Resumability

Runs can exceed the maximum timeout on serverless platforms and can survive server restarts.

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How does this work?

1. When a Run is created, it is given a unique ID. This ID is used to identify the Run.
2. Tasks have a cacheKey which is a string and is the first parameter. This should be stable and unique inside that run function.
3. When a Task is completed, its output is stored.
4. If a Run exceeds the timeout, or your server restarts, the Run will be “replayed”.
5. The second+ time it is run, Tasks that have already successfully completed will immediately return their first output. The code inside them won’t re-run.

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How to use cache keys

Like we mentioned above, we use Task cache keys to determine which Tasks have already been executed. They are defined by you inside your run function, for example when you call io.slack.postMessage:

await io.slack.postMessage("⭐️ New Star", {
  channel: "C04GWUTDC3W",
  text: `@${starredBy} just starred ${repoName}!`,
});

In this example, the cache key is the string "⭐️ New Star". This means that if the Job is interrupted and then resumed, the slack.postMessage Task will be skipped because it has already been executed.

If you make multiple calls to slack.postMessage, you should use different cache keys for each call. For example:

await io.slack.postMessage("⭐️ New Star", {
  channel: "C04GWUTDC3W",
  text: `@${starredBy} just starred ${repoName}!`,
});

await io.slack.postMessage("🚨 Critical Issue", {
  channel: "C04GWUTDC3W",
  text: `@${assignee} just opened a critical issue in ${repoName}!`,
});

If you are calling a Task multiple times with the same key, it will only be executed once. For example, if you call slack.postMessage with the key "⭐️ New Star" twice, it will only be executed once.

See our Task concept guide for more information about tasks and how they are crucial to the resumability of your Jobs.

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How to use cache keys with loops

If you are using a loop, you should use the loop index as the key. For example:

for (let i = 0; i < 10; i++) {
  await ctx.waitFor(`Wait ${i}`, { seconds: 30 });

  await slack.postMessage(`⭐️ New Star ${i}`, {
    channelName: "github-stars",
    text: `@${starredBy} just starred ${repoName}!`,
  });
}