事务花费太多时间（Node + Meteor + MongoDB）

Question

我已经按照本文中的描述在MongoDB中实现了事务： https://forums.meteor.com/t/solved-transactions-with-mongodb-meteor-methods/48677

Utils.js

import { MongoInternals } from 'meteor/mongo';

// utility async function to wrap async raw mongo operations with a transaction
export const runTransactionAsync = async function (asyncRawMongoOperations, errorCode) {

// setup a transaction
const { client } = MongoInternals.defaultRemoteCollectionDriver().mongo;
const session = await client.startSession();
await session.startTransaction();
try {
    // running the async operations
    let result = await asyncRawMongoOperations(session);
    await session.commitTransaction();
    // transaction committed - return value to the client
    return result;
} catch (err) {
    await session.abortTransaction();
    console.error(err.message);
    // transaction aborted - report error to the client
    throw new Meteor.Error(errorCode, err.message);
} finally {
    session.endSession();
}
};

使用交易的示例：

Meteor.methods({
   'changeLanguage': async function(poemId, newLanguageId) {

        // define the operations we want to run in transaction
        const asyncRawMongoOperations = async session => {

            const poem = Poems.findOne({ _id: poemId });
            const prevLanguage = poem.languageId;

            const profile = Profiles.findOne({ userId: this.userId });

            await Profiles.rawCollection().update(
                { userId: this.userId }, 
                    { 
                        $inc: { 
                            ['countLanguages.' + prevLanguage]: -1,
                            ['countLanguages.' + newLanguageId]: 1 
                        },
                        $addToSet: { languages: newLanguageId }
                    }, 
                    { session: session }
                );

            await Poems.rawCollection().update({
                    '_id': poemId,
                    'userId': this.userId
                },
                {
                    $set: {
                        languageId: newLanguageId
                    }
                }, 
                { session: session }
            );

            return true; // will be the result in the client
        };

        let result = await runTransactionAsync(asyncRawMongoOperations, 'Error-01');

        return result;
    }
});

交易正常，但速度太慢。最多可能需要7秒钟。

MongoDB托管为MongoDB.Atlas。 MongoDB版本是4.0.12。

在这种情况下瓶颈在哪里？