> For the complete documentation index, see [llms.txt](https://docs.joobq.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.joobq.io/core.md).

# Core Concepts

Understand what a job becomes between enqueueing and completion.

A **job** is a serializable unit of work. A **queue** holds jobs for a configured job type. **Workers** claim work from that queue and run `perform`. Redis stores queued and processing payloads; the worker applies the result through JoobQ's processing APIs.

## The standard job lifecycle

```mermaid
stateDiagram-v2
  [*] --> Enqueued: enqueue
  [*] --> Scheduled: delay
  Scheduled --> Enqueued: due
  Enqueued --> Running: worker claims
  Running --> Completed: perform returns
  Running --> Retrying: exception with retry budget
  Retrying --> Enqueued: backoff elapsed
  Running --> Dead: retries exhausted
  Enqueued --> Expired: expiration reached
  Running --> Expired: expired work detected
  Dead --> Enqueued: eligible DLQ replay
  Completed --> [*]
```

These names follow `JoobQ::Job::Status`. **DLQ** names the dead-letter store, not a separate enum value. Retry and expiry handling also update Redis structures; the diagram is a conceptual lifecycle, not an audit stream of every internal write. A running side effect cannot be undone just by changing its job status.

## Choose the right guide

* [Queues and workers](/core/queues-workers.md): registration, capacity, and process ownership.
* [Retries and dead letters](/core/retries-dlq.md): retry budget, backoff, and safe replay.
* [Scheduling](/core/scheduling.md): delayed jobs and recurring work.
* [Delivery](/core/delivery.md): a separate, opt-in leased API with receipts.

Use [Pro workflows](/pro/workflows.md) when the unit of work is a graph of dependent activities rather than one `perform` call. The same idempotency rules still apply.


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