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Arkouda (αρκούδα): NumPy-like arrays at massive scale backed by Chapel.

NOTE: Arkouda is under the MIT license.

Online Documentation

Arkouda docs at Github Pages

Nightly Arkouda Performance Charts

Arkouda nightly performance charts

Gitter channels

Arkouda Gitter channel

Chapel Gitter channel

Arkouda Weekly Call

We have a weekly zoom call to talk about what is going on with Arkouda development and people's general desires. Anyone with an interest in Arkouda is invited, come join in the discussion! Here is a link to the Arkouda Weekly Call Repo the there contains the meeting details.

Talks on Arkouda

Mike Merrill's SIAM PP-22 Talk

Arkouda Hack-a-thon videos

Bill Reus' March 2021 talk at the NJIT Data Science Seminar

Bill Reus' CHIUW 2020 Keynote video and slides

Mike Merrill's CHIUW 2019 talk

Bill Reus' CLSAC 2019 talk

(PAW-ATM) talk and abstract


Exploratory data analysis (EDA) is a prerequisite for all data science, as illustrated by the ubiquity of Jupyter notebooks, the preferred interface for EDA among data scientists. The operations involved in exploring and transforming the data are often at least as computationally intensive as downstream applications (e.g. machine learning algorithms), and as datasets grow, so does the need for HPC-enabled EDA. However, the inherently interactive and open-ended nature of EDA does not mesh well with current HPC usage models. Meanwhile, several existing projects from outside the traditional HPC space attempt to combine interactivity and distributed computation using programming paradigms and tools from cloud computing, but none of these projects have come close to meeting our needs for high-performance EDA.

To fill this gap, we have developed a software package, called Arkouda, which allows a user to interactively issue massively parallel computations on distributed data using functions and syntax that mimic NumPy, the underlying computational library used in the vast majority of Python data science workflows. The computational heart of Arkouda is a Chapel interpreter that accepts a pre-defined set of commands from a client (currently implemented in Python) and uses Chapel's built-in machinery for multi-locale and multithreaded execution. Arkouda has benefited greatly from Chapel's distinctive features and has also helped guide the development of the language.

In early applications, users of Arkouda have tended to iterate rapidly between multi-node execution with Arkouda and single-node analysis in Python, relying on Arkouda to filter a large dataset down to a smaller collection suitable for analysis in Python, and then feeding the results back into Arkouda computations on the full dataset. This paradigm has already proved very fruitful for EDA. Our goal is to enable users to progress seamlessly from EDA to specialized algorithms by making Arkouda an integration point for HPC implementations of expensive kernels like FFTs, sparse linear algebra, and graph traversal. With Arkouda serving the role of a shell, a data scientist could explore, prepare, and call optimized HPC libraries on massive datasets, all within the same interactive session.

Arkouda is not trying to replace Pandas but to allow for some Pandas-style operation at a much larger scale. In our experience Pandas can handle dataframes up to about 500 million rows before performance becomes a real issue, this is provided that you run on a sufficently capable compute server. Arkouda breaks the shared memory paradigm and scales its operations to dataframes with over 200 billion rows, maybe even a trillion. In practice we have run Arkouda server operations on columns of one trillion elements running on 512 compute nodes. This yielded a >20TB dataframe in Arkouda.

Table of Contents

  1. Prerequisites
  2. Building Arkouda
  3. Testing Arkouda
  4. Installing Arkouda Python libs and deps
  5. Running arkouda_server
  6. Logging
  7. Type Checking in Arkouda
  8. Environment Variables
  9. Versioning
  10. Contributing

Prerequisites toc

For a complete list of requirements for Arkouda, please review

For detailed prerequisite information and installation guides, please review

Building Arkouda toc

In order to run the Arkouda server, it must first be compiled. Detailed instructions on the build process can be found at

Testing Arkouda toc

(click to see more)

There are two unit test suites for Arkouda, one for Python and one for Chapel. As mentioned above, the Arkouda
Python test harness leverages multiple libraries such as pytest and pytest-env that must be installed via pip3 install -e .[dev], whereas the Chapel test harness does not require any external librares.

The default Arkouda test executes the Python test harness and is invoked as follows:

make test

The Chapel unit tests can be executed as follows:

make test-chapel

Both the Python and Chapel unit tests are executed as follows:

make test-all

For more details regarding Arkouda testing, please consult the Python test README and Chapel test README, respectively.

Running arkouda_server toc

The command-line invocation depends on whether you built a single-locale version (with CHPL_COMM=none) or multi-locale version (with CHPL_COMM set to the desired number of locales).

Single-locale startup:


Multi-locale startup (user selects the number of locales):

./arkouda_server -nl 2

Memory tracking is turned on by default now, you can run server with memory tracking turned off by

./arkouda_server --memTrack=false

By default, the server listens on port 5555. This value can be overridden with the command-line flag --ServerPort=1234

Memory tracking is turned on by default and turned off by using the --memTrack=false flag

Trace logging messages are turned on by default and turned off by using the --trace=false flag

Other command line options are available and can be viewed by using the --help flag

./arkouda-server --help

Sanity check arkouda_server toc

To sanity check the arkouda server, you can run

make check

This will start the server, run a few computations, and shut the server down. In addition, the check script can be executed against a running server by running the following Python command:

python3 tests/ localhost 5555

Token-Based Authentication in Arkouda toc

Arkouda features a token-based authentication mechanism analogous to Jupyter, where a randomized alphanumeric string is generated or loaded at arkouda_server startup. The command to start arkouda_server with token authentication is as follows:

./arkouda_server --authenticate

The generated token is saved to the tokens.txt file which is contained in the .arkouda directory located in the same working directory the arkouda_server is launched from. The arkouda_server will re-use the same token until the .arkouda/tokens.txt file is removed, which forces arkouda_server to generate a new token and corresponding tokens.txt file.

