Contributing#

You’re welcome to come and procrastinate with us :)

TL;DR#

$ source ./dev-env

Of course, feel free to read the script before launching it.

This script is intended to be a one-liner that sets up everything you need. It makes the following assumptions:

You’re using MacOS or Linux, and bash or zsh.
You already have python3 available
You have poetry installed
Either you’ve already setup a PostgreSQL database and environment variables (PG*) are set or you have docker-compose available and port 5432 is free.
Either psql and other libpq executables are available in the PATH or they are located in usr/local/opt/libpq/bin (Homebrew).

The dev-env script will add the scripts folder to your $PATH for the current shell, so in the following documentation, if you see scripts/foo, you’re welcome to call foo directly.

Instructions for contribution#

Environment variables#

The export command below will be necessary whenever you want to interact with the database (using the project locally, launching tests, …). These are standard libpq environment variables environment variables, and the values used below correspond to the Docker setup. Feel free to adjust them as necessary (The dev-env script will set them for you).

$ export PGDATABASE=procrastinate PGHOST=localhost PGUSER=postgres PGPASSWORD=password

Create your development database#

The development database can be launched using Docker with a single command. The PostgreSQL database we used is a fresh standard out-of-the-box database on the latest stable version.

$ docker-compose up -d postgres

If you want to try out the project locally, it’s useful to have postgresql-client installed. It will give you both a PostgreSQL console (psql) and specialized commands like createdb we use below.

$ # Ubuntu
$ sudo apt install postgresql-client
$ createdb

$ # MacOS
$ brew install libpq
$ /usr/local/opt/libpq/bin/createdb

Set up your development environment#

The development environment is managed by poetry. It’s a tool that manages dependencies and virtual environments. We also use pre-commit to keep the code clean.

If you don’t already have poetry or pre-commit installed, you can install them with:

$ scripts/bootstrap

This will install pipx if necessary and use it to install poetry and pre-commit.

Then, install Procrastinate with development dependencies in a virtual environment:

$ poetry env use 3.{x}  # Select the Python version you want to use (replace {x})
$ poetry install
$ poetry shell  # Activate the virtual environment

You can check that your Python environment is properly activated:

(venv) $ which python
/path/to/current/folder/.venv/bin/python

Run the project automated tests#

With a running database:

(venv) $ pytest  # Test the code with the current interpreter

If you’re not familiar with Pytest, do yourself a treat and look into this fabulous tool.

To look at coverage in the browser after launching the tests, use:

$ scripts/htmlcov

Keep your code clean#

This project uses pre-commit to keep the code clean. It’s a tool that runs automated checks on your code before you commit it. Install the pre-commit hooks with:

$ pre-commit install

This will keep you from creating a commit if there’s a linting problem.

In addition, an editorconfig file will help your favorite editor to respect procrastinate coding style. It is automatically used by most famous IDEs, such as Pycharm and VS Code.

Write the documentation#

The documentation is written in Markdown and built with Sphinx and MyST. Docstrings are written in reStructuredText (because writing them in MyST is still a bit complicated, it seems).

Build the documentation#

Build with:

$ scripts/docs  # build the html doc
$ scripts/htmldoc  # browse the doc in you browser

If Sphinx’s console output is localized and you would rather have it in English, (which make google-based debugging much easier), use the environment variable export LC_ALL=C.utf-8

Migrations#

Create database migration scripts#

If you make changes to the database structure (procrastinate/sql/schema.sql) you also need to create a corresponding migration script in the procrastinate/sql/migrations directory.

