# Changelog

All notable changes to `Oban` are documented here.

_🌟 Looking for changes to Web or Pro? Check the [Oban.Pro Changelog][opc] or
the [Oban.Web Changelog][owc]. 🌟_


## [2.10.1] — 2021-11-09

### Removed

- [Oban.Telemetry] Remove the customizable prefix for telemetry events in favor
  of workarounds such as `keep/drop` in [Telemetry Metrics][tel-fil].


## [2.10.0] — 2021-11-09

**Retired: This version is retired and superseded by v2.10.1 due to the
immediate reversion of telemetry prefixes**

### Added

- [Oban.Telemetry] Add customizable prefix for all telemetry events.

  For example, a telemetry prefix of `[:my_app, :oban]` would span job start
  telemetry events as `[:my_app, :oban, :job, :start]`. The default is
  `[:oban]`, which matches the existing functionality.

### Fixed

- [Oban.Plugins.Stager] Use the notifier to broadcast inserted and available
  jobs rather than inlining them into a Postgres query.

  With this change the notifier is entirely swappable and there **isn't any
  reason to use the `Repeater` plugin in production**.

- [Oban.Plugins.Cron] Validate job options on init.

  Providing invalid job args in the cron tab, e.g. `priority: 5` or `unique:
  []`, wasn't caught until runtime. At that point each insert attempt would
  fail, crashing the plugin.

- [Oban.Queue.Producer] Prevent crashing on exception formatting when a job
  exits without a stacktrace, most notably with `{:EXIT, pid}`.

- [Oban.Testing] Return invalid results from `perform_job`, rather than always
  returning `nil`.

- [Oban] Validate that a queue exists when controlling or checking locally, e.g.
  calls to `Oban.check_queue` or `Oban.scale_queue`.

- [Oban.Telemetry] Use module capture for telemetry logging to prevent warnings.

## [2.9.2] — 2021-09-27

- [Oban] Loosen telemetry requirement to allow either `0.4` or `1.0` without
  forcing apps to use an override.

## [2.9.1] — 2021-09-23

### Fixed

- [Oban] Correctly handle `prefix` in `cancel_job` and `cancel_all_jobs`.

- [Oban] Safely guard against empty changeset lits passed to `insert_all/2,4`.

## [2.9.0] — 2021-09-15

### Optionally Use Meta for Unique Jobs

It's now possible to use the `meta` field for unique jobs. Unique jobs have
always supported `worker`, `queue`, and `args` fields. That was flexible, but
forced applications to put ad-hoc unique values in `args` when they should
really be in `meta`.

The `meta` field supports `keys`, just like `args`. That makes it possible to
use highly efficient fingerprint style uniqueness (and possibly drop the index
on `args`, if desired).

Here's an example of using a single "fingerprint" key in `meta` for uniqueness:

defmodule MyApp.FingerprintWorker do
  use Oban.Worker, unique: [fields: [:worker, :meta], keys: [:fingerprint]]

  @impl Worker
  def new(args, opts) do
    fingerprint = :erlang.phash2(args)

    super(args, Keyword.put(opts, :meta, %{fingerprint: fingerprint}))

For backward compatiblity `meta` isn't included in unique `fields` by default.

### Expanded Start and Scale Options

After extensive refactoring to queue option management and validation, now it's
possible to start and scale queues with all supported options. Previously
start/stop functions only supported the `limit` option for dynamic scaling,
reducing runtime flexibility considerably.

Now it's possible to start a queue in the paused state:

Oban.start_queue(queue: :dynamic, paused: true)

Even better, for apps that use an alternative engine like the SmartEngine from
Oban Pro, it's possible to start a dynamic queue with options like global
concurrency or rate limiting:

Oban.start_queue(queue: :dynamic, local_limit: 10, global_limit: 50)

All options are also passed through `scale_queue`, locally or globally, even
allowing you to reconfigure a feature like rate limiting at runtime:

Oban.scale_queue(queue: :dynamic, rate_limit: [allowed: 50, period: 60])

### Added

- [Oban] Add `Oban.cancel_all_jobs/1,2` to cancel multiple jobs at once, within
  an atomic transaction. The function accepts a `Job` query for complete control
  over which jobs are cancelled.

- [Oban] Add `Oban.retry_all_jobs/1,2` to retry multiple jobs at once, within an
  atomic transaction. Like `cancel_all_jobs`, it accepts a query for
  fine-grained control.

- [Oban] Add `with_limit` option to `drain_queue/2`, which controls the number
  of jobs that are fetched and executed concurrently. When paired with
  `with_recursion` this can drastically speed up interdependent job draining,
  i.e. workflows.

- [Oban.Telemetry] Add telemetry span events for all engine and notifier
  actions. Now all database operations are covered by spans.

