Transaction management in Web services

Question

Our client follows SOA principles and have design web services that are very fine grained like createCustomer, deleteCustomer, etc.

I am not sure if fine grained services are desirable as they create transactional related issues. for e.g. if a business requirement is every Customer must have a Address when it's created. So in this case, the presentation component will invoke createCustomer first and then createAddress. The services internally use simple JDBC to update the respective tables in db. As a service is invoked by external component, it has not way of fulfilling transactional requirement here i.e. if createAddress fails, createCustomer operation must be rolledback.

I guess, one of the approach to deal with this is to either design course grained services (that creates a Customer and associated Address in one single JDBC transaction) or perhaps simple create a reversing service (deleteCustomer) that simply reverses the action of createCustomer.

any suggestions. thanks

Answer 1

If transactionality is required, a coarser-grained single operation that can implement transaction-semantics on the server is definitely going to be much simpler to implement.

That said, certainly it is possible to construct some scheme where the target of the operations is not committed until all of the necessary fine-grained operations have succeeded. For instance, have a Commit operation that checks some flag associated with the object on the server; the flag is not set until all of the necessary steps in the transaction have completed, and Commit fails if the flag is not set.

Of course, if having light-weight, fine grained operations is an important design requirement, perhaps the need to have transactionality should be re-thought.

Answer 2

The short answer: services should be designed for the convenience of the service client. If the client is told "call this, then cdon't forget to call that" you're making their lives too difficult. There should be a coarse-grained service.

A long answer: Can a Customer reasonably be entered with no Address? So we call

createCustomer( stuff but no address)

and the result is a valid (if maybe not ideal) state for a customer. Later we call

changeCustomerAddress ( customerId, Address)

and now the persisted customer is more useful.

In this scenario the API is just fine. The key point is that the system's integrity does not depend upon the client code "remembering" to do something, in this case to add the address. However, more likely we don't want a customer in the system without an address in which case I see it as the service's responsibility to ensure that this happens, and to give the caller the fewest possibilities of getting it wrong.

I would see a coarse-grained createCompleteCustomer() method as by far the best way to go - this allows the service provider to solve the problem once rather then require every client programmer to implement the logic.

Alternatives:

a). There are web Services specs for Atomic Transactions and major vendors do support these specs. In principle you could actually implement using fine-grained methods and true transactions. Practically, I think you enter a world of complexity when you go down this route.

b). A stateful interface (work, work, commit) as mentioned by @mtreit. Generally speaking statefulness either adds complexity or obstructs scalability. Where does the service hold the intermediate state? If in memeory, then we require affinity to a particular service instance and hence introduce scaling and reliability problems. If in some State or Work-in-progress database then we have significant additional implementation complexity.

My article discusses other related design issues.

Answer 3

Ok, lets start:

Our client follows SOA principles and have design web services that are very fine grained like createCustomer, deleteCustomer, etc.

No, the client has forgotten to reach the SOA principles and put up what most people do - a molass of badly defined interfaces. For SOA principles, the clinent would have gone to a coarser interface (such asfor example the OData meachsnism to update data) or followed the advice of any book on multi tiered architecture written in like the last 25 years. SOA is just another word for what was invented with CORBA and all the mistakes SOA dudes do today where basically well known design stupidities 10 years ago with CORBA. Not that any of the people doing SOA today has ever heard of CORBA.

I am not sure if fine grained services are desirable as they create transactional related issues.

Only for users and platforms not supporting web services. Seriously. Naturally you get transactional issues if you - ignore transactional issues in your programming. The trick here is that people further up the food chain did not, just your client decided to ignore common knowledge (again, see my first remark on Corba).

The people designing web services were well aware of transactional issues, which is why web service specification (WS*) contains actually mechanisms for handling transactional integrity by moving commit operations up to the client calling the web service. The particular spec your client and you should read is WS-Atomic.

If you use the current technology to expose your web service (a.k.a. WCF on the MS platform, similar technologies exist in the java world) then you can expose transaction flow information to the client and let the client handle transaction demarcation. This has its own share iof problems - like clients keeping transactions open maliciously - but is still pretty much the only way to handle transactions that do get defined in the client.

As you give no platform and just mention java, I am pointing you to some MS example how that can look: http://msdn.microsoft.com/en-us/library/ms752261.aspx

Web services, in general, are a lot more powerfull and a lot more thought out than what most people doing SOA ever think about. Most of the problems they see have been solved a long time ago. But then, SOA is just a buzz word for multi tiered architecture, but most people thinking it is the greatest thing since sliced bread just dont even know what was around 10 years ago.

As your customer I would be a lot more carefull about the performance side. Fine grained non-semantic web services like he defines are a performance hog for non-casual use because the amount of times you cross the network to ask / update small small small small stuff makes the network latency kill you. Creating an order for like 10 goods can easily take 30-40 network calls in this scenario which will really possibly take a lot of time. SOA preaches, ever since the beginning (if you ignore the ramblings of those who dont know history) to NOT use fine grained calls but to go for a coarse grained exchange of documents and / or a semantical approach, much like the OData system.