问题
Is there any situation where it makes sense to use both realtime and firestore in conjunction? What situations lend themselves more favorably to firebase realtime vs firestore, or a combination? I keep reading about horror stories of people getting hit with huge costs is there anyway to test before hand.
For context I am looking to work with an auction based market place of over 50,000 products. The idea is to be able to filter those products as needed, create, modify and delete bids for those products, favorite items and retrieve Users bids. From what I was reading the general suggestion (to keep cost low) for market places using firebase seems to suggest storing products in realtime db and the user objects, sales etc. in firestore. Kinds of queries I will need are find products with the lowest/highest bids, most favorited items, as well as fetching users current and purchases.
When would it be optimal to store in realtime vs firestore, from a cost perspective?
My current logic is to store the product objects in realtime since they will be referenced more frequently. Alternatively I am thinking it makes sense to store the user info, their bids, and purchases in one document in a firestore as that would incur just one read cost, and for a highly active user could result in a large amount of data to be transferred. Where I am confused comes with things like viewing the previous sales of a given product vs getting a user's previous sales, should sales be stored in realtime (as their own object or embedded in the product object) or firestore (embedded in the User doc) or both?
回答1:
Looking at your app that you plan to make, let have a short talk regarding it.
A bidding app, first someone wants to sell their stuff so they post it in your app. Then every single user of your app may see it start bidding on it. Now as I don't know how your app is going to work but here's my assumption you will store the data of bidders and the bids they make in firebase realtime database.
This will involve lots of read, write operations. Now Firestore does offer you 20K operations/day, but if you cross the limit it will barely cost you $0.18/100K writes and $0.06/100K reads. Now the choice entirely depends on scale of your app. If your app has large number of audience, go for Realtime-Database. You can download upto 10GB of data per month for free and a dollar per GB beyond that. But this has a catch, if you stick to the spark plan, you can have only 100 simultaneous connections to the database so I doubt the performance if you have large number of users. It can go upto 200K using Blaze plan and that too per database. So if you create another database you will have more. I will personally suggest create multiple databases as per the region or any parameter to spread the traffic. [Again it's upto how many people use your app]
In my opinion, you should use the Firebase Realtime database your app. [Make sure you utilize the firebase storage as well for storing large photos of the things on sale].
Lastly, use firestore when you have less number of operations but are larger in size. Use firebase realtime database when you have many small tasks like updating the highest bid value or number of users currently bidding for a particular thing, use Realtime DB. In my opinion, go for realtime database. I too use it for some game stuff like to store user stats and update it as the user progresses. This involves lots of read/write/update/delete operations so I stick with realtime-database.
When to use Firestore along with the real-time database?
As you have mentioned user profile, I will suggest use Firestore to store those credentials. Because user's won't generally update their profile so this won't cost much writes. Also the bidders would be much interest in bidding rather than watching others profiles. So even if if a few users check other's profile. This won't cost you much reads. But even if your app is designed in such a way that bidder must check seller's profile once, then firestore will definitely help you reduce usage of realtime database's [GB Downloaded] quota.
Every time someone queries data from your realtime database, you consume some part of the 10 GB of free download limit.
Also as I have mentioned the simultaneous connections to the database, if you host user profile data in Firestore then firestore will take care of profile visits so that bidders get faster response from your application. Just make sure you utilise all the free quotas from firebase storage, firestore and the realtime database and make sure your app is designed in such a way that it spreads traffic evenly between all services. Use the cloud functions on your back-end, and don't make your application [.apk] too heavy on client side as the app needs a lot to code.
So the conclusion, use firestore to store data which won't be accessed frequently like the user credentials and whatever stuff they have on sell. Use realtime database to store bidding data. Oh and yes, if you also want to store some stats like how many purchases has someone made or some information that changes too frequently put that in firebase realtime database. You can simply create a child node users/${username} and keep the frequent stuff in realtime database. This won't cost you much storage but take of that download limit. Shouldn't be expensive much especially talking of your app is going to address 50000 products XD.
I am looking to work with an auction based market place of over 50,000 products.
If you have comparatively less number of users, realtime database is sufficient but who knows when there may be a huge rise in your app users. So it's better to spread the data in both Firestore and Real-time database as mentioned above.
Just a caution: This is what I faced, then searched over stackoverflow and found this. Firestore counts READS even if you are just scrolling over the data tab in firestore. So make sure you don't just get surfing over there. I made 2 writes and was just looking at how the data is being stored and I already got 27 reads ...
来源：https://stackoverflow.com/questions/61324279/when-does-it-make-sense-to-use-firebase-realtime-db-and-firestore-together