In situations where a user-specified token string is preferred, this can be specified in the ARKOUDA_SERVER_TOKEN environment variable. As is the case with an Arkouda-generated token, the user-supplied token is saved to the .arkouda/tokens.txt file for re-use.

Connecting to Arkouda toc

The client connects to the arkouda_server either by supplying a host and port or by providing a connect_url connect string:

arkouda.connect(server='localhost', port=5555)

When arkouda_server is launched in authentication-enabled mode, clients connect by either specifying the access_token parameter or by adding the token to the end of the connect_url connect string:

arkouda.connect(server='localhost', port=5555, access_token='dcxCQntDQllquOsBNjBp99Pu7r3wDJn')

Note: once a client has successfully connected to an authentication-enabled arkouda_server, the token is cached in the user's $ARKOUDA_HOME .arkouda/tokens.txt file. As long as the arkouda_server token remains the same, the user can connect without specifying the token via the access_token parameter or token url argument.

Logging toc

The Arkouda server features a Chapel logging framework that prints out the module name, function name and line number for all logged messages. An example is shown below:

2021-04-15:06:22:59 [ConcatenateMsg] concatenateMsg Line 193 DEBUG [Chapel] creating pdarray id_4 of type Int64
2021-04-15:06:22:59 [ServerConfig] overMemLimit Line 175 INFO [Chapel] memory high watermark = 44720 memory limit = 30923764531
2021-04-15:06:22:59 [MultiTypeSymbolTable] addEntry Line 127 DEBUG [Chapel] adding symbol: id_4 

Available logging levels are ERROR, CRITICAL, WARN, INFO, and DEBUG. The default logging level is INFO where all messages at the ERROR, CRITICAL, WARN, and INFO levels are printed. The log level can be set globally by passing in the --logLevel parameter upon arkouda_server startup. For example, passing the --logLevel=LogLevel.DEBUG parameter as shown below sets the global log level to DEBUG:

./arkouda_server --logLevel=LogLevel.DEBUG

In addition to setting the global logging level, the logging level for individual Arkouda modules can also be configured. For example, to set MsgProcessing to DEBUG for the purposes of debugging Arkouda array creation, pass the MsgProcessing.logLevel=LogLevel.DEBUG parameter upon arkouda_server startup as shown below:

./arkouda_server --MsgProcessing.logLevel=LogLevel.DEBUG --logLevel=LogLevel.WARN

In this example, the logging level for all other Arkouda modules will be set to the global value WARN.

Type Checking in Arkouda toc

Both static and runtime type checking are becoming increasingly popular in Python, especially for large Python code bases such as those found at dropbox. Arkouda uses mypy for static type checking and typeguard for runtime type checking.

(click to see more)

Enabling runtime as well as static type checking in Python starts with adding type hints, as shown below to a method signature:

def connect(server : str="localhost", port : int=5555, timeout : int=0, 
                           access_token : str=None, connect_url=None) -> None:

mypy static type checking can be invoked either directly via the mypy command or via make:

$ mypy arkouda
Success: no issues found in 16 source files
$ make mypy
python3 -m mypy arkouda
Success: no issues found in 16 source files

Runtime type checking is enabled at the Python method level by annotating the method if interest with the @typechecked decorator, an example of which is shown below:

def save(self, prefix_path : str, dataset : str='array', mode : str='truncate') -> str:

Type checking in Arkouda is implemented on an "opt-in" basis. Accordingly, Arkouda continues to support duck typing for parts of the Arkouda API where type checking is too confining to be useful. As detailed above, both runtime and static type checking require type hints. Consequently, to opt-out of type checking, simply leave type hints out of any method declarations where duck typing is desired.

Environment Variables toc

The various Arkouda aspects (compilation, run-time, client, tests, etc.) can be configured using a number of environment variables (env vars). See the ENVIRONMENT documentation for more details.

Versioning toc

Beginning after tag v2019.12.10 versioning is now performed using Versioneer which determines the version based on the location in git.

An example using a hypothetical tag

git checkout
python -m arkouda |tail -n 2
>> Client Version:

# If you were to make uncommitted changes and repeat the command you might see something like:
python -m arkouda|tail -n 2
>> Client Version:

# If you commit those changes you would see something like
python -m arkouda|tail -n 2
>> Client Version:

In the hypothetical cases above Versioneer tells you the version and how far / how many commits beyond the tag your repo is.

When building the server-side code the same versioning information is included in the build. If the server and client do not match you will receive a warning. For developers this is a useful reminder when you switch branches and forget to rebuild.

# Starting the arkouda when built from tag shows the following in the startup banner 
arkouda server version =

# If you built from an arbitrary branch the version string is based on the derived coordinates from the "closest" tag
arkouda server version = v2019.12.10+1679.abc2f48a

# The .dirty extension denotes a build from uncommitted changes, or a "dirty branch" in git vernacular
arkouda server version = v2019.12.10+1679.abc2f48a.dirty

For maintainers, creating a new version is as simple as creating a tag in the repository; i.e.

git checkout master
git tag
python -m arkouda |tail -n 2
>> Client Version:
git push --tags

Contributing to Arkouda toc

If you'd like to contribute, we'd love to have you! Before jumping in and adding issues or writing code, please see