CODEWITHSUNDEEP
couchdb
pewpewlasers
pewpewlasers

Reputation: 3215

Couchdb locking documents on bulk update

Is there a way to create locks in Couchdb while performing bulk save? I believe there is no inbuilt method to achieve this, but would it be possible to solve this with a workaround? I have a scenario similar to following (I use Node.js to interact with couchdb database):

User pays another user creating a new document object as follows:

{
    _id: SOMEID
    type: "PAYMENT"
    username: SOMEUSER
    paidto: ANOTHERUSER
    amount: 10
}

When this is saved I also need to update remaining balance the user has in his/her account document (subtract 10 from his/her wallet). Then I save both of these documents at once with bulk_docs (newly created transaction document and the updated account document).

But if during this process the user makes changes to the account document through some other method (let's say in another tab) we have an issue where the new transaction document is saved while the account document cannot be updated. This creates a big issue and consistency problem.

To solve this we will have to lock account document until the bulk save process ends, during which process in second tab waits for the lock to be released.

I am trying to deploy Couchdb is an environment where consistency between documents is quite important but without locks, this is turning out to be very difficult.

Upvotes: 2

Views: 285

Answers (1)

Aurélien Bénel
Aurélien Bénel

Reputation: 3852

When this is saved I also need to update remaining balance the user has in his/her account document (subtract 10 from his/her wallet).

Don't. Banking is a very well documented example for document databases. Best practices is to store only transactions as documents, and consider account balance as a query to a view (of transactions indexed by accounts).

Map

function(o) {
  if (o.paidto && o.amount && o.username) {
    emit(o.paidto, o.amount);
    emit(o.username, -o.amount);
  }
}

Reduce

_sum

Query

GET /mydb/_design/mydesign/_view/myview/?group=true&key=SOMEUSER

Upvotes: 1

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