MongoDB Transaction 例子

MongoDB Transaction

init replset mongodb env

$mkdir db1 && mkdir db2 && mkdir db3
$mongod --port 27017 --dbpath ./db --replSet rstest1
$mongod --port 37017 --dbpath ./db2 --replSet rstest1
$mongod --port 47017 --dbpath ./db3 --replSet rstest1

$mongo --port 27017

rs.initiate( { _id : "rstest1", members: [ { _id: 0, host: "127.0.0.1:27017" }, { _id: 1, host: "127.0.0.1:37017" }, { _id: 1, host: "127.0.0.1:47017" }, ] })

  const mongoose = require('mongoose')
  const mongoUri = 'mongodb://localhost:27017,localhost:37017,localhost:47017/test'
  const client = mongoose.createConnection(mongoUri, { replicaSet: 'rstest' })
  let Acc = client.model('Account', new mongoose.Schema({
      name: String,
      balance: Number
  }))
  async function initTest() {
      await Acc.create({ 'name': 'James', 'balance': 3000 })
      await Acc.create({ 'name': 'Wade', 'balance': 0 })
  }
  async function afterWork() {
      await Acc.remove({ 'name': 'James' })
      await Acc.remove({ 'name': 'Wade' })
  }
  async function transferTest(transfer) {
      let session = await Acc.startSession()
      session.startTransaction()
      try {
          const opts = { session, new: true }
          let a = await Acc.findOneAndUpdate({
              'name': 'James'
          }, {
              $inc: { 'balance': -transfer }
          }, opts)
          console.log(a.toObject());
          let b = await Acc.findOneAndUpdate({
              'name': 'Wade',
          }, {
              $inc: { 'balance': transfer }
          }, opts)
          console.log(b.toObject());
          await session.commitTransaction()
      } catch (err) {
          session.abortTransaction()
          console.error(err)
      } finally {
          session.endSession()
      }

  }
  async function test() {
      await afterWork()
      await initTest()
      await transferTest(100)
          // await afterWork()
  }
  test()

set a debug point or sleep point at

  console.log(a.toObject());

to stop the process
then run code to read them
`
{ "_id" : ObjectId("5cb752de57e8791edf030e9d"), "name" : "James", "balance" : 3000, "__v" : 0 }
{ "_id" : ObjectId("5cb752de57e8791edf030e9e"), "name" : "Wade", "balance" : 0, "__v" : 0 }

`
it works fine

then run :
`
rstest:PRIMARY> db.accounts.update({"name":"Wade"}, { $inc:{'balance':10}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

`

this will return immediately, when the debug point continue, it ran into exception

null: MongoError: WriteConflict MongoError: Attempted illegal state transition from [TRANSACTION_ABORTED] to [TRANSACTION_ABORTED] ....

PAY attention

In MongoDB, clients can see the results of writes before the writes are durable:
clients using "local" by default can see the result of a write operation before the write operation is acknowledged to the issuing client.
read isolation

Thus , in the case of we need to read own writes we need to read concern set "majority", wirte concern "majority"

how to config this

further info read-concern

read-your-own-writes

read concern : you can disable read concern by setting either:

• -- enableMajorityReadConcern command line option to false.
• replication.enableMajorityReadConcern configuration file setting to false

write concern : your code write-concern option, example :

  const schema = new Schema({ name: String }, {
    writeConcern: {
      w: 'majority',
      j: true
    }
});

more ref