1brc - 1️⃣🐝🏎️ The One Billion Row Challenge -- A fun exploration of how quickly 1B rows from a text file can be aggregated with Java

Created at: 2023-12-28 17:13:24
Language: Java
License: Apache-2.0

1️⃣🐝🏎️ The One Billion Row Challenge

Status Jan 1: This challenge is open for submissions!

The One Billion Row Challenge (1BRC) is a fun exploration of how far modern Java can be pushed for aggregating one billion rows from a text file. Grab all your (virtual) threads, reach out to SIMD, optimize your GC, or pull any other trick, and create the fastest implementation for solving this task!


The text file contains temperature values for a range of weather stations. Each row is one measurement in the format <string: station name>;<double: measurement>, with the measurement value having exactly one fractional digit. The following shows ten rows as an example:

St. John's;15.2

The task is to write a Java program which reads the file, calculates the min, mean, and max temperature value per weather station, and emits the results on stdout like this (i.e. sorted alphabetically by station name, and the result values per station in the format <min>/<mean>/<max>, rounded to one fractional digit):

{Abha=-23.0/18.0/59.2, Abidjan=-16.2/26.0/67.3, Abéché=-10.0/29.4/69.0, Accra=-10.1/26.4/66.4, Addis Ababa=-23.7/16.0/67.0, Adelaide=-27.8/17.3/58.5, ...}

Submit your implementation by Jan 31 2024 and become part of the leaderboard!


# Result (m:s.ms) Implementation JDK Submitter
1. 00:07.999 link 21.0.1-graal Roy van Rijn
2 00:10.589 link 21.0.1-graal Artsiom Korzun
3. 00:10.613 link 21.0.1-graal Sam Pullara
00:10.870 link 21.0.1-graalce Elliot Barlas
00:12.988 link 21.0.1-open Jamie Stansfield
00:13.430 link 21.0.1-open Johannes Schüth
00:13.463 link 21.0.1-open yemreinci
00:13.857 link 21.0.1-graal Filip Hrisafov
00:14.411 link 21.0.1-open deemkeen
00:16.196 link 21.0.1-open Parth Mudgal
00:17.905 link 21.0.1-open Peter Lawrey
00:18.789 link 21.0.1-open Nick Palmer
00:19.561 link 21.0.1-open Gabriel Reid
00:22.709 link 21.0.1-graal Markus Ebner
00:23.078 link 21.0.1-open Richard Startin
00:24.351 link 21.0.1-graal Yavuz Tas
00:24.879 link 21.0.1-open David Kopec
00:26.576 link 21.0.1-open Roman Romanchuk
00:27.787 link 21.0.1-open Nils Semmelrock
00:28.167 link 21.0.1-open Roman Schweitzer
00:32.764 link 21.0.1-open Moysés Borges Furtado
00:34.848 link 21.0.1-open Arman Sharif
00:36.518 link 21.0.1-open Ramzi Ben Yahya
00:38.510 link 21.0.1-open Hampus Ram
00:50.547 link 21.0.1-open Aurelian Tutuianu
00:51.678 link 21.0.1-tem Tobi
00:53.679 link 21.0.1-open Chris Riccomini
01:24.721 link 21.0.1-open Ujjwal Bharti
01:27.912 link 21.0.1-open Jairo Graterón
01:58.536 link 21.0.1-open Kuduwa Keshavram
02:00.101 link 21.0.1-open khmarbaise
02:08.315 link 21.0.1-open itaske
02:16.635 link 21.0.1-open twohardthings
02:23.316 link 21.0.1-open Abhilash
03:42.297 link 21.0.1-open Samson
04:13.449 link (baseline) 21.0.1-open Gunnar Morling

See below for instructions how to enter the challenge with your own implementation.


Java 21 must be installed on your system.

Running the Challenge

This repository contains two programs:

  • dev.morling.onebrc.CreateMeasurements (invoked via create_measurements.sh): Creates the file measurements.txt in the root directory of this project with a configurable number of random measurement values
  • dev.morling.onebrc.CalculateAverage (invoked via calculate_average_baseline.sh): Calculates the average values for the file measurements.txt

Execute the following steps to run the challenge:

  1. Build the project using Apache Maven:

    ./mvnw clean verify
  2. Create the measurements file with 1B rows (just once):

    ./create_measurements.sh 1000000000

    This will take a few minutes. Attention: the generated file has a size of approx. 12 GB, so make sure to have enough diskspace.

  3. Calculate the average measurement values:


    The provided naive example implementation uses the Java streams API for processing the file and completes the task in ~2 min on environment used for result evaluation. It serves as the base line for comparing your own implementation.

  4. Optimize the heck out of it:

    Adjust the CalculateAverage program to speed it up, in any way you see fit (just sticking to a few rules described below). Options include parallelizing the computation, using the (incubating) Vector API, memory-mapping different sections of the file concurrently, using AppCDS, GraalVM, CRaC, etc. for speeding up the application start-up, choosing and tuning the garbage collector, and much more.


A tip is that if you have jbang installed, you can get a flamegraph of your program by running async-profiler via ap-loader:

jbang --javaagent=ap-loader@jvm-profiling-tools/ap-loader=start,event=cpu,file=profile.html -m dev.morling.onebrc.CalculateAverage_yourname target/average-1.0.0-SNAPSHOT.jar

or directly on the .java file:

jbang --javaagent=ap-loader@jvm-profiling-tools/ap-loader=start,event=cpu,file=profile.html src/main/java/dev/morling/onebrc/CalculateAverage_yourname

When you run this, it will generate a flamegraph in profile.html. You can then open this in a browser and see where your program is spending its time.

