First things first, take a good look at Firestore's pricing documentation. You need to get a handle on the costs for reads, writes, and storage. Every time you write a document, it counts towards your quota. And remember, there's a cap on how many operations you can do per minute.

Try to bundle your write operations together. Firestore lets you do up to 500 writes in one go. This way, you cut down on the number of individual requests and keep things atomic.

const batch = db.batch();

const doc1Ref = db.collection('cities').doc('NYC');
batch.set(doc1Ref, { name: 'New York City' });

const doc2Ref = db.collection('cities').doc('LA');
batch.set(doc2Ref, { name: 'Los Angeles' });

await batch.commit();

Make sure your indexing is spot on. Don't go overboard with composite indexes because they can slow down writes and rack up your write counts.

Think about your data model. Try to design it in a way that cuts down on the number of document writes. Use subcollections or nested structures to keep related data together and reduce separate write operations.

Spread out your write operations over time. You can use queuing systems like Cloud Tasks or add some custom logic to your app to delay writes when you're close to hitting your quota.

function throttleWrites(writeFunc, interval) {
  let queue = [];
  setInterval(() => {
    if (queue.length) {
      const operation = queue.shift();
      writeFunc(operation.data).catch(err => console.error(err));
    }
  }, interval);
  
  return (data) => queue.push({ data });
}

const throttledWrite = throttleWrites(writeDataFunction, 1000); // 1 write per second
throttledWrite({ name: 'San Francisco' });

Keep your transactions lean. Only include the writes you really need. Transactions can retry if there's a conflict, which can lead to a lot more write operations.

await db.runTransaction(async (t) => {
  const doc = await t.get(docRef);
  if (doc.exists) {
    t.update(docRef, { population: doc.data().population + 1 });
  } else {
    t.set(docRef, { population: 1 });
  }
});

Keep an eye on your Firestore usage through the Firebase Console. Set up alerts for high usage so you can quickly adjust your database operations.

gcloud firestore operations list

Based on what you see, tweak your strategies to stay within your quota limits while keeping your app running smoothly.