- [Oban.Migrations] Add `create_schema` option to prevent automatic schema
  creation in migrations.

### Changed

- [Oban] Consistently include a `:snoozed` count in `drain_queue/2` output.
  Previously the count was only included when there was at least one snoozed

- [Oban.Testing] Default to `attempt: 1` for `perform_job/3`, as a worker's
  `perform/1` would never be called with `attempt: 0`.

### Fixed

- [Oban.Queue.Supervisor] Change supervisor strategy to `:one_for_all`.

  Queue supervisors used a `:rest_for_one` strategy, which allowed the task
  supervisor to keep running when a producer crashed. That allowed duplicate
  long-lived jobs to run simultaneously, which is a bug in itself, but could
  also cause `attempt > max_attempts` violations.

- [Oban.Plugins.Cron] Start step ranges from the minimum value, rather than for
  the entire set. Now the range `8-23/4` correctly includes `[8, 12, 16, 20]`.

- [Oban.Plugins.Cron] Correcly parse step ranges with a single value, e.g. `0 1/2 * * *`

- [Oban.Telemetry] Comply with `:telemetry.span/3` by exposing errors as `reason` in metadata

## [2.8.0] — 2021-07-30

### Time Unit Scheduling

It's now possible to specify a unit for `:schedule_in`, rather than always
assuming seconds. This makes it possible to schedule a job using clearer
minutes, hours, days, or weeks, e.g. `schedule_in: {1, :minute}` or
`schedule_in: {3, :days}`.

### Changed

- [Oban.Testing] Accept non-map args to `perform_job/3` for compatibility with
  overridden `` callbacks.

- [Oban.Queue.Producer] Include some jitter when scheduling queue refreshes to
  prevent queues from refreshing simultaneously. In extreme cases, refresh
  contention could cause producers to crash.

### Fixed

- [Oban.Queue.Executor] Restore logged warnings for unexpected job results by
  retaining the `safe` flag during normal execution.

- [Oban.Plugins.Gossip] Catch and discard unexpected messages rather than
  crashing the plugin.

- [Oban.Testing] Eliminate dialyzer warnings by including `repo` option in
  the `Oban.Testing.perform_job/3` spec.

## [2.7.2] — 2021-06-10

### Fixed

- [Oban.Plugins.Pruner] Consider `cancelled_at` or `discarded_at` timestamps
  when querying prunable jobs. The previous query required an `attempted_at`
  value, even for `cancelled` or `discarded` jobs. If a job was cancelled before
  it was attempted then it wouldn't ever be pruned.

- [Oban.Plugins.Gossip] Correct exit handling during safe checks. Occasionally,
  producer checks time out and the previous `catch` block didn't handle exits

## [2.7.1] — 2021-05-26

### Fixed

- [Oban.Telemetry] Restore the `:job` key to `[:oban, :job, :start]` events. It
  was mistakenly removed during a refactoring.

## [2.7.0] — 2021-05-25

### Pluggable Notifier

The PubSub functionality Oban relies on for starting, stopping, scaling, and
pausing queues is now pluggable. The previous notifier was hard-coded to use
Postgres for PubSub via `LISTEN/NOTIFY`. Unfortunately, `LISTEN/NOTIFY` doesn't
work for PG Bouncer in "Transaction Mode." While relatively few users run in
"Transaction Mode," it is increasingly common and deserved a work-around.

`Oban.Notifier` defines a minimal behaviour and Oban ships with a default
implementation, `Oban.PostgresNotifier`, based on the old `LISTEN/NOTIFY`
module. You can specify a different notifier in your Oban configuration:

config :my_app, Oban,
  notifier: MyApp.CustomNotifier,
  repo: MyApp.Repo,

An alternate [`pg/pg2` based notifier][pgn] is available in Oban Pro.

[pgn]: pg.html

### Replacing Opts on Unique Conflict

The `replace_args` option for updating args on unique conflict is replaced with
a highly flexible `replace` option. Using `replace`, you can update any job
field when there is a conflict. Replace works for any of the following fields:
`args`, `max_attempts`, `meta`, `priority`, `queue`, `scheduled_at`, `tags`,

For example, to change the `priority` to 0 and increase `max_attempts` to 5 when
there is a conflict:

  max_attempts: 5,
  priority: 0,
  replace: [:max_attempts, :priority]