Rules and limits

  • Any of these Java distributions may be used:
    • Any builds provided by SDKMan
    • Early access builds available on openjdk.net may be used (including EA builds for OpenJDK projects like Valhalla)
    • Builds on builds.shipilev.net If you want to use a build not available via these channels, reach out to discuss whether it can be considered.
  • No external library dependencies may be used
  • Implementations must be provided as a single source file
  • The computation must happen at application runtime, i.e. you cannot process the measurements file at build time (for instance, when using GraalVM) and just bake the result into the binary
  • Input value ranges are as follows:
    • Station name: non null UTF-8 string of min length 1 character and max length 100 characters
    • Temperature value: non null double between -99.9 (inclusive) and 99.9 (inclusive), always with one fractional digit
  • There is a maximum of 10,000 unique station names
  • Implementations must not rely on specifics of a given data set, e.g. any valid station name as per the constraints above and any data distribution (number of measurements per station) must be supported

Entering the Challenge

To submit your own implementation to 1BRC, follow these steps:

  • Create a fork of the onebrc GitHub repository.
  • Create a copy of CalculateAverage.java, named CalculateAverage_<your_GH_user>.java, e.g. CalculateAverage_doloreswilson.java.
  • Make that implementation fast. Really fast.
  • Create a copy of calculate_average_baseline.sh, named calculate_average_<your_GH_user>.sh, e.g. calculate_average_doloreswilson.sh.
  • Adjust that script so that it references your implementation class name. If needed, provide any JVM arguments via the JAVA_OPTS variable in that script. Make sure that script does not write anything to standard output other than calculation results.
  • OpenJDK 21 is the default. If a custom JDK build is required, include the SDKMAN command sdk use java [version] in the launch shell script prior to application start.
  • (Optional) If you'd like to use native binaries (GraalVM), adjust the pom.xml file so that it builds that binary.
  • Run the test suite by executing /test.sh <your_GH_user>; if any differences are reported, fix them before submitting your implementation.
  • Create a pull request against the upstream repository, clearly stating
    • The name of your implementation class.
    • The execution time of the program on your system and specs of the same (CPU, number of cores, RAM). This is for informative purposes only, the official runtime will be determined as described below.
  • I will run the program and determine its performance as described in the next section, and enter the result to the scoreboard.

Note: I reserve the right to not evaluate specific submissions if I feel doubtful about the implementation (I.e. I won't run your Bitcoin miner ;).

If you'd like to discuss any potential ideas for implementing 1BRC with the community, you can use the GitHub Discussions of this repository. Please keep it friendly and civil.

The challenge runs until Jan 31 2024. Any submissions (i.e. pull requests) created after Jan 31 2024 23:59 UTC will not be considered.

Evaluating Results

Results are determined by running the program on a Hetzner Cloud CCX33 instance (8 dedicated vCPU, 32 GB RAM). The time program is used for measuring execution times, i.e. end-to-end times are measured. Each contender will be run five times in a row. The slowest and the fastest runs are discarded. The mean value of the remaining three runs is the result for that contender and will be added to the results table above. The exact same measurements.txt file is used for evaluating all contenders.

If you'd like to spin up your own box for testing on Hetzner Cloud, you may find these set-up scripts (based on Terraform and Ansible) useful. Note this will incur cost you are responsible for, I am not going to pay your cloud bill :)


If you enter this challenge, you may learn something new, get to inspire others, and take pride in seeing your name listed in the scoreboard above. Rumor has it that the winner may receive a unique 1️⃣🐝🏎️ t-shirt, too!


Q: Can I use Kotlin or other JVM languages other than Java?
A: No, this challenge is focussed on Java only. Feel free to inofficially share implementations significantly outperforming any listed results, though.

Q: Can I use non-JVM languages and/or tools?
A: No, this challenge is focussed on Java only. Feel free to inofficially share interesting implementations and results though. For instance it would be interesting to see how DuckDB fares with this task.

Q: I've got an implementation—but it's not in Java. Can I share it somewhere?
A: Whilst non-Java solutions cannot be formally submitted to the challenge, you are welcome to share them over in the Show and tell GitHub discussion area.

Q: Can I use JNI?
A: Submissions must be completely implemented in Java, i.e. you cannot write JNI glue code in C/C++. You could use AOT compilation of Java code via GraalVM though, either by AOT-compiling the entire application, or by creating a native library (see here.

Q: What is the encoding of the measurements.txt file?
A: The file is encoded with UTF-8.

Q: Can I make assumptions on the names of the weather stations showing up in the data set?
A: No, while only a fixed set of station names is used by the data set generator, any solution should work with arbitrary UTF-8 station names (for the sake of simplicity, names are guaranteed to contain no ; character).

Q: Can I copy code from other submissions?
A: Yes, you can. The primary focus of the challenge is about learning something new, rather than "winning". When you do so, please give credit to the relevant source submissions. Please don't re-submit other entries with no or only trivial improvements.

Q: Which operating system is used for evaluation?
A: Fedora 39.

Q: Why 1️⃣🐝🏎️ ?
A: It's the abbreviation of the project name: One Billion Row Challenge.


This code base is available under the Apache License, version 2.

Code of Conduct

Be excellent to each other! More than winning, the purpose of this challenge is to have fun and learn something new.