CODEWITHSUNDEEP
arraysfirebasegoogle-cloud-firestoretransactionsgoogle-cloud-functions
shaimo
shaimo

Reputation: 376

Unreliable Google Firebase transactions

In my (greatly simplified) model I have users, accounts and account_types. Each user can have multiple accounts of each account_type. When an account of type TT is created I'm updating the "users" field of that object so it keeps the users which have accounts of that types, and the number of such accounts they have.

users: {
  some fields
},
accounts: {
  userID: UU,
  type: TT
},
account_type: 
  users: { UU: 31 }
}

I use the onCreate and onDelete cloud triggers for accounts to update the account_type object. Since multiple accounts can be created simultaneously I have to use transactions:

exports.onCreateAccount = functions.firestore
    .document('accounts/{accountID}')
    .onCreate((account, context) => {
      const acc_user = account.data().userID;
      const acc_type = account.data().type;
      return admin.firestore().runTransaction(transaction => {
        // This code may get re-run multiple times if there are conflicts.
        const accountTypeRef = admin.firestore().doc("account_types/"+acc_type);
        return transaction.get(accountTypeRef).then(accTypeDoc => {
          var users = accTypeDoc.data().users;
          if (users === undefined) {
            users = {};
          }
          if (users[acc_user] === undefined) {
            users[acc_user] = 1;
          } else {
            users[acc_user]++;
          }
          transaction.update(accountTypeRef, {users: users});          
          return;
        })
      })
      .catch(error => {
        console.log("AccountType create transaction failed. Error: "+error);
      });
    });

In my tests I'm first populating the database with some data so I'm also adding a user and 30 accounts of the same type. With the local emulator this works just fine and at the end of the addition I see that the account_type object contains the user with the counter at 30. But when deployed to Firebase and running the same functions the counter gets to less than 30. My suspicion is that since Firebase is much slower and transactions take longer, more of them are conflicted and fail and eventually don't execute at all. The transaction failure documentation (https://firebase.google.com/docs/firestore/manage-data/transactions) says:

"The transaction read a document that was modified outside of the transaction. In this case, the transaction automatically runs again. The transaction is retried a finite number of times."

So my questions:

  1. What does "finite" mean?
  2. Any way to control this number?
  3. How can I make sure my transactions are executed at some point and don't get dropped like that so my data is consistent?
  4. Any other idea as to why I'm not getting the correct results when deployed to the cloud?

Upvotes: 0

Views: 355

Answers (1)

Doug Stevenson
Doug Stevenson

Reputation: 317362

What does "finite" mean?

It's the opposite of "unlimited". It will retry no more than a set number of times.

Any way to control this number?

Other than modifying the source code of the SDK, no. The SDK itself advertise a specific number, as it might change.

How can I make sure my transactions are executed at some point and don't get dropped like that so my data is consistent?

Detect the error and retry in your app. If you aren't seeing the transaction fail with an error, then nothing went wrong.

Any other idea as to why I'm not getting the correct results when deployed to the cloud?

Since we can't see what exactly you're doing to trigger the function, and have no specific expected results to compare to, it's not really possible to say.

Upvotes: 1

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