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Pefect Orion Database

The Prefect Orion database persists data used by many features of Prefect to persist and track the state of your flow runs, including:

  • Flow and task state
  • Run history
  • Logs
  • Deployments
  • Flow and task run concurrency limits
  • Storage blocks for flow and task results
  • Work queue configuration and status

Currently Prefect Orion supports the following databases:

  • SQLite: The default in Prefect Orion, and our recommendation for lightweight, single-server deployments. SQLite requires essentially no setup.
  • PostgreSQL: Best for connecting to external databases, but does require additional setup (such as Docker). Prefect Orion uses the pg_trgm extension, so it must be installed and enabled.

Using the database

A local SQLite database is the default for Prefect Orion, and a local SQLite database is configured on installation.

When you first install Prefect, your database will be located at ~/.prefect/orion.db.

If at any point in your testing you'd like to reset your database, run the CLI command: 

$ prefect orion database reset -y

This will completely clear all data and reapply the schema.

Configuring the database

To configure the database location, you can specify a connection URL with the PREFECT_ORION_DATABASE_CONNECTION_URL environment variable:

$ export PREFECT_ORION_DATABASE_CONNECTION_URL="sqlite+aiosqlite:////full/path/to/a/location/orion.db"

Configuring a PostgreSQL database

To connect Orion to a PostgreSQL database, you can set the following environment variable:

$ export PREFECT_ORION_DATABASE_CONNECTION_URL="postgresql+asyncpg://postgres:yourTopSecretPassword@localhost:5432/orion"

The above environment variable assumes that:

  • You have a username called postgres
  • Your password is set to yourTopSecretPassword
  • Your database runs on the same host as the Orion instance, localhost
  • You use the default PostgreSQL port 5432
  • Your PostgreSQL instance has a database called orion

If you want to quickly start a PostgreSQL instance that can be used as your Prefect Orion database, you can use the following command that will start a Docker container running PostgreSQL:

$ docker run -d --name orion_postgres -v oriondb:/var/lib/postgresql/data -p 5432:5432 -e POSTGRES_USER=postgres -e POSTGRES_PASSWORD=yourTopSecretPassword -e POSTGRES_DB=orion postgres:latest

The above command:

  • Pulls the latest version of the official postgres Docker image, which is compatible with Prefect 2.
  • Starts a container with the name orion_postgres.
  • Creates a database orion with a user postgres and yourTopSecretPassword password.
  • Mounts the PostgreSQL data to a Docker volume called oriondb to provide persistence if you ever have to restart or rebuild that container.

You can inspect your profile to be sure that the environment variable has been set properly:

$ prefect config view --show-sources

Start the Prefect Orion server and it should from now on use your PostgreSQL database instance:

$ prefect orion start

In-memory databases

One of the benefits of SQLite is in-memory database support.

To use an in-memory SQLite database, set the following environment variable:

$ export PREFECT_ORION_DATABASE_CONNECTION_URL="sqlite+aiosqlite:///file::memory:?cache=shared&uri=true&check_same_thread=false"

In-memory databases for testing only

In-memory databases are only supported by Prefect Orion for testing purposes and are not compatible with multiprocessing.

Database versions

The following database versions are required for use with Prefect:

  • SQLite 3.24 or newer
  • PostgreSQL 13.0 or newer