# `DDD.Outbox.Retention`
[🔗](https://github.com/blackuprise/vicander/blob/v0.1.1/lib/ddd/events/outbox/retention.ex#L1)

Deleting old events from the outbox, so `domain_events` doesn't grow forever.

    DDD.Outbox.Retention.prune(MyApp.Repo, older_than_days: 30)
    # => {:ok, %{deleted: 1204}}

Or from the command line: `mix vic.outbox.prune --older-than-days 30`. To prune on a schedule,
give the supervisor `retention: [older_than_days: 30]` (see `DDD.Supervisor`) or call
`prune/2` from your own scheduler.

What is deleted, once it is older than the limit:

  * events that were **published** (every handler succeeded or rejected them), together with
    their delivery records
  * dead letters that were **resolved** (discarded or replayed)

What is never deleted: events still waiting, events being retried, and dead letters nobody has
resolved.

**Pruning is a choice with a cost.** A projection's `rebuild/0` replays the events in this
table; once the old ones are gone, a rebuild can only rebuild from what is left. Prune after
the longest history you are willing to rebuild from, or archive the table first.

# `prune`

```elixir
@spec prune(module(), keyword()) :: {:ok, %{deleted: non_neg_integer()}}
```

Delete old events. Options:

  * `:older_than_days` - (required) how old, in days, an event must be. There is no default:
    deleting is not something to do by accident.
  * `:batch` - rows deleted per statement (default 5000), so a big backlog doesn't hold
    long locks

Returns `{:ok, %{deleted: count}}`.

---

*Consult [api-reference.md](api-reference.md) for complete listing*