I have a cloud function project where I use Firestore as the database. I have a function that works as a RESTapi. I do also have a cloud function trigger which will run on document create.

Scenario

1. The frontend sends a request to the RESTapi which creates a one document
2. onCreate trigger get called

When the onCreate trigger get call, I send a request to a 3rd party API. That API returns an ID which I will set back to the recently created document in Firestore.

  // Runs inside onCreate trigger "some-collection/{someId}"
  const result = await fetchIdFromA3rdPartyAPI(query);
  if (result) {
    try {
        await firestore()
         .collection("some-collection")
         .doc(docId)
         .set({
           someId: parseInt(result)
         }, { merge: true });
    } catch (err) {
      // log to gcp Cloud Logging
      console.log(err);
    }
  }

The problem

If this onCreate get invoked after a cold start it takes upto 4 minute to update the document with the someId field.

If I split the update call as below,

   const doc = await firestore().collection("some-collection").doc(docId);
   // console.log('reached here', doc);
   await doc.set({...})

Now I can see the console log “reached here”, which means it takes 4 min to resolve set() call ( Also tried with update() as well ).

If I trigger the onCreate immediately after this resolved, it works without any delay. So it seems like happens on cold start only.

All functions runs with following configurations

timeouteSeconds: 540
memory: 4GB
maxInstance: 1
version: v1

Also nothing throws. I cannot see any errors on the log as well.

What could possibly be the reason for this ?