Why is the same function being called twice?

[adaboese]

I've been debugging this for many hours.

I send an event like this:

console.log('SENDING aimd/suggest-article-sources.start');

return inngest.send({
  data: {
    suggestArticleSourcesId: id,
  },
  id: `suggest-article-sources-${id}`,
  name: 'aimd/suggest-article-sources.start',
});

This is the only place the event is ever sent.

Then I log when my function is invocation:

SENDING aimd/suggest-article-sources.start
| +29.2s      RECEIVED aimd/suggest-article-sources.start 49 (ATTEMPT 0)
| +1.4s       searchGoogle took 1051ms
| +1.9s       searchGoogle took 858ms
found 20 search results
| +1.5s       invoking download article 3513
| +144ms      invoking download article 3514
| +298ms      invoking download article 3515
| +148ms      invoking download article 3516
| +178ms      invoking download article 3517
| +210ms      invoking download article 3518
| +145ms      invoking download article 3519
| +91ms       downloading article #3513
| +48ms       invoking download article 3520
| +298ms      invoking download article 3521
| +154ms      invoking download article 3522
| +504ms      invoking download article 3523
| +509ms      invoking download article 3524
| +271ms      invoking download article 3525
| +291ms      invoking download article 3526
| +106ms      fetchArticle took 1910ms
| +226ms      extractArticleMarkdown took 226ms
| +75ms       done downloading #3513
| +1ms        invoking download article 3527
waiting for invocations
| +1.4s       RECEIVED aimd/suggest-article-sources.start 49 (ATTEMPT 0)
| +1.1s       searchGoogle took 691ms
| +2.4s       searchGoogle took 783ms

Here is a meta code:

export const suggestArticleSources = inngest.createFunction(
  {
    id: 'suggestArticleSources',
    retries: 0,
  },
  { event: 'aimd/suggest-article-sources.start' },
  async ({ event, step, runId, logger, attempt }) => {
    const { suggestArticleSourcesId } = event.data;
    
    const invocations = [];

    for (const ...) {
      invocations.push(
        step
          .invoke(id, {
            data: {
              sourceArticleId: newSourceArticleId,
            },
            function: downloadArticle,
          })
      );
    }

    console.log('waiting for invocations');

    await Promise.all(invocations);

    console.log('done');

    return {
      status: 'OK',
    };
  },
);

Notice how:

• "SENDING" log appears only once ✅
• "RECEIVED aimd/suggest-article-sources.start 49 (ATTEMPT 0)" appears twice ❌
• "waiting for invocations" appears twice ❌
• "done" appears even though only 1 of the invoked functions completed ❌

What is happening?

---

WOAH, very confusing. I stripped the code to just:

export const suggestArticleSources = inngest.createFunction(
  {
    id: 'suggestArticleSources',
    retries: 0,
  },
  { event: 'aimd/suggest-article-sources.start' },
  async ({ event, step, attempt }) => {
    const { suggestArticleSourcesId } = event.data;

    log(
      'RECEIVED aimd/suggest-article-sources.start %d (ATTEMPT %d)',
      suggestArticleSourcesId,
      attempt,
    );

    const invocations: Array<Promise<void>> = [];

    for (const newSourceArticleId of [1, 2, 3]) {
      await step.invoke('test-' + newSourceArticleId, {
        data: {
          sourceArticleId: newSourceArticleId,
        },
        function: downloadArticle,
      });
    }

    console.log('waiting for invocations');

    await Promise.all(invocations);

    console.log('done');

    return {
      status: 'OK',
    };
  },
);

and seeing this...

SENDING aimd/suggest-article-sources.start
| +25.3s      RECEIVED aimd/suggest-article-sources.start 53 (ATTEMPT 0)
| +1.1s       downloading article #1
| +1.3s       RECEIVED aimd/suggest-article-sources.start 53 (ATTEMPT 0)
| +1.1s       downloading article #2
| +1.2s       RECEIVED aimd/suggest-article-sources.start 53 (ATTEMPT 0)
| +1.3s       downloading article #3
| +1.1s       RECEIVED aimd/suggest-article-sources.start 53 (ATTEMPT 0)
waiting for invocations
done

Why does it keep invoking itself?

---

But I don't see anything weird in the UI. So why is the same function getting called repeatedly?

[adaboese]

Wow, this took a long time to figure out.

Basically, if you read the documentation carefully, you will find that you are supposed to wrap all code that is non-pure using step.run, e.g.

Do not do this:

export const suggestArticleSources = inngest.createFunction(
  {
    id: 'suggestArticleSources',
    retries: 0,
  },
  { event: 'aimd/suggest-article-sources.start' },
  async ({ event, step, runId, logger }) => {
    const ids = [Math.random(), Math.random(), Math.random()];

    await doSomethingWithIds(ids);
  }
);

Instead, do this:

export const suggestArticleSources = inngest.createFunction(
  {
    id: 'suggestArticleSources',
    retries: 0,
  },
  { event: 'aimd/suggest-article-sources.start' },
  async ({ event, step, runId, logger }) => {
    const ids = await step.run('get-ids', () => {
      return [Math.random(), Math.random(), Math.random()];;
    })

    await step.run('run-something', () => {
      return doSomethingWithIds(ids);
    });
  }
);

Makes sense, but really wish this was illustrated better in the documentation.

[JureSotosek]

I had the same problem and was really confused 😅

[Yamayamaaya]

Hello, and thank you for the insights shared here. I encountered a similar issue, and while using step.run() helped prevent repeated execution, I still don’t fully understand why the initial duplication of logs occurs.

These points closely match my situation, though not exactly the same:

1. The “SENDING” log appears only once. ✅
2. The log “RECEIVED aimd/suggest-article-sources.start 49 (ATTEMPT 0)” appears twice. ❌
3. “waiting for invocations” also appears twice. ❌
4. The “done” log appears, even though only one of the invoked functions completed. ❌

I’m particularly puzzled by the second and third points. If retries aren’t explicitly configured, what could cause the duplication of these logs? Is this a result of internal retry logic or perhaps a behavior related to Inngest’s distributed environment? Any insights on the underlying mechanism here would be greatly appreciated.

Thanks in advance!