Another example is bumping the scheduled time to 1 second in the future on
conflict. Either `scheduled_at` or `schedule_in` values will work, but the
replace option is always `scheduled_at`.

```elixir, schedule_in: 1, replace: [:scheduled_at])

### Added

- [Oban.Job] A new `conflict?` field indicates whether a unique job conflicted
  with an existing job on insert.

- [Oban.Telemetry] Always populate the `unsaved_error` field for `error` or
  `discard` events. Previously, the field was empty for `discard` events.

- [Oban.Queue.Engine] Define a `cancel_job/2` callback in the engine and
  move cancellation from the query module to the `BasicEngine`.

### Changed

- [Oban.Testing] Thanks to a slight refactoring, the `perform_job/3` helper now
  emits the same telemetry events that you'd have in production. The refactoring
  also exposed and fixed an inconsistency around invalid snooze handlers.

- [Oban.Testing] Expose `Testing.all_enqueued/0`, an alternate clause that
  doesn't require any options. This new clause makes it possible to check for
  any enqueued jobs without filters.

- [Oban.Plugins.Stager] Limit the number of jobs staged at one time to prevent
  timeout errors while staging a massive number of jobs.

### Fixed

- [Oban.Repo] Respect ongoing transactions when using `get_dynamic_repo`. Prior
  to this fix, calls that use `Oban.Repo`, such as `Oban.insert/2`, could use a
  different repo than the one used in the current transaction.

## [2.6.1] — 2021-04-02

### Fixed

- [Oban.Drainer] Always use the `BasicEngine` for draining, regardless of the
  currently configured engine.

## [2.6.0] — 2021-04-02

_🌟 Web and Pro users should check the [v2.6 upgrade guide][v26ug] for a
complete walkthrough._

### Pluggable Queue Engines

Queue producers now use an "engine" callback module to manage demand and work
with the database. The engine provides a clean way to expand and enhance the
functionality of queue producers without modifying the solid foundation of queue
supervision trees. Engines make enhanced functionality such as global
concurrency, local rate limiting and global rate limiting possible!

The `BasicEngine` is the default, and it retains the _exact_ functionality of
previous Oban versions. To specify the engine explicitly, or swap in an
alternate engine, set it in your configuration:

config :my_app, Oban,
  engine: Oban.Queue.BasicEngine,

See the [v2.6 upgrade guide][v26ug] for instructions on swapping in an alternate

### Recursive Queue Draining

The ever-handy `Oban.drain_queue/1,2` function gained a new `with_recursion`
option, which makes it possible to test jobs that _insert more jobs_ when they
execute. When `with_recursion` is enabled the queue will keep executing until no
jobs are available. It even composes with `with_scheduled`!

In practice, this is especially useful for testing dependent workflows.

### Gossip Plugin for Queue Monitoring

The new gossip plugin uses PubSub to efficiently exchange queue state
information between all interested nodes. This allows Oban instances to
broadcast state information regardless of which engine they are using, and
without storing anything in the database.

See the [v2.6 upgrade guide][v26ug] for details on switching to the gossip

[v26ug]: v2-6.html

### Added

- [Oban.Job] Inject the current conf into the jobs struct as virtual field,
  making the complete conf available within `perform/1`.

- [Oban.Notifier] Add `unlisten/2`, used to stop a process from receiving
  notifications for one or more channels.

### Changed

- [Oban.Telemetry] Stop emitting circuit events for queue producers. As
  producers no longer poll, the circuit breaker masked real errors more than it
  guarded against sporatic issues.

- [Oban.Telemetry] Delay `[:oban, :supervisor, :init]` event until the complete
  supervision tree finishes initialization.

- [Oban.Migration] Stop creating an `oban_beats` table entirely.

### Fixed

- [Oban.Plugins.Cron] Prevent schedule overflow right before midnight

## [2.5.0] — 2021-02-26

### Top of the Minute Cron

Rather than scheduling cron evaluation 60 seconds after the server starts,
evaluation is now scheduled at the top of the next minute. This yields several

- More predictable timing for cron jobs now that they are inserted at the top of
  the minute. Note that jobs may execute later depending on how busy queues are.
- Minimize contention between servers inserting jobs, thanks to the transaction
  lock acquired by each plugin.
- Prevent duplicate inserts for jobs that omit the `completed` state (when
  server start time is staggered the transaction lock has no effect)

### Repeater Plugin for Transaction Pooled Databases

Environments that can't make use of PG notifications, i.e. because they use
PgBouncer with transaction pooling, won't process available jobs reliably. The
new `Repeater` plugin provides a workaround that simulates polling functionality
for producers.

Simply include the `Repeater` in your plugin list:

