A PostgreSQL-based oracle for leader election using database leases.

Uses a single table with atomic upserts to manage leadership leases. The table is created automatically (no migrations needed).

Options

• :repo (required) - an Ecto.Repo module
• :duration (optional, default 30) - lease duration in seconds
• :crown_name (injected by Crown) - used as the lock name

Example

{Crown,
 name: :my_worker,
 oracle: {Crown.Oracles.PostgresLease, repo: MyApp.Repo},
 child_spec: MyApp.SingletonWorker}