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  1. Core Server
  2. SERVER-37792

Strange behavior of Multi-Document Transaction

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    • Type: Icon: Question Question
    • Resolution: Done
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: 4.0.2
    • Component/s: JavaScript, Replication
    • Labels:
      None

      First of all, sorry for my english.
      I'm trying to implement a simple example of ACID transaction in MongoDB, using NodeJS driver. I also use Mongoose. I'm just experimenting with transaction to understand how it works and to foresee and prevent all possible errors.
      I have a collection 'testcollection', and i have a single document in it, like:

       

      var testcollection = new mongoose.Schema({
 id: Number,
 name: String,
 number: Number
});

      This is code:

       

      var mongoDB = require('./libs/db');
var _ = require('underscore');

mongoDB.connect("mongodb://testuser:name32@localhost:27018/testbase");

var testcoll = require('./libs/db/models/testcollection');

var _session = mongoose.startSession({readPreference: {mode: "primary"}});
(async () => _session = await _session)(); // wait for ClientSession

async function transactionOperations(id, session){

     async function transactionOperations(id, session){ await      testcoll.updateOne({name: "ilya", id: 1}, {$inc: {number: 2}}).session(session);      // change document as transaction !!!

     await testcoll.updateOne({name: "ilya", id: 1}, {$inc: {number: 3}}); 
// this is not transaction!!!
}

var performTransaction = function(id){    
    async function commit() {
        try {
            await _session.commitTransaction();
        } catch (error) {
            if (error.errorLabels && error.errorLabels.indexOf('UnknownTransactionCommitResult') >= 0) {
                console.warn('UnknownTransactionCommitResult, retrying commit operation.', error);
                await commit();
            } else {
                console.error('Transaction aborted. Caught exception during transaction.', error);
            }
        }
    }
    
    async function runTransactionWithRetry(txnFunc, _transactionOperations) {
        try {
            await txnFunc(_transactionOperations);
        } catch (error) {
            if (error.errorLabels && error.errorLabels.indexOf('TransientTransactionError') >= 0) {
                console.warn('TransientTransactionError, retrying transaction.', error);
                await _session.abortTransaction();
                await runTransactionWithRetry(txnFunc, _transactionOperations);
            } else {
                if(_session.inTransaction()){
                    await runTransactionWithRetry(txnFunc, _transactionOperations);
                } else {
                    await _session.abortTransaction();
                    console.error('Transaction aborted. Caught exception during transaction.', error);
                }
            }
        }
    }

    async function createTransaction(_transactionOperations) {        
        // wait for ClientSession
        _session = await _session;
        console.log("START " + id + " TRANSACTION");
        _session.startTransaction({
            readConcern: { level: 'snapshot' },
            writeConcern: { w: 'majority',}
        });
        // ----- all transaction operations here -----        
        await _transactionOperations(id, _session);         
        // ----- all transaction operations here -----        

        try {
            await commit();
        } catch (error) {
            await _session.abortTransaction();
            console.error('Transaction aborted. Caught exception during transaction.', error);
        }
    }    runTransactionWithRetry(createTransaction, transactionOperations);
}

      In my transaction i'm trying to simulate the situation, when at first i change document as a transaction (increment field 'number' +2), and than change it not as a transaction (increment same field +3 in same doc, but i don't pass session parameter in query function). So it must cuase some write conflict, and throw some error.

      When i running this transaction, it waits for a 60 seconds (as i understood, max txn time), and than throw an error:

        errorLabels: [ 'TransientTransactionError' ],
  operationTime: Timestamp { _bsontype: 'Timestamp', low_: 1, high_: 1540719109 },
  ok: 0,
  errmsg: 'Transaction 1 has been aborted.',
  code: 251,
  codeName: 'NoSuchTransaction'

      It seems, that transaction runs, can't perform update operation because of write conflict and than just waiting for txn timeout. If i'm not mistaking, this is a specific write-conflict error, so why it wait 60 seconds and throws 'NoSuchTransaction' MongoError?

      BUT!!! Somitimes (for example, when i add some console.log-s in transaction body) it throws another error, such as:

        errorLabels: [ 'TransientTransactionError' ],
  operationTime: Timestamp { _bsontype: 'Timestamp', low_: 1, high_: 1540719759 },
  ok: 0,
  errmsg: 'Unable to acquire lock \'{8613801417341912551: Database, 1696272389700830695}\' within a max lock request timeout of \'5ms\' milliseconds.',
  code: 24,
  codeName: 'LockTimeout'

      Here transaction don't have enough time (5ms) to lock the document. As i understood, transactions in mongo locks document not in the time, when calls session.startTransaction(), but when the operations, that are assosiated with this session and transaction, are executing.

       

      So, what i should do with this problem? How can i handle correctly this write conflicts? Why in one situation i catch one MongoError, and in other situation - another, but both errors is caused by single reason?
      Thanks a lot.

            Assignee:
            daniel.hatcher@mongodb.com Danny Hatcher (Inactive)
            Reporter:
            sinilya Ilya
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              Created:
              Updated:
              Resolved: