serkan-ozal: Initial impl (#553)

* Initial impl

* Fix bad file descriptor error in the `calculate_average_serkan-ozal.sh`

* Disable Epsilon GC and rely on default GC. Because apparently, JIT and Epsilon GC don't play well together in the eval machine for short lived Vector API's `ByteVector` objects

* Take care of byte order before processing key length with bit shift operators

* Fix key equality check for long keys

2 files changed, 704 insertions, 0 deletions

diff --git a/calculate_average_serkan-ozal.sh b/calculate_average_serkan-ozal.sh
new file mode 100755
index 0000000..a903c1d
--- /dev/null
+++ b/calculate_average_serkan-ozal.sh
@@ -0,0 +1,30 @@
+#!/bin/bash
+#
+#  Copyright 2023 The original authors
+#
+#  Licensed 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.
+#
+
+JAVA_OPTS="--enable-preview --enable-native-access=ALL-UNNAMED --add-modules=jdk.incubator.vector"
+JAVA_OPTS="$JAVA_OPTS -XX:-TieredCompilation -XX:MaxInlineSize=10000 -XX:InlineSmallCode=10000 -XX:FreqInlineSize=10000"
+JAVA_OPTS="$JAVA_OPTS -Djdk.incubator.vector.VECTOR_ACCESS_OOB_CHECK=0"
+#JAVA_OPTS="$JAVA_OPTS -XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC -Xms256m -Xmx256m -XX:+AlwaysPreTouch"
+if [[ ! "$(uname -s)" = "Darwin" ]]; then
+  JAVA_OPTS="$JAVA_OPTS -XX:+UseTransparentHugePages"
+fi
+
+#echo "Process started at $(date +%s%N | cut -b1-13)"
+eval "exec 3< <({ CLOSE_STDOUT_ON_RESULT=true USE_SHARED_ARENA=true java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_serkan_ozal; })"
+read <&3 result
+echo -e "$result"
+#echo "Process finished at $(date +%s%N | cut -b1-13)"
diff --git a/src/main/java/dev/morling/onebrc/CalculateAverage_serkan_ozal.java b/src/main/java/dev/morling/onebrc/CalculateAverage_serkan_ozal.java
new file mode 100644
index 0000000..b025383
--- /dev/null
+++ b/src/main/java/dev/morling/onebrc/CalculateAverage_serkan_ozal.java
@@ -0,0 +1,674 @@
+/*
+ *  Copyright 2023 The original authors
+ *
+ *  Licensed 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 dev.morling.onebrc;
+
+import jdk.incubator.vector.ByteVector;
+import jdk.incubator.vector.VectorOperators;
+import jdk.incubator.vector.VectorSpecies;
+import sun.misc.Unsafe;
+
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.lang.foreign.Arena;
+import java.lang.foreign.MemorySegment;
+import java.lang.reflect.Field;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.channels.FileChannel;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * @author serkan-ozal
+ */
+public class CalculateAverage_serkan_ozal {
+
+    private static final String FILE = "./measurements.txt";
+
+    private static final VectorSpecies<Byte> BYTE_SPECIES = ByteVector.SPECIES_PREFERRED.length() >= 16
+            // Since majority (99%) of the city names <= 16 bytes, according to my experiments,
+            // 128 bit (16 byte) vectors perform better than 256 bit (32 byte) or 512 bit (64 byte) vectors
+            // even though supported by platform.