config :my_app, Oban,
  plugins: [

### Include Perform Result in Job Telemetry Metadata

The metadata for `[:oban, :job, :stop]` telemetry events now include the job's
`perform/1` return value. That makes it possible to extract job output from
other processes:

def handle_event([:oban, :job, :stop], _timing, meta, _opts) do
  IO.inspect(meta.result, label: "return from #{meta.job.worker}")


### Added

- [Oban] Support a changeset function in addition to a changeset in
  `insert_all/4`. Inserting jobs within a multi is even more powerful.

- [Oban.Queue.Executor] Stash a timed job's pid to enable inner process
  messaging, notably via telemetry events.

### Changed

- [Oban] Upgrade minimum Elixir version from 1.8 to 1.9.

- [Oban.Plugins.Cron] Individually validate crontab workers and options,
  providing more descriptive errors at the collection and entry level.

- [Oban] Simplify the job cancelling flow for consistency. Due to race
  conditions it was always possible for a job to complete before it was
  cancelled, now that flow is much simpler.

- [Oban.Queue.Producer] Replace dispatch cooldown with a simpler debounce

- [Oban.Plugins.Stager] Limit the number of notify events to one per queue,
  rather than one per available job.

### Fixed

- [Oban.Queue.Producer] Handle unclean exits without an error and stack, which
  prevents "zombie" jobs. This would occur after multiple hot upgrades when the
  worker module changed, as the VM would forcibly terminate any processes
  running the old modules.

- [Oban] Specify that the `changeset_wrapper` type allows keys other than
  `:changesets`, fixing a dialyzer type mismatch.

### Removed

- [Oban] Remove the undocumented `version/0` function in favor of using the
  standard `Application.spec/2`

## [2.4.3] — 2021-02-07

### Fixed

- [Oban.Telemetry] Use `conf` rather than `config` in meta for `:job` and
  `:circuit` telemetry events.

## [2.4.2] — 2021-01-28

### Fixed

- [Oban.Plugins.Stager] Notify queues of all available jobs, not only jobs that
  were most recently staged. In some circumstances, such as reboot or retries,
  jobs are available without previously being scheduled.

## [2.4.1] — 2021-01-27

### Fixed

- [Oban.Migrations] Correctly migrate up between sequential versions. The V10
  migration adds check constraints, which can't be re-run safely. An attempted
  work-around prevented re-runs, but broke sequential upgrades like 9->10.

- [Oban.Queue.Producer] Kick off an initial dispatch to start processing
  available jobs on startup, to compensate for a lack of incoming jobs or

- [Oban.Plugins.Stager] Keep rescheduling staging messages after the initial

## [2.4.0] — 2021-01-26

### Centralized Stager Plugin

Queue producers no longer poll every second to stage scheduled jobs. Instead,
the new `Oban.Plugins.Stager` plugin efficiently handles staging from a single
location. This reduces overall load on the BEAM and PostgreSQL, allowing apps to
easily run hundreds of queues simultaneously with little additional overhead.

In a test with a single Ecto connection and **512 queues** the CPU load went
from 60.0% BEAM / 21.5% PostgreSQL in v2.3.4 to 0.5% BEAM / 0.0% PostgreSQL.

The stager plugin is automatically injected into Oban instances and there isn't
any additional configuration necessary. However, if you've set a `poll_interval`
for Oban or an individual queue you can safely remove it.

### Overhauled Cron

The CRON parser is entirely rewritten to be simpler and _dramatically_ smaller.
The previous parser was built on `nimble_parsec` and while it was fast, the
compiled parser added ~5,500LOC to the code base. Thanks to a suite of property
tests we can be confident that the new parser behaves identically to the
previous one, and has much clearer error messages when parsing fails.

Along with a new parser the `crontab` functionality is extracted into the
`Oban.Plugins.Cron` plugin. For backward compatibility, top-level `crontab` and
`timezone` options are transformed into a plugin declaration. If you'd like to
start configuring the plugin directly change your config from:

    config :my_app, Oban,
      crontab: [{"* * * * *", MyApp.Worker}],
      timezone: "America/Chicago"

To this:

    config :my_app, Oban,
      plugins: [
         crontab: [{"* * * * *", MyApp.Worker}],
         timezone: "America/Chicago"}

The plugin brings a cleaner implementation, simplified supervision tree, and
eliminates the need to set `crontab: false` in test configuration.

### Improved Indexes for Unique Jobs

Applications may have thousands to millions of completed jobs in storage. As the
table grows the performance of inserting unique jobs can slow drastically. A new
V10 migration adds necessary indexes, and paired with improved query logic it
alleviates insert slowdown entirely.

For comparison, a local benchmark showed that in v2.3.4 inserting a unique job
into a table of 1 million jobs runs around 4.81 IPS. In v2.4.0 it runs at 925.34
