Update, Jan 8th 2021

👋 I’ve updated my initial post and the title to be more specific, based on the problems still being discussed in this thread:

Cold Start performance issues seem to correlate closely with gRPC libraries (like Firestore). Folks switching to HTTP dependencies, from gRPC, have seen performance improvements (this seems to point to gRPC as well).

If the problems you’re running into do not seem to correlate to gRPC SDKs, such as Firestore, please don’t hesitate to open an issue and we will investigate (Also, I’ve pulled together a Tips & Tricks post, based on some of what I’ve learned investigating this thread which might help).

We continue to work on cross cutting features that will help cold start performance in general, e.g., Min Instances for Cloud Functions, and will keep this thread updated as features roll out.

Problem you have encountered:

We've had a long standing issue on GitHub related to cold start performance of Cloud Functions.

The original issue was that the grpc dependency was quite large, and could lead to several additional seconds in load times. We have since moved to @grpc/gprc-js. this issue has been addressed, and the load times of modules themselves during cold start seem reasonable:

256MB functions saw around 1.5 second load times for @google-cloud/firestore.
512MB functions saw around 750 ms load times for @google-cloud/firestore.
1024MB functions saw around 400 ms load times for @google-cloud/firestore.

Despite module load times being reasonable, customers are seeing long delays when accessing cloud functions on cold starts:

Here's the log of the function call that took 5016ms from an API consumer perspective. The log says the execution only took 1073ms so as @manwithsteelnerves pointed out there must be a 4 second delay even before the "Function execution started" message is printed.

I tried with the above code and it took 5.6secs to finish (where the above code was a minimal cloud function with the import of firebase-functions). 5334.827399 ms just to start execution of function 277ms for exact function code execution.

What you expected to happen:

A cold start time in a reasonable threshold, ideally <1s, vs., 5s.

Steps to reproduce:

The below code can be used to benchmark the time spent loading modules, during GCF initialization:

const requireSoSlow = require('require-so-slow');
const shim = require('require-so-slow/build/src/shim')

require('@google-cloud/firestore')

let events;
exports.main = async (req, res) => {
  if (!events) {
    events = shim.getAndClearEvents()
  }
  res.set('Access-Control-Allow-Origin', '*');
  res.status(200).send(events);
}

The URL of the Cloud Function can then be plugged into Timeline Viewer.

Customers indicate that, on cold starts, the time to first byte in the browser is significantly delayed from the observed load time of the function.