Update submission (#385)
* feat(flippingbits): Improve parsing of station names * chore(flippingbits): Remove obsolete import * feat(flippingbits): Use custom hash map * feat(flippingbits): Use UNSAFE * fix(flippingbits): Support very small files * chore(flippingbits): Few cleanups * chore(flippingbits): Align names * fix(flippingbits): Initialize hash with first byte * fix(flippingbits): Fix initialization of hash value
This commit is contained in:
Stefan Sprenger
GitHub
parent
fc6fca4315
commit
3fbc4a2fa8
@ -15,5 +15,5 @@
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# limitations under the License.
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#
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JAVA_OPTS="--add-modules=jdk.incubator.vector"
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JAVA_OPTS="--add-modules=jdk.incubator.vector --enable-preview"
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java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_flippingbits
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@ -18,8 +18,13 @@ package dev.morling.onebrc;
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import jdk.incubator.vector.ShortVector;
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import jdk.incubator.vector.VectorOperators;
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import sun.misc.Unsafe;
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import java.lang.foreign.Arena;
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import java.lang.reflect.Field;
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import java.io.IOException;
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import java.io.RandomAccessFile;
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import java.nio.channels.FileChannel;
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import java.nio.charset.StandardCharsets;
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import java.util.*;
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@ -34,14 +39,31 @@ public class CalculateAverage_flippingbits {
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private static final String FILE = "./measurements.txt";
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private static final long CHUNK_SIZE = 10 * 1024 * 1024; // 10 MB
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private static final long MINIMUM_FILE_SIZE_PARTITIONING = 10 * 1024 * 1024; // 10 MB
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private static final int SIMD_LANE_LENGTH = ShortVector.SPECIES_MAX.length();
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private static final int MAX_STATION_NAME_LENGTH = 100;
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private static final int NUM_STATIONS = 10_000;
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private static final int HASH_MAP_OFFSET_CAPACITY = 200_000;
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private static final Unsafe UNSAFE = initUnsafe();
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private static int HASH_PRIME_NUMBER = 31;
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private static Unsafe initUnsafe() {
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try {
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Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
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theUnsafe.setAccessible(true);
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return (Unsafe) theUnsafe.get(Unsafe.class);
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}
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catch (NoSuchFieldException | IllegalAccessException e) {
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throw new RuntimeException(e);
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}
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}
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public static void main(String[] args) throws IOException {
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var result = Arrays.asList(getSegments()).stream()
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var result = Arrays.asList(getSegments()).parallelStream()
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.map(segment -> {
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try {
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return processSegment(segment[0], segment[1]);
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@ -50,126 +72,137 @@ public class CalculateAverage_flippingbits {
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throw new RuntimeException(e);
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}
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})
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.parallel()
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.reduce((firstMap, secondMap) -> {
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for (var entry : secondMap.entrySet()) {
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PartitionAggregate firstAggregate = firstMap.get(entry.getKey());
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if (firstAggregate == null) {
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firstMap.put(entry.getKey(), entry.getValue());
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}
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else {
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firstAggregate.mergeWith(entry.getValue());
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}
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}
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return firstMap;
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})
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.map(TreeMap::new).get();
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.reduce(FasterHashMap::mergeWith)
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.get();
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System.out.println(result);
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var sortedMap = new TreeMap<String, Station>();
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for (Station station : result.getEntries()) {
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sortedMap.put(station.getName(), station);
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}
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System.out.println(sortedMap);
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}
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private static long[][] getSegments() throws IOException {
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try (var file = new RandomAccessFile(FILE, "r")) {
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var fileSize = file.length();
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var channel = file.getChannel();
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var fileSize = channel.size();
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var startAddress = channel
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.map(FileChannel.MapMode.READ_ONLY, 0, fileSize, Arena.global())
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.address();
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// Split file into segments, so we can work around the size limitation of channels
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var numSegments = (int) (fileSize / CHUNK_SIZE);
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var numSegments = (fileSize > MINIMUM_FILE_SIZE_PARTITIONING)
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? Runtime.getRuntime().availableProcessors()
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: 1;
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var segmentSize = fileSize / numSegments;
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var boundaries = new long[numSegments + 1][2];
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var endPointer = 0L;
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var boundaries = new long[numSegments][2];
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var endPointer = startAddress;
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for (var i = 0; i < numSegments; i++) {
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for (var i = 0; i < numSegments - 1; i++) {
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// Start of segment
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boundaries[i][0] = Math.min(Math.max(endPointer, i * CHUNK_SIZE), fileSize);
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// Seek end of segment, limited by the end of the file
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file.seek(Math.min(boundaries[i][0] + CHUNK_SIZE - 1, fileSize));
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boundaries[i][0] = endPointer;
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// Extend segment until end of line or file
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while (file.read() != '\n') {
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endPointer = endPointer + segmentSize;
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while (UNSAFE.getByte(endPointer) != '\n') {
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endPointer++;
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}
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// End of segment
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endPointer = file.getFilePointer();
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boundaries[i][1] = endPointer;
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boundaries[i][1] = endPointer++;
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}
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boundaries[numSegments][0] = Math.max(endPointer, numSegments * CHUNK_SIZE);
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boundaries[numSegments][1] = fileSize;