IPS, nearly **200x faster**.

The V10 migration is optional. If you decide to migrate, first create a new

mix ecto.gen.migration upgrade_oban_jobs_to_v10

Next, call `Oban.Migrations` in the generated migration:

defmodule MyApp.Repo.Migrations.UpdateObanJobsToV10 do
  use Ecto.Migration

  def up do
    Oban.Migrations.up(version: 10)

  def down do
    Oban.Migrations.down(version: 9)

### Added

- [Oban] Add `[:oban, :supervisor, :init]` event emitted when an Oban supervisor

- [Oban.Telemetry] Wrap built-in plugins with telemetry spans and consistently
  include `conf` in all telemetry events.

- [Oban.Config] Improve the error messages raised during initial validation.
  Also, the `Config` module is now public with light documentation.

- [Oban.Testing] Support specifying a default prefix for all test assertions.
  This comes with improved assertion messages that now include the prefix.

- [Oban.Repo] Add `delete/3` as a convenient wrapper around

- [Oban.Job] New check constraints prevent inserting jobs with an invalid
  `priority`, negative `max_attempts` or an `attempt` number beyond the maximum.

### Changed

- [Oban.Telemetry] Deprecate and replace `span/3` usage in favor of the official
  `:telemetry.span/3`, which wasn't available when `span/3` was implemented.

### Fixed

- [Oban] Inspect the error reason for a failed `insert!/2` call before it is
  raised as an error. When `insert!/2` was called in a transaction the error
  could be `:rollback`, which wasn't a valid error.

## [2.3.4] — 2020-12-02

### Fixed

- [Oban.Worker] Update `from_string/1` to correctly work with modules that
  weren't loaded.

## [2.3.3] — 2020-11-10

### Changed

- [Oban.Migration] Conditionally skip altering `oban_job_state` if the
  `cancelled` state is already present. This allows for a smoother upgrade path
  for users running PG < 12. See the notes for v2.3.0 for more details.

## [2.3.2] — 2020-11-06

### Fixed

- [Oban.Migration] Restore indexes possibly removed by changing
  `oban_job_state`. This only applies to PG older than version 12.

- [Oban.Plugins.Pruner] Prune `cancelled` jobs along with `completed` or

## [2.3.1] — 2020-11-06

### Changed

- [Oban.Migration] Conditionally alter `oban_job_state` if the PG version is 12
  or greater. This is **vastly** faster than the renaming, adding and dropping
  required for older PG versions.

## [2.3.0] — 2020-11-06

**Migration Required (V9)**

Migration V9 brings the new `cancelled` state, a `cancelled_at` column, and job

Older versions of PostgreSQL, prior to version 12, don't allow altering an enum
within a transaction. If you're running an older version and want to prevent a
table rewrite you can add the new cancelled at state before running the V9

Create a migration with `@disable_ddl_transaction true` declared and run the
command `ALTER TYPE oban_job_state ADD VALUE IF NOT EXISTS 'cancelled'`. The V9
migration will see that the cancelled value exists and won't attempt to modify
the enum.

After you've sorted adding the `cancelled` state (or ignored the issue, because
you're either running PG >= 12 or don't have many jobs retained), generate a new

mix ecto.gen.migration upgrade_oban_jobs_to_v9

Next, call `Oban.Migrations` in the generated migration:

defmodule MyApp.Repo.Migrations.UpdateObanJobsToV9 do
  use Ecto.Migration

  def up do
    Oban.Migrations.up(version: 9)

  def down do
    Oban.Migrations.down(version: 8)

Oban will manage upgrading to V9 regardless of the version your application is
currently using, and it will roll back a single version.

### Added

- [Oban.Job] Add new `meta` field for storing arbitrary job data that isn't
  appropriate as `args`.

- [Oban.Job] Introduce a `cancelled` state, along with a new `cancelled_at`
  timestamp field. Cancelling a job via `Oban.cancel_job` (or via Oban Web) now
  marks the job as `cancelled` rather than `discarded`.

- [Oban.Worker] Add `from_string/1` for improved worker module resolution.

- [Oban.Telemetry] Pass the full `job` schema in telemetry metadata, not only
  select fields. Individual fields such as `args`, `worker`, etc. are still
  passed for backward compatibility. However, their use is deprecated and they
  are no longer documented.

### Fixed

- [Oban.Notifier] Fix resolution of `Oban.Notifier` child process in `Oban.Notifier.listen/2`.

- [Oban.Queue.Producer] Fix cancelling jobs without a supervised process. In
  some circumstances, namely a hot code upgrade, the job's process could
  terminate without the producer tracking it and leave the job un-killable.

- [Oban] Only convert invalid changesets into `ChangesetError` from `insert!`.
  This prevents unexpected errors when `insert!` is called within a transaction
  after the transaction has rolled back.

## [2.2.0] — 2020-10-12

### Added

- [Oban] Replace local dynamically composed names with a registry. This
  dramatically simplifies locating nested children, avoids unnecessary atom