+            ? ByteVector.SPECIES_128
+            : ByteVector.SPECIES_64;
+    private static final int BYTE_SPECIES_SIZE = BYTE_SPECIES.vectorByteSize();
+
+    private static final ByteOrder NATIVE_BYTE_ORDER = ByteOrder.nativeOrder();
+    private static final char NEW_LINE_SEPARATOR = '\n';
+    private static final char KEY_VALUE_SEPARATOR = ';';
+    private static final int MAX_LINE_LENGTH = 128;
+
+    // Get configurations
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    private static final boolean VERBOSE = getBooleanConfig("VERBOSE", false);
+    private static final int THREAD_COUNT = getIntegerConfig("THREAD_COUNT", Runtime.getRuntime().availableProcessors());
+    private static final boolean USE_VTHREADS = getBooleanConfig("USE_VTHREADS", false);
+    private static final int VTHREAD_COUNT = getIntegerConfig("VTHREAD_COUNT", 1024);
+    private static final int REGION_COUNT = getIntegerConfig("REGION_COUNT", -1);
+    private static final boolean USE_SHARED_ARENA = getBooleanConfig("USE_SHARED_ARENA", false);
+    private static final int MAP_CAPACITY = getIntegerConfig("MAP_CAPACITY", 1 << 17);
+    private static final boolean CLOSE_STDOUT_ON_RESULT = getBooleanConfig("CLOSE_STDOUT_ON_RESULT", false);
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    // My dear old friend Unsafe
+    private static final Unsafe U;
+
+    static {
+        try {
+            Field f = Unsafe.class.getDeclaredField("theUnsafe");
+            f.setAccessible(true);
+            U = (Unsafe) f.get(null);
+        }
+        catch (Exception e) {
+            throw new IllegalStateException(e);
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        long start = System.currentTimeMillis();
+        if (VERBOSE) {
+            System.out.println("Processing started at " + start);
+            System.out.println("Vector byte size: " + BYTE_SPECIES.vectorByteSize());
+            System.out.println("Use shared memory arena: " + USE_SHARED_ARENA);
+            if (USE_VTHREADS) {
+                System.out.println("Virtual thread count: " + VTHREAD_COUNT);
+            }
+            else {
+                System.out.println("Thread count: " + THREAD_COUNT);
+            }
+            System.out.println("Map capacity: " + MAP_CAPACITY);
+        }
+
+        int concurrency = USE_VTHREADS ? VTHREAD_COUNT : THREAD_COUNT;
+        int regionCount = REGION_COUNT > 0 ? REGION_COUNT : concurrency;
+        ByteBuffer lineBuffer = getByteBuffer(MAX_LINE_LENGTH);
+        Result result = new Result();
+
+        RandomAccessFile file = new RandomAccessFile(FILE, "r");
+        FileChannel fc = file.getChannel();
+        Arena arena = USE_SHARED_ARENA ? Arena.ofShared() : null;
+        try {
+            long fileSize = fc.size();
+            long regionSize = fileSize / regionCount;
+            long startPos = 0;
+            ExecutorService executor = USE_VTHREADS
+                    ? Executors.newVirtualThreadPerTaskExecutor()
+                    : Executors.newFixedThreadPool(concurrency, new RegionProcessorThreadFactory());
+
+            // Split whole file into regions and start region processors to handle those regions
+            List<Future<Response>> futures = new ArrayList<>(regionCount);
+            for (int i = 0; i < regionCount; i++) {
+                long endPos = Math.min(fileSize, startPos + regionSize);
+                // Lines might split into different regions.
+                // If so, move back to the line starting at the end of previous region
+                long closestLineEndPos = (i < regionCount - 1)
+                        ? findClosestLineEnd(fc, endPos, lineBuffer)
+                        : fileSize;
+                Request request = new Request(fc, arena, startPos, closestLineEndPos, result);
+                RegionProcessor regionProcessor = createRegionProcessor(request);
+                Future<Response> future = executor.submit(regionProcessor);
+                futures.add(future);
+                startPos = closestLineEndPos;
+            }
+
+            // Wait processors to complete
+            for (Future<Response> future : futures) {
+                future.get();
+            }
+
+            long finish = System.currentTimeMillis();
+            if (VERBOSE) {
+                System.out.println("Processing completed at " + finish);
+                System.out.println("Processing completed in " + (finish - start) + " milliseconds");
+            }
+
+            // Print result to stdout
+            result.print();
+
+            if (CLOSE_STDOUT_ON_RESULT) {
+                // After printing result, close stdout.
