Durable Objects alarms

Cloudflare documents how Durable Object alarms are scheduled, retried, and deleted.

Products: Durable Objects
Source: Official docsCloudflare Docs

Key points

Each Durable Object can have one alarm at a time; calling setAlarm while one is scheduled overrides it. Alarms let work run without incoming requests keeping the object alive, and the alarm() handler can set future alarms.
alarm() has at-least-once execution. When it throws an uncaught exception, it is retried with exponential backoff starting at 2 seconds, up to 6 retries; this applies only to the most recent setAlarm() call.
If the constructor calls setAlarm, the docs say to check first whether an alarm is already set, because the constructor runs before alarm() when an inactive object wakes. Calling deleteAlarm() inside alarm() may prevent retries only on a best-effort basis.

Original sources

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Durable Objects pricing: alarm invocations count toward billed requests. With SQLite-backed storage, each setAlarm() is billed as one row written; with key-value storage, as one write request unit.
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Key points

Original sources

Original post

Durable Objects pricing: alarm invocations count toward billed requests. With SQLite-backed storage, each setAlarm() is billed as one row written; with key-value storage, as one write request unit.

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