  creation at runtime and improves the performance of config lookups.

- [Oban.Repo] The new `Oban.Repo` module wraps interactions with underlying Ecto
  repos. This ensures consistent prefix and log level handling, while also
  adding full dynamic repo support.

  The `Oban.Repo` wrapper should be used when authoring plugins.

- [Oban.Job] Augment the unique keys option with `replace_args`, which allows
  enqueuing a unique job and replacing the args subsequently. For example, given
  a job with these args:

    %{some_value: 1, id: 123}

  Attempting to insert a new job:

    %{some_value: 2, id: 123}
    |> 10, replace_args: true unique: [keys: [:id]])
    |> Oban.insert()

  Will result in a single job with the args:

    %{some_value: 2, id: 123}

- [Oban] Add `Oban.check_queue/1,2` for runtime introspection of a queue's
  state. It displays a compactly formatted breakdown of the queue's
  configuration, a list of running jobs, and static identity information.

- [Oban] Add `Oban.retry_job/1,2`, used to manually retry a `discarded` or
  `retryable` job.

- [Oban.Telemetry] Include `tags` as part of the metadata for job events.

### Changed

- [Oban.Worker] The default backoff algorithm now includes a small amount of
  jitter. The jitter helps prevent jobs that fail simultaneously from repeatedly
  retrying together.

### Fixed

- [Oban.Job] Don't include `discarded` state by default when accounting for

- [Oban.Cron] Fully support weekday ranges in crontab expressions. Previously,
  given a weekday range like `MON-WED` the parser would only retain the `MON`.

## [2.1.0] — 2020-08-21

### Fixed

- [Oban.Testing] Modify the behaviour checking in `perform_job/3` so that it
  considers all behaviours.

- [Oban.Plugins.Pruner] Use distinct names when running multiple Oban instances
  in the same application.

### Added

- [Oban] In addition to the standard queue-name / limit keyword syntax it is now
  possible to define per-queue options such as `:poll_interval`,
  `:dispatch_cooldown`, `:paused`, and even override the `:producer` module.

- [Oban] Cancelling a running job now records an error on the job if it was
  _running_ at the time it was cancelled.

- [Oban.Job] Allow using `:discarded` as a unique state and expose all possible
  states through `Oban.Job.states/0`.

- [Oban.Worker] Allow returning `{:discard, reason}` from `perform/1`, where the
  reason is recorded in the job's errors array. If no reason is provided then a
  default of "None" is used. All discarded jobs will have an error now, whether
  discarded manually or automatically.

- [Oban.Job] Add support for uniqueness across sub-args with the `:keys`
  attribute. This makes it possible to only use a few values from a job to
  determine uniqueness. For example, a job that includes a lot of metadata but
  must be considered unique based on a `:url` field can specify `keys: [:url]`.

### Changed

- [Oban.Worker] Wrap `{:error, reason}` and `{:discard, reason}` in a proper
  `Oban.PerformError` exception with a customized message. This ensures that the
  `:error` value passed to telemetry handlers is an exception and not a raw

- [Oban.Worker] Wrap job timeouts in `Oban.TimeoutError` with a customized
  message indicating the worker and timeout value. This replaces the raw
  `:timeout` atom that was reported before.

- [Oban.Worker] Wrap caught exits and throws in `Oban.CrashError` with a
  formatted message. This means the `:error` value passed to telemetry is
  _always_ a proper exception and easier to report.

- [Oban.Worker] Stop reporting internal stacktraces for timeouts, discards or
  error tuples. The stacktrace was useless and potentially misleading as it
  appeared that the error originated from Oban rather than the worker module.

## [2.0.0] — 2020-07-10

No changes from [2.0.0-rc.3][].

## [2.0.0-rc.3] — 2020-07-01

### Fixed

- [Oban.Crontab.Cron] Do not raise an `ArgumentError` exception when the
  crontab configuration includes a step of 1, which is a valid step value.

- [Oban.Telemetry] Correctly record `duration` and `queue_time` using native
  time units, but log them using microseconds. Previously they used a mixture of
  native and microseconds, which yielded inconsistent values.

### Added

- [Oban.Telemetry] Include job `queue_time` in the default logger output.

### Changed

- [Oban.Plugins.Pruner] The `FixedPruner` is renamed to `Pruner` and allows
  users to configure the `max_age` value. This partially reverses the breaking
  change imposed by the move from `prune` to the `FixedPruner` plugin, though
  there isn't any support for `max_len` or dynamic pruning.

## [2.0.0-rc.2] — 2020-06-23

### Breaking Changes

- [Oban] The interface for `pause_queue/2`, `resume_queue/2` and `scale_queue/3`
  now matches the recently changed `start_queue/2` and `stop_queue/2`. All queue
  manipulation functions now have a consistent interface, including the ability
