Updating same MongoDB document from two different sources while avoiding race conditions

Question

We have a MongoDB collection, let's call it Accounts. Each account holds an array of devices.

const accountSchema = new mongoose.Schema(
  {
     ...
     devices: [devicesSchema],
     ...
  }
);

const devicesSchema: Schema = new mongoose.Schema(
  {
    deviceId: String,
    platform: String,
    ...
  },
  { _id: false, toJSON: { virtuals: true }, toObject: { virtuals: true } }
);

We have a webhook that receives account events that update this array of devices. For example, in a happy path situation, a webhook event executes this code:

const existingDevices = account.devices;
const newDevices = existingDevices.filter(...).map(...).concat(...) // do stuff to the existingDevices array

await Account.findOneAndUpdate(
  { _id: account._id },
  {
    devices: newDevices
  }
);

This works fine. However, when two webhooks for the same account are received, we are in danger of both webhooks trying to update the same array, resulting in a race condition where only one of the two updates are completed.

Is there a MongoDB way of solving this? I am familiar with other ways such as passing the event from a webhook to a queue that processes events sequantially, or webhook gateways that will send events to our webhook sequentially, but I was specifically interested in knowing if there is any efficient way of doing this natively in MongoDB - for example, some locking mechanism.

Answer 1

mongoDB does provides optimistic conurrency. here is a similar issue - https://www.mongodb.com/community/forums/t/does-mongodb-transactions-implement-optimistic-concurrency-locking-by-default/234943

you can do this, it might help but iam afraid if contention is very much high then it might conflict again.

const res=await Account.findOneAndUpdate(
  { _id: account._id, __v: account.__v },  // __v is the version field
  {
    devices: newDevices,
    $inc: { __v: 1 }  // Increment the version field
  }
);
if (!res) { 
  console.log('Update conflict: Document version mismatch');
}

let me know if it worked :)