cloudFunction.ts

export const batchUpdateUser = functions.database.ref('/triggerUsers').onWrite(async (_change) => {
  const updateUsers = async (lastKey: string = '', iteration: number = 0, records: number = 0) => {
    const snapshots: DataSnapshot = await admin.database().ref('/users')
      .orderByKey()
      .startAt(lastKey)
      .limitToFirst(10)
      .once('value');

    const batchUpdate = {};
    let nextKey = null;
    let counter = 0;

    snapshots.forEach(snapshot => {
      const userId = snapshot.key;

      if (userId !== lastKey) {
        counter++;
        batchUpdate[`/users/${userId}/lastProcessed`] = admin.database.ServerValue.TIMESTAMP;

        nextKey = userId;
      }

      return false;
    });

    await admin.database().ref('/')
      .update(batchUpdate);

    if (nextKey) {
      await updateUsers(nextKey, iteration + 1, counter + records);
    } else {
      console.log(`Finished: ${iteration} iterations, ${counter + records} records updated.`);
    }
  };

  return updateUsers();
});