  to work in `:local_only` mode. See the notes around `start_queue/2` and
  `stop_queue/2` in [2.0.0-rc.1][] for help upgrading.

- [Oban] Replace `drain_queue/3` with `drain_queue/2`, which now has an
  interface consistent with the other `*_queue/2` operations.

  Where you previously called `drain_queue/2,3` like this:

    Oban.drain_queue(:myqueue, with_safety: false)

  You'll now it with options, like this:

    Oban.drain_queue(queue: :myqueue, with_safety: false)

### Fixed

- [Oban.Breaker] Prevent connection bomb when the Notifier experiences repeated

- [Oban.Queue.Executor] Fix error reporting when a worker fails to resolve.

- [Oban.Telemetry] Stop logging the `:error` value for circuit trip events. The
  error is a struct that isn't JSON encodable. We include the normalized
  Postgrex / DBConnection message already, so the error is redundant.

### Added

- [Oban.Crontab] Add `@reboot` special case to crontab scheduling

- [Oban.Telemetry] Add new `:producer` events for descheduling and dispatching
  jobs from queue producers.

### Removed

- [Oban] Removed `kill_job/2`, which wasn't as flexible as `Oban.cancel_job/2`.

  Use `Oban.cancel_job/2` instead to safely discard scheduled jobs or killing
  executing jobs.

## [2.0.0-rc.1] — 2020-06-12

### Breaking Changes

- [Oban.Config] The `:verbose` setting is renamed to `:log`. The setting started
  off as a simple boolean, but it has morphed to align with the log values
  accepted by calls to `Ecto.Repo`.

  To migrate, replace any `:verbose` declarations:

    config :my_app, Oban,
      verbose: false,

  With use of `:log` instead:

    config :my_app, Oban,
      log: false,

- [Oban] The interface for `start_queue/3` is replaced with `start_queue/2` and
  `stop_queue/2` no longer accepts a queue name as the second argument. Instead,
  both functions now accept a keyword list of options. This enables the new
  `local_only` flag, which allows you to dynamically start and stop queues only
  for the local node.

  Where you previously called `start_queue/2,3` or `stop_queue/2` like this:

    :ok = Oban.start_queue(:myqueue, 10)
    :ok = Oban.stop_queue(:myqueue)

  You'll now call them with options, like this:

    :ok = Oban.start_queue(queue: :myqueue, limit: 10)
    :ok = Oban.stop_queue(queue: :myqueue)

  Or, to only control the queue locally:

    :ok = Oban.start_queue(queue: :myqueue, limit: 10, local_only: true)
    :ok = Oban.stop_queue(queue: :myqueue, local_only: true)

## [2.0.0-rc.0] — 2020-06-03

### Breaking Changes

- [Oban.Worker] The `perform/2` callback is replaced with `perform/1`, where the
  only argument is an `Oban.Job` struct. This unifies the interface for all
  `Oban.Worker` callbacks and helps to eliminate confusion around pattern
  matching on arguments.

  To migrate change all worker definitions from accepting an `args` map and a
  `job` struct:

    def perform(%{"id" => id}, _job), do: IO.inspect(id)

  To accept a single `job` struct and match on the `args` key directly:

    def perform(%Job{args: %{"id" => id}}), do: IO.inspect(id)

- [Oban.Worker] The `backoff/1` callback now expects a job struct instead of an
  integer. That allows applications to finely control backoff based on more than
  just the current attempt number. Use of `backoff/1` with an integer is
  no longer supported.

  To migrate change any worker definitions that used a raw `attempt` like this:

    def backoff(attempt), do: attempt * 60

  To match on a job struct instead, like this:

    def backoff(%Job{attempt: attempt}), do: attempt * 60

- [Oban.Telemetry] The format for telemetry events has changed to match the new
  telemetry `span` convention. This listing maps the old event to the new one:

    * `[:oban, :started]` -> `[:oban, :job, :start]`
    * `[:oban, :success]` -> `[:oban, :job, :stop]`
    * `[:oban, :failure]` -> `[:oban, :job, :exception]`
    * `[:oban, :trip_circuit]` -> `[:oban, :circuit, :trip]`
    * `[:oban, :open_circuit]` -> `[:oban, :circuit, :open]`

  In addition, for exceptions the stacktrace meta key has changed from `:stack`
  to the standardized `:stacktrace`.

- [Oban.Prune] Configurable pruning is no longer available. Instead, pruning is
  handled by the new plugin system. A fixed period pruning module is enabled as
  a default plugin. The plugin always retains "prunable" (discarded or complete)
  jobs for 60 seconds.

  Remove any `:prune`, `:prune_interval` or `prune_limit` settings from your
  config. To disable the pruning plugin in test mode set `plugins: false`

- [Oban.Beat] Pulse tracking and periodic job rescue are no longer available.
  Pulse tracking and rescuing will be handled by an external plugin. This is
  primarily an implementation detail, but it means that jobs may be left in the
  `executing` state after a crash or forced shutdown.

  Remove any `:beats_maxage`, `:rescue_after` or `:rescue_interval` settings
  from your config.

### Fixed

- [Oban.Scheduler] Ensure isolation between transaction locks in different
