How to retry the mongodb transaction?

Question

I have two different API endpoints that update the same field of a collection(wallet field of user collection). In both API transactions are implemented by using mongoose. When I hit both endpoints at the same time then one endpoint executes successfully and another one getting error of "WriteConflict" with label "TransientTransactionError".

I have read in MongoDB documentation that it provides the transaction retry functionality on the "TransientTransactionError" error. So, please suggest how to retry the transaction when I get this kind of error.

I'm receiving this error when I'm updating the same document with different endpoints at the same time.

MongoError: WriteConflict
    at Connection.<anonymous> (/Users/node_modules/mongodb-core/lib/connection/pool.js:443:61)
    at Connection.emit (events.js:196:13)
    at Connection.EventEmitter.emit (domain.js:471:20)
    at processMessage (/Users/node_modules/mongodb-core/lib/connection/connection.js:364:10)
    at TLSSocket.<anonymous> (/Users/node_modules/mongodb-core/lib/connection/connection.js:533:15)
    at TLSSocket.emit (events.js:196:13)
    at TLSSocket.EventEmitter.emit (domain.js:471:20)
    at addChunk (_stream_readable.js:290:12)
    at readableAddChunk (_stream_readable.js:271:11)
    at TLSSocket.Readable.push (_stream_readable.js:226:10)
    at TLSWrap.onStreamRead (internal/stream_base_commons.js:166:17) {
  errorLabels: [ 'TransientTransactionError' ],
  operationTime: Timestamp { _bsontype: 'Timestamp', low_: 2, high_: 1591772061 },
  ok: 0,
  errmsg: 'WriteConflict',
  code: 112,
  codeName: 'WriteConflict',
  '$clusterTime': {
    clusterTime: Timestamp { _bsontype: 'Timestamp', low_: 2, high_: 1591772061 },
    signature: { hash: [Binary], keyId: [Long] }
  },
  name: 'MongoError',
  [Symbol(mongoErrorContextSymbol)]: {}
}

Thanks in advance

Answer 1

The documentation provides examples of how to properly use transactions. Click on "nodejs" to see the node examples.

The withTransaction function in the driver implements the retry functionality.

Answer 2

You can implement a function that retries the transaction when a commit error occurs:

const commitWithRetry = async (session) => {
  for (;;) {
    try {
      await session.commitTransaction();
      session.endSession();
      break;
    } catch (error) {
      const isTransientError = Object.prototype.hasOwnProperty.call(error, 'errorLabels')
          && error.errorLabels.includes('UnknownTransactionCommitResult');
      if (!isTransientError) {
        throw error;
      }
    }
  }
};

To commit with retries, invoke the function on your session object:

await commitWithRetry(session);

Hope this helps.

EDIT: I'm unaware why this answer was downvoted but to provide added context, an example of this approach's usage can be found in the MongoDB documentation here .