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DTM is a distributed transaction framework which provides cross-service eventual data consistency. It provides saga, tcc, xa, 2-phase message, outbox patterns for a variety of application scenarios. It also supports multiple languages and multiple store engine to form up a transaction as following:

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git clone https://github.com/dtm-labs/dtm && cd dtm
go run main.go

Suppose we want to perform an inter-bank transfer. The operations of transfer out (TransOut) and transfer in (TransIn) are coded in separate micro-services.

Here is an example to illustrate a solution of dtm to this problem:

git clone https://github.com/dtm-labs/dtmcli-go-sample && cd dtmcli-go-sample
go run main.go

  // business micro-service address
  const qsBusi = "http://localhost:8081/api/busi_saga"
  // The address where DtmServer serves DTM, which is a url
  DtmServer := "http://localhost:36789/api/dtmsvr"
  req := &gin.H{"amount": 30} // micro-service payload
	// DtmServer is the address of DTM micro-service
	saga := dtmcli.NewSaga(DtmServer, shortuuid.New()).
		// add a TransOut subtraction，forward operation with url: qsBusi+"/TransOut", reverse compensation operation with url: qsBusi+"/TransOutCom"
		Add(qsBusi+"/TransOut", qsBusi+"/TransOutCom", req).
		// add a TransIn subtraction, forward operation with url: qsBusi+"/TransIn", reverse compensation operation with url: qsBusi+"/TransInCom"
		Add(qsBusi+"/TransIn", qsBusi+"/TransInCom", req)
	// submit the created saga transaction，dtm ensures all subtractions either complete or get revoked
	err := saga.Submit()

When the above code runs, we can see in the console that services TransOut, TransIn has been called.

A timing diagram for a successfully completed SAGA transaction would be as follows:

If any forward operation fails, DTM invokes the corresponding compensating operation of each sub-transaction to roll back, after which the transaction is successfully rolled back.

Let's purposely fail the forward operation of the second sub-transaction and watch what happens

app.POST(qsBusiAPI+"/TransIn", func(c *gin.Context) {
  log.Printf("TransIn")
  // c.JSON(200, "")
  c.JSON(409, "") // Status 409 for Failure. Won't be retried
})

The timing diagram for the intended failure is as follows:

The above example mainly demonstrates the flow of a distributed transaction. More on this, including practical examples of how to interface with an actual database, how to do compensation, how to do rollback, etc. please refer to dtm-examples for more examples.

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