Failover logic may have the opposite effect to the intended

[alexey-milovidov]

I use Promise.race to use the first reply among the self-managed and Cloud service - so we can break and experiment with the Cloud service fearlessly, but it still provides scalability benefits.

But my implementation has the following flaws:

• When a database quickly answers with an error, the promise is fulfilled, and that's how a totally broken database breaks the whole UI. In fact, there are two asynchronous operations - one is to receive the HTTP response headers, and another for receiving the body.
• A browser like Chrome has a limit on the number of requests in flight. It means that if one of the databases is slow, after a while we will have a lot of pending, unneeded requests. If we don't cancel them, the service hangs after a while.

[alexey-milovidov]

Zach (3 days ago)

you should use Promise.any() instead of Promise.race() I think - this should achieve the behavior you're looking for Since you're already using fetch API, you can create some abortController s to cancel any remaining requests once the Promise.any() is fulfilled (I think it may work)

Fabio Neves (3 days ago)

Promise.any gives the desired semantics. With the AbortController we can prevent running out of max requests

const fetchRequests = [];
const abortController = new AbortController();

for (let i = 0; i < N; i++) {
  const fetchRequest = fetch(url, { signal: abortController.signal })
    .then(response => {
      if (response.ok) {
        abortController.abort();
        return response.json();
      }
      throw new Error('Request failed');
    })
    .catch(error => {
      console.error(error);
    });

  fetchRequests.push(fetchRequest);
}
Promise.any(fetchRequests)
    .then(data => {
      console.log('First request succeeded:', data);
      abortController.abort();
    })
    .catch(error => {
      console.error('All requests failed:', error);
    });

I think this is a sample that mimics what we want

[alexey-milovidov]

Done.

Ideally, we can also cancel all pending requests on query change or on Zoom.