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boundaries[numSegments - 1][0] = endPointer;
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boundaries[numSegments - 1][1] = startAddress + fileSize;
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return boundaries;
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}
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}
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private static Map<String, PartitionAggregate> processSegment(long startOfSegment, long endOfSegment)
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throws IOException {
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Map<String, PartitionAggregate> stationAggregates = new HashMap<>(50_000);
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var byteChunk = new byte[(int) (endOfSegment - startOfSegment)];
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var stationBuffer = new byte[MAX_STATION_NAME_LENGTH];
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try (var file = new RandomAccessFile(FILE, "r")) {
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file.seek(startOfSegment);
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file.read(byteChunk);
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var i = 0;
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while (i < byteChunk.length) {
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// Station name has at least one byte
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stationBuffer[0] = byteChunk[i];
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private static FasterHashMap processSegment(long startOfSegment, long endOfSegment) throws IOException {
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var fasterHashMap = new FasterHashMap();
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for (var i = startOfSegment; i < endOfSegment; i += 3) {
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// Read station name
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int nameHash = UNSAFE.getByte(i);
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final var nameStartAddress = i++;
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var character = UNSAFE.getByte(i);
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while (character != ';') {
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nameHash = nameHash * HASH_PRIME_NUMBER + character;
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i++;
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// Read station name
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var j = 1;
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while (byteChunk[i] != ';') {
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stationBuffer[j] = byteChunk[i];
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j++;
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i++;
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}
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var station = new String(stationBuffer, 0, j, StandardCharsets.UTF_8);
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i++;
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// Read measurement
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var isNegative = byteChunk[i] == '-';
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var measurement = 0;
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if (isNegative) {
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i++;
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while (byteChunk[i] != '.') {
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measurement = measurement * 10 + byteChunk[i] - '0';
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i++;
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}
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measurement = (measurement * 10 + byteChunk[i + 1] - '0') * -1;
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}
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else {
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while (byteChunk[i] != '.') {
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measurement = measurement * 10 + byteChunk[i] - '0';
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i++;
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}
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measurement = measurement * 10 + byteChunk[i + 1] - '0';
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}
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// Update aggregate
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var aggregate = stationAggregates.computeIfAbsent(station, x -> new PartitionAggregate());
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aggregate.addMeasurementAndComputeAggregate((short) measurement);
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i += 3;
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character = UNSAFE.getByte(i);
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}
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stationAggregates.values().forEach(PartitionAggregate::aggregateRemainingMeasurements);
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var nameLength = (int) (i - nameStartAddress);
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i++;
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// Read measurement
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var isNegative = UNSAFE.getByte(i) == '-';
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var measurement = 0;
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if (isNegative) {
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i++;
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character = UNSAFE.getByte(i);
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while (character != '.') {
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measurement = measurement * 10 + character - '0';
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i++;
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character = UNSAFE.getByte(i);
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}
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measurement = (measurement * 10 + UNSAFE.getByte(i + 1) - '0') * -1;
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}
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else {
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character = UNSAFE.getByte(i);
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while (character != '.') {
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measurement = measurement * 10 + character - '0';
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i++;
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character = UNSAFE.getByte(i);
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}
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measurement = measurement * 10 + UNSAFE.getByte(i + 1) - '0';
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}
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fasterHashMap.addEntry(nameHash, nameLength, nameStartAddress, (short) measurement);
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}
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return stationAggregates;
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for (Station station : fasterHashMap.getEntries()) {
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station.aggregateRemainingMeasurements();
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}
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return fasterHashMap;
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}
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private static class PartitionAggregate {
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final short[] doubleLane = new short[SIMD_LANE_LENGTH * 2];
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private static class Station {
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final short[] measurements = new short[SIMD_LANE_LENGTH * 2];
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// Assume that we do not have more than Integer.MAX_VALUE measurements for the same station per partition
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int count = 0;
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int count = 1;
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long sum = 0;
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short min = Short.MAX_VALUE;
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short max = Short.MIN_VALUE;
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final long nameAddress;
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final int nameLength;
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final int nameHash;
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public Station(int nameHash, int nameLength, long nameAddress, short measurement) {
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this.nameHash = nameHash;
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this.nameLength = nameLength;
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this.nameAddress = nameAddress;
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measurements[0] = measurement;
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}
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public String getName() {
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byte[] name = new byte[nameLength];
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UNSAFE.copyMemory(null, nameAddress, name, Unsafe.ARRAY_BYTE_BASE_OFFSET, nameLength);
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return new String(name, StandardCharsets.UTF_8);
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}
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public void addMeasurementAndComputeAggregate(short measurement) {