+                // So parent process can complete without waiting this process completed.
+                // Saves a few hundred milliseconds caused by unmap.
+                System.out.close();
+            }
+        }
+        finally {
+            // Close memory arena if it is managed globally here (shared arena)
+            if (arena != null) {
+                arena.close();
+            }
+            fc.close();
+            if (VERBOSE) {
+                long finish = System.currentTimeMillis();
+                System.out.println("All completed at " + finish);
+                System.out.println("All Completed in " + ((finish - start)) + " milliseconds");
+            }
+        }
+    }
+
+    private static boolean getBooleanConfig(String envVarName, boolean defaultValue) {
+        String envVarValue = System.getenv(envVarName);
+        if (envVarValue == null) {
+            return defaultValue;
+        }
+        else {
+            return Boolean.parseBoolean(envVarValue);
+        }
+    }
+
+    private static int getIntegerConfig(String envVarName, int defaultValue) {
+        String envVarValue = System.getenv(envVarName);
+        if (envVarValue == null) {
+            return defaultValue;
+        }
+        else {
+            return Integer.parseInt(envVarValue);
+        }
+    }
+
+    private static ByteBuffer getByteBuffer(int size) {
+        ByteBuffer bb = ByteBuffer.allocateDirect(size);
+        bb.order(NATIVE_BYTE_ORDER);
+        return bb;
+    }
+
+    private static long findClosestLineEnd(FileChannel fc, long endPos, ByteBuffer lineBuffer) throws IOException {
+        long lineCheckStartPos = Math.max(0, endPos - MAX_LINE_LENGTH);
+        lineBuffer.rewind();
+        fc.read(lineBuffer, lineCheckStartPos);
+        int i = MAX_LINE_LENGTH;
+        while (lineBuffer.get(i - 1) != NEW_LINE_SEPARATOR) {
+            i--;
+        }
+        return lineCheckStartPos + i;
+    }
+
+    private static RegionProcessor createRegionProcessor(Request request) {
+        return new RegionProcessor(request);
+    }
+
+    private static class RegionProcessorThreadFactory implements ThreadFactory {
+
+        @Override
+        public Thread newThread(Runnable r) {
+            Thread t = new Thread(r);
+            t.setDaemon(true);
+            t.setPriority(Thread.MAX_PRIORITY);
+            return t;
+        }
+
+    }
+
+    /**
+     * Region processor
+     */
+    private static class RegionProcessor implements Callable<Response> {
+
+        private final FileChannel fc;
+        private final Arena arena;
+        private final long start;
+        private final long end;
+        private final long size;
+        private final OpenMap map;
+        private final Result result;
+
+        private RegionProcessor(Request request) {
+            this.fc = request.fileChannel;
+            this.arena = request.arena;
+            this.start = request.start;
+            this.end = request.end;
+            this.size = end - start;
+            this.map = new OpenMap();
+            this.result = request.result;
+        }
+
+        @Override
+        public Response call() throws Exception {
+            if (VERBOSE) {
+                System.out.println("[Processor-" + Thread.currentThread().getName() + "] Processing started at " + System.currentTimeMillis());
+            }
+            try {
+                processRegion();
+                return new Response(map);
+            }
+            finally {
+                if (VERBOSE) {
+                    System.out.println("[Processor-" + Thread.currentThread().getName() + "] Processing finished at " + System.currentTimeMillis());
+                }
+            }
+        }
+
+        private void processRegion() throws Exception {
+            boolean arenaGiven = arena != null;
+            // If no shared global memory arena is used, create and use its own local memory arena
+            Arena a = arenaGiven ? arena : Arena.ofConfined();
+            try {
+                MemorySegment region = fc.map(FileChannel.MapMode.READ_ONLY, start, size, a);
+
+                doProcessRegion(region);
+                if (VERBOSE) {
+                    System.out.println("[Processor-" + Thread.currentThread().getName() + "] Region processed at " + System.currentTimeMillis());
+                }
+
+                // Some threads/processors might finish slightly before others.
