node.js - Firebase realtime database transaction handler gets called twice most of the time

Question

I am using transactions to write to a specific location in firebase realtime database with firebase admin api in my nodejs app. I observed that the transaction handler gets called twice, even when there are no other clients using the database.

Following is a minimal code which displays this behavior.

firebaseAdmin.database().ref('some/path').transaction(currentData => {
    console.log('transaction handler got called');
    return {'abc': 'def'};
}, null, false).then(value => {
    console.log('transaction complete')
}).catch(reason => {
    console.log('transaction failed. ' + reason);
});

I can observe that transaction handler got called gets logged twice for each execution of above code.

I understand that the handler can get called multiple times if some other client writes to the db path in the window between currentData is read for a transaction and the new data is attempted to be committed to the db path. But, there are no other clients in my case, so I cannot understand why the transaction handler needs to get called twice.

Does anyone know what is the reason for this?

Answer 1

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