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Small optimizations (#426)

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This commit is contained in:
Arjen Wisse
2024-01-15 20:00:52 +01:00
committed by GitHub
parent 987da54906
commit 702d41df15
2 changed files with 26 additions and 23 deletions
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47
src/main/java/dev/morling/onebrc/CalculateAverage_arjenw.java
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@@ -40,37 +40,40 @@ import java.util.stream.IntStream;
// * memory-mapped file approach: 0m3.2s (also way simpler and neater code; inspired by spullara)
// * smarter number parsing: 0m2.95s (inspired by iziamos)
// * switching back to 21-tem vm 0m2.6s
// * small optimizations 0m2.5s (skip byte-array copy, optimal StationList array size avoiding collisions)
public class CalculateAverage_arjenw {
private static final int TWO_BYTE_TO_INT = 480 + 48;
private static final int TWO_BYTE_TO_INT = 480 + 48; // 48 is the ASCII code for '0'
private static final int THREE_BYTE_TO_INT = 4800 + 480 + 48;
private static final String FILE = "./measurements.txt";
public static void main(String[] args) {
var file = new File(FILE);
var file = new File(args.length > 0 ? args[0] : FILE);
var fileSize = file.length();
var numberOfProcessors = fileSize > 1_000_000 ? Runtime.getRuntime().availableProcessors() : 1;
var segmentSize = fileSize / numberOfProcessors;
var results = IntStream.range(0, numberOfProcessors)
var segmentSize = (int) Math.min(Integer.MAX_VALUE, fileSize / numberOfProcessors); // bytebuffer position is an int, so can be max Integer.MAX_VALUE
var segmentCount = (int) (fileSize / segmentSize);
var results = IntStream.range(0, segmentCount)
.mapToObj(segmentNr -> parseSegment(file, fileSize, segmentSize, segmentNr))
.parallel()
.reduce(StationList::merge)
.orElseGet(StationList::new)
.toStringArray();
Arrays.sort(results, Comparator.comparing(o -> take(o, '=')));
Arrays.sort(results, Comparator.comparing(o -> takeUntil(o, '=')));
System.out.format("{%s}%n", String.join(", ", results));
}
private static StationList parseSegment(File file, long fileSize, long segmentSize, int segmentNr) {
long segmentStart = segmentNr * segmentSize;
private static StationList parseSegment(File file, long fileSize, int segmentSize, int segmentNr) {
long segmentStart = segmentNr * (long) segmentSize;
long segmentEnd = Math.min(fileSize, segmentStart + segmentSize + 100);
StationList stationList = new StationList();
try (var fileChannel = (FileChannel) Files.newByteChannel(file.toPath(), StandardOpenOption.READ)) {
var bb = fileChannel.map(FileChannel.MapMode.READ_ONLY, segmentStart, segmentEnd - segmentStart);
if (segmentStart > 0) {
// noinspection StatementWithEmptyBody
while (bb.get() != '\n')
; // skip to first new line
}
StationList stationList = new StationList();
var buffer = new byte[100];
while (bb.position() < segmentSize) {
byte b;
@@ -103,8 +106,10 @@ public class CalculateAverage_arjenw {
bb.get(); // new line
}
stationList.add(buffer, i, Math.abs(hash), value);
if (stationList.add(buffer, i, Math.abs(hash), value))
buffer = new byte[100]; // station was new, create new buffer to contain the next station's name
}
return stationList;
}
catch (IOException e) {
@@ -155,31 +160,29 @@ public class CalculateAverage_arjenw {
}
private static class StationList implements Iterable<Station> {
private final static int MAX_ENTRY = 32767; // choose a value that is binary all 1's.
private final Station[] array = new Station[MAX_ENTRY + 1];
private final static int MAX_ENTRY = 65375; // choose a value that _eliminates_ collisions on the test set.
private final Station[] array = new Station[MAX_ENTRY];
private int size = 0;
private void add(int hash, Supplier<Station> create, Consumer<Station> update) {
var position = hash & MAX_ENTRY;
private boolean add(int hash, Supplier<Station> create, Consumer<Station> update) {
var position = hash % MAX_ENTRY;
Station existing;
while ((existing = array[position]) != null && existing.hash != hash) {
position = (position + 1) & MAX_ENTRY;
position = (position + 1) % MAX_ENTRY;
}
if (existing == null) {
array[position] = create.get();
size++;
return true;
}
else {
update.accept(existing);
return false;
}
}
public void add(byte[] data, int stationNameLength, int stationHash, int value) {
add(stationHash, () -> {
var stationName = new byte[stationNameLength];
System.arraycopy(data, 0, stationName, 0, stationNameLength);
return new Station(stationName, stationNameLength, stationHash, value);
}, existing -> existing.append(value));
public boolean add(byte[] data, int stationNameLength, int stationHash, int value) {
return add(stationHash, () -> new Station(data, stationNameLength, stationHash, value), existing -> existing.append(value));
}
public void add(Station station) {
@@ -210,7 +213,7 @@ public class CalculateAverage_arjenw {
@Override
public boolean hasNext() {
Station station = null;
while (index <= MAX_ENTRY && (station = array[index]) == null)
while (index < MAX_ENTRY && (station = array[index]) == null)
index++;
return station != null;
}
@@ -226,7 +229,7 @@ public class CalculateAverage_arjenw {
}
}
private static String take(String s, char c) {
private static String takeUntil(String s, char c) {
var pos = s.indexOf(c);
return pos > -1 ? s.substring(0, pos) : s;
}