Use a larger buffer size for java.util.zip.*Stream classes

[EdSchouten]

DeflaterInputStream, GZIPInputStream, GZIPOutputStream, and InflaterInputStream, all use an internal byte buffer of 512 bytes by default.

Whenever the wrapped stream exceeds this size, a full copy to a new buffer will occur, which will increase at increments of the same size. For example, a stream of length 2K will be copied four times. Increasing the size of the buffer we use can result in significant reductions in CPU usage (read: copies).

Examples in the repository

There are already two places where we increase the default size of these buffers:

• //src/main/java/com/google/devtools/build/lib/bazel/repository/TarGzFunction.java
• //src/main/java/com/google/devtools/build/lib/bazel/repository/downloader/HttpStream.java

Prior art

There is an open enhancement issue in the OpenJDK tracker on this which contains a benchmark for InflaterOutputStream:

Increase the default, internal buffer size of the Streams in java.util.zip
https://bugs.openjdk.org/browse/JDK-8242864

A similar change was merged in for JDK15+ in 2020:

Improve performance of InflaterOutputStream.write()
https://bugs.openjdk.org/browse/JDK-8242848

Providing a simple benchmark

I'm inlining a simple jmh benchmark and the results underneath it for one GzipInputStream case.

The benchmark:

@Fork(1)
@Threads(1)
@Warmup(iterations = 2)
@State(Scope.Benchmark)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class GZIPInputStreamBenchmark {
    @Param({"1024", "3072", "9216"})
    long inputLength;
    @Param({"512", "1024", "4096", "8192"})
    int bufferSize;
    private byte[] content;

    @Setup(Level.Iteration)
    public void setup() throws IOException {
        var baos = new ByteArrayOutputStream();
        // No need to set the buffer size on this as it's a one-time cost for setup and not counted in the result.
        var gzip = new GZIPOutputStream(baos);

        var inputBytes = generateRandomByteArrayOfLength(inputLength);
        gzip.write(inputBytes);
        gzip.finish();

        this.content = baos.toByteArray();
    }

    @Benchmark
    @BenchmarkMode(Mode.AverageTime)
    public void getGzipInputStream(Blackhole bh) throws IOException {
        try (var is = new ByteArrayInputStream(this.content);
             var gzip = new GZIPInputStream(is, bufferSize)) {
            bh.consume(gzip.readAllBytes());
        }
    }

    byte[] generateRandomByteArrayOfLength(long length) {
        var random = new Random();
        var intStream = random.ints(0, 5000).limit(length).boxed();

        return intStream.collect(
                ByteArrayOutputStream::new,
                (baos, i) -> baos.write(i.intValue()),
                (baos1, baos2) -> baos1.write(baos2.toByteArray(), 0, baos2.size())
        ).toByteArray();
    }
}

The results:

Benchmark                                    (bufferSize)  (inputLength)  Mode  Cnt      Score    Error  Units
GZIPInputStreamBenchmark.getGzipInputStream           512           1024  avgt    5   3207.217 ± 24.919  ns/op
GZIPInputStreamBenchmark.getGzipInputStream           512           3072  avgt    5   5874.191 ±  5.827  ns/op
GZIPInputStreamBenchmark.getGzipInputStream           512           9216  avgt    5  15567.345 ± 93.281  ns/op
GZIPInputStreamBenchmark.getGzipInputStream          1024           1024  avgt    5   2580.566 ± 14.566  ns/op
GZIPInputStreamBenchmark.getGzipInputStream          1024           3072  avgt    5   4154.582 ± 16.016  ns/op
GZIPInputStreamBenchmark.getGzipInputStream          1024           9216  avgt    5   9942.521 ± 61.215  ns/op
GZIPInputStreamBenchmark.getGzipInputStream          4096           1024  avgt    5   2150.255 ± 52.770  ns/op
GZIPInputStreamBenchmark.getGzipInputStream          4096           3072  avgt    5   2289.185 ± 71.396  ns/op
GZIPInputStreamBenchmark.getGzipInputStream          4096           9216  avgt    5   5656.891 ± 28.499  ns/op
GZIPInputStreamBenchmark.getGzipInputStream          8192           1024  avgt    5   2177.427 ± 30.896  ns/op
GZIPInputStreamBenchmark.getGzipInputStream          8192           3072  avgt    5   2517.390 ± 21.296  ns/op
GZIPInputStreamBenchmark.getGzipInputStream          8192           9216  avgt    5   5227.932 ± 55.525  ns/op

Patch by: Kushal Pisavadia

[google-cla]

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[fmeum]

Cc @meteorcloudy

[meteorcloudy]

Thanks!! Just to clarify, we are already using JDK 21 as the embedded JDK, do we still need this change? Or is this mostly aiming to improve performance when running Bazel without the embedded JDK?

[fmeum]

@bazel-io flag

[EdSchouten]

As stated in the PR description, there is an open issue to standardise all buffers on 8192, as those in java.util.zip are smaller for historic reasons: https://bugs.openjdk.org/browse/JDK-8242864

If you’re looking at the latest JDK22 (+25) tag, which is further along than JDK21, it’s still set to use 512 as the default: https://github.com/openjdk/jdk/blob/jdk-22%2B25/src/java.base/share/classes/java/util/zip/GZIPInputStream.java#L91

[meteorcloudy]

@bazel-io fork 7.0.0

[meisterT]

What does Patch by: Kushal Pisavadia mean? @EdSchouten did you pair program this with someone else? Did they also sign CLA?

[sgowroji]

Hi @EdSchouten, Could you respond for the above comment. This PR is awaiting to merge .

[EdSchouten]

Hey there,

Yes, Kushal is a colleague of mine. I'm still waiting for him to be added to the right Google Group for the CLA approval to go through. I'll keep you posted when that's done.

[EdSchouten]

CLA has been sorted out. I've added

Co-authored-by: Kushal Pisavadia <REDACTED>

to the commit message, and the CLA bot picked it up.

[meisterT]

Thanks @EdSchouten and @KushalP!

[iancha1992]

The changes in this PR have been included in Bazel 7.1.0 RC1. Please test out the release candidate and report any issues as soon as possible. If you're using Bazelisk, you can point to the latest RC by setting USE_BAZEL_VERSION=last_rc.
Thanks!