Runs a library's deferred backfills in the running app.

Add it to the host's supervision tree after the repo, or to the library's PhoenixMountable.children/1:

{PhoenixMountable.Backfill.Runner, migrations: MyLib.Migrations, repo: MyApp.Repo}

On start it runs every pending backfill, batch by batch, recording the cursor after each batch, so a restart resumes where it stopped. On Postgres and MySQL it takes a database lock per backfill, so several nodes can run the runner and each backfill still runs once at a time. A batch that fails marks the backfill failed with the error; it is retried with a backoff.

Options

• :migrations (required), :repo (required), :prefix
• :retry_after — milliseconds before retrying a failed backfill. Defaults to 30_000.