CODEWITHSUNDEEP
google-cloud-firestorequeuegoogle-cloud-functions
Blue
Blue

Reputation: 1448

Do Firebase/Firestore Transactions create internal queues?

I'm wondering if transactions (https://firebase.google.com/docs/firestore/manage-data/transactions) are viable tools to use in something like a ticketing system where users maybe be attempting to read/write to the same collection/document and whoever made the request first will be handled first and second will be handled second etc.

If not what would be a good structure for such a need with firestore?

Upvotes: 2

Views: 902

Answers (1)

Doug Stevenson
Doug Stevenson

Reputation: 317467

Transactions just guarantee atomic consistent update among the documents involved in the transaction. It doesn't guarantee the order in which those transactions complete, as the transaction handler might get retried in the face of contention.

Since you tagged this question with google-cloud-functions (but didn't mention it in your question), it sounds like you might be considering writing a database trigger to handle incoming writes. Cloud Functions triggers also do not guarantee any ordering when under load.

Ordering of any kind at the scale on which Firestore and other Google Cloud products operate is a really difficult problem to solve (please read that link to get a sense of that). There is not a simple database structure that will impose an order where changes are made. I suggest you think carefully about your need for ordering, and come up with a different solution.

The best indication of order you can get is probably by adding a server timestamp to individual documents, but you will still have to figure out how to process them. The easiest thing might be to have a backend periodically query the collection, ordered by that timestamp, and process things in that order, in batch.

Upvotes: 4

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