For example, let’s say you want to add a column named extra to the procrastinate_jobs table. You will first edit procrastinate/sql/schema.sql and change the definition of the table to add that column. That would be sufficient for new Procrastinate users, but existing users, whose database already includes Procrastinate objects (tables, indexes, …), need to be able to migrate their existing schema into the new one. For that reason, as a Procrastinate developer, you’ll also need to create a migration script, whose content would look like this:

-- add a column extra to the procrastinate_jobs table
ALTER TABLE procrastinate_jobs ADD COLUMN extra TEXT;

The name of migration scripts must follow a specific pattern:

xx.yy.zz_ab_very_short_description_of_your_changes.sql

xx.yy.zz is the number of the latest released version of Procrastinate. (The latest release is the one marked Latest release on the Procrastinate releases page.) xx, yy and zz must be 2-digit numbers, with leading zeros if necessary. ab is the 2-digit migration script’s serial number, 01 being the first number in the series. And, finally, very_short_description_of_your_changes is a very short description of the changes (wow). It is important to use underscores between the different parts, and between words in the short description.

For example, let’s say the latest released version of Procrastinate is 1.0.1, and that the migrations directory already includes a migration script whose serial number is 01 for that release number. In that case, if you need to add a migration script, its name will start with 01.00.01_02_.

Backward-compatibility#

As a Procrastinate developer, the changes that you make to the Procrastinate database schema must be compatible with the Python code of previous Procrastinate versions.

For example, let’s say that the current Procrastinate database schema includes an SQL function

procrastinate_func(arg1 integer, arg2 text, arg3 timestamp)

that you want to change to

procrastinate_func(arg1 integer, arg2 text)

The straightforward way to do that would be to edit the schema.sql file and just replace the old function by the new one, and add a migration script that removes the old function and adds the new one:

DROP FUNCTION procrastinate_func(integer, text, timestamp);
CREATE FUNCTION procrastinate_func(arg1 integer, arg2 text)
RETURNS INT
...

But if you do that you will break the Procrastinate Python code that uses the old version of the procrastinate_func function. The direct consequence of that is that Procrastinate users won’t be able to upgrade Procrastinate without incurring a service outage.

So when you make changes to the Procrastinate database schema you must ensure that the new schema still works with old versions of the Procrastinate Python code.

Going back to our procrastinate_func example. Instead of replacing the old function by the new one in schema.sql, you will leave the old function, and just add the new one. And your migration script will just involve adding the new version of the function:

CREATE FUNCTION procrastinate_func(arg1 integer, arg2 text)
RETURNS INT
...

The question that comes next is: when can the old version of procrastinate_func be removed? Or more generally, when can the SQL compatibility layer be removed?

The answer is some time after the next major version of Procrastinate!

For example, if the current Procrastinate version is 1.5.0, the SQL compatibility layer will be removed after 2.0.0 is released. The 2.0.0 release will be a pivot release, in the sense that Procrastinate users who want to upgrade from, say, 1.5.0 to 2.5.0, will need to upgrade from 1.5.0 to 2.0.0 first, and then from 2.0.0 to 2.5.0. And they will always migrate the database schema before updating the code.

The task of removing the SQL compatibility layer after the release of a major version (e.g. 2.0.0) is the responsibility of Procrastinate maintainers. More specifically, for the 2.1.0 release, Procrastinate maintainers will need to edit schema.sql and remove the SQL compatibility layer.

But, as a standard developer, when you make changes to the Procrastinate database schema that involves leaving or adding SQL statements for compatibility reasons, it’s a good idea to add a migration script for the removal of the SQL compatibility layer. This will greatly help the Procrastinate maintainers.

For example, let’s say the current released version of Procrastinate is 1.5.0, and you want to change the signature of procrastinate_func as described above. You will add a 1.5.0 migration script (e.g. 01.05.00_01_add_new_version_procrastinate_func.sql) that adds the new version of the function, as already described above. And you will also add a 2.0.0 migration script (e.g. 02.00.00_01_remove_old_version_procrastinate_func.sql) that takes care of removing the old version of the function:

DROP FUNCTION procrastinate_func(integer, text, timestamp);

In this way, you provide the new SQL code, the compatibility layer, and the migration for the removal of the compatibility layer.