+                // So, instead of releasing their cores idle, merge their own results here.
+
+                // If there is no another processor merging its results now, merge now.
+                // Otherwise (there is already another thread/processor got the lock of merging),
+                // Close current processor's own local memory arena (if no shared global memory arena is used) now
+                // and merge its own results after then.
+
+                boolean merged = result.tryMergeInto(map);
+                if (VERBOSE && merged) {
+                    System.out.println("[Processor-" + Thread.currentThread().getName() + "] Result merged at " + System.currentTimeMillis());
+                }
+                if (!merged) {
+                    if (!arenaGiven) {
+                        a.close();
+                        a = null;
+                        if (VERBOSE) {
+                            System.out.println("[Processor-" + Thread.currentThread().getName() + "] Arena closed at " + System.currentTimeMillis());
+                        }
+                    }
+                    result.mergeInto(map);
+                    if (VERBOSE) {
+                        System.out.println("[Processor-" + Thread.currentThread().getName() + "] Result merged at " + System.currentTimeMillis());
+                    }
+                }
+            }
+            finally {
+                // If local memory arena is managed here and not closed yet, close it here
+                if (!arenaGiven && a != null) {
+                    a.close();
+                    if (VERBOSE) {
+                        System.out.println("[Processor-" + Thread.currentThread().getName() + "] Arena closed at " + System.currentTimeMillis());
+                    }
+                }
+            }
+        }
+
+        private void doProcessRegion(MemorySegment region) {
+            final long regionAddress = region.address();
+            final long regionSize = region.byteSize();
+            final int vectorSize = BYTE_SPECIES.vectorByteSize();
+            final long regionMainLimit = regionSize - MAX_LINE_LENGTH;
+
+            int regionPtr;
+
+            // Read and process region - main
+            for (regionPtr = 0; regionPtr < regionMainLimit;) {
+                regionPtr = doProcessLine(region, regionAddress, vectorSize, regionPtr);
+            }
+
+            // Read and process region - tail
+            for (int i = regionPtr, j = regionPtr; i < regionSize;) {
+                byte b = U.getByte(regionAddress + i);
+                if (b == KEY_VALUE_SEPARATOR) {
+                    long baseOffset = map.putKey(null, regionAddress, j, i - j);
+                    i = extractValue(regionAddress, i + 1, map, baseOffset);
+                    j = i;
+                }
+                else {
+                    i++;
+                }
+            }
+        }
+
+        private int doProcessLine(MemorySegment region, long regionAddress, int vectorSize, int i) {
+            // Find key/value separator
+            ////////////////////////////////////////////////////////////////////////////////////////////////////////
+            int keyStartIdx = i;
+
+            // Vectorized search for key/value separator
+            ByteVector keyVector = ByteVector.fromMemorySegment(BYTE_SPECIES, region, i, NATIVE_BYTE_ORDER);
+            int keyValueSepOffset = keyVector.compare(VectorOperators.EQ, KEY_VALUE_SEPARATOR).firstTrue();
+            // Check whether key/value separator is found in the first vector (city name is <= vector size)
+            if (keyValueSepOffset == vectorSize) {
+                i += vectorSize;
+                keyValueSepOffset = 0;
+                for (; U.getByte(regionAddress + i) != KEY_VALUE_SEPARATOR; i++)
+                    ;
+                // I have tried vectorized search for key/value separator in the remaining part,
+                // but since majority (99%) of the city names <= 16 bytes
+                // and other a few longer city names (have length < 16 and <= 32) not close to 32 bytes,
+                // byte by byte search is better in terms of performance (according to my experiments) and simplicity.
