workerd error: scheduled event missed, worker overloaded

Not specified by the original author.

workerd error: scheduled event missed, worker overloaded

TL;DR

The worker was too busy to run the scheduled event, so the tick was missed. Shed load, make the handler faster, or split the cron work so a tick fits comfortably. Missed crons are a capacity signal.

workerd error: scheduled event missed (worker overloaded)

Steps

1. Check worker load around the missed tick: CPU, concurrent requests. Expected: The overload is confirmed.

2. Make the cron handler fast and idempotent: it must tolerate being skipped and re-run. Expected: Misses are harmless.

3. Shed load: move heavy work out of the cron tick into queues. Expected: The tick fits easily.

4. Monitor scheduled-event execution as a metric; alert on misses. Expected: The next miss pages.

5. If crons are critical, reduce trigger frequency or shard the work. Expected: The schedule fits capacity.

When to use

• scheduled events are missed
• the worker is busy at tick time
• cron handlers are heavy

When not to use

• the schedule is wrong (check the cron expression first)
• the handler throws (that is an error, not a miss)
• crons are disabled (check the config)

Tool compatibility

• workerd
• scheduled workers

Variant phrasings

• "workerd scheduled event missed"
• "cron missed worker overloaded"
• "scheduled worker skipped overloaded"

Why it happens

Scheduled events fire on the worker, and an overloaded worker cannot always run them: the runtime skips the tick rather than queue it indefinitely. A missed cron is the system telling you the worker is over capacity. The handler must also be idempotent, because 'at most once' is the reality.

Edge cases

• idempotency is non-negotiable; a retried tick must not double-apply
• the cron expression is in UTC; verify the intended times
• alerting on misses needs the execution metric, not just logs

Provenance

Resolved from the public thread: https://vectle.com/posts/psteAvZdthVB1TCTz6Z4s4lA

Resolved from the public thread: https://vectle.com/posts/psteAvZdthVB1TCTz6Z4s4lA

Thread query: workerd error: scheduled event missed, worker overloaded

TL;DR: The worker was too busy to run the scheduled event, so the tick was missed. Shed load, make the handler faster, or split the cron work so a tick fits comfortably. Missed crons are a capacity signal.