  prefixes. A node with multiple prefix-isolated instances (i.e. "public" and
  "private") would always attempt to schedule cron jobs at the same moment. The
  first scheduler would acquire a lock and block out the second, preventing the
  second scheduler from ever scheduling jobs.

- [Oban.Query] Correctly prefix unprepared unique queries. Unique queries always
  targeted the "public" prefix, which either caused incorrect results when there
  were both "public" and an alternate prefix. In situations where there wasn't
  a public `oban_jobs` table at all it would cause cryptic transaction errors.

- [Oban.Query] Wrap all job fetching in an explicit transaction to enforce `FOR
  UPDATE SKIP LOCKED` semantics. Prior to this it was possible to run the same
  job at the same time on multiple nodes.

- [Oban.Crontab] Fix weekday matching for Sunday, which is represented as `0` in

### Added

- [Oban] Bubble up errors and exits when draining queues by passing
  `with_safety: false` as an option to `Oban.drain_queue/2`.

- [Oban] Add `Oban.cancel_job/2` for safely discarding scheduled jobs or killing
  executing jobs. This deprecates `kill_job/2`, which isn't as flexible.

- [Oban.Worker] Support returning `{:snooze, seconds}` from `perform/1` to
  re-schedule a job some number of seconds in the future. This is useful for
  recycling jobs that aren't ready to run yet, e.g. because of rate limiting.

- [Oban.Worker] Support returning `:discard` from `perform/1` to immediately
  discard a job. This is useful when a job encounters an error that won't
  resolve with time, e.g. invalid arguments or a missing record.

- [Oban.Job] Introduce a virtual `unsaved_error` field, which is populated with
  an error map after failed execution. The `unsaved_error` field is set before
  any calls to the worker's `backoff/1` callback, allowing workers to calculate
  a custom backoff depending on the error that failed the job.

- [Oban.Worker] Add `:infinity` option for unique period.

- [Oban.Telemetry] Add `span/3` for reporting normalized `:start`, `:stop` and
  `:exception` events with timing information.

- [Oban.Telemetry] Include the configured `prefix` in all event metadata. This
  makes it possible to identify which schema prefix a job ran with, which is
  useful for differentiating errors in a multi-tenant system.

- [Oban.Telemetry] Include `queue_time` as a measurement with `stop` and
  `exception` events. This is a measurement in milliseconds of the amount of
  time between when a job was scheduled to run and when it was last attempted.

- [Oban.Testing] Add `perform_job/2,3` helper to automate validating,
  normalizing and performing jobs while unit testing. This is now the preferred
  way to unit test workers.

  To update your tests replace any calls to `perform/1,2` with the new
  `Oban.Testing.perform_job/2,3` helper:

  defmodule MyApp.WorkerTest do
    use MyApp.DataCase, async: true

    use Oban.Testing, repo: MyApp.Repo

    alias MyApp.Worker

    test "doing business in my worker" do
      assert :ok = perform_job(Worker, %{id: 1})

  The `perform_job/2,3` helper will verify the worker, the arguments and any
  provided options. It will then verify that your worker returns a valid result
  and return the value for you to assert on.

- [Oban.Crontab] Add support for non-standard expressions such as `@daily`,
  `@hourly`, `@midnight`, etc.

- [Oban.Crontab] Add support for using step values in conjunction with ranges,
  enabling expressions like `10-30/2`, `15-45/3`, etc.

### Changed

- [Oban.Notifier] Make the module public and clean up the primary function
  interfaces. Listening for and delivering notifications is simplified and no
  longer requires macros for pattern matching.

  Notifier dispatching performance is slightly improved as well. It is now a
  no-op if no processes are listening to a notification's channel.

- [Oban.Query] The `completed_at` timestamp is no longer set for failed jobs,
  whether they are put in the `discarded` or `retryable` state. However, the
  information is still available and is recorded in the `errors` array as the
  `at` value with the error for that attempt.

  This corrects a long standing inconsistency between discarding a job manually
  or automatically when it exhausts retries.

- [Oban.Producer] Stop dispatching jobs immediately on queue startup. Instead,
  only dispatch on the first poll. This makes it possible to send the producer
  a message or allow sandboxed connection access before the initial dispatch.

- [Oban.Worker] Limit default backoff calculations to 20 attempts, or roughly 24
  days. The change addresses an issue with snoozing, which can increase a job's
  attempts into the hundreds or thousands. In this situation the algorithm
  calculates the backoff using a ratio of attempts to max attempts, but is still
  limited to roughly 24 days.

For changes prior to 2.0 see the [1.2 branch][1.2]