问题
I've built an app that let people sell tickets for events. Whenever a ticket is sold, I update the document that represents the ticket of the event in firestore to update the stats.
On peak times, this document is updated quite a lot (10x a second maybe). Sometimes transactions to this item document fail due to the fact that there is "too much contention", which results in inaccurate stats since the stat update is dropped. I guess this is the result of the high load on the document.
To resolve this problem, I am considering to move the stats of the items from the item document in firestore to the realtime database. Before I do, I want to be sure that this will actually resolve the problem I had with the contention on my item document. Can the realtime database handle such load better than a firestore document? Is it considered good practice to move such data to the realtime database?
回答1:
The issue you're running into is a documented limit of Firestore. There is a limit to the rate of sustained writes to a single document of 1 per second. You might be able to burst writes faster than that for a while, but eventually the writes will fail, as you're seeing.
Realtime Database has different documented limits. It's measured in the total volume of data written to the entire database. That limit is 64MB per minute. If you want to move to Realtime Database, as long as you are under that limit, you should be OK.
If you are effectively implementing a counter or some other data aggregation in Firestore, you should also look into the distributed counter solution that works around the per-document write limit by sharding data across multiple documents. Your client code would then have to use all of these document shards in order to present data.
As for whether or not any one of these is a "good practice", that's a matter of opinion, which is off topic for Stack Overflow. Do whatever works for your use case. I've heard of people successfully using either one.
回答2:
On peak times, this document is updated quite a lot (10x a second maybe). Sometimes transactions to this item document fail due to the fact that there is "too much contention"
This is happening because Firestore cannot handle such a rate. According to the official documentation regarding quotas for writes and transactions:
Maximum write rate to a document: 1 per second
Sometimes it might work for two or even three writes per second but at some time will definitely fail. 10 writes per second are way too much.
To resolve this problem, I am considering to move the stats of the items from the item document in Firestore to the realtime database.
That's a solution that I even I use it for such cases.
According to the official documentation regarding usage and limits in Firebase Realtime database, there is no such limitation there. But it's up to you to decide if it fits your needs or not.
There one more thing that you need to into consideration, which is distributed counter. It can solve your problem for sure.
来源：https://stackoverflow.com/questions/59667469/firestore-document-too-much-contention-such-thing-in-realtime-database