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// Add measurement to buffer, which is later processed by SIMD instructions
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doubleLane[count % doubleLane.length] = measurement;
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measurements[count % measurements.length] = measurement;
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count++;
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// Once lane is full, use SIMD instructions to calculate aggregates
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if (count % doubleLane.length == 0) {
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var firstVector = ShortVector.fromArray(ShortVector.SPECIES_MAX, doubleLane, 0);
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var secondVector = ShortVector.fromArray(ShortVector.SPECIES_MAX, doubleLane, SIMD_LANE_LENGTH);
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if (count % measurements.length == 0) {
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var firstVector = ShortVector.fromArray(ShortVector.SPECIES_MAX, measurements, 0);
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var secondVector = ShortVector.fromArray(ShortVector.SPECIES_MAX, measurements, SIMD_LANE_LENGTH);
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var simdMin = firstVector.min(secondVector).reduceLanes(VectorOperators.MIN);
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min = (short) Math.min(min, simdMin);
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@ -182,19 +215,35 @@ public class CalculateAverage_flippingbits {
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}
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public void aggregateRemainingMeasurements() {
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for (var i = 0; i < count % doubleLane.length; i++) {
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var measurement = doubleLane[i];
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for (var i = 0; i < count % measurements.length; i++) {
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var measurement = measurements[i];
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min = (short) Math.min(min, measurement);
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max = (short) Math.max(max, measurement);
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sum += measurement;
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}
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}
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public void mergeWith(PartitionAggregate otherAggregate) {
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min = (short) Math.min(min, otherAggregate.min);
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max = (short) Math.max(max, otherAggregate.max);
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count = count + otherAggregate.count;
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sum = sum + otherAggregate.sum;
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public void mergeWith(Station otherStation) {
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min = (short) Math.min(min, otherStation.min);
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max = (short) Math.max(max, otherStation.max);
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count = count + otherStation.count;
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sum = sum + otherStation.sum;
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}
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public boolean nameEquals(long otherNameAddress) {
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var swarLimit = (nameLength / Long.BYTES) * Long.BYTES;
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var i = 0;
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for (; i < swarLimit; i += Long.BYTES) {
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if (UNSAFE.getLong(nameAddress + i) != UNSAFE.getLong(otherNameAddress + i)) {
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return false;
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}
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}
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for (; i < nameLength; i++) {
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if (UNSAFE.getByte(nameAddress + i) != UNSAFE.getByte(otherNameAddress + i)) {
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return false;
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}
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}
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return true;
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}
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public String toString() {
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@ -206,4 +255,67 @@ public class CalculateAverage_flippingbits {
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(max / 10.0));
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}
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}
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/**
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* Use two arrays for implementing the hash map:
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* - The array `entries` holds the map values, in our case instances of the class Station.
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* - The array `offsets` maps hashes of the keys to indexes in the `entries` array.
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*
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* We create `offsets` with a much larger capacity than `entries`, so we minimize collisions.
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*/
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private static class FasterHashMap {
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// Using 16-bit integers (shorts) for offsets supports up to 2^15 (=32,767) entries
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// If you need to store more entries, consider replacing short with int
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short[] offsets = new short[HASH_MAP_OFFSET_CAPACITY];
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Station[] entries = new Station[NUM_STATIONS + 1];
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int slotsInUse = 0;
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private int getOffsetIdx(int nameHash, int nameLength, long nameAddress) {
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var offsetIdx = nameHash & (offsets.length - 1);
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var offset = offsets[offsetIdx];
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while (offset != 0 &&
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(nameLength != entries[offset].nameLength || !entries[offset].nameEquals(nameAddress))) {
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offsetIdx = (offsetIdx + 1) % offsets.length;
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offset = offsets[offsetIdx];
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}
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return offsetIdx;
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}
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public void addEntry(int nameHash, int nameLength, long nameAddress, short measurement) {
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var offsetIdx = getOffsetIdx(nameHash, nameLength, nameAddress);
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var offset = offsets[offsetIdx];
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if (offset == 0) {
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slotsInUse++;
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entries[slotsInUse] = new Station(nameHash, nameLength, nameAddress, measurement);
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offsets[offsetIdx] = (short) slotsInUse;
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}
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else {
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entries[offset].addMeasurementAndComputeAggregate(measurement);
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}
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}
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public FasterHashMap mergeWith(FasterHashMap otherMap) {
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for (Station station : otherMap.getEntries()) {
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var offsetIdx = getOffsetIdx(station.nameHash, station.nameLength, station.nameAddress);
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var offset = offsets[offsetIdx];
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if (offset == 0) {
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slotsInUse++;
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entries[slotsInUse] = station;
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offsets[offsetIdx] = (short) slotsInUse;
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}
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else {
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entries[offset].mergeWith(station);
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}
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}
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return this;
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}
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public List<Station> getEntries() {
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return Arrays.asList(entries).subList(1, slotsInUse + 1);
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}
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}
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}
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