System dependencies

• Ruby 2.3+
• local PostgreSQL instance
• libpq-dev (when pg gem fails to build native extension)
• local RabbitMQ instance

Database creation

CREATE USER zmora WITH PASSWORD 'szatan';
CREATE DATABASE "zmora-test";
CREATE DATABASE "zmora-ror";
GRANT ALL PRIVILEGES ON DATABASE "zmora-test" to zmora;
GRANT ALL PRIVILEGES ON DATABASE "zmora-ror" to zmora;

Typically you will execute this script from psql console (sudo -u postgres psql).

Setting up development environment (Ubuntu)

Install system packages

sudo apt install ruby postgresql libpq-dev rabbitmq-server

Start services

sudo systemctl start postgresql
sudo systemctl start rabbitmq-server

These services will NOT start automatically after reboot, so you need to start them before development. You can enable services to start automatically by running:

sudo systemctl enable postgresql
sudo systemctl enable rabbitmq-server

Set up database user and create databases

Run sudo -u postgres psql then copy-paste script from the database creation section.

Install bundler and local gems

Run gem install bundler and bin/bundle install --path vendor/bundle.

Run database migrations

Run bin/rails db:migrate RAILS_ENV=development.

Start the server

Run bin/rails s. The server should be accessible from http://localhost:3001.

Retrying failed DB transactions (requeueing judge results)

Judge results consumed from RabbitMQ queue are persistently stored in database. When DB transaction fails (e.g. due to DB unavailability, constraint violation or other errors), source message (judge result) will be moved to error queue (by default tasksResultsError.)

Pending messages can be reprocessed by moving messages from error queue – this is time where RabbitMQ shovel plugin kicks in. To enable it, type:

rabbitmq-plugins enable rabbitmq_shovel rabbitmq_shovel_management

(This command enables GUI management plugin too.)

Now you can move pending messages by running

rabbitmqctl set_parameter shovel results '{"src-uri": "amqp://", "src-queue": "taskResultsError", "dest-uri": "amqp://", "dest-queue": "taskResults", "delete-after": "queue-length"}'

This command should be run periodically in production environment (e.g. by cron.)