,
diskSegments,
ioSortFactor,
numInMemSegments,
tmpDir,
comparator,
reporter,
false,
spilledRecordsCounter,
null,
thisPhase);
diskSegments.clear();
if (0 == finalSegments.size()) {
return diskMerge;
}
finalSegments.add(
new Segment<K, V>(new RawKVIteratorReader(diskMerge, onDiskBytes), true, rawBytes));
}
return Merger.merge(
job,
fs,
keyClass,
valueClass,
finalSegments,
finalSegments.size(),
tmpDir,
comparator,
reporter,
spilledRecordsCounter,
null,
null);
}
@Override
public void merge(List<InMemoryMapOutput<K, V>> inputs) throws IOException {
if (inputs == null || inputs.size() == 0) {
return;
}
// name this output file same as the name of the first file that is
// there in the current list of inmem files (this is guaranteed to
// be absent on the disk currently. So we don't overwrite a prev.
// created spill). Also we need to create the output file now since
// it is not guaranteed that this file will be present after merge
// is called (we delete empty files as soon as we see them
// in the merge method)
// figure out the mapId
TaskAttemptID mapId = inputs.get(0).getMapId();
TaskID mapTaskId = mapId.getTaskID();
List<Segment<K, V>> inMemorySegments = new ArrayList<Segment<K, V>>();
long mergeOutputSize = createInMemorySegments(inputs, inMemorySegments, 0);
int noInMemorySegments = inMemorySegments.size();
Path outputPath =
mapOutputFile
.getInputFileForWrite(mapTaskId, mergeOutputSize)
.suffix(Task.MERGED_OUTPUT_PREFIX);
Writer<K, V> writer =
new Writer<K, V>(
jobConf,
rfs,
outputPath,
(Class<K>) jobConf.getMapOutputKeyClass(),
(Class<V>) jobConf.getMapOutputValueClass(),
codec,
null);
RawKeyValueIterator rIter = null;
CompressAwarePath compressAwarePath;
try {
LOG.info("Initiating in-memory merge with " + noInMemorySegments + " segments...");
rIter =
Merger.merge(
jobConf,
rfs,
(Class<K>) jobConf.getMapOutputKeyClass(),
(Class<V>) jobConf.getMapOutputValueClass(),
inMemorySegments,
inMemorySegments.size(),
new Path(reduceId.toString()),
(RawComparator<K>) jobConf.getOutputKeyComparator(),
reporter,
spilledRecordsCounter,
null,
null);
if (null == combinerClass) {
Merger.writeFile(rIter, writer, reporter, jobConf);
} else {
combineCollector.setWriter(writer);
combineAndSpill(rIter, reduceCombineInputCounter);
}
writer.close();
compressAwarePath =
new CompressAwarePath(outputPath, writer.getRawLength(), writer.getCompressedLength());
LOG.info(
reduceId
+ " Merge of the "
+ noInMemorySegments
+ " files in-memory complete."
+ " Local file is "
+ outputPath
+ " of size "
+ localFS.getFileStatus(outputPath).getLen());
} catch (IOException e) {
// make sure that we delete the ondisk file that we created
// earlier when we invoked cloneFileAttributes
localFS.delete(outputPath, true);
throw e;
}
// Note the output of the merge
closeOnDiskFile(compressAwarePath);
}