+            }
+            i += keyValueSepOffset;
+            int keyLength = i - keyStartIdx;
+            i++;
+            ////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+            // Put key and get map offset to put value
+            long baseOffset = map.putKey(keyVector, regionAddress, keyStartIdx, keyLength);
+
+            // Extract value, put it into map and return next position in the region to continue processing from there
+            return extractValue(regionAddress, i, map, baseOffset);
+        }
+
+    }
+
+    // Credits: merykitty
+    private static int extractValue(long regionAddress, int idx, OpenMap map, long baseOffset) {
+        long word = U.getLong(regionAddress + idx);
+        if (NATIVE_BYTE_ORDER == ByteOrder.BIG_ENDIAN) {
+            word = Long.reverseBytes(word);
+        }
+
+        // Parse and extract value
+        int decimalSepPos = Long.numberOfTrailingZeros(~word & 0x10101000);
+        int shift = 28 - decimalSepPos;
+        long signed = (~word << 59) >> 63;
+        long designMask = ~(signed & 0xFF);
+        long digits = ((word & designMask) << shift) & 0x0F000F0F00L;
+        long absValue = ((digits * 0x640a0001) >>> 32) & 0x3FF;
+        int value = (int) ((absValue ^ signed) - signed);
+
+        // Put extracted value into map
+        map.putValue(baseOffset, value);
+
+        // Return new position
+        return idx + (decimalSepPos >>> 3) + 3;
+    }
+
+    /**
+     * Region processor request
+     */
+    private static final class Request {
+
+        private final FileChannel fileChannel;
+        private final Arena arena;
+        private final long start;
+        private final long end;
+        private final Result result;
+
+        private Request(FileChannel fileChannel, Arena arena, long start, long end, Result result) {
+            this.fileChannel = fileChannel;
+            this.arena = arena;
+            this.start = start;
+            this.end = end;
+            this.result = result;
+        }
+
+    }
+
+    /**
+     * Region processor response
+     */
+    private static final class Response {
+
+        private final OpenMap map;
+
+        private Response(OpenMap map) {
+            this.map = map;
+        }
+
+    }
+
+    /**
+     * Result of each key (city)
+     */
+    private static final class KeyResult {
+
+        private int count;
+        private int minValue;
+        private int maxValue;
+        private long sum;
+
+        private KeyResult(int count, int minValue, int maxValue, long sum) {
+            this.count = count;
+            this.minValue = minValue;
+            this.maxValue = maxValue;
+            this.sum = sum;
+        }
+
+        private void merge(KeyResult result) {
+            count += result.count;
+            minValue = Math.min(minValue, result.minValue);
+            maxValue = Math.max(maxValue, result.maxValue);
+            sum += result.sum;
+        }
+
+        @Override
+        public String toString() {
+            return (minValue / 10.0) + "/" + round(sum / (double) (count * 10)) + "/" + (maxValue / 10.0);
+        }
+
+        private double round(double value) {
+            return Math.round(value * 10.0) / 10.0;
+        }
+
+    }
+
+    /**
+     * Global result
+     */
+    private static final class Result {
+
+        private final Lock lock = new ReentrantLock();
+        private final Map<String, KeyResult> resultMap;
+
+        private Result() {
+            this.resultMap = new TreeMap<>();
+        }
+
+        private boolean tryMergeInto(OpenMap map) {
+            // Use lock (not "synchronized" block) to be virtual threads friendly
+            if (!lock.tryLock()) {
+                return false;
+            }
+            try {
+                map.merge(this.resultMap);
+                return true;
+            }
+            finally {
+                lock.unlock();
+            }
+        }
+
+        private void mergeInto(OpenMap map) {
+            // Use lock (not "synchronized" block) to be virtual threads friendly
+            lock.lock();
+            try {
+                map.merge(this.resultMap);
+            }
+            finally {
+                lock.unlock();
+            }
+        }
+
+        private void print() {