Note

The migration scripts that remove the SQL compatibility code are to be added to the future_migrations directory instead of the migrations directory. And it will be the responsibility of Procrastinate maintainers to move them to the migrations directory after the next major release.

Migration tests#

The continuous integration contains tests that will check that the schema and the migrations succeed in producing the same database structure. The migration tests are included in the normal test suite, but you can run them specifically with:

(venv) $ pytest tests/migration

Try our demos#

See the demos page for instructions on how to run the demos (Demos).

Use Docker for Procrastinate development#

In the development setup described above, Procrastinate, its dependencies, and the development tools (tox, black, pytest, etc.) are installed in a virtual Python environment on the host system. Alternatively, they can be installed in a Docker image, and Procrastinate and all the development tools can be run in Docker containers. Docker is useful when you can’t, or don’t want to, install system requirements.

This section shows, through docker-compose command examples, how to test and run Procrastinate in Docker.

Build the procrastinate Docker image:

$ export UID GID
$ docker-compose build procrastinate

Run the automated tests:

$ docker-compose run --rm procrastinate pytest

Docker Compose is configured (in docker-compose.yml) to mount the local directory on the host system onto /src in the container. This means that local changes made to the Procrastinate code are visible in Procrastinate containers.

The UID and GID environment variables are set and exported for the Procrastinate container to be run with the current user id and group id. If not set or exported, the Procrastinate container will run as root, and files owned by root may be created in the developer’s working directory.

In the definition of the procrastinate service in docker-compose.yml the PROCRASTINATE_APP variable is set to procrastinate_demo.app.app (the Procrastinate demo application). So procrastinate commands run in Procrastinate containers are always run as if they were passed --app procrastinate_demo.app.app.

Run the procrastinate command :

$ docker-compose run --rm procrastinate procrastinate -h

Apply the Procrastinate database schema:

$ docker-compose run --rm procrastinate procrastinate schema --apply

Run the Procrastinate healthchecks:

$ docker-compose run --rm procrastinate procrastinate healthchecks

Start a Procrastinate worker (-d used to start the container in detached mode):

$ docker-compose up -d procrastinate

Run a command (bash here) in the Procrastinate worker container just started:

$ docker-compose exec procrastinate bash

Watch the Procrastinate worker logs:

$ docker-compose logs -ft procrastinate

Use the procrastinate defer command to create a job:

$ docker-compose run --rm procrastinate procrastinate defer procrastinate_demo.tasks.sum '{"a":3, "b": 5}'

Or run the demo main file:

$ docker-compose run --rm procrastinate python -m procrastinate_demo

Stop and remove all the containers (including the postgres container):

$ docker-compose down

Wait, there are `async` and `await` keywords everywhere!?#

Yes, in order to provide both a synchronous and asynchronous API, Procrastinate needs to be asynchronous at core.

When possible, we’re trying to avoid duplicating code, with designs such as “hoisting the I/O”.

Core contributor additional documentation#

Issues#

Please remember to tag Issues with appropriate labels.

Pull Requests#

PR labels help pre-filling the next release draft. They’re not mandatory, but releasing will be easier if they’re present.

Release a new version#

Draft a new release, Generate release notes, add ## Migrations. Make relevant edits to the changelog, (see TODO). Click on Release, that’s it, the rest is automated. This works with pre-release too.

When creating the release, GitHub will save the release info and create a tag with the provided version. The new tag will be seen by GitHub Actions, which will then create a wheel (using the tag as version number, thanks to poetry-dynamic-versioning), and push it to PyPI (using Trusted publishing). That tag should also trigger a ReadTheDocs build, which will read GitHub releases (thanks to our changelog extension) which will write the changelog in the published documentation (transformed from Markdown to RestructuredText).

After a new major version is released (e.g. 2.0.0), in preparation for the next minor release (2.1.0), the migration scripts in the future_migrations directory that remove the SQL compatibility code must be moved to the migrations directory. And the schema.sql file must be updated accordingly.