Scheduled Events and Task Queues

Two Mendix features for work that runs outside a user request. They are unrelated and easy to confuse:

• A scheduled event is Mendix’s cron — it runs a microflow on a repeating schedule.
• A task queue bounds how many queued microflow calls run at once.

A scheduled event does not go through a task queue. Its own concurrency control is OnOverlap, which decides what happens when a run is still going when the next one is due.

Scheduled Events

Inspecting

-- All scheduled events, or one module's
LIST SCHEDULED EVENTS;
LIST SCHEDULED EVENTS IN Ops;

-- Re-executable MDL for one event
DESCRIBE SCHEDULED EVENT Ops.NightlyCleanup;

SHOW is accepted as a synonym for LIST.

CREATE SCHEDULED EVENT

CREATE [OR MODIFY] SCHEDULED EVENT <Module>.<Name> (
  Microflow: <Module>.<Microflow>,
  Repeat: <repeat>,
  <fields of that repeat>,
  <optional properties>
);

Microflow and Repeat are always required.

Repeat variants

The repeat rule is stored as one of eight Mendix schedule types, and they differ in which fields they carry — not just in their values. MDL mirrors that: each repeat takes only its own fields, and a field belonging to another repeat is refused by both mxcli check (rule MDL-SCHED01) and mxcli exec rather than silently dropped.

Field values:

A value outside its range is an error, not a truncation: a schedule that is stored but can never fire is worse than a refusal, because nothing downstream reports it.

Optional properties

SkipNext drops a run that would overlap the previous one; DelayNext queues it until the previous one finishes.

Examples

-- Every night at 04:00 in the server's timezone
CREATE SCHEDULED EVENT Ops.NightlyCleanup (
  Microflow: Ops.SE_Cleanup,
  Repeat: Daily,
  HourOfDay: 4,
  MinuteOfHour: 0,
  TimeZone: Server,
  Enabled: true
);

-- Every two hours, 23 minutes past
CREATE SCHEDULED EVENT Ops.HourlyPing (
  Microflow: Ops.SE_Ping,
  Repeat: Hourly,
  Multiplier: 2,
  MinuteOffset: 23
);

-- Mondays and Fridays at 09:30
CREATE SCHEDULED EVENT Ops.WeeklyReport (
  Microflow: Ops.SE_Report,
  Repeat: Weekly,
  Weekdays: 'Monday, Friday',
  HourOfDay: 9,
  MinuteOfHour: 30
);

-- The last Friday of every third month, at 18:00
CREATE SCHEDULED EVENT Ops.QuarterEnd (
  Microflow: Ops.SE_Close,
  Repeat: MonthlyByWeekday,
  Multiplier: 3,
  MonthOffset: 2,
  DaySelector: Last,
  Weekday: Friday,
  HourOfDay: 18
);

DROP SCHEDULED EVENT Ops.HourlyPing;

A note on Interval / IntervalType

Stored events also carry an Interval and IntervalType pair. These predate the Schedule child and Studio Pro does not keep them in sync with it — a real Mendix module ships an event storing 0 / Minute next to a daily schedule of 01:00. MDL has no syntax for them: a new event gets the pair that matches its repeat, and CREATE OR MODIFY carries whatever is stored through untouched. DESCRIBE reports them as a comment so the output stays re-executable.

Task Queues

A task queue bounds how many instances of a queued microflow call run at once.

CREATE [OR MODIFY] QUEUE <Module>.<Name> [(
  Parallelism: <expression>,
  ClusterWide: true|false,
  Documentation: '<text>'
)];

LIST QUEUES [IN <Module>];
DESCRIBE QUEUE <Module>.<Name>;
DROP QUEUE <Module>.<Name>;

Mendix stores parallelism as an expression string, so a bare integer and a quoted one mean the same thing and an arbitrary expression is legal:

CREATE QUEUE Ops.OrderProcessing ( Parallelism: 3, ClusterWide: true );
CREATE QUEUE Ops.Mail;                      -- defaults: 1, per-instance
CREATE OR MODIFY QUEUE Ops.OrderProcessing ( Parallelism: '$MyModule.Workers' );

Binding a call to a queue is not yet expressible

MDL cannot yet author a queued call — the binding lives on the call activity inside a microflow, not on the queue. Because rebuilding a microflow would drop an existing binding, CREATE OR REPLACE|MODIFY MICROFLOW is refused when the stored microflow has a queued call, naming the queues that would be lost. Change those microflows in Studio Pro.

Without that refusal the binding was written back as null and the project then looked healthier than before — mx check stopped reporting CE1613 "The selected task queue no longer exists", because the configuration the error was about had been deleted.