+            System.out.println(resultMap);
+        }
+
+    }
+
+    private static final class OpenMap {
+
+        // Layout
+        // ================================
+        // 0 : 4 bytes - count
+        // 4 : 2 bytes - min value
+        // 6 : 2 bytes - max value
+        // 8 : 8 bytes - value sum
+        // 16 : 4 bytes - key size
+        // 20 : 4 bytes - padding
+        // 24 : 100 bytes - key
+        // 124 : 4 bytes - padding
+        // ================================
+        // 128 bytes - total
+
+        private static final int ENTRY_SIZE = 128;
+        private static final int COUNT_OFFSET = 0;
+        private static final int MIN_VALUE_OFFSET = 4;
+        private static final int MAX_VALUE_OFFSET = 6;
+        private static final int VALUE_SUM_OFFSET = 8;
+        private static final int KEY_SIZE_OFFSET = 16;
+        private static final int KEY_OFFSET = 24;
+
+        private static final int ENTRY_HASH_MASK = MAP_CAPACITY - 1;
+        private static final int MAP_SIZE = ENTRY_SIZE * MAP_CAPACITY;
+        private static final int ENTRY_MASK = MAP_SIZE - 1;
+
+        private final byte[] data;
+
+        private OpenMap() {
+            this.data = new byte[MAP_SIZE];
+        }
+
+        // Credits: merykitty
+        private static int calculateKeyHash(long address, int keyLength) {
+            int seed = 0x9E3779B9;
+            int rotate = 5;
+            int x, y;
+            if (keyLength >= Integer.BYTES) {
+                x = U.getInt(address);
+                y = U.getInt(address + keyLength - Integer.BYTES);
+            }
+            else {
+                x = U.getByte(address);
+                y = U.getByte(address + keyLength - Byte.BYTES);
+            }
+            return (Integer.rotateLeft(x * seed, rotate) ^ y) * seed;
+        }
+
+        private long putKey(ByteVector keyVector, long regionAddress, long keyStartIdx, int keyLength) {
+            long keyStartAddress = regionAddress + keyStartIdx;
+            // Calculate hash of key
+            int keyHash = calculateKeyHash(keyStartAddress, keyLength);
+            // and get the position of the entry in the linear map based on calculated hash
+            int idx = keyHash & ENTRY_HASH_MASK;
+
+            // Start searching from the calculated position
+            // and continue until find an available slot in case of hash collision
+            // TODO Prevent infinite loop if all the slots are in use for other keys
+            for (long baseOffset = Unsafe.ARRAY_BYTE_BASE_OFFSET + (idx * ENTRY_SIZE);; baseOffset = (baseOffset + ENTRY_SIZE) & ENTRY_MASK) {
+                int keyStartOffset = (int) baseOffset + KEY_OFFSET;
+                int keySize = U.getInt(data, baseOffset + KEY_SIZE_OFFSET);
+                // Check whether current index is empty (no another key is inserted yet)
+                if (keySize == 0) {
+                    // Initialize entry slot for new key
+                    U.putShort(data, baseOffset + MIN_VALUE_OFFSET, Short.MAX_VALUE);
+                    U.putShort(data, baseOffset + MAX_VALUE_OFFSET, Short.MIN_VALUE);
+                    U.putInt(data, baseOffset + KEY_SIZE_OFFSET, keyLength);
+                    U.copyMemory(null, keyStartAddress, data, keyStartOffset, keyLength);
+                    return baseOffset;
+                }
+                // Check for hash collision (hashes are same, but keys are different).
+                // If there is no collision (both hashes and keys are equals), return current slot's offset.
+                // Otherwise, continue iterating until find an available slot.
+                if (keySize == keyLength && keysEqual(keyVector, keyStartAddress, keyLength, keyStartOffset)) {
+                    return baseOffset;
+                }
+            }
+        }
+
+        private boolean keysEqual(ByteVector keyVector, long keyStartAddress, int keyLength, int keyStartOffset) {
+            int keyCheckIdx = 0;
+            if (keyVector != null) {
+                // Use vectorized search for the comparison of keys.
+                // Since majority of the city names >= 8 bytes and <= 16 bytes,
+                // this way is more efficient (according to my experiments) than any other comparisons (byte by byte or 2 longs).
