280Puzzle: What's up with Vector?

Author: Dr Heinz M. KabutzDate: 2020-06-23Java Version: 8+Category: Performance

Abstract: For today's puzzle, we are getting elements from Vector, sequentially and in parallel. But why is the performance so much worse in Java 15-ea+28?

Welcome to the 280th edition of The Java(tm) Specialists' Newsletter, sent to you from the Island of Crete. We spent the past three weeks doing live classes on topics like concurrency, design patterns and dynamic proxies. It was a lot of fun and the feedback from the students was amazing. Even though we repeated the content in the afternoons, some of the students liked the sessions so much that they came to both. Please let me know by email if you would like me to teach private live classes to your team of programmers.

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Puzzle: What's up with Vector?

So I wrote this little class this afternoon:

import java.util.*;
import java.util.stream.*;

public class VectorBench {
  public static void main(String... args) {
    for (int i = 0; i < 10; i++) {
      test(false);
      test(true);
    }
  }

  private static void test(boolean parallel) {
    IntStream range = IntStream.range(1, 100_000_000);
    if (parallel) range = range.parallel();
    long time = System.nanoTime();
    try {
      ThreadLocal<List<Integer>> lists =
          ThreadLocal.withInitial(() -> {
            List<Integer> result = new Vector<>();
            for (int i = 0; i < 1024; i++) result.add(i);
            return result;
          });
      range.map(i -> lists.get().get(i & 1023)).sum();
    } finally {
      time = System.nanoTime() - time;
      System.out.printf("%s %dms%n",
          parallel?"parallel":"sequential", (time / 1_000_000));
    }
  }
}

Here are the results for different versions of Java running on my 1-6-2 MacBook Pro Late 2018 model.

Java 8 and 9 have similar performance characteristics:

openjdk version "1.8.0_252"
OpenJDK Runtime Environment (build 1.8.0_252-b14)
OpenJDK 64-Bit Server VM (build 25.252-b14, mixed mode)
sequential 1576ms
parallel 233ms
sequential 1560ms
parallel 185ms
sequential 1538ms
parallel 101ms
sequential 538ms
parallel 103ms
sequential 560ms
parallel 103ms
sequential 549ms
parallel 102ms
sequential 554ms
parallel 103ms
sequential 546ms
parallel 103ms
sequential 556ms
parallel 103ms
sequential 548ms
parallel 104ms

openjdk version "9.0.7.1"
OpenJDK Runtime Environment
OpenJDK 64-Bit Server VM
sequential 1618ms
parallel 220ms
sequential 1512ms
parallel 192ms
sequential 1516ms
parallel 103ms
sequential 557ms
parallel 105ms
sequential 556ms
parallel 106ms
sequential 559ms
parallel 111ms
sequential 587ms
parallel 108ms
sequential 554ms
parallel 104ms
sequential 564ms
parallel 105ms
sequential 599ms
parallel 131ms

In Java 10, the first few results are faster, but later results are roughly the same:

openjdk version "10.0.2" 2018-07-17
OpenJDK Runtime Environment
OpenJDK 64-Bit Server VM
sequential 717ms
parallel 148ms
sequential 591ms
parallel 107ms
sequential 581ms
parallel 106ms
sequential 592ms
parallel 106ms
sequential 561ms
parallel 107ms
sequential 555ms
parallel 109ms
sequential 572ms
parallel 108ms
sequential 566ms
parallel 110ms
sequential 558ms
parallel 105ms
sequential 568ms
parallel 121ms

openjdk version "11.0.7" 2020-04-14 LTS
OpenJDK Runtime Environment
OpenJDK 64-Bit Server VM
sequential 612ms
parallel 154ms
sequential 560ms
parallel 118ms
sequential 599ms
parallel 110ms
sequential 567ms
parallel 109ms
sequential 562ms
parallel 122ms
sequential 578ms
parallel 109ms
sequential 571ms
parallel 109ms
sequential 569ms
parallel 109ms
sequential 572ms
parallel 113ms
sequential 565ms
parallel 120ms

openjdk version "12.0.2" 2019-07-16
OpenJDK Runtime Environment
OpenJDK 64-Bit Server VM
sequential 597ms
parallel 141ms
sequential 526ms
parallel 103ms
sequential 518ms
parallel 104ms
sequential 549ms
parallel 105ms
sequential 522ms
parallel 107ms
sequential 572ms
parallel 107ms
sequential 531ms
parallel 108ms
sequential 534ms
parallel 104ms
sequential 531ms
parallel 107ms
sequential 536ms
parallel 120ms

openjdk version "13.0.3" 2020-04-14
OpenJDK Runtime Environment
OpenJDK 64-Bit Server VM
sequential 606ms
parallel 140ms
sequential 538ms
parallel 106ms
sequential 540ms
parallel 108ms
sequential 528ms
parallel 113ms
sequential 536ms
parallel 108ms
sequential 533ms
parallel 107ms
sequential 530ms
parallel 108ms
sequential 534ms
parallel 107ms
sequential 545ms
parallel 116ms
sequential 553ms
parallel 120ms

openjdk version "14.0.1" 2020-04-14
OpenJDK Runtime Environment (build 14.0.1+7)
OpenJDK 64-Bit Server VM (build 14.0.1+7, mixed mode, sharing)
sequential 705ms
parallel 136ms
sequential 579ms
parallel 112ms
sequential 572ms
parallel 113ms
sequential 583ms
parallel 112ms
sequential 579ms
parallel 111ms
sequential 566ms
parallel 111ms
sequential 571ms
parallel 109ms
sequential 591ms
parallel 108ms
sequential 572ms
parallel 110ms
sequential 573ms
parallel 120ms

Things improved a bit in Java 15 (last month's JDK).

openjdk version "15-ea" 2020-09-15
OpenJDK Runtime Environment (build 15-ea+23-1098)
OpenJDK 64-Bit Server VM (build 15-ea+23-1098, mixed mode, sharing)
sequential 709ms
parallel 133ms
sequential 547ms
parallel 98ms
sequential 551ms
parallel 97ms
sequential 537ms
parallel 97ms
sequential 545ms
parallel 100ms
sequential 540ms
parallel 98ms
sequential 540ms
parallel 99ms
sequential 543ms
parallel 98ms
sequential 552ms
parallel 109ms
sequential 586ms
parallel 107ms

Or maybe not?

openjdk version "15-ea" 2020-09-15
OpenJDK Runtime Environment (build 15-ea+28-1400)
OpenJDK 64-Bit Server VM (build 15-ea+28-1400, mixed mode, sharing)
sequential 1508ms
parallel 236ms
sequential 1553ms
parallel 199ms
sequential 1517ms
parallel 201ms
sequential 1449ms
parallel 211ms
sequential 1568ms
parallel 205ms
sequential 1478ms
parallel 199ms
sequential 1540ms
parallel 205ms
sequential 1488ms
parallel 204ms
sequential 1499ms
parallel 203ms
sequential 1523ms
parallel 202ms

What is going on? Please let me know your guesses by return email. Best explanation gets a mention in the next newsletter :-)

Kind regards from Crete

Heinz

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