Firestore request produces unexpected number of reads

Question

After i execute my Firestore-Test-App made with Flutter i look at the Firestore analytics to see how many request my Test-App made. It shows me that i make a minimum of 20 up to 60 document reads with 1 start of the Test. The problem is, the test should result in a maximum of ~1-3 reads as i understand it.

I've read https://firebase.google.com/docs/firestore/pricing. It did help to understand the billing logic of firestore, but following that logic in the article i should be making a maximum of ~5 reads. This thread: Firestore - unexpected reads also suggests that maybe, the document reads come from the opened Firebase console, viewing the documents. So i closed it before the test and opened it 30 min after. This did not change the result. I also set breakpoints and the code did only execute once.

I opened a completly new Flutter Project to test it. This is the only part making read requests:

 CollectionReference dbUsers = dbInstance.collection("Users"); 
 var user = dbUsers
      .where("docId", isEqualTo: fireAppUser.user.uid)
      .limit(1)
      .snapshots();

  var _userSub = user.listen((value) {
    if (value.documents.isNotEmpty && value.documents.first.data != null)
      print(value.documents.first.data);
  });
_userSub.cancel()

Below my firestore rule, which is on default settings for now.

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write;
    }
  }
}

I have exactly 5 documents in my Database.

I expect to have a maximum of ~5 document reads. Please help me to undestand why this Snippet causes an unexpected number of reads. What could cause it?

Edit: forgot to append the cancel() to the snippet

score 0 · Answer 1 · answered Sep 18 '19 at 08:21

0

That code can make a nearly unlimited number of reads, since it's adding a listener to the document. It will cost 1 read the first time you run it, and continue to incur reads as the listener remains added, as the document changes over time.

If the accounting doesn't make sense to you, contact Firebase support with your exact reproduction instructions.

answered Sep 18 '19 at 08:21

Doug Stevenson

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oops, the snippet is not copied right. I do cancel the subscribtion right after subscribing to it. Just for testing. – Marc Ma Sep 18 '19 at 08:35
Looks like you're canceling the listener before it even gets its first callback. – Doug Stevenson Sep 18 '19 at 08:39
i know, thats ok, its just a test. nonetheless that snippet causes an to high number of document reads. Any idea why? – Marc Ma Sep 18 '19 at 09:38

Firestore request produces unexpected number of reads

1 Answers1