+                int keyCheckLength = Math.min(BYTE_SPECIES_SIZE, keyLength);
+                ByteVector entryKeyVector = ByteVector.fromArray(BYTE_SPECIES, data, keyStartOffset - Unsafe.ARRAY_BYTE_BASE_OFFSET);
+                long eqMask = keyVector.compare(VectorOperators.EQ, entryKeyVector).toLong();
+                int eqCount = Long.numberOfTrailingZeros(~eqMask);
+                if (eqCount < keyCheckLength) {
+                    return false;
+                }
+                if (keyCheckLength == keyLength) {
+                    return true;
+                }
+                keyCheckIdx = BYTE_SPECIES_SIZE;
+            }
+
+            // Compare remaining parts of the keys
+
+            int normalizedKeyLength = keyLength;
+            if (NATIVE_BYTE_ORDER == ByteOrder.BIG_ENDIAN) {
+                normalizedKeyLength = Integer.reverseBytes(normalizedKeyLength);
+            }
+
+            int alignedKeyLength = normalizedKeyLength & 0xFFFFFFF8;
+            int i;
+            for (i = keyCheckIdx; i < alignedKeyLength; i += Long.BYTES) {
+                if (U.getLong(keyStartAddress + i) != U.getLong(data, keyStartOffset + i)) {
+                    return false;
+                }
+            }
+
+            long wordA = U.getLong(keyStartAddress + i);
+            long wordB = U.getLong(data, keyStartOffset + i);
+            if (NATIVE_BYTE_ORDER == ByteOrder.BIG_ENDIAN) {
+                wordA = Long.reverseBytes(wordA);
+                wordB = Long.reverseBytes(wordB);
+            }
+            int halfShift = (Long.BYTES - (normalizedKeyLength & 0x00000007)) << 2;
+            long mask = (0xFFFFFFFFFFFFFFFFL >>> halfShift) >> halfShift;
+            wordA = wordA & mask;
+            // No need to mask "wordB" (word from key in the map), because it is already padded with 0s
+            return wordA == wordB;
+        }
+
+        private void putValue(long baseOffset, int value) {
+            U.putInt(data, baseOffset + COUNT_OFFSET,
+                    U.getInt(data, baseOffset + COUNT_OFFSET) + 1);
+            U.putShort(data, baseOffset + MIN_VALUE_OFFSET,
+                    (short) Math.min(value, U.getShort(data, baseOffset + MIN_VALUE_OFFSET)));
+            U.putShort(data, baseOffset + MAX_VALUE_OFFSET,
+                    (short) Math.max(value, U.getShort(data, baseOffset + MAX_VALUE_OFFSET)));
+            U.putLong(data, baseOffset + VALUE_SUM_OFFSET,
+                    value + U.getLong(data, baseOffset + VALUE_SUM_OFFSET));
+        }
+
+        private void merge(Map<String, KeyResult> resultMap) {
+            // Merge this local map into global result map
+            for (int i = 0; i < MAP_SIZE; i += ENTRY_SIZE) {
+                int baseOffset = Unsafe.ARRAY_BYTE_BASE_OFFSET + i;
+                int keyLength = U.getInt(data, baseOffset + KEY_SIZE_OFFSET);
+                if (keyLength == 0) {
+                    // No entry is available for this index, so continue iterating
+                    continue;
+                }
+                String key = new String(data, i + KEY_OFFSET, keyLength, StandardCharsets.UTF_8);
+                int count = U.getInt(data, baseOffset + COUNT_OFFSET);
+                short minValue = U.getShort(data, baseOffset + MIN_VALUE_OFFSET);
+                short maxValue = U.getShort(data, baseOffset + MAX_VALUE_OFFSET);
+                long sum = U.getLong(data, baseOffset + VALUE_SUM_OFFSET);
+                KeyResult result = new KeyResult(count, minValue, maxValue, sum);
+                KeyResult existingResult = resultMap.get(key);
+                if (existingResult == null) {
+                    resultMap.put(key, result);
+                }
+                else {
+                    existingResult.merge(result);
+                }
+            }
+        